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\title{A History of Science,\\
{\large Volume III, Modern Development of the Physical Sciences}}


\author{Henry Smith Williams, M.D., LL.D.\\
{\normalsize assisted by Edward H. Williams, M.D.}}

\maketitle
\noindent \vspace*{\stretch{1}}\\
This public-domain (U.S.) text was scanned by Charles Keller with
\textbf{OmniPage} Professional OCR software. The Project Gutenberg
edition ({}``3hsci10'') was subsequently converted to \LaTeX{} by
means of \textbf{GutenMark} software (version Jan 5 2003), and edited
for formatting purposes by Ron Burkey. Illustrations missing in the
Project Gutenberg edition were replaced from alternate online sources;
they were scanned by S.\ A.\ Cohen. Problems in the reprint of Mayer's
1842 paper in Chapter VIII were corrected against an alternate online
translation of that paper. Report problems to info@sandroid.org.

\noindent \begin{center}Revision: A\\
Date: 03/01/03\end{center}

\vspace{\stretch{1}}

 \frontmatter


\pagestyle{myheadings}
{\small \tableofcontents}

 \newpage


\newpage\ \newpage

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{3hsci10-Wil3Sfro}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small The Results of Erosion by Running
Water}\end{center}
\end{figure}


\mainmatter



\chapter*{\raggedright FOREWORD}

\addcontentsline{toc}{chapter}{FOREWORD}

\markboth{A HISTORY OF SCIENCE, BOOK III}{FOREWORD}

With the present book we enter the field of the distinctively modern.
There is no precise date at which we take up each of the successive
stories, but the main sweep of development has to do in each case
with the nineteenth century. We shall see at once that this is a time
both of rapid progress and of great differentiation. We have heard
almost nothing hitherto of such sciences as paleontology, geology,
and meteorology, each of which now demands full attention. Meantime,
astronomy and what the workers of the elder day called natural philosophy
become wonderfully diversified and present numerous phases that would
have been startling enough to the star-gazers and philosophers of
the earlier epoch.

Thus, for example, in the field of astronomy, Herschel is able, thanks
to his perfected telescope, to discover a new planet and then to reach
out into the depths of space and gain such knowledge of stars and
nebul\ae{} as hitherto no one had more than dreamed of. Then, in
rapid sequence, a whole coterie of hitherto unsuspected minor planets
is discovered, stellar distances are measured, some members of the
starry galaxy are timed in their flight, the direction of movement
of the solar system itself is investigated, the spectroscope reveals
the chemical composition even of suns that are unthinkably distant,
and a tangible theory is grasped of the universal cycle which includes
the birth and death of worlds.

Similarly the new studies of the earth's surface reveal secrets of
planetary formation hitherto quite inscrutable. It becomes known that
the strata of the earth's surface have been forming throughout untold
ages, and that successive populations differing utterly from one another
have peopled the earth in different geological epochs. The entire
point of view of thoughtful men becomes changed in contemplating the
history of the world in which we live---albeit the newest thought
harks back to some extent to those days when the inspired thinkers
of early Greece dreamed out the wonderful theories with which our
earlier chapters have made our readers familiar.

In the region of natural philosophy progress is no less pronounced
and no less striking. It suffices here, however, by way of anticipation,
simply to name the greatest generalization of the century in physical
science---the doctrine of the conservation of energy.


\chapter*{\raggedright I. THE SUCCESSORS OF NEWTON IN ASTRONOMY}

\addcontentsline{toc}{chapter}{I. THE SUCCESSORS OF NEWTON IN\\
ASTRONOMY}

\markboth{A HISTORY OF SCIENCE, BOOK III}{I. THE SUCCESSORS OF NEWTON}


\section*{\raggedright HEVELIUS AND HALLEY}

\addcontentsline{toc}{section}{HEVELIUS AND HALLEY}

Strangely enough, the decade immediately following Newton was one
of comparative barrenness in scientific progress, the early years
of the eighteenth century not being as productive of great astronomers
as the later years of the seventeenth, or, for that matter, as the
later years of the eighteenth century itself. Several of the prominent
astronomers of the later seventeenth century lived on into the opening
years of the following century, however, and the younger generation
soon developed a coterie of astronomers, among whom Euler, Lagrange,
Laplace, and Herschel, as we shall see, were to accomplish great things
in this field before the century closed.

One of the great seventeenth-century astronomers, who died just before
the close of the century, was Johannes Hevelius (1611-1687), of Dantzig,
who advanced astronomy by his accurate description of the face and
the spots of the moon. But he is remembered also for having retarded
progress by his influence in refusing to use telescopic sights in
his observations, preferring until his death the plain sights long
before discarded by most other astronomers. The advantages of these
telescope sights have been discussed under the article treating of
Robert Hooke, but no such advantages were ever recognized by Hevelius.
So great was Hevelius's reputation as an astronomer that his refusal
to recognize the advantage of the telescope sights caused many astronomers
to hesitate before accepting them as superior to the plain; and even
the famous Halley, of whom we shall speak further in a moment, was
sufficiently in doubt over the matter to pay the aged astronomer a
visit to test his skill in using the old-style sights. Side by side,
Hevelius and Halley made their observations, Hevelius with his old
instrument and Halley with the new. The results showed slightly in
the younger man's favor, but not enough to make it an entirely convincing
demonstration. The explanation of this, however, did not lie in the
lack of superiority of the telescopic instrument, but rather in the
marvellous skill of the aged Hevelius, whose dexterity almost compensated
for the defect of his instrument. What he might have accomplished
could he have been induced to adopt the telescope can only be surmised.

Halley himself was by no means a tyro in matters astronomical at that
time. As the only son of a wealthy soap-boiler living near London,
he had been given a liberal education, and even before leaving college
made such novel scientific observations as that of the change in the
variation of the compass. At nineteen years of age he discovered a
new method of determining the elements of the planetary orbits which
was a distinct improvement over the old. The year following he sailed
for the Island of St.\ Helena to make observations of the heavens
in the southern hemisphere.

It was while in St.\ Helena that Halley made his famous observation
of the transit of Mercury over the sun's disk, this observation being
connected, indirectly at least, with his discovery of a method of
determining the parallax of the planets. By parallax is meant the
apparent change in the position of an object, due really to a change
in the position of the observer. Thus, if we imagine two astronomers
making observations of the sun from opposite sides of the earth at
the same time, it is obvious that to these observers the sun will
appear to be at two different points in the sky. Half the angle measuring
this difference would be known as the sun's parallax. This would depend,
then, upon the distance of the earth from the sun and the length of
the earth's radius. Since the actual length of this radius has been
determined, the parallax of any heavenly body enables the astronomer
to determine its exact distance.

The parallaxes can be determined equally well, however, if two observers
are separated by exactly known distances, several hundreds or thousands
of miles apart. In the case of a transit of Venus across the sun's
disk, for example, an observer at New York notes the image of the
planet moving across the sun's disk, and notes also the exact time
of this observation. In the same manner an observer at London makes
similar observations. Knowing the distance between New York and London,
and the different time of the passage, it is thus possible to calculate
the difference of the parallaxes of the sun and a planet crossing
its disk. The idea of thus determining the parallax of the planets
originated, or at least was developed, by Halley, and from this phenomenon
he thought it possible to conclude the dimensions of all the planetary
orbits. As we shall see further on, his views were found to be correct
by later astronomers.

In 1721 Halley succeeded Flamsteed as astronomer royal at the Greenwich
Observatory. Although sixty-four years of age at that time his activity
in astronomy continued unabated for another score of years. At Greenwich
he undertook some tedious observations of the moon, and during those
observations was first to detect the acceleration of mean motion.
He was unable to explain this, however, and it remained for Laplace
in the closing years of the century to do so, as we shall see later.

Halley's book, the \emph{Synopsis Astronomi}\ae{} \emph{Cometic}\ae{},
is one of the most valuable additions to astronomical literature since
the time of Kepler. He was first to attempt the calculation of the
orbit of a comet, having revived the ancient opinion that comets belong
to the solar system, moving in eccentric orbits round the sun, and
his calculation of the orbit of the comet of 1682 led him to predict
correctly the return of that comet in 1758. 


\subsection*{\raggedright{}Halley's Study of Meteors.}

\addcontentsline{toc}{subsection}{Halley's Study of Meteors}

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{3hsci10-Wil3Sci7}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Edmund Halley}\end{center}{\small \par}

\noindent \emph{\footnotesize (From a painting ascribed to Dahl in
the possession of the Royal Society.)}
\end{figure}
Like other astronomers of his time be was greatly puzzled over the
well-known phenomena of shooting-stars, or meteors, making many observations
himself, and examining carefully the observations of other astronomers.
In 1714 he gave his views as to the origin and composition of these
mysterious visitors in the earth's atmosphere. As this subject will
be again referred to in a later chapter, Halley's views, representing
the most advanced views of his age, are of interest.

\begin{quotation}
{}``The theory of the air seemeth at present,''\ he says, {}``to
be perfectly well understood, and the differing densities thereof
at all altitudes; for supposing the same air to occupy spaces reciprocally
proportional to the quantity of the superior or incumbent air, I have
elsewhere proved that at forty miles high the air is rarer than at
the surface of the earth at three thousand times; and that the utmost
height of the atmosphere, which reflects light in the \emph{Crepusculum},
is not fully forty-five miles, notwithstanding which 'tis still manifest
that some sort of vapors, and those in no small quantity, arise nearly
to that height. An instance of this may be given in the great light
the society had an account of (\emph{vide Transact}.\ Sep., 1676)
from Dr.\ Wallis, which was seen in very distant counties almost
over all the south part of England. Of which though the doctor could
not get so particular a relation as was requisite to determine the
height thereof, yet from the distant places it was seen in, it could
not but be very many miles high.

{}``So likewise that meteor which was seen in 1708, on the 31st of
July, between nine and ten o'clock at night, was evidently between
forty and fifty miles perpendicularly high, and as near as I can gather,
over Shereness and the buoy on the Nore. For it was seen at London
moving horizontally from east by north to east by south at least fifty
degrees high, and at Redgrove, in Suffolk, on the Yarmouth road, about
twenty miles from the east coast of England, and at least forty miles
to the eastward of London, it appeared a little to the westward of
the south, suppose south by west, and was seen about thirty degrees
high, sliding obliquely downward. I was shown in both places the situation
thereof, which was as described, but could wish some person skilled
in astronomical matters had seen it, that we might pronounce concerning
its height with more certainty. Yet, as it is, we may securely conclude
that it was not many more miles westerly than Redgrove, which, as
I said before, is about forty miles more easterly than London. Suppose
it, therefore, where perpendicular, to have been thirty-five miles
east from London, and by the altitude it appeared at in London---\textit{viz}.,
fifty degrees---its tangent will be forty-two miles, for the height
of the meteor above the surface of the earth; which also is rather
of the least, because the altitude of the place shown me is rather
more than less than fifty degrees; and the like may be concluded from
the altitude it appeared in at Redgrove, near seventy miles distant.
Though at this very great distance, it appeared to move with an incredible
velocity, darting, in a very few seconds of time, for about twelve
degrees of a great circle from north to south, being very bright at
its first appearance; and it died away at the east of its course,
leaving for some time a pale whiteness in the place, with some remains
of it in the track where it had gone; but no hissing sound as it passed,
or bounce of an explosion were heard.

{}``It may deserve the honorable society's thoughts, how so great
a quantity of vapor should be raised to the top of the atmosphere,
and there collected, so as upon its ascension or otherwise illumination,
to give a light to a circle of above one hundred miles diameter, not
much inferior to the light of the moon; so as one might see to take
a pin from the ground in the otherwise dark night. 'Tis hard to conceive
what sort of exhalations should rise from the earth, either by the
action of the sun or subterranean heat, so as to surmount the extreme
cold and rareness of the air in those upper regions: but the fact
is indisputable, and therefore requires a solution.''
\end{quotation}
{}

From this much of the paper it appears that there was a general belief
that this burning mass was heated vapor thrown off from the earth
in some mysterious manner, yet this is unsatisfactory to Halley, for
after citing various other meteors that have appeared within his knowledge,
he goes on to say:\ 

\begin{quotation}
{}``What sort of substance it must be, that could be so impelled
and ignited at the same time; there being no \emph{Vulcano} or other
\emph{Spiraculum} of subterraneous fire in the northeast parts of
the world, that we ever yet heard of, from whence it might be projected.

{}``I have much considered this appearance, and think it one of the
hardest things to account for that I have yet met with in the phenomena
of meteors, and I am induced to think that it must be some collection
of matter formed in the \ae{}ther, as it were, by some fortuitous
concourse of atoms, and that the earth met with it as it passed along
in its orb, then but newly formed, and before it had conceived any
great impetus of descent towards the sun. For the direction of it
was exactly opposite to that of the earth, which made an angle with
the meridian at that time of sixty-seven grads,%
\footnote{1 grad = 0.9 degrees---R.B.%
} that is, its course was from west southwest to east northeast, wherefore
the meteor seemed to move the contrary way. And besides falling into
the power of the earth's gravity, and losing its motion from the opposition
of the medium, it seems that it descended towards the earth, and was
extinguished in the Tyrrhene Sea, to the west southwest of Leghorn.
The great blow being heard upon its first immersion into the water,
and the rattling like the driving of a cart over stones being what
succeeded upon its quenching; something like this is always heard
upon quenching a very hot iron in water. These facts being past dispute,
I would be glad to have the opinion of the learned thereon, and what
objection can be reasonably made against the above hypothesis, which
I humbly submit to their censure.''%
\footnote{{}``An Account of Several Extraordinary Meteors or Lights in the
Sky,'' by Dr.\ Edmund Halley. \emph{Phil. Trans.\ of Royal Society
of London}, vol.\ XXIX, pp.\ 159-162. Read before the Royal Society
in the autumn of 1714. %
}
\end{quotation}
{}

These few paragraphs, coming as they do from a leading eighteenth-century
astronomer, convey more clearly than any comment the actual state
of the meteorological learning at that time. That this ball of fire,
rushing {}``at a greater velocity than the swiftest cannon-ball,''\ was
simply a mass of heated rock passing through our atmosphere, did not
occur to him, or at least was not credited. Nor is this surprising
when we reflect that at that time universal gravitation had been but
recently discovered; heat had not as yet been recognized as simply
a form of motion; and thunder and lightning were unexplained mysteries,
not to be explained for another three-quarters of a century. In the
chapter on meteorology we shall see how the solution of this mystery
that puzzled Halley and his associates all their lives was finally
attained.


\section*{\raggedright BRADLEY AND THE ABERRATION OF LIGHT}

\addcontentsline{toc}{section}{BRADLEY AND THE ABERRATION OF LIGHT}

Halley was succeeded as astronomer royal by a man whose useful additions
to the science were not to be recognized or appreciated fully until
brought to light by the Prussian astronomer Bessel early in the nineteenth
century. This was Dr.\ James Bradley, an ecclesiastic, who ranks
as one of the most eminent astronomers of the eighteenth century.
His most remarkable discovery was the explanation of a peculiar motion
of the pole-star, first observed, but not explained, by Picard a century
before. For many years a satisfactory explanation was sought unsuccessfully
by Bradley and his fellow-astronomers, but at last he was able to
demonstrate that the star $\gamma $ Draconis, on which he was making
his observations, described, or appeared to describe, a small ellipse.
If this observation was correct, it afforded a means of computing
the aberration of any star at all times. The explanation of the physical
cause of this aberration, as Bradley thought, and afterwards demonstrated,
was the result of the combination of the motion of light with the
annual motion of the earth. Bradley first formulated this theory in
1728, but it was not until 1748---twenty years of continuous struggle
and observation by him---that he was prepared to communicate the results
of his efforts to the Royal Society. This remarkable paper is thought
by the Frenchman, Delambre, to entitle its author to a place in science
beside such astronomers as Hipparchus and Kepler.

Bradley's studies led him to discover also the libratory motion of
the earth's axis. {}``As this appearance of $\gamma $ Draconis indicated
a diminution of the inclination of the earth's axis to the plane of
the ecliptic,''\ he says; {}``and as several astronomers have supposed
\textit{that} inclination to diminish regularly; if this phenomenon
depended upon such a cause, and amounted to 18''\ in nine years,
the obliquity of the ecliptic would, at that rate, alter a whole minute
in thirty years; which is much faster than any observations, before
made, would allow. I had reason, therefore, to think that some part
of this motion at the least, if not the whole, was owing to the moon's
action upon the equatorial parts of the earth; which, I conceived,
might cause a libratory motion of the earth's axis. But as I was unable
to judge, from only nine years observations, whether the axis would
entirely recover the same position that it had in the year 1727, I
found it necessary to continue my observations through a whole period
of the moon's nodes; at the end of which I had the satisfaction to
see, that the stars, returned into the same position again; as if
there had been no alteration at all in the inclination of the earth's
axis; which fully convinced me that I had guessed rightly as to the
cause of the phenomena. This circumstance proves likewise, that if
there be a gradual diminution of the obliquity of the ecliptic, it
does not arise only from an alteration in the position of the earth's
axis, but rather from some change in the plane of the ecliptic itself;
because the stars, at the end of the period of the moon's nodes, appeared
in the same places, with respect to the equator, as they ought to
have done, if the earth's axis had retained the same inclination to
an invariable plane.''%
\footnote{\emph{Phil. Trans.\ of Royal Society of London} for 1748, vol.\ XLV.,
pp.\ 8, 9. From {}``A Letter to the Right Honorable George, Earl
of Macclesfield, concerning an Apparent Motion observed in some of
the Fixed Stars,'' by James Bradley, D.D., Astronomer Royal and F.R.S.%
}


\section*{\raggedright FRENCH ASTRONOMERS}

\addcontentsline{toc}{section}{FRENCH ASTRONOMERS}

Meanwhile, astronomers across the channel were by no means idle. In
France several successful observers were making many additions to
the already long list of observations of the first astronomer of the
Royal Observatory of Paris, Dominic Cassini (1625-1712), whose reputation
among his contemporaries was much greater than among succeeding generations
of astronomers. Perhaps the most deserving of these successors was
Nicolas Louis de Lacaille (1713-1762), a theologian who had been educated
at the expense of the Duke of Bourbon, and who, soon after completing
his clerical studies, came under the patronage of Cassini, whose attention
had been called to the young man's interest in the sciences. One of
Lacaille's first undertakings was the remeasuring of the French arc
of the meridian, which had been incorrectly measured by his patron
in 1684. This was begun in 1739, and occupied him for two years before
successfully completed. As a reward, however, he was admitted to the
academy and appointed mathematical professor in Mazarin College.

In 1751 he went to the Cape of Good Hope for the purpose of determining
the sun's parallax by observations of the parallaxes of Mars and Venus,
and incidentally to make observations on the other southern hemisphere
stars. The results of this undertaking were most successful, and were
given in his \emph{Coelum australe stelligerum}, \textit{etc}., published
in 1763. In this he shows that in the course of a single year he had
observed some ten thousand stars, and computed the places of one thousand
nine hundred and forty-two of them, measured a degree of the meridian,
and made many observations of the moon---productive industry seldom
equalled in a single year in any field. These observations were of
great service to the astronomers, as they afforded the opportunity
of comparing the stars of the southern hemisphere with those of the
northern, which were being observed simultaneously by Lelande at Berlin.

Lacaille's observations followed closely upon the determination of
an absorbing question which occupied the attention of the astronomers
in the early part of the century. This question was as to the shape
of the earth---whether it was actually flattened at the poles. To
settle this question once for all the Academy of Sciences decided
to make the actual measurement of the length of two degrees, one as
near the pole as possible, the other at the equator. Accordingly,
three astronomers, Godin, Bouguer, and La Condamine, made the journey
to a spot on the equator in Peru, while four astronomers, Camus, Clairaut,
Maupertuis, and Lemonnier, made a voyage to a place selected in Lapland.
The result of these expeditions was the determination that the globe
is oblately spheroidal.

A great contemporary and fellow-countryman of Lacaille was Jean Le
Rond d'Alembert (1717-1783), who, although not primarily an astronomer,
did so much with his mathematical calculations to aid that science
that his name is closely connected with its progress during the eighteenth
century. D'Alembert, who became one of the best-known men of science
of his day, and whose services were eagerly sought by the rulers of
Europe, began life as a foundling, having been exposed in one of the
markets of Paris. The sickly infant was adopted and cared for in the
family of a poor glazier, and treated as a member of the family. In
later years, however, after the foundling had become famous throughout
Europe, his mother, Madame Tencin, sent for him, and acknowledged
her relationship. It is more than likely that the great philosopher
believed her story, but if so he did not allow her the satisfaction
of knowing his belief, declaring always that Madame Tencin could {}``not
be nearer than a step-mother to him, since his mother was the wife
of the glazier.''

D'Alembert did much for the cause of science by his example as well
as by his discoveries. By living a plain but honest life, declining
magnificent offers of positions from royal patrons, at the same time
refusing to grovel before nobility, he set a worthy example to other
philosophers whose cringing and pusillanimous attitude towards persons
of wealth or position had hitherto earned them the contempt of the
upper classes.

His direct additions to astronomy are several, among others the determination
of the nutation of the axis of the earth. He also determined the ratio
of the attractive forces of the sun and moon, which he found to be
about as seven to three. From this he reached the conclusion that
the earth must be seventy times greater than the moon. The first two
volumes of his \emph{Researches on the Systems of the World}, published
in 1754, are largely devoted to mathematical and astronomical problems,
many of them of little importance now, but of great interest to astronomers
at that time.

Another great contemporary of D'Alem\-bert, whose name is closely
associated and frequently confounded with his, was Jean Baptiste Joseph
Delambre (1749- 1822). More fortunate in birth as also in his educational
advantages, Delambre as a youth began his studies under the celebrated
poet Delille. Later he was obliged to struggle against poverty, supporting
himself for a time by making translations from Latin, Greek, Italian,
and English, and acting as tutor in private families. The turning-point
of his fortune came when the attention of Lalande was called to the
young man by his remarkable memory, and Lalande soon showed his admiration
by giving Delambre certain difficult astronomical problems to solve.
By performing these tasks successfully his future as an astronomer
became assured. At that time the planet Uranus had just been discovered
by Herschel, and the Academy of Sciences offered as the subject for
one of its prizes the determination of the planet's orbit. Delambre
made this determination and won the prize---a feat that brought him
at once into prominence.

By his writings he probably did as much towards perfecting modern
astronomy as any one man. His \emph{History of Astronomy} is not merely
a narrative of progress of astronomy but a complete abstract of all
the celebrated works written on the subject. Thus he became famous
as an historian as well as an astronomer.


\section*{\raggedright LEONARD EULER}

\addcontentsline{toc}{section}{LEONARD EULER}

Still another contemporary of D'Alembert and Delambre, and somewhat
older than either of them, was Leonard Euler (1707-1783), of Basel,
whose fame as a philosopher equals that of either of the great Frenchmen.
He is of particular interest here in his capacity of astronomer, but
astronomy was only one of the many fields of science in which he shone.
Surely something out of the ordinary was to be expected of the man
who could {}``repeat the \emph{\AE{}neid} of Virgil from the beginning
to the end without hesitation, and indicate the first and last line
of every page of the edition which he used.'' Something was expected,
and he fulfilled these expectations.

In early life he devoted himself to the study of theology and the
Oriental languages, at the request of his father, but his love of
mathematics proved too strong, and, with his father's consent, he
finally gave up his classical studies and turned to his favorite study,
geometry. In 1727 he was invited by Catharine I.\ to reside in St.\ Petersburg,
and on accepting this invitation he was made an associate of the Academy
of Sciences. A little later he was made professor of physics, and
in 1733 professor of mathematics. In 1735 he solved a problem in three
days which some of the eminent mathematicians would not undertake
under several months. In 1741 Frederick the Great invited him to Berlin,
where he soon became a member of the Academy of Sciences and professor
of mathematics; but in 1766 he returned to St.\ Petersburg. Towards
the close of his life be became virtually blind, being obliged to
dictate his thoughts, sometimes to persons entirely ignorant of the
subject in hand. Nevertheless, his remarkable memory, still further
heightened by his blindness, enabled him to carry out the elaborate
computations frequently involved.

Euler's first memoir, transmitted to the Academy of Sciences of Paris
in 1747, was on the planetary perturbations. This memoir carried off
the prize that had been offered for the analytical theory of the motions
of Jupiter and Saturn. Other memoirs followed, one in 1749 and another
in 1750, with further expansions of the same subject. As some slight
errors were found in these, such as a mistake in some of the formul\ae{}
expressing the secular and periodic inequalities, the academy proposed
the same subject for the prize of 1752. Euler again competed, and
won this prize also. The contents of this memoir laid the foundation
for the subsequent demonstration of the permanent stability of the
planetary system by Laplace and Lagrange.

It was Euler also who demonstrated that within certain fixed limits
the eccentricities and places of the aphelia of Saturn and Jupiter
are subject to constant variation, and he calculated that after a
lapse of about thirty thousand years the elements of the orbits of
these two planets recover their original values.


\chapter*{\raggedright II. THE PROGRESS OF MODERN ASTRONOMY}

\addcontentsline{toc}{chapter}{II. THE PROGRESS OF MODERN\\
ASTRONOMY}

\markboth{A HISTORY OF SCIENCE, BOOK III}{II. MODERN ASTRONOMY}

A \textit{\emph{new}} epoch in astronomy begins with the work of William
Herschel, the Hanoverian, whom England made hers by adoption. He was
a man with a positive genius for sidereal discovery. At first a mere
amateur in astronomy, he snatched time from his duties as music-teacher
to grind him a telescopic mirror, and began gazing at the stars. Not
content with his first telescope, he made another and another, and
he had such genius for the work that he soon possessed a better instrument
than was ever made before. His patience in grinding the curved reflective
surface was monumental. Sometimes for sixteen hours together he must
walk steadily about the mirror, polishing it, without once removing
his hands. Meantime his sister, always his chief lieutenant, cheered
him with her presence, and from time to time put food into his mouth.
The telescope completed, the astronomer turned night into day, and
from sunset to sunrise, year in and year out, swept the heavens unceasingly,
unless prevented by clouds or the brightness of the moon. His sister
sat always at his side, recording his observations. They were in the
open air, perched high at the mouth of the reflector, and sometimes
it was so cold that the ink froze in the bottle in Caroline Herschel's
hand; but the two enthusiasts hardly noticed a thing so common-place
as terrestrial weather. They were living in distant worlds.

The results? What could they be? Such enthusiasm would move mountains.
But, after all, the moving of mountains seems a liliputian task compared
with what Herschel really did with those wonderful telescopes. He
moved worlds, stars, a universe---even, if you please, a galaxy of
universes; at least he proved that they move, which seems scarcely
less wonderful; and he expanded the cosmos, as man conceives it, to
thousands of times the dimensions it had before. As a mere beginning,
he doubled the diameter of the solar system by observing the great
outlying planet which we now call Uranus, but which he christened
Georgium Sidus, in honor of his sovereign, and which his French contemporaries,
not relishing that name, preferred to call Herschel.

This discovery was but a trifle compared with what Herschel did later
on, but it gave him world-wide reputation none the less. Comets and
moons aside, this was the first addition to the solar system that
had been made within historic times, and it created a veritable furor
of popular interest and enthusiasm. Incidentally King George was flattered
at having a world named after him, and he smiled on the astronomer,
and came with his court to have a look at his namesake. The inspection
was highly satisfactory; and presently the royal favor enabled the
astronomer to escape the thraldom of teaching music and to devote
his entire time to the more congenial task of star-gazing.

Thus relieved from the burden of mundane embarrassments, he turned
with fresh enthusiasm to the skies, and his discoveries followed one
another in bewildering profusion. He found various hitherto unseen
moons of our sister planets; he made special studies of Saturn, and
proved that this planet, with its rings, revolves on its axis; he
scanned the spots on the sun, and suggested that they influence the
weather of our earth; in short, he extended the entire field of solar
astronomy. But very soon this field became too small for him, and
his most important researches carried him out into the regions of
space compared with which the span of our solar system is a mere point.
With his perfected telescopes he entered abysmal vistas which no human
eve ever penetrated before, which no human mind had hitherto more
than vaguely imagined. He tells us that his forty-foot reflector will
bring him light from a distance of {}``at least eleven and three-fourths
millions of millions of millions of miles''---light which left its
source two million years ago. The smallest stars visible to the unaided
eye are those of the sixth magnitude; this telescope, he thinks, has
power to reveal stars of the 1342d magnitude.

But what did Herschel learn regarding these awful depths of space
and the stars that people them? That was what the world wished to
know. Copernicus, Galileo, Kepler, had given us a solar system, but
the stars had been a mystery. What says the great reflector---are
the stars points of light, as the ancients taught, and as more than
one philosopher of the eighteenth century has still contended, or
are they suns, as others hold? Herschel answers, they are suns, each
and every one of all the millions---suns, many of them, larger than
the one that is the centre of our tiny system. Not only so, but they
are moving suns. Instead of being fixed in space, as has been thought,
they are whirling in gigantic orbits about some common centre. Is
our sun that centre? Far from it. Our sun is only a star like all
the rest, circling on with its attendant satellites---our giant sun
a star, no different from myriad other stars, not even so large as
some; a mere insignificant spark of matter in an infinite shower of
sparks.

Nor is this all. Looking beyond the few thousand stars that are visible
to the naked eye, Herschel sees series after series of more distant
stars, marshalled in galaxies of millions; but at last he reaches
a distance beyond which the galaxies no longer increase. And yet---so
he thinks---he has not reached the limits of his vision. What then?
He has come to the bounds of the sidereal system---seen to the confines
of the universe. He believes that he can outline this system, this
universe, and prove that it has the shape of an irregular globe, oblately
flattened to almost disklike proportions, and divided at one edge---a
bifurcation that is revealed even to the naked eye in the forking
of the Milky Way.

This, then, is our universe as Herschel conceives it---a vast galaxy
of suns, held to one centre, revolving, poised in space. But even
here those marvellous telescopes do not pause. Far, far out beyond
the confines of our universe, so far that the awful span of our own
system might serve as a unit of measure, are revealed other systems,
other universes, like our own, each composed, as he thinks, of myriads
of suns, clustered like our galaxy into an isolated system---mere
islands of matter in an infinite ocean of space. So distant from our
universe are these now universes of Herschel's discovery that their
light reaches us only as a dim, nebulous glow, in most cases invisible
to the unaided eye. About a hundred of these nebul\ae{} were known
when Herschel began his studies. Before the close of the century he
had discovered about two thousand more of them, and many of these
had been resolved by his largest telescopes into clusters of stars.
He believed that the farthest of these nebul\ae{} that he could see
was at least three hundred thousand times as distant from us as the
nearest fixed star. Yet that nearest star---so more recent studies
prove---is so remote that its light, travelling one hundred and eighty
thousand miles a second, requires three and one-half years to reach
our planet.

As if to give the finishing touches to this novel scheme of cosmology,
Herschel, though in the main very little given to unsustained theorizing,
allows himself the privilege of one belief that he cannot call upon
his telescope to substantiate. He thinks that all the myriad suns
of his numberless systems are instinct with life in the human sense.
Giordano Bruno and a long line of his followers had held that some
of our sister planets may be inhabited, but Herschel extends the thought
to include the moon, the sun, the stars---all the heavenly bodies.
He believes that he can demonstrate the habitability of our own sun,
and, reasoning from analogy, he is firmly convinced that all the suns
of all the systems are {}``well supplied with inhabitants.'' In
this, as in some other inferences, Herschel is misled by the faulty
physics of his time. Future generations, working with perfected instruments,
may not sustain him all along the line of his observations, even,
let alone his inferences. But how one's egotism shrivels and shrinks
as one grasps the import of his sweeping thoughts!

Continuing his observations of the innumerable nebul\ae{}, Herschel
is led presently to another curious speculative inference. He notes
that some star groups are much more thickly clustered than others,
and he is led to infer that such varied clustering tells of varying
ages of the different nebul\ae{}. He thinks that at first all space
may have been evenly sprinkled with the stars and that the grouping
has resulted from the action of gravitation.

\begin{quotation}
{}``That the Milky Way is a most extensive stratum of stars of various
sizes admits no longer of lasting doubt,'' he declares, {}``and
that our sun is actually one of the heavenly bodies belonging to it
is as evident. I have now viewed and gauged this shining zone in almost
every direction and find it composed of stars whose number\ \ldots{}\ constantly
increases and decreases in proportion to its apparent brightness to
the naked eye.

{}``Let us suppose numberless stars of various sizes, scattered over
an indefinite portion of space in such a manner as to be almost equally
distributed throughout the whole. The laws of attraction which no
doubt extend to the remotest regions of the fixed stars will operate
in such a manner as most probably to produce the following effects:\ 

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{3hsci10-Wil3Sc24}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Herschel and his Sister at
the Telescope}\end{center}
\end{figure}
{}``In the first case, since we have supposed the stars to be of
various sizes, it will happen that a star, being considerably larger
than its neighboring ones, will attract them more than they will be
attracted by others that are immediately around them; by which means
they will be, in time, as it were, condensed about a centre, or, in
other words, form themselves into a cluster of stars of almost a globular
figure, more or less regular according to the size and distance of
the surrounding stars\ldots{}.

{}``The next case, which will also happen almost as frequently as
the former, is where a few stars, though not superior in size to the
rest, may chance to be rather nearer one another than the surrounding
ones,\ldots{}\ and this construction admits of the utmost variety
of shapes\ldots{}.

{}``From the composition and repeated conjunction of both the foregoing
formations, a third may be derived when many large stars, or combined
small ones, are spread in long, extended, regular, or crooked rows,
streaks, or branches; for they will also draw the surrounding stars,
so as to produce figures of condensed stars curiously similar to the
former which gave rise to these condensations.

{}``We may likewise admit still more extensive combinations; when,
at the same time that a cluster of stars is forming at the one part
of space, there may be another collection in a different but perhaps
not far-distant quarter, which may occasion a mutual approach towards
their own centre of gravity.

{}``In the last place, as a natural conclusion of the former cases,
there will be formed great cavities or vacancies by the retreating
of the stars towards the various centres which attract them.''%
\footnote{William Herschel, \emph{Phil.\ Trans.}\ for 1783, vol.\ LXXIII. %
}
\end{quotation}
{}

Looking forward, it appears that the time must come when all the suns
of a system will be drawn together and destroyed by impact at a common
centre. Already, it seems to Herschel, the thickest clusters have
{}``outlived their usefulness''\ and are verging towards their
doom.

But again, other nebul\ae{} present an appearance suggestive of an
opposite condition. They are not resolvable into stars, but present
an almost uniform appearance throughout, and are hence believed to
be composed of a shining fluid, which in some instances is seen to
be condensed at the centre into a glowing mass. In such a nebula Herschel
thinks he sees a sun in process of formation.


\section*{\raggedright THE NEBULAR HYPOTHESIS OF KANT}

\addcontentsline{toc}{section}{THE NEBULAR HYPOTHESIS OF KANT}

Taken together, these two conceptions outline a majestic cycle of
world formation and world destruction---a broad scheme of cosmogony,
such as had been vaguely adumbrated two centuries before by Kepler
and in more recent times by Wright and Swedenborg. This so-called
{}``nebular hypothesis''\ assumes that in the beginning all space
was uniformly filled with cosmic matter in a state of nebular or {}``fire-mist''\ diffusion,
{}``formless and void.'' It pictures the condensation---coagulation,
if you will---of portions of this mass to form segregated masses,
and the ultimate development out of these masses of the sidereal bodies
that we see.

Perhaps the first elaborate exposition of this idea was that given
by the great German philosopher Immanuel Kant (born at K\"{o}nigsberg
in 1724, died in 1804), known to every one as the author of the \emph{Critique
of Pure Reason}. Let us learn from his own words how the imaginative
philosopher conceived the world to have come into existence.

\begin{quotation}
{}``I assume,''\ says Kant, {}``that all the material of which
the globes belonging to our solar system---all the planets and comets---consist,
at the beginning of all things was decomposed into its primary elements,
and filled the whole space of the universe in which the bodies formed
out of it now revolve. This state of nature, when viewed in and by
itself without any reference to a system, seems to be the very simplest
that can follow upon nothing. At that time nothing has yet been formed.
The construction of heavenly bodies at a distance from one another,
their distances regulated by their attraction, their form arising
out of the equilibrium of their collected matter, exhibit a later
state\ldots{}. In a region of space filled in this manner, a universal
repose could last only a moment. The elements have essential forces
with which to put each other in motion, and thus are themselves a
source of life. Matter immediately begins to strive to fashion itself.
The scattered elements of a denser kind, by means of their attraction,
gather from a sphere around them all the matter of less specific gravity;
again, these elements themselves, together with the material which
they have united with them, collect in those points where the particles
of a still denser kind are found; these in like manner join still
denser particles, and so on. If we follow in imagination this process
by which nature fashions itself into form through the whole extent
of chaos, we easily perceive that all the results of the process would
consist in the formation of divers masses which, when their formation
was complete, would by the equality of their attraction be at rest
and be forever unmoved.

{}``But nature has other forces in store which are specially exerted
when matter is decomposed into fine particles. They are those forces
by which these particles repel one another, and which, by their conflict
with attractions, bring forth that movement which is, as it were,
the lasting life of nature. This force of repulsion is manifested
in the elasticity of vapors, the effluences of strong-smelling bodies,
and the diffusion of all spirituous matters. This force is an uncontestable
phenomenon of matter. It is by it that the elements, which may be
falling to the point attracting them, are turned sideways promiscuously
from their movement in a straight line; and their perpendicular fall
thereby issues in circular movements, which encompass the centre towards
which they were falling. In order to make the formation of the world
more distinctly conceivable, we will limit our view by withdrawing
it from the infinite universe of nature and directing it to a particular
system, as the one which belongs to our sun. Having considered the
generation of this system, we shall be able to advance to a similar
consideration of the origin of the great world-systems, and thus to
embrace the infinitude of the whole creation in one conception.

{}``From what has been said, it will appear that if a point is situated
in a very large space where the attraction of the elements there situated
acts more strongly than elsewhere, then the matter of the elementary
particles scattered throughout the whole region will fall to that
point. The first effect of this general fall is the formation of a
body at this centre of attraction, which, so to speak, grows from
an infinitely small nucleus by rapid strides; and in the proportion
in which this mass increases, it also draws with greater force the
surrounding particles to unite with it. When the mass of this central
body has grown so great that the velocity with which it draws the
particles to itself with great distances is bent sideways by the feeble
degree of repulsion with which they impede one another, and when it
issues in lateral movements which are capable by means of the centrifugal
force of encompassing the central body in an orbit, then there are
produced whirls or vortices of particles, each of which by itself
describes a curved line by the composition of the attracting force
and the force of revolution that had been bent sideways. These kinds
of orbits all intersect one another, for which their great dispersion
in this space gives place. Yet these movements are in many ways in
conflict with one another, and they naturally tend to bring one another
to a uniformity---that is, into a state in which one movement is as
little obstructive to the other as possible. This happens in two ways:
first by the particles limiting one another's movement till they all
advance in one direction; and, secondly, in this way, that the particles
limit their vertical movements in virtue of which they are approaching
the centre of attraction, till they all move horizontally---i.e.,
in parallel circles round the sun as their centre, no longer intercept
one another, and by the centrifugal force becoming equal with the
falling force they keep themselves constantly in free circular orbits
at the distance at which they move. The result, finally, is that only
those particles continue to move in this region of space which have
acquired by their fall a velocity, and through the resistance of the
other particles a direction, by which they can continue to maintain
a \textit{free} \textit{circular} \textit{movement}\ldots{}.

{}``The view of the formation of the planets in this system has the
advantage over every other possible theory in holding that the origin
of the movements, and the position of the orbits in arising at that
same point of time---nay, more, in showing that even the deviations
from the greatest possible exactness in their determinations, as well
as the accordances themselves, become clear at a glance. The planets
are formed out of particles which, at the distance at which they move,
have exact movements in circular orbits; \emph{and therefore the masses
composed out of them will continue the same movements and at the same
rate and in the same direction}.''%
\footnote{Kant's \emph{Cosmogony}, ed.\ and trans.\ by W.\ Hartie, D.D.,
Glasgow, 900, pp.\ 74-81.%
}
\end{quotation}
{}

It must be admitted that this explanation leaves a good deal to be
desired. It is the explanation of a metaphysician rather than that
of an experimental scientist. Such phrases as {}``matter immediately
begins to strive to fashion itself,''\ for example, have no place
in the reasoning of inductive science. Nevertheless, the hypothesis
of Kant is a remarkable conception; it attempts to explain along rational
lines something which hitherto had for the most part been considered
altogether inexplicable.

But there are various questions that at once suggest themselves which
the Kantian theory leaves unanswered. How happens it, for example,
that the cosmic mass which gave birth to our solar system was divided
into several planetary bodies instead of remaining a single mass?
Were the planets struck from the sun by the chance impact of comets,
as Buffon has suggested?\ or thrown out by explosive volcanic action,
in accordance with the theory of Dr.\ Darwin?\ or do they owe their
origin to some unknown law? In any event, how chanced it that all
were projected in nearly the same plane as we now find them?


\section*{\raggedright LAPLACE AND THE NEBULAR HYPOTHESIS}

\addcontentsline{toc}{section}{LAPLACE AND THE NEBULAR\\
HYPOTHESIS}

It remained for a mathematical astronomer to solve these puzzles.
The man of all others competent to take the subject in hand was the
French astronomer Laplace. For a quarter of a century he had devoted
his transcendent mathematical abilities to the solution of problems
of motion of the heavenly bodies. Working in friendly rivalry with
his countryman Lagrange, his only peer among the mathematicians of
the age, he had taken up and solved one by one the problems that Newton
left obscure. Largely through the efforts of these two men the last
lingering doubts as to the solidarity of the Newtonian hypothesis
of universal gravitation had been removed. The share of Lagrange was
hardly less than that of his co-worker; but Laplace will longer be
remembered, because he ultimately brought his completed labors into
a system, and, incorporating with them the labors of his contemporaries,
produced in the \emph{M\'{e}canique C\'{e}leste} the undisputed
mathematical monument of the century, a fitting complement to the
\emph{Principia} of Newton, which it supplements and in a sense completes.

In the closing years of the eighteenth century Laplace took up the
nebular hypothesis of cosmogony, to which we have just referred, and
gave it definite proportions; in fact, made it so thoroughly his own
that posterity will always link it with his name. Discarding the crude
notions of cometary impact and volcanic eruption, Laplace filled up
the gaps in the hypothesis with the aid of well-known laws of gravitation
and motion. He assumed that the primitive mass of cosmic matter which
was destined to form our solar system was revolving on its axis even
at a time when it was still nebular in character, and filled all space
to a distance far beyond the present limits of the system. As this
vaporous mass contracted through loss of heat, it revolved more and
more swiftly, and from time to time, through balance of forces at
its periphery, rings of its substance were whirled off and left revolving
there, subsequently to become condensed into planets, and in their
turn whirl off minor rings that became moons. The main body of the
original mass remains in the present as the still contracting and
rotating body which we call the sun.

Let us allow Laplace to explain all this in detail:\ 

\begin{quotation}
{}``In order to explain the prime movements of the planetary system,''\ he
says, {}``there are the five following phenomena: The movement of
the planets in the same direction and very nearly in the same plane;
the movement of the satellites in the same direction as that of the
planets; the rotation of these different bodies and the sun in the
same direction as their revolution, and in nearly the same plane;
the slight eccentricity of the orbits of the planets and of the satellites;
and, finally, the great eccentricity of the orbits of the comets,
as if their inclinations had been left to chance.

{}``Buffon is the only man I know who, since the discovery of the
true system of the world, has endeavored to show the origin of the
planets and their satellites. He supposes that a comet, in falling
into the sun, drove from it a mass of matter which was reassembled
at a distance in the form of various globes more or less large, and
more or less removed from the sun, and that these globes, becoming
opaque and solid, are now the planets and their satellites.

{}``This hypothesis satisfies the first of the five preceding phenomena;
for it is clear that all the bodies thus formed would move very nearly
in the plane which passed through the centre of the sun, and in the
direction of the torrent of matter which was produced; but the four
other phenomena appear to be inexplicable to me by this means. Indeed,
the absolute movement of the molecules of a planet ought then to be
in the direction of the movement of its centre of gravity; but it
does not at all follow that the motion of the rotation of the planets
should be in the same direction. Thus the earth should rotate from
east to west, but nevertheless the absolute movement of its molecules
should be from east to west; and this ought also to apply to the movement
of the revolution of the satellites, in which the direction, according
to the hypothesis which he offers, is not necessarily the same as
that of the progressive movement of the planets.

{}``A phenomenon not only very difficult to explain under this hypothesis,
but one which is even contrary to it, is the slight eccentricity of
the planetary orbits. We know, by the theory of central forces, that
if a body moves in a closed orbit around the sun and touches it, it
also always comes back to that point at every revolution; whence it
follows that if the planets were originally detached from the sun,
they would touch it at each return towards it, and their orbits, far
from being circular, would be very eccentric. It is true that a mass
of matter driven from the sun cannot be exactly compared to a globe
which touches its surface, for the impulse which the particles of
this mass receive from one another and the reciprocal attractions
which they exert among themselves, could, in changing the direction
of their movements, remove their perihelions from the sun; but their
orbits would be always most eccentric, or at least they would not
have slight eccentricities except by the most extraordinary chance.
Thus we cannot see, according to the hypothesis of Buffon, why the
orbits of more than a hundred comets already observed are so elliptical.
This hypothesis is therefore very far from satisfying the preceding
phenomena. Let us see if it is possible to trace them back to their
true cause.

%
\begin{figure}
\noindent \begin{center}\includegraphics[  width=1.0\columnwidth]{3hsci10-Wil3Sc34}\end{center}

\noindent \begin{center}\noun{\small Pierre Simon de Laplace}\end{center}{\small \par}

\noindent \begin{center}\emph{\footnotesize (From a painting by Nedeon)}\end{center}
\end{figure}
{}``Whatever may be its ultimate nature, seeing that it has caused
or modified the movements of the planets, it is necessary that this
cause should embrace every body, and, in view of the enormous distances
which separate them, it could only have been a fluid of immense extent.
In order to have given them an almost circular movement in the same
direction around the sun, it is necessary that this fluid should have
enveloped the sun as in an atmosphere. The consideration of the planetary
movements leads us then to think that, on account of excessive heat,
the atmosphere of the sun originally extended beyond the orbits of
all the planets, and that it was successively contracted to its present
limits.

{}``In the primitive condition in which we suppose the sun to have
been, it resembled a nebula such as the telescope shows is composed
of a nucleus more or less brilliant, surrounded by a nebulosity which,
on condensing itself towards the centre, forms a star. If it is conceived
by analogy that all the stars were formed in this manner, it is possible
to imagine their previous condition of nebulosity, itself preceded
by other states in which the nebulous matter was still more diffused,
the nucleus being less and less luminous. By going back as far as
possible, we thus arrive at a nebulosity so diffused that its existence
could hardly be suspected.

{}``For a long time the peculiar disposition of certain stars, visible
to the unaided eye, has struck philosophical observers. Mitchell has
already remarked how little probable it is that the stars in the Pleiades,
for example, could have been contracted into the small space which
encloses them by the fortuity of chance alone, and he has concluded
that this group of stars, and similar groups which the skies present
to us, are the necessary result of the condensation of a nebula, with
several nuclei, and it is evident that a nebula, by continually contracting,
towards these various nuclei, at length would form a group of stars
similar to the Pleiades. The condensation of a nebula with two nuclei
would form a system of stars close together, turning one upon the
other, such as those double stars of which we already know the respective
movements.

{}``But how did the solar atmosphere determine the movements of the
rotation and revolution of the planets and satellites? If these bodies
had penetrated very deeply into this atmosphere, its resistance would
have caused them to fall into the sun. We can therefore conjecture
that the planets were formed at their successive limits by the condensation
of a zone of vapors which the sun, on cooling, left behind, in the
plane of his equator.

{}``Let us recall the results which we have given in a preceding
chapter. The atmosphere of the sun could not have extended indefinitely.
Its limit was the point where the centrifugal force due to its movement
of rotation balanced its weight. But in proportion as the cooling
contracted the atmosphere, and those molecules which were near to
them condensed upon the surface of the body, the movement of the rotation
increased; for, on account of the Law of Areas, the sum of the areas
described by the vector of each molecule of the sun and its atmosphere
and projected in the plane of the equator being always the same, the
rotation should increase when these molecules approach the centre
of the sun. The centrifugal force due to this movement becoming thus
larger, the point where the weight is equal to it is nearer the sun.
Supposing, then, as it is natural to admit, that the atmosphere extended
at some period to its very limits, it should, on cooling, leave molecules
behind at this limit and at limits successively occasioned by the
increased rotation of the sun. The abandoned molecules would continue
to revolve around this body, since their centrifugal force was balanced
by their weight. But this equilibrium not arising in regard to the
atmospheric molecules parallel to the solar equator, the latter, on
account of their weight, approached the atmosphere as they condensed,
and did not cease to belong to it until by this motion they came upon
the equator.

{}``Let us consider now the zones of vapor successively left behind.
These zones ought, according to appearance, by the condensation and
mutual attraction of their molecules, to form various concentric rings
of vapor revolving around the sun. The mutual gravitational friction
of each ring would accelerate some and retard others, until they had
all acquired the same angular velocity. Thus the actual velocity of
the molecules most removed from the sun would be the greatest. The
following cause would also operate to bring about this difference
of speed. The molecules farthest from the sun, and which by the effects
of cooling and condensation approached one another to form the outer
part of the ring, would have always described areas proportional to
the time since the central force by which they were controlled has
been constantly directed towards this body. But this constancy of
areas necessitates an increase of velocity proportional to the distance.
It is thus seen that the same cause would diminish the velocity of
the molecules which form the inner part of the ring.

{}``If all the molecules of the ring of vapor continued to condense
without disuniting, they would at length form a ring either solid
or fluid. But this formation would necessitate such a regularity in
every part of the ring, and in its cooling, that this phenomenon is
extremely rare; and the solar system affords us, indeed, but one example---namely,
in the ring of Saturn. In nearly every case the ring of vapor was
broken into several masses, each moving at similar velocities, and
continuing to rotate at the same distance around the sun. These masses
would take a spheroid form with a rotatory movement in the direction
of the revolution, because their inner molecules had less velocity
than the outer. Thus were formed so many planets in a condition of
vapor. But if one of them were powerful enough to reunite successively
by its attraction all the others around its centre of gravity, the
ring of vapor would be thus transformed into a single spheroidical
mass of vapor revolving around the sun with a rotation in the direction
of its revolution. The latter case has been that which is the most
common, but nevertheless the solar system affords us an instance of
the first case in the four small planets which move between Jupiter
and Mars; at least, if we do not suppose, as does M.\ Olbers, that
they originally formed a single planet which a mighty explosion broke
up into several portions each moving at different velocities.

{}``According to our hypothesis, the comets are strangers to our
planetary system. In considering them, as we have done, as minute
nebulosities, wandering from solar system to solar system, and formed
by the condensation of the nebulous matter everywhere existent in
profusion in the universe, we see that when they come into that part
of the heavens where the sun is all-powerful, he forces them to describe
orbits either elliptical or hyperbolic, their paths being equally
possible in all directions, and at all inclinations of the ecliptic,
conformably to what has been observed. Thus the condensation of nebulous
matter, by which we have at first explained the motions of the rotation
and revolution of the planets and their satellites in the same direction,
and in nearly approximate planes, explains also why the movements
of the comets escape this general law.''%
\footnote{\emph{Exposition du syst\`{e}me du monde} (included in \emph{\OE{}uvres
Completes}), by M.\ l\'{e} Marquis de Laplace, vol.\ VI., p.\ 498. %
}
\end{quotation}
{}

The nebular hypothesis thus given detailed completion by Laplace is
a worthy complement of the grand cosmologic scheme of Herschel. Whether
true or false, the two conceptions stand as the final contributions
of the eighteenth century to the history of man's ceaseless efforts
to solve the mysteries of cosmic origin and cosmic structure. The
world listened eagerly and without prejudice to the new doctrines;
and that attitude tells of a marvellous intellectual growth of our
race. Mark the transition. In the year 1600, Bruno was burned at the
stake for teaching that our earth is not the centre of the universe.
In 1700, Newton was pronounced {}``impious and heretical''\ by
a large school of philosophers for declaring that the force which
holds the planets in their orbits is universal gravitation. In 1800,
Laplace and Herschel are honored for teaching that gravitation built
up the system which it still controls; that our universe is but a
minor nebula, our sun but a minor star, our earth a mere atom of matter,
our race only one of myriad races peopling an infinity of worlds.
Doctrines which but the span of two human lives before would have
brought their enunciators to the stake were now pronounced not impious,
but sublime.


\section*{\raggedright ASTEROIDS AND SATELLITES}

\addcontentsline{toc}{section}{ASTEROIDS AND SATELLITES}

The first day of the nineteenth century was fittingly signalized by
the discovery of a new world. On the evening of January 1, 1801, an
Italian astronomer, Piazzi, observed an apparent star of about the
eighth magnitude (hence, of course, quite invisible to the unaided
eye), which later on was seen to have moved, and was thus shown to
be vastly nearer the earth than any true star. He at first supposed,
as Herschel had done when he first saw Uranus, that the unfamiliar
body was a comet; but later observation proved it a tiny planet, occupying
a position in space between Mars and Jupiter. It was christened Ceres,
after the tutelary goddess of Sicily.

Though unpremeditated, this discovery was not unexpected, for astronomers
had long surmised the existence of a planet in the wide gap between
Mars and Jupiter. Indeed, they were even preparing to make concerted
search for it, despite the protests of philosophers, who argued that
the planets could not possibly exceed the magic number seven, when
Piazzi forestalled their efforts. But a surprise came with the sequel;
for the very next year Dr.\ Olbers, the wonderful physician-astronomer
of Bremen, while following up the course of Ceres, happened on another
tiny moving star, similarly located, which soon revealed itself as
planetary. Thus two planets were found where only one was expected.

The existence of the supernumerary was a puzzle, but Olbers solved
it for the moment by suggesting that Ceres and Pallas, as he called
his captive, might be fragments of a \emph{quondam} planet, shattered
by internal explosion or by the impact of a comet. Other similar fragments,
he ventured to predict, would be found when searched for. William
Herschel sanctioned this theory, and suggested the name asteroids
for the tiny planets. The explosion theory was supported by the discovery
of another asteroid, by Harding, of Lilienthal, in 1804, and it seemed
clinched when Olbers himself found a fourth in 1807. The new-comers
were named Juno and Vesta respectively.

There the case rested till 1845, when a Prussian amateur astronomer
named Hencke found another asteroid, after long searching, and opened
a new epoch of discovery. From then on the finding of asteroids became
a commonplace. Latterly, with the aid of photography, the list has
been extended to above four hundred, and as yet there seems no dearth
in the supply, though doubtless all the larger members have been revealed.
Even these are but a few hundreds of miles in diameter, while the
smaller ones are too tiny for measurement. The combined bulk of these
minor planets is believed to be but a fraction of that of the earth.

Olbers's explosion theory, long accepted by astronomers, has been
proven open to fatal objections. The minor planets are now believed
to represent a ring of cosmical matter, cast off from the solar nebula
like the rings that went to form the major planets, but prevented
from becoming aggregated into a single body by the perturbing mass
of Jupiter.


\subsection*{\raggedright The Discovery of Neptune}

\addcontentsline{toc}{subsection}{The Discovery of Neptune}

As we have seen, the discovery of the first asteroid confirmed a conjecture;
the other important planetary discovery of the nineteenth century
fulfilled a prediction. Neptune was found through scientific prophecy.
No one suspected the existence of a trans-Uranian planet till Uranus
itself, by hair-breadth departures from its predicted orbit, gave
out the secret. No one saw the disturbing planet till the pencil of
the mathematician, with almost occult divination, had pointed out
its place in the heavens. The general predication of a trans-Uranian
planet was made by Bessel, the great K\"{o}nigsberg astronomer, in
1840; the analysis that revealed its exact location was undertaken,
half a decade later, by two independent workers---John Couch Adams,
just graduated senior wrangler at Cambridge, England, and U.\ J.\ J.\ Leverrier,
the leading French mathematician of his generation.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{3hsci10-Wil3Sc42}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Friedrich Wilhelm Bessel}\end{center}
\end{figure}
Adams's calculation was first begun and first completed. But it had
one radical defect---it was the work of a young and untried man. So
it found lodgment in a pigeon-hole of the desk of England's Astronomer
Royal, and an opportunity was lost which English astronomers have
never ceased to mourn. Had the search been made, an actual planet
would have been seen shining there, close to the spot where the pencil
of the mathematician had placed its hypothetical counterpart. But
the search was not made, and while the prophecy of Adams gathered
dust in that regrettable pigeon-hole, Leverrier's calculation was
coming on, his tentative results meeting full encouragement from Arago
and other French savants. At last the laborious calculations proved
satisfactory, and, confident of the result, Leverrier sent to the
Berlin observatory, requesting that search be made for the disturber
of Uranus in a particular spot of the heavens. Dr.\ Galle received
the request September 23, 1846. That very night he turned his telescope
to the indicated region, and there, within a single degree of the
suggested spot, he saw a seeming star, invisible to the unaided eye,
which proved to be the long-sought planet, henceforth to be known
as Neptune. To the average mind, which finds something altogether
mystifying about abstract mathematics, this was a feat savoring of
the miraculous.

Stimulated by this success, Leverrier calculated an orbit for an interior
planet from perturbations of Mercury, but though prematurely christened
Vulcan, this hypothetical nursling of the sun still haunts the realm
of the undiscovered, along with certain equally hypothetical trans-Neptunian
planets whose existence has been suggested by {}``residual perturbations''\ of
Uranus, and by the movements of comets. No other veritable additions
of the sun's planetary family have been made in our century, beyond
the finding of seven small moons, which chiefly attest the advance
in telescopic powers. Of these, the tiny attendants of our Martian
neighbor, discovered by Professor Hall with the great Washington refractor,
are of greatest interest, because of their small size and extremely
rapid flight. One of them is poised only six thousand miles from Mars,
and whirls about him almost four times as fast as he revolves, seeming
thus, as viewed by the Martian, to rise in the west and set in the
east, and making the month only one-fourth as long as the day.


\subsection*{\raggedright The Rings of Saturn}

\addcontentsline{toc}{subsection}{The Rings of Saturn}

The discovery of the inner or crape ring of Saturn, made simultaneously
in 1850 by William C.\ Bond, at the Harvard observatory, in America,
and the Rev.\ W.\ R.\ Dawes in England, was another interesting
optical achievement; but our most important advances in knowledge
of Saturn's unique system are due to the mathematician. Laplace, like
his predecessors, supposed these rings to be solid, and explained
their stability as due to certain irregularities of contour which
Herschel had pointed out. But about 1851 Professor Peirce, of Harvard,
showed the untenability of this conclusion, proving that were the
rings such as Laplace thought them they must fall of their own weight.
Then Professor J.\ Clerk-Maxwell, of Cambridge, took the matter in
hand, and his analysis reduced the puzzling rings to a cloud of meteoric
particles---a {}``shower of brickbats''---each fragment of which
circulates exactly as if it were an independent planet, though of
course perturbed and jostled more or less by its fellows. Mutual perturbations,
and the disturbing pulls of Saturn's orthodox satellites, as investigated
by Maxwell, explain nearly all the phenomena of the rings in a manner
highly satisfactory.

After elaborate mathematical calculations covering many pages of his
paper entitled {}``On the Stability of Saturn's Rings,''\ he summarizes
his deductions as follows:\ 

\begin{quotation}
{}``Let us now gather together the conclusions we have been able
to draw from the mathematical theory of various kinds of conceivable
rings.

{}``We found that the stability of the motion of a solid ring depended
on so delicate an adjustment, and at the same time so unsymmetrical
a distribution of mass, that even if the exact conditions were fulfilled,
it could scarcely last long, and, if it did, the immense preponderance
of one side of the ring would be easily observed, contrary to experience.
These considerations, with others derived from the mechanical structure
of so vast a body, compel us to abandon any theory of solid rings.

{}``We next examined the motion of a ring of equal satellites, and
found that if the mass of the planet is sufficient, any disturbances
produced in the arrangement of the ring will be propagated around
it in the form of waves, and will not introduce dangerous confusion.
If the satellites are unequal, the propagations of the waves will
no longer be regular, but disturbances of the ring will in this, as
in the former case, produce only waves, and not growing confusion.
Supposing the ring to consist, not of a single row of large satellites,
but a cloud of evenly distributed unconnected particles, we found
that such a cloud must have a very small density in order to be permanent,
and that this is inconsistent with its outer and inner parts moving
with the same angular velocity. Supposing the ring to be fluid and
continuous, we found that it will be necessarily broken up into small
portions.

{}``We conclude, therefore, that the rings must consist of disconnected
particles; these must be either solid or liquid, but they must be
independent. The entire system of rings must, therefore, consist either
of a series of many concentric rings each moving with its own velocity
and having its own system of waves, or else of a confused multitude
of revolving particles not arranged in rings and continually coming
into collision with one another.

{}``Taking the first case, we found that in an indefinite number
of possible cases the mutual perturbations of two rings, stable in
themselves, might mount up in time to a destructive magnitude, and
that such cases must continually occur in an extensive system like
that of Saturn, the only retarding cause being the irregularity of
the rings.

{}``The result of long-continued disturbance was found to be the
spreading-out of the rings in breadth, the outer rings pressing outward,
while the inner rings press inward.

{}``The final result, therefore, of the mechanical theory is that
the only system of rings which can exist is one composed of an indefinite
number of unconnected particles, revolving around the planet with
different velocities, according to their respective distances. These
particles may be arranged in series of narrow rings, or they may move
through one another irregularly. In the first case the destruction
of the system will be very slow, in the second case it will be more
rapid, but there may be a tendency towards arrangement in narrow rings
which may retard the process.

{}``We are not able to ascertain by observation the constitution
of the two outer divisions of the system of rings, but the inner ring
is certainly transparent, for the limb of Saturn has been observed
through it. It is also certain that though the space occupied by the
ring is transparent, it is not through the material parts of it that
the limb of Saturn is seen, for his limb was observed without distortion;
which shows that there was no refraction, and, therefore, that the
rays did not pass through a medium at all, but between the solar or
liquid particles of which the ring is composed. Here, then, we have
an optical argument in favor of the theory of independent particles
as the material of the rings. The two outer rings may be of the same
nature, but not so exceedingly rare that a ray of light can pass through
their whole thickness without encountering one of the particles.

{}``Finally, the two outer rings have been observed for two hundred
years, and it appears, from the careful analysis of all the observations
of M.\ Struve, that the second ring is broader than when first observed,
and that its inner edge is nearer the planet than formerly. The inner
ring also is suspected to be approaching the planet ever since its
discovery in 1850. These appearances seem to indicate the same slow
progress of the rings towards separation which we found to be the
result of theory, and the remark that the inner edge of the inner
ring is more distinct seems to indicate that the approach towards
the planet is less rapid near the edge, as we had reason to conjecture.
As to the apparent unchangeableness of the exterior diameter of the
outer ring, we must remember that the outer rings are certainly far
more dense than the inner one, and that a small change in the outer
rings must balance a great change in the inner one. It is possible,
however, that some of the observed changes may be due to the existence
of a resisting medium. If the changes already suspected should be
confirmed by repeated observations with the same instruments, it will
be worth while to investigate more carefully whether Saturn's rings
are permanent or transitory elements of the solar system, and whether
in that part of the heavens we see celestial immutability or terrestrial
corruption and generation, and the old order giving place to the new
before our eyes.''%
\footnote{From \emph{The Scientific Papers of J.\ Clerk-Maxwell}, edited by
W.\ D.\ Nevin, M.A.\ (2 vols.), vol.\ I., pp.\ 372-374. This
is a reprint of Clerk-Maxwell's prize paper of 1859.%
}
\end{quotation}

\subsection*{\raggedright Studies of the Moon}

\addcontentsline{toc}{subsection}{Studies of the Moon}

But perhaps the most interesting accomplishments of mathematical astronomy---from
a mundane standpoint, at any rate---are those that refer to the earth's
own satellite. That seemingly staid body was long ago discovered to
have a propensity to gain a little on the earth, appearing at eclipses
an infinitesimal moment ahead of time. Astronomers were sorely puzzled
by this act of insubordination; but at last Laplace and Lagrange explained
it as due to an oscillatory change in the earth's orbit, thus fully
exonerating the moon, and seeming to demonstrate the absolute stability
of our planetary system, which the moon's misbehavior had appeared
to threaten.

This highly satisfactory conclusion was an orthodox belief of celestial
mechanics until 1853, when Professor Adams of Neptunian fame, with
whom complex analyses were a pastime, reviewed Laplace's calculation,
and discovered an error which, when corrected, left about half the
moon's acceleration unaccounted for. This was a momentous discrepancy,
which at first no one could explain. But presently Professor Helmholtz,
the great German physicist, suggested that a key might be found in
tidal friction, which, acting as a perpetual brake on the earth's
rotation, and affecting not merely the waters but the entire substance
of our planet, must in the long sweep of time have changed its rate
of rotation. Thus the seeming acceleration of the moon might be accounted
for as actual retardation of the earth's rotation---a lengthening
of the day instead of a shortening of the month.

Again the earth was shown to be at fault, but this time the moon could
not be exonerated, while the estimated stability of our system, instead
of being re-established, was quite upset. For the tidal retardation
is not an oscillatory change which will presently correct itself,
like the orbital wobble, but a perpetual change, acting always in
one direction. Unless fully counteracted by some opposing reaction,
therefore (as it seems not to be), the effect must be cumulative,
the ultimate consequences disastrous. The exact character of these
consequences was first estimated by Professor G.\ H.\ Darwin in
1879. He showed that tidal friction, in retarding the earth, must
also push the moon out from the parent planet on a spiral orbit. Plainly,
then, the moon must formerly have been nearer the earth than at present.
At some very remote period it must have actually touched the earth;
must, in other words, have been thrown off from the then plastic mass
of the earth, as a polyp buds out from its parent polyp. At that time
the earth was spinning about in a day of from two to four hours.

Now the day has been lengthened to twenty-four hours, and the moon
has been thrust out to a distance of a quarter-million miles; but
the end is not yet. The same progress of events must continue, till,
at some remote period in the future, the day has come to equal the
month, lunar tidal action has ceased, and one face of the earth looks
out always at the moon with that same fixed stare which even now the
moon has been brought to assume towards her parent orb. Should we
choose to take even greater liberties with the future, it may be made
to appear (though some astronomers dissent from this prediction)\ that,
as solar tidal action still continues, the day must finally exceed
the month, and lengthen out little by little towards coincidence with
the year; and that the moon meantime must pause in its outward flight,
and come swinging back on a descending spiral, until finally, after
the lapse of untold \ae{}ons, it ploughs and ricochets along the
surface of the earth, and plunges to catastrophic destruction.

But even though imagination pause far short of this direful culmination,
it still is clear that modern calculations, based on inexorable tidal
friction, suffice to revolutionize the views formerly current as to
the stability of the planetary system. The eighteenth-century mathematician
looked upon this system as a vast celestial machine which had been
in existence about six thousand years, and which was destined to run
on forever. The analyst of to-day computes both the past and the future
of this system in millions instead of thousands of years, yet feels
well assured that the solar system offers no contradiction to those
laws of growth and decay which seem everywhere to represent the immutable
order of nature.


\section*{\raggedright COMETS AND METEORS}

\addcontentsline{toc}{section}{COMETS AND METEORS}

Until the mathematician ferreted out the secret, it surely never could
have been suspected by any one that the earth's serene attendant,\begin{verse}\footnotesize\ \\

\mbox{``That orbed maiden, with white fire laden,}\\*

\mbox{Whom mortals call the moon,''}\\

\ \end{verse}could be plotting injury to her parent orb. But there is another inhabitant
of the skies whose purposes have not been similarly free from popular
suspicion. Needless to say I refer to the black sheep of the sidereal
family, that {}``celestial vagabond''\ the comet.

Time out of mind these wanderers have been supposed to presage war,
famine, pestilence, perhaps the destruction of the world. And little
wonder. Here is a body which comes flashing out of boundless space
into our system, shooting out a pyrotechnic tail some hundreds of
millions of miles in length; whirling, perhaps, through the very atmosphere
of the sun at a speed of three or four hundred miles a second; then
darting off on a hyperbolic orbit that forbids it ever to return,
or an elliptical one that cannot be closed for hundreds or thousands
of years; the tail meantime pointing always away from the sun, and
fading to nothingness as the weird voyager recedes into the spatial
void whence it came. Not many times need the advent of such an apparition
coincide with the outbreak of a pestilence or the death of a C\ae{}sar
to stamp the race of comets as an ominous clan in the minds of all
superstitious generations.

It is true, a hard blow was struck at the prestige of these alleged
supernatural agents when Newton proved that the great comet of 1680
obeyed Kepler's laws in its flight about the sun; and an even harder
one when the same visitant came back in 1758, obedient to Halley's
prediction, after its three-quarters of a century of voyaging but
in the abyss of space. Proved thus to bow to natural law, the celestial
messenger could no longer fully sustain its r\^{o}le. But long-standing
notoriety cannot be lived down in a day, and the comet, though proved
a {}``natural''\ object, was still regarded as a very menacing
one for another hundred years or so. It remained for the nineteenth
century to completely unmask the pretender and show how egregiously
our forebears had been deceived.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{3hsci10-Wil3Sc52}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Heinrich Wilhelm Matthias Olbers}\end{center}
\end{figure}
The unmasking began early in the century, when Dr.\ Olbers, then
the highest authority on the subject, expressed the opinion that the
spectacular tail, which had all along been the comet's chief stock-in-trade
as an earth-threatener, is in reality composed of the most filmy vapors,
repelled from the cometary body by the sun, presumably through electrical
action, with a velocity comparable to that of light. This luminous
suggestion was held more or less in abeyance for half a century. Then
it was elaborated by Z\"{o}llner, and particularly by Bredichin,
of the Moscow observatory, into what has since been regarded as the
most plausible of cometary theories. It is held that comets and the
sun are similarly electrified, and hence mutually repulsive. Gravitation
vastly outmatches this repulsion in the body of the comet, but yields
to it in the case of gases, because electrical force varies with the
surface, while gravitation varies only with the mass. From study of
atomic weights and estimates of the velocity of thrust of cometary
tails, Bredichin concluded that the chief components of the various
kinds of tails are hydrogen, hydrocarbons, and the vapor of iron;
and spectroscopic analysis goes far towards sustaining these assumptions.

But, theories aside, the unsubstantialness of the comet's tail has
been put to a conclusive test. Twice during the nineteenth century
the earth has actually plunged directly through one of these threatening
appendages---in 1819, and again in 1861, once being immersed to a
depth of some three hundred thousand miles in its substance. Yet nothing
dreadful happened to us. There was a peculiar glow in the atmosphere,
so the more imaginative observers thought, and that was all. After
such fiascos the cometary train could never again pose as a world-destroyer.

But the full measure of the comet's humiliation is not yet told. The
pyrotechnic tail, composed as it is of portions of the comet's actual
substance, is tribute paid the sun, and can never be recovered. Should
the obeisance to the sun be many times repeated, the train-forming
material will be exhausted, and the comet's chiefest glory will have
departed. Such a fate has actually befallen a multitude of comets
which Jupiter and the other outlying planets have dragged into our
system and helped the sun to hold captive here. Many of these tailless
comets were known to the eighteenth-century astronomers, but no one
at that time suspected the true meaning of their condition. It was
not even known how closely some of them are enchained until the German
astronomer Encke, in 1822, showed that one which he had rediscovered,
and which has since borne his name, was moving in an orbit so contracted
that it must complete its circuit in about three and a half years.
Shortly afterwards another comet, revolving in a period of about six
years, was discovered by Biela, and given his name. Only two more
of these short-period comets were discovered during the first half
of last century, but latterly they have been shown to be a numerous
family. Nearly twenty are known which the giant Jupiter holds so close
that the utmost reach of their elliptical tether does not let them
go beyond the orbit of Saturn. These aforetime wanderers have adapted
themselves wonderfully to planetary customs, for all of them revolve
in the same direction with the planets, and in planes not wide of
the ecliptic.

Checked in their proud hyperbolic sweep, made captive in a planetary
net, deprived of their trains, these \emph{quondam} free-lances of
the heavens are now mere shadows of their former selves. Considered
as to mere bulk, they are very substantial shadows, their extent being
measured in hundreds of thousands of miles; but their actual mass
is so slight that they are quite at the mercy of the gravitational
pulls of their captors. And worse is in store for them. So persistently
do sun and planets tug at them that they are doomed presently to be
torn into shreds.

Such a fate has already overtaken one of them, under the very eyes
of the astronomers, within the relatively short period during which
these ill-fated comets have been observed. In 1832 Biela's comet passed
quite near the earth, as astronomers measure distance, and in doing
so created a panic on our planet. It did no greater harm than that,
of course, and passed on its way as usual. The very next time it came
within telescopic hail it was seen to have broken into two fragments.
Six years later these fragments were separated by many millions of
miles; and in 1852, when the comet was due again, astronomers looked
for it in vain. It had been completely shattered.

What had become of the fragments? At that time no one positively knew.
But the question was to be answered presently. It chanced that just
at this period astronomers were paying much attention to a class of
bodies which they had hitherto somewhat neglected, the familiar shooting-stars,
or meteors. The studies of Professor Newton, of Yale, and Professor
Adams, of Cambridge, with particular reference to the great meteor-shower
of November, 1866, which Professor Newton had predicted and shown
to be recurrent at intervals of thirty-three years, showed that meteors
are not mere sporadic swarms of matter flying at random, but exist
in isolated swarms, and sweep about the sun in regular elliptical
orbits.

Presently it was shown by the Italian astronomer Schiaparelli that
one of these meteor swarms moves in the orbit of a previously observed
comet, and other coincidences of the kind were soon forthcoming. The
conviction grew that meteor swarms are really the debris of comets;
and this conviction became a practical certainty when, in November,
1872, the earth crossed the orbit of the ill-starred Biela, and a
shower of meteors came whizzing into our atmosphere in lieu of the
lost comet.

And so at last the full secret was out. The awe-inspiring comet, instead
of being the planetary body it had all along been regarded, is really
nothing more nor less than a great aggregation of meteoric particles,
which have become clustered together out in space somewhere, and which
by jostling one another or through electrical action become luminous.
So widely are the individual particles separated that the cometary
body as a whole has been estimated to be thousands of times less dense
than the earth's atmosphere at sea-level. Hence the ease with which
the comet may be dismembered and its particles strung out into streaming
swarms.

So thickly is the space we traverse strewn with this cometary dust
that the earth sweeps up, according to Professor Newcomb's estimate,
a million tons of it each day. Each individual particle, perhaps no
larger than a millet seed, becomes a shooting-star, or meteor, as
it burns to vapor in the earth's upper atmosphere. And if one tiny
planet sweeps up such masses of this cosmic matter, the amount of
it in the entire stretch of our system must be beyond all estimate.
What a story it tells of the myriads of cometary victims that have
fallen prey to the sun since first he stretched his planetary net
across the heavens!


\section*{\raggedright THE FIXED STARS}

\addcontentsline{toc}{section}{THE FIXED STARS}

When Biela's comet gave the inhabitants of the earth such a fright
in 1832, it really did not come within fifty millions of miles of
us. Even the great comet through whose filmy tail the earth passed
in 1861 was itself fourteen millions of miles away. The ordinary mind,
schooled to measure space by the tiny stretches of a pygmy planet,
cannot grasp the import of such distances; yet these are mere units
of measure compared with the vast stretches of sidereal space. Were
the comet which hurtles past us at a speed of, say, a hundred miles
a second to continue its mad flight unchecked straight into the void
of space, it must fly on its frigid way eight thousand years before
it could reach the very nearest of our neighbor stars; and even then
it would have penetrated but a mere arm's-length into the vistas where
lie the dozen or so of sidereal residents that are next beyond. Even
to the trained mind such distances are only vaguely imaginable. Yet
the astronomer of our century has reached out across this unthinkable
void and brought back many a secret which our predecessors thought
forever beyond human grasp.

A tentative assault upon this stronghold of the stars was being made
by Herschel at the beginning of the century. In 1802 that greatest
of observing astronomers announced to the Royal Society his discovery
that certain double stars had changed their relative positions towards
one another since he first carefully charted them twenty years before.
Hitherto it had been supposed that double stars were mere optical
effects. Now it became clear that some of them, at any rate, are true
{}``binary systems,''\ linked together presumably by gravitation
and revolving about one another. Halley had shown, three-quarters
of a century before, that the stars have an actual or {}``proper''\ motion
in space; Herschel himself had proved that the sun shares this motion
with the other stars. Here was another shift of place, hitherto quite
unsuspected, to be reckoned with by the astronomer in fathoming sidereal
secrets.


\subsection*{\raggedright Double Stars}

\addcontentsline{toc}{subsection}{Double Stars}

When John Herschel, the only son and the worthy successor of the great
astronomer, began star-gazing in earnest, after graduating senior
wrangler at Cambridge, and making two or three tentative professional
starts in other directions to which his versatile genius impelled
him, his first extended work was the observation of his father's double
stars. His studies, in which at first he had the collaboration of
Mr.\ James South, brought to light scores of hitherto unrecognized
pairs, and gave fresh data for the calculation of the orbits of those
longer known. So also did the independent researches of F.\ G.\ W.\ Struve,
the enthusiastic observer of the famous Russian observatory at the
university of Dorpat, and subsequently at Pulkowa. Utilizing data
gathered by these observers, M.\ Savary, of Paris, showed, in 1827,
that the observed elliptical orbits of the double stars are explicable
by the ordinary laws of gravitation, thus confirming the assumption
that Newton's laws apply to these sidereal bodies. Henceforth there
could be no reason to doubt that the same force which holds terrestrial
objects on our globe pulls at each and every particle of matter throughout
the visible universe.

The pioneer explorers of the double stars early found that the systems
into which the stars are linked are by no means confined to single
pairs. Often three or four stars are found thus closely connected
into gravitation systems; indeed, there are all gradations between
binary systems and great clusters containing hundreds or even thousands
of members. It is known, for example, that the familiar cluster of
the Pleiades is not merely an optical grouping, as was formerly supposed,
but an actual federation of associated stars, some two thousand five
hundred in number, only a few of which are visible to the unaided
eve. And the more carefully the motions of the stars are studied,
the more evident it becomes that widely separated stars are linked
together into infinitely complex systems, as yet but little understood.
At the same time, all instrumental advances tend to resolve more and
more seemingly single stars into close pairs and minor clusters. The
two Herschels between them discovered some thousands of these close
multiple systems; Struve and others increased the list to above ten
thousand; and Mr.\ S.\ W. Burnham, of late years the most enthusiastic
and successful of double-star pursuers, added a thousand new discoveries
while he was still an amateur in astronomy, and by profession the
stenographer of a Chicago court. Clearly the actual number of multiple
stars is beyond all present estimate.

The elder Herschel's early studies of double stars were undertaken
in the hope that these objects might aid him in ascertaining the actual
distance of a star, through measurement of its annual parallax---that
is to say, of the angle which the diameter of the earth's orbit would
subtend as seen from the star. The expectation was not fulfilled.
The apparent shift of position of a star as viewed from opposite sides
of the earth's orbit, from which the parallax might be estimated,
is so extremely minute that it proved utterly inappreciable, even
to the almost preternaturally acute vision of Herschel, with the aid
of any instrumental means then at command. So the problem of star
distance allured and eluded him to the end, and he died in 1822 without
seeing it even in prospect of solution. His estimate of the minimum
distance of the nearest star, based though it was on the fallacious
test of apparent brilliancy, was a singularly sagacious one, but it
was at best a scientific guess, not a scientific measurement.


\subsection*{\raggedright The Distance of the Stars}

\addcontentsline{toc}{subsection}{The Distance of the Stars}

Just about this time, however, a great optician came to the aid of
the astronomers. Joseph Fraunhofer perfected the refracting telescope,
as Herschel had perfected the reflector, and invented a wonderfully
accurate {}``heliometer,''\ or sun-measurer. With the aid of these
instruments the old and almost infinitely difficult problem of star
distance was solved. In 1838 Bessel announced from the K\"{o}nigsberg
observatory that he had succeeded, after months of effort, in detecting
and measuring the parallax of a star. Similar claims had been made
often enough before, always to prove fallacious when put to further
test; but this time the announcement carried the authority of one
of the greatest astronomers of the age, and scepticism was silenced.

Nor did Bessel's achievement long await corroboration. Indeed, as
so often happens in fields of discovery, two other workers had almost
simultaneously solved the same problem---Struve at Pulkowa, where
the great Russian observatory, which so long held the palm over all
others, had now been established; and Thomas Henderson, then working
at the Cape of Good Hope, but afterwards the Astronomer Royal of Scotland.
Henderson's observations had actual precedence in point of time, but
Bessel's measurements were so much more numerous and authoritative
that he has been uniformly considered as deserving the chief credit
of the discovery, which priority of publication secured him.

By an odd chance, the star on which Henderson's observations were
made, and consequently the first star the parallax of which was ever
measured, is our nearest neighbor in sidereal space, being, indeed,
some ten billions of miles nearer than the one next beyond. Yet even
this nearest star is more than two hundred thousand times as remote
from us as the sun. The sun's light flashes to the earth in eight
minutes, and to Neptune in about three and a half hours, but it requires
three and a half years to signal Alpha Centauri. And as for the great
majority of the stars, had they been blotted out of existence before
the Christian era, we of to-day should still receive their light and
seem to see them just as we do. When we look up to the sky, we study
ancient history; we do not see the stars as they \textit{are}, but
as they \textit{were} years, centuries, even millennia ago.

The information derived from the parallax of a star by no means halts
with the disclosure of the distance of that body. Distance known,
the proper motion of the star, hitherto only to be reckoned as so
many seconds of arc, may readily be translated into actual speed of
progress; relative brightness becomes absolute lustre, as compared
with the sun; and in the case of the double stars the absolute mass
of the components may be computed from the laws of gravitation. It
is found that stars differ enormously among themselves in all these
regards. As to speed, some, like our sun, barely creep through space---compassing
ten or twenty miles a second, it is true, yet even at that rate only
passing through the equivalent of their own diameter in a day. At
the other extreme, among measured stars, is one that moves two hundred
miles a second; yet even this {}``flying star,''\ as seen from
the earth, seems to change its place by only about three and a half
lunar diameters in a thousand years. In brightness, some stars yield
to the sun, while others surpass him as the arc-light surpasses a
candle. Arcturus, the brightest measured star, shines like two hundred
suns; and even this giant orb is dim beside those other stars which
are so distant that their parallax cannot be measured, yet which greet
our eyes at first magnitude. As to actual bulk, of which apparent
lustre furnishes no adequate test, some stars are smaller than the
sun, while others exceed him hundreds or perhaps thousands of times.
Yet one and all, so distant are they, remain mere disklike points
of light before the utmost powers of the modern telescope.


\subsection*{\raggedright Revelations of the Spectroscope}

\addcontentsline{toc}{subsection}{Revelations of the Spectroscope}

All this seems wonderful enough, but even greater things were in store.
In 1859 the spectroscope came upon the scene, perfected by Kirchhoff
and Bunsen, along lines pointed out by Fraunhofer almost half a century
before. That marvellous instrument, by revealing the telltale lines
sprinkled across a prismatic spectrum, discloses the chemical nature
and physical condition of any substance whose light is submitted to
it, telling its story equally well, provided the light be strong enough,
whether the luminous substance be near or far---in the same room or
at the confines of space. Clearly such an instrument must prove a
veritable magic wand in the hands of the astronomer.

Very soon eager astronomers all over the world were putting the spectroscope
to the test. Kirchhoff himself led the way, and Donati and Father
Secchi in Italy, Huggins and Miller in England, and Rutherfurd in
America, were the chief of his immediate followers. The results exceeded
the dreams of the most visionary. At the very outset, in 1860, it
was shown that such common terrestrial substances as sodium, iron,
calcium, magnesium, nickel, barium, copper, and zinc exist in the
form of glowing vapors in the sun, and very soon the stars gave up
a corresponding secret. Since then the work of solar and sidereal
analysis has gone on steadily in the hands of a multitude of workers
(prominent among whom, in this country, are Professor Young of Princeton,
Professor Langley of Washington, and Professor Pickering of Harvard),
and more than half the known terrestrial elements have been definitely
located in the sun, while fresh discoveries are in prospect.

It is true the sun also contains some seeming elements that are unknown
on the earth, but this is no matter for surprise. The modern chemist
makes no claim for his elements except that they have thus far resisted
all human efforts to dissociate them; it would be nothing strange
if some of them, when subjected to the crucible of the sun, which
is seen to vaporize iron, nickel, silicon, should fail to withstand
the test. But again, chemistry has by no means exhausted the resources
of the earth's supply of raw material, and the substance which sends
its message from a star may exist undiscovered in the dust we tread
or in the air we breathe. In the year 1895 two new terrestrial elements
were discovered; but one of these had for years been known to the
astronomer as a solar and suspected as a stellar element, and named
helium because of its abundance in the sun. The spectroscope had reached
out millions of miles into space and brought back this new element,
and it took the chemist a score of years to discover that he had all
along had samples of the same substance unrecognized in his sublunary
laboratory. There is hardly a more picturesque fact than that in the
entire history of science.

But the identity in substance of earth and sun and stars was not more
clearly shown than the diversity of their existing physical conditions.
It was seen that sun and stars, far from being the cool, earthlike,
habitable bodies that Herschel thought them (surrounded by glowing
clouds, and protected from undue heat by other clouds), are in truth
seething caldrons of fiery liquid, or gas made viscid by condensation,
with lurid envelopes of belching flames. It was soon made clear, also,
particularly by the studies of Rutherfurd and of Secchi, that stars
differ among themselves in exact constitution or condition. There
are white or Sirian stars, whose spectrum revels in the lines of hydrogen;
yellow or solar stars (our sun being the type), showing various metallic
vapors; and sundry red stars, with banded spectra indicative of carbon
compounds; besides the purely gaseous stars of more recent discovery,
which Professor Pickering had specially studied. Z\"{o}llner's famous
interpretation of these diversities, as indicative of varying stages
of cooling, has been called in question as to the exact sequence it
postulates, but the general proposition that stars exist under widely
varying conditions of temperature is hardly in dispute.

The assumption that different star types mark varying stages of cooling
has the further support of modern physics, which has been unable to
demonstrate any way in which the sun's radiated energy may be restored,
or otherwise made perpetual, since meteoric impact has been shown
to be---under existing conditions, at any rate---inadequate. In accordance
with the theory of Helmholtz, the chief supply of solar energy is
held to be contraction of the solar mass itself; and plainly this
must have its limits. Therefore, unless some means as yet unrecognized
is restoring the lost energy to the stellar bodies, each of them must
gradually lose its lustre, and come to a condition of solidification,
seeming sterility, and frigid darkness. In the case of our own particular
star, according to the estimate of Lord Kelvin, such a culmination
appears likely to occur within a period of five or six million years.


\subsection*{\raggedright The Astronomy of the Invisible}

\addcontentsline{toc}{subsection}{The Astronomy of the Invisible}

But by far the strongest support of such a forecast as this is furnished
by those stellar bodies which even now appear to have cooled to the
final stage of star development and ceased to shine. Of this class
examples in miniature are furnished by the earth and the smaller of
its companion planets. But there are larger bodies of the same type
out in stellar space---veritable {}``dark stars''---invisible, of
course, yet nowadays clearly recognized.

The opening up of this {}``astronomy of the invisible'' is another
of the great achievements of the nineteenth century, and again it
is Bessel to whom the honor of discovery is due. While testing his
stars for parallax; that astute observer was led to infer, from certain
unexplained aberrations of motion, that various stars, Sirius himself
among the number, are accompanied by invisible companions, and in
1840 he definitely predicated the existence of such {}``dark stars.''
The correctness of the inference was shown twenty years later, when
Alvan Clark, Jr., the American optician, while testing a new lens,
discovered the companion of Sirius, which proved thus to be faintly
luminous. Since then the existence of other and quite invisible star
companions has been proved incontestably, not merely by renewed telescopic
observations, but by the curious testimony of the ubiquitous spectroscope.

One of the most surprising accomplishments of that instrument is the
power to record the flight of a luminous object directly in the line
of vision. If the luminous body approaches swiftly, its Fraunhofer
lines are shifted from their normal position towards the violet end
of the spectrum; if it recedes, the lines shift in the opposite direction.
The actual motion of stars whose distance is unknown may be measured
in this way. But in certain cases the light lines are seen to oscillate
on the spectrum at regular intervals. Obviously the star sending such
light is alternately approaching and receding, and the inference that
it is revolving about a companion is unavoidable. From this extraordinary
test the orbital distance, relative mass, and actual speed of revolution
of the absolutely invisible body may be determined. Thus the spectroscope,
which deals only with light, makes paradoxical excursions into the
realm of the invisible. What secrets may the stars hope to conceal
when questioned by an instrument of such necromantic power?

But the spectroscope is not alone in this audacious assault upon the
strongholds of nature. It has a worthy companion and assistant in
the photographic film, whose efficient aid has been invoked by the
astronomer even more recently. Pioneer work in celestial photography
was, indeed, done by Arago in France and by the elder Draper in America
in 1839, but the results then achieved were only tentative, and it
was not till forty years later that the method assumed really important
proportions. In 1880, Dr.\ Henry Draper, at Hastings-on-the-Hudson,
made the first successful photograph of a nebula. Soon after, Dr.\ David
Gill, at the Cape observatory, made fine photographs of a comet, and
the flecks of starlight on his plates first suggested the possibilities
of this method in charting the heavens.

Since then star-charting with the film has come virtually to supersede
the old method. A concerted effort is being made by astronomers in
various parts of the world to make a complete chart of the heavens,
and before the close of our century this work will be accomplished,
some fifty or sixty millions of visible stars being placed on record
with a degree of accuracy hitherto unapproachable. Moreover, other
millions of stars are brought to light by the negative, which are
too distant or dim to be visible with any telescopic powers yet attained---a
fact which wholly discredits all previous inferences as to the limits
of our sidereal system. Hence, notwithstanding the wonderful instrumental
advances of the nineteenth century, knowledge of the exact form and
extent of our universe seems more unattainable than it seemed a century
ago.


\subsection*{\raggedright The Structure of Nebul\ae{}}

\addcontentsline{toc}{subsection}{The Structure of Nebul\ae{}}

Yet the new instruments, while leaving so much untold, have revealed
some vastly important secrets of cosmic structure. In particular,
they have set at rest the long-standing doubts as to the real structure
and position of the mysterious nebul\ae{}---those lazy masses, only
two or three of them visible to the unaided eye, which the telescope
reveals in almost limitless abundance, scattered everywhere among
the stars, but grouped in particular about the poles of the stellar
stream or disk which we call the Milky Way.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth,
  height=0.90\paperwidth,
  keepaspectratio]{3hsci10-Wil3Sc68}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Lord Rosse's Telescope}\end{center}{\small \par}

\noindent \begin{center}\emph{\footnotesize (From a photograph by
W. Lawrence, Dublin.)}\end{center}
\end{figure}
Herschel's later view, which held that some at least of the nebul\ae{}
are composed of a {}``shining fluid,''\ in process of condensation
to form stars, was generally accepted for almost half a century. But
in 1844, when Lord Rosse's great six-foot reflector---the largest
telescope ever yet constructed---was turned on the nebul\ae{}, it
made this hypothesis seem very doubtful. Just as Galileo's first lens
had resolved the Milky Way into stars, just as Herschel had resolved
nebul\ae{} that resisted all instruments but his own, so Lord Rosse's
even greater reflector resolved others that would not yield to Herschel's
largest mirror. It seemed a fair inference that with sufficient power,
perhaps some day to be attained, all nebul\ae{} would yield, hence
that all are in reality what Herschel had at first thought them---vastly
distant {}``island universes,''\ composed of aggregations of stars,
comparable to our own galactic system.

But the inference was wrong; for when the spectroscope was first applied
to a nebula in 1864, by Dr.\ Huggins, it clearly showed the spectrum
not of discrete stars, but of a great mass of glowing gases, hydrogen
among others. More extended studies showed, it is true, that some
nebul\ae{} give the continuous spectrum of solids or liquids, but
the different types intermingle and grade into one another. Also,
the closest affinity is shown between nebul\ae{} and stars. Some
nebul\ae{} are found to contain stars, singly or in groups, in their
actual midst; certain condensed {}``planetary''\ nebul\ae{} are
scarcely to be distinguished from stars of the gaseous type; and recently
the photographic film has shown the presence of nebulous matter about
stars that to telescopic vision differ in no respect from the generality
of their fellows in the galaxy. The familiar stars of the Pleiades
cluster, for example, appear on the negative immersed in a hazy blur
of light. All in all, the accumulated impressions of the photographic
film reveal a prodigality of nebulous matter in the stellar system
not hitherto even conjectured.

And so, of course, all question of {}``island universes'' vanishes,
and the nebul\ae{} are relegated to their true position as component
parts of the one stellar system---the one universe---that is open
to present human inspection. And these vast clouds of world-stuff
have been found by Professor Keeler, of the Lick observatory, to be
floating through space at the starlike speed of from ten to thirty-eight
miles per second.

The linking of nebul\ae{} with stars, so clearly evidenced by all
these modern observations, is, after all, only the scientific corroboration
of what the elder Herschel's later theories affirmed. But the nebul\ae{}
have other affinities not until recently suspected; for the spectra
of some of them are practically identical with the spectra of certain
comets. The conclusion seems warranted that comets are in point of
fact minor nebul\ae{} that are drawn into our system; or, putting
it otherwise, that the telescopic nebul\ae{} are simply gigantic
distant comets.


\subsection*{\raggedright Lockyer's Meteoric Hypothesis}

\addcontentsline{toc}{subsection}{Lockyer's Meteoric Hypothesis}

Following up the surprising clews thus suggested, Sir Norman Lockyer,
of London, has in recent years elaborated what is perhaps the most
comprehensive cosmogonic guess that has ever been attempted. His theory,
known as the {}``meteoric hypothesis,''\ probably bears the same
relation to the speculative thought of our time that the nebular hypothesis
of Laplace bore to that of the eighteenth century. Outlined in a few
words, it is an attempt to explain all the major phenomena of the
universe as due, directly or indirectly, to the gravitational impact
of such meteoric particles, or specks of cosmic dust, as comets are
composed of. Nebul\ae{} are vast cometary clouds, with particles
more or less widely separated, giving off gases through meteoric collisions,
internal or external, and perhaps glowing also with electrical or
phosphorescent light. Gravity eventually brings the nebular particles
into closer aggregations, and increased collisions finally vaporize
the entire mass, forming planetary nebul\ae{} and gaseous stars.
Continued condensation may make the stellar mass hotter and more luminous
for a time, but eventually leads to its liquefaction, and ultimate
consolidation---the aforetime nebul\ae{} becoming in the end a dark
or planetary star.

The exact correlation which Lockyer attempts to point out between
successive stages of meteoric condensation and the various types of
observed stellar bodies does not meet with unanimous acceptance. Mr.\ Ranyard,
for example, suggests that the visible nebul\ae{} may not be nascent
stars, but emanations from stars, and that the true pre-stellar nebul\ae{}
are invisible until condensed to stellar proportions. But such details
aside, the broad general hypothesis that all the bodies of the universe
are, so to speak, of a single species---that nebul\ae{} (including
comets), stars of all types, and planets, are but varying stages in
the life history of a single race or type of cosmic organisms---is
accepted by the dominant thought of our time as having the highest
warrant of scientific probability.

All this, clearly, is but an amplification of that nebular hypothesis
which, long before the spectroscope gave us warrant to accurately
judge our sidereal neighbors, had boldly imagined the development
of stars out of nebul\ae{} and of planets out of stars. But Lockyer's
hypothesis does not stop with this. Having traced the developmental
process from the nebular to the dark star, it sees no cause to abandon
this dark star to its fate by assuming, as the original speculation
assumed, that this is a culminating and final stage of cosmic existence.
For the dark star, though its molecular activities have come to relative
stability and impotence, still retains the enormous potentialities
of molar motion; and clearly, where motion is, stasis is not. Sooner
or later, in its ceaseless flight through space, the dark star must
collide with some other stellar body, as Dr.\ Croll imagines of the
dark bodies which his {}``pre-nebular theory''\ postulates. Such
collision may be long delayed; the dark star may be drawn in comet-like
circuit about thousands of other stellar masses, and be hurtled on
thousands of diverse parabolic or elliptical orbits, before it chances
to collide---but that matters not: {}``billions are the units in
the arithmetic of eternity,'' and sooner or later, we can hardly
doubt, a collision must occur. Then without question the mutual impact
must shatter both colliding bodies into vapor, or vapor combined with
meteoric fragments; in short, into a veritable nebula, the matrix
of future worlds. Thus the dark star, which is the last term of one
series of cosmic changes, becomes the first term of another series---at
once a post-nebular and a pre-nebular condition; and the nebular hypothesis,
thus amplified, ceases to be a mere linear scale, and is rounded out
to connote an unending series of cosmic cycles, more nearly satisfying
the imagination.

In this extended view, nebul\ae{} and luminous stars are but the
infantile and adolescent stages of the life history of the cosmic
individual; the dark star, its adult stage, or time of true virility.
Or we may think of the shrunken dark star as the germ-cell, the pollen-grain,
of the cosmic organism. Reduced in size, as becomes a germ-cell, to
a mere fraction of the nebular body from which it sprang, it yet retains
within its seemingly non-vital body all the potentialities of the
original organism, and requires only to blend with a fellow-cell to
bring a new generation into being. Thus may the cosmic race, whose
aggregate census makes up the stellar universe, be perpetuated---individual
solar systems, such as ours, being born, and growing old, and dying
to live again in their descendants, while the universe as a whole
maintains its unified integrity throughout all these internal mutations---passing
on, it may be, by infinitesimal stages, to a culmination hopelessly
beyond human comprehension.


\chapter*{\raggedright III. THE NEW SCIENCE OF PALEONTOLOGY}

\addcontentsline{toc}{chapter}{III. THE NEW SCIENCE OF\\
PALEONTOLOGY}

\markboth{A HISTORY OF SCIENCE, BOOK III}{III. PALEONTOLOGY}


\section*{\raggedright WILLIAM SMITH AND FOSSIL SHELLS}

\addcontentsline{toc}{section}{WILLIAM SMITH AND FOSSIL SHELLS}

Ever since Leonardo da Vinci first recognized the true character of
fossils, there had been here and there a man who realized that the
earth's rocky crust is one gigantic mausoleum. Here and there a dilettante
had filled his cabinets with relics from this monster crypt; here
and there a philosopher had pondered over them---questioning whether
perchance they had once been alive, or whether they were not mere
abortive souvenirs of that time when the fertile matrix of the earth
was supposed to have\begin{verse}\footnotesize

~~~~~~~~~~~~~~~~~~~~~~~``teemed at a birth\\*

\mbox{Innumerous living creatures, perfect forms,}\\*

Limbed and full grown.''

\end{verse}

Some few of these philosophers---as Robert Hooke and Steno in the
seventeenth century, and Moro, Leibnitz, Buffon, Whitehurst, Werner,
Hutton, and others in the eighteenth---had vaguely conceived the importance
of fossils as records of the earth's ancient history, but the wisest
of them no more suspected the full import of the story written in
the rocks than the average stroller in a modern museum suspects the
meaning of the hieroglyphs on the case of a mummy.

It was not that the rudiments of this story are so very hard to decipher---though
in truth they are hard enough---but rather that the men who made the
attempt had all along viewed the subject through an atmosphere of
preconception, which gave a distorted image. Before this image could
be corrected it was necessary that a man should appear who could see
without prejudice, and apply sound common-sense to what he saw. And
such a man did appear towards the close of the century, in the person
of William Smith, the English surveyor. He was a self-taught man,
and perhaps the more independent for that, and he had the gift, besides
his sharp eyes and receptive mind, of a most tenacious memory. By
exercising these faculties, rare as they are homely, he led the way
to a science which was destined, in its later developments, to shake
the structure of established thought to its foundations.

Little enough did William Smith suspect, however, that any such dire
consequences were to come of his act when he first began noticing
the fossil shells that here and there are to be found in the stratified
rocks and soils of the regions over which his surveyor's duties led
him. Nor, indeed, was there anything of such apparent revolutionary
character in the facts which he unearthed; yet in their implications
these facts were the most disconcerting of any that had been revealed
since the days of Copernicus and Galileo. In its bald essence, Smith's
discovery was simply this: that the fossils in the rocks, instead
of being scattered haphazard, are arranged in regular systems, so
that any given stratum of rock is labelled by its fossil population;
and that the order of succession of such groups of fossils is always
the same in any vertical series of strata in which they occur. That
is to say, if fossil A underlies fossil B in any given region, it
never overlies it in any other series; though a kind of fossils found
in one set of strata may be quite omitted in another. Moreover, a
fossil once having disappeared never reappears in any later stratum.

From these novel facts Smith drew the common-sense inference that
the earth had had successive populations of creatures, each of which
in its turn had become extinct. He partially verified this inference
by comparing the fossil shells with existing species of similar orders,
and found that such as occur in older strata of the rocks had no counterparts
among living species. But, on the whole, being eminently a practical
man, Smith troubled himself but little about the inferences that might
be drawn from his facts. He was chiefly concerned in using the key
he had discovered as an aid to the construction of the first geological
map of England ever attempted, and he left to others the untangling
of any snarls of thought that might seem to arise from his discovery
of the succession of varying forms of life on the globe.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{3hsci10-Wil3Sc76}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small William Smith}\end{center}
\end{figure}
He disseminated his views far and wide, however, in the course of
his journeyings---quite disregarding the fact that peripatetics went
out of fashion when the printing-press came in---and by the beginning
of the nineteenth century he had begun to have a following among the
geologists of England. It must not for a moment be supposed, however,
that his contention regarding the succession of strata met with immediate
or general acceptance. On the contrary, it was most bitterly antagonized.
For a long generation after the discovery was made, the generality
of men, prone as always to strain at gnats and swallow camels, preferred
to believe that the fossils, instead of being deposited in successive
ages, had been swept all at once into their present positions by the
current of a mighty flood---and that flood, needless to say, the Noachian
deluge. Just how the numberless successive strata could have been
laid down in orderly sequence to the depth of several miles in one
such fell cataclysm was indeed puzzling, especially after it came
to be admitted that the heaviest fossils were not found always at
the bottom; but to doubt that this had been done in some way was rank
heresy in the early days of the nineteenth century.


\section*{\raggedright CUVIER AND FOSSIL VERTEBRATES}

\addcontentsline{toc}{section}{CUVIER AND FOSSIL VERTEBRATES}

But once discovered, William Smith's unique facts as to the succession
of forms in the rocks would not down. There was one most vital point,
however, regarding which the inferences that seem to follow from these
facts needed verification---the question, namely, whether the disappearance
of a \emph{fauna} from the register in the rocks really implies the
extinction of that \emph{fauna}. Everything really depended upon the
answer to that question, and none but an accomplished naturalist could
answer it with authority. Fortunately, the most authoritative naturalist
of the time, George Cuvier, took the question in hand---not, indeed,
with the idea of verifying any suggestion of Smith's, but in the course
of his own original studies---at the very beginning of the century,
when Smith's views were attracting general attention.

Cuvier and Smith were exact contemporaries, both men having been born
in 1769, that {}``fertile year'' which gave the world also Chateaubriand,
von Humboldt, Wellington, and Napoleon. But the French naturalist
was of very different antecedents from the English surveyor. He was
brilliantly educated, had early gained recognition as a scientist,
and while yet a young man had come to be known as the foremost comparative
anatomist of his time. It was the anatomical studies that led him
into the realm of fossils. Some bones dug out of the rocks by workmen
in a quarry were brought to his notice, and at once his trained eye
told him that they were different from anything he had seen before.
Hitherto such bones, when not entirely ignored, had been for the most
part ascribed to giants of former days, or even to fallen angels.
Cuvier soon showed that neither giants nor angels were in question,
but elephants of an unrecognized species. Continuing his studies,
particularly with material gathered from gypsum beds near Paris, he
had accumulated, by the beginning of the nineteenth century, bones
of about twenty-five species of animals that he believed to be different
from any now living on the globe.

The fame of these studies went abroad, and presently fossil bones
poured in from all sides, and Cuvier's conviction that extinct forms
of animals are represented among the fossils was sustained by the
evidence of many strange and anomalous forms, some of them of gigantic
size. In 1816 the famous \emph{Ossements Fossiles}, describing these
novel objects, was published, and vertebrate paleontology became a
science. Among other things of great popular interest the book contained
the first authoritative description of the hairy elephant, named by
Cuvier the mammoth, the remains of which had been found embedded in
a mass of ice in Siberia in 1802, so wonderfully preserved that the
dogs of the Tungusian fishermen actually ate its flesh. Bones of the
same species had been found in Siberia several years before by the
naturalist Pallas, who had also found the carcass of a rhinoceros
there, frozen in a mud-bank; but no one then suspected that these
were members of an extinct population---they were supposed to be merely
transported relics of the flood.

Cuvier, on the other hand, asserted that these and the other creatures
he described had lived and died in the region where their remains
were found, and that most of them have no living representatives upon
the globe. This, to be sure, was nothing more than William Smith had
tried all along to establish regarding lower forms of life; but flesh
and blood monsters appeal to the imagination in a way quite beyond
the power of mere shells; so the announcement of Cuvier's discoveries
aroused the interest of the entire world, and the \emph{Ossements
Fossiles} was accorded a popular reception seldom given a work of
technical science---a reception in which the enthusiastic approval
of progressive geologists was mingled with the bitter protests of
the conservatives.

\begin{quotation}
{}``Naturalists certainly have neither explored all the continents,''\ said
Cuvier, {}``nor do they as yet even know all the quadrupeds of those
parts which have been explored. New species of this class are discovered
from time to time; and those who have not examined with attention
all the circumstances belonging to these discoveries may allege also
that the unknown quadrupeds, whose fossil bones have been found in
the strata of the earth, have hitherto remained concealed in some
islands not yet discovered by navigators, or in some of the vast deserts
which occupy the middle of Africa, Asia, the two Americas, and New
Holland.

{}``But if we carefully attend to the kind of quadrupeds that have
been recently discovered, and to the circumstances of their discovery,
we shall easily perceive that there is very little chance indeed of
our ever finding alive those which have only been seen in a fossil
state.

{}``Islands of moderate size, and at a considerable distance from
the large continents, have very few quadrupeds. These must have been
carried to them from other countries. Cook and Bougainville found
no other quadrupeds besides hogs and dogs in the South Sea Islands;
and the largest quadruped of the West India Islands, when first discovered,
was the agouti, a species of the cavy, an animal apparently between
the rat and the rabbit.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{3hsci10-Wil3Sc80}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Baron de Cuvier}\end{center}
\end{figure}
{}``It is true that the great continents, as Asia, Africa, the two
Americas, and New Holland, have large quadrupeds, and, generally speaking,
contain species common to each; insomuch, that upon discovering countries
which are isolated from the rest of the world, the animals they contain
of the class of quadruped were found entirely different from those
which existed in other countries. Thus, when the Spaniards first penetrated
into South America, they did not find it to contain a single quadruped
exactly the same with those of Europe, Asia, and Africa. The puma,
the jaguar, the tapir, the capybara, the llama, or glama, and vicuna,
and the whole tribe of sapajous, were to them entirely new animals,
of which they had not the smallest idea\ldots{}.

{}``If there still remained any great continent to be discovered,
we might perhaps expect to be made acquainted with new species of
large quadrupeds, among which some might be found more or less similar
to those of which we find the \emph{exuvi}\ae{} in the bowels of
the earth. But it is merely sufficient to glance the eye over the
maps of the world and observe the innumerable directions in which
navigators have traversed the ocean, in order to be satisfied that
there does not remain any large land to be discovered, unless it may
be situated towards the Antarctic Pole, where eternal ice necessarily
forbids the existence of animal life.''%
\footnote{Baron de Cuvier, \emph{Theory of the Earth}, New York, 1818, p.\ 98. %
}
\end{quotation}
{}

Cuvier then points out that the ancients were well acquainted with
practically all the animals on the continents of Europe, Asia, and
Africa now known to scientists. He finds little grounds, therefore,
for belief in the theory that at one time there were monstrous animals
on the earth which it was necessary to destroy in order that the present
\emph{fauna} and men might flourish. After reviewing these theories
and beliefs in detail, he takes up his {}``Inquiry Respecting the
Fabulous Animals of the Ancients.'' {}``It is easy,''\ he says,
{}``to reply to the foregoing objections, by examining the descriptions
that are left us by the ancients of those unknown animals, and by
inquiring into their origins. Now that the greater number of these
animals have an origin, the descriptions given of them bear the most
unequivocal marks; as in almost all of them we see merely the different
parts of known animals united by an unbridled imagination, and in
contradiction to every established law of nature.''

Having shown how the fabulous monsters of ancient times and of foreign
nations, such as the Chinese, were simply products of the imagination,
having no prototypes in nature, Cuvier takes up the consideration
of the difficulty of distinguishing the fossil bones of quadrupeds.

We shall have occasion to revert to this part of Cuvier's paper in
another connection. Here it suffices to pass at once to the final
conclusion that the fossil bones in question are the remains of an
extinct \emph{fauna}, the like of which has no present-day representation
on the earth. Whatever its implications, this conclusion now seemed
to Cuvier to be fully established.

In England the interest thus aroused was sent to fever-heat in 1821
by the discovery of abundant beds of fossil bones in the stalagmite-covered
floor of a cave at Kirkdale, Yorkshire which went to show that England,
too, had once had her share of gigantic beasts. Dr.\ Buckland, the
incumbent of the chair of geology at Oxford, and the most authoritative
English geologist of his day, took these finds in hand and showed
that the bones belonged to a number of species, including such alien
forms as elephants, rhinoceroses, hippopotami, and hyenas. He maintained
that all of these creatures had actually lived in Britain, and that
the caves in which their bones were found had been the dens of hyenas.

The claim was hotly disputed, as a matter of course. As late as 1827
books were published denouncing Buckland, doctor of divinity though
he was, as one who had joined in an {}``unhallowed cause,''\ and
reiterating the old cry that the fossils were only remains of tropical
species washed thither by the deluge. That they were found in solid
rocks or in caves offered no difficulty, at least not to the fertile
imagination of Granville Penn, the leader of the conservatives, who
clung to the old idea of Woodward and Cattcut that the deluge had
dissolved the entire crust of the earth to a paste, into which the
relics now called fossils had settled. The caves, said Mr.\ Penn,
are merely the result of gases given off by the carcasses during decomposition---great
air-bubbles, so to speak, in the pasty mass, becoming caverns when
the waters receded and the paste hardened to rocky consistency.

But these and such-like fanciful views were doomed even in the day
of their utterance. Already in 1823 other gigantic creatures, christened
ichthyosaurus and plesiosaurus by Conybeare, had been found in deeper
strata of British rocks; and these, as well as other monsters whose
remains were unearthed in various parts of the world, bore such strange
forms that even the most sceptical could scarcely hope to find their
counterparts among living creatures. Cuvier's contention that all
the larger vertebrates of the existing age are known to naturalists
was borne out by recent explorations, and there seemed no refuge from
the conclusion that the fossil records tell of populations actually
extinct. But if this were admitted, then Smith's view that there have
been successive rotations of population could no longer be denied.
Nor could it be in doubt that the successive faunas, whose individual
remains have been preserved in myriads, representing extinct species
by thousands and tens of thousands, must have required vast periods
of time for the production and growth of their countless generations.

As these facts came to be generally known, and as it came to be understood
in addition that the very matrix of the rock in which fossils are
imbedded is in many cases one gigantic fossil, composed of the remains
of microscopic forms of life, common-sense, which, after all, is the
final tribunal, came to the aid of belabored science. It was conceded
that the only tenable interpretation of the record in the rocks is
that numerous populations of creatures, distinct from one another
and from present forms, have risen and passed away; and that the geologic
ages in which these creatures lived were of inconceivable length.
The rank and file came thus, with the aid of fossil records, to realize
the import of an idea which James Hutton, and here and there another
thinker, had conceived with the swift intuition of genius long before
the science of paleontology came into existence. The Huttonian proposition
that time is long had been abundantly established, and by about the
close of the first third of the last century geologists had begun
to speak of {}``ages''\ and {}``untold \ae{}ons of time''\ with
a familiarity which their predecessors had reserved for days and decades.


\section*{\raggedright CHARLES LYELL COMBATS CATASTROPHISM}

\addcontentsline{toc}{section}{CHARLES LYELL COMBATS\\
CATASTROPHISM}

And now a new question pressed for solution. If the earth has been
inhabited by successive populations of beings now extinct, how have
all these creatures been destroyed? That question, however, seemed
to present no difficulties. It was answered out of hand by the application
of an old idea. All down the centuries, whatever their varying phases
of cosmogonic thought, there had been ever present the idea that past
times were not as recent times; that in remote epochs the earth had
been the scene of awful catastrophes that have no parallel in {}``these
degenerate days.'' Naturally enough, this thought, embalmed in every
cosmogonic speculation of whatever origin, was appealed to in explanation
of the destruction of these hitherto unimagined hosts, which now,
thanks to science, rose from their abysmal slumber as incontestable,
but also as silent and as thought-provocative, as Sphinx or pyramid.
These ancient hosts, it was said, have been exterminated at intervals
of odd millions of years by the recurrence of catastrophes of which
the Mosaic deluge is the latest, but perhaps not the last.

This explanation had fullest warrant of scientific authority. Cuvier
had prefaced his classical work with a speculative disquisition whose
very title (\emph{Discours sur les Revolutions du Globe})\ is ominous
of catastrophism, and whose text fully sustains the augury. And Buckland,
Cuvier's foremost follower across the Channel, had gone even beyond
the master, naming the work in which he described the Kirkdale fossils,
\emph{Reliqui}\ae{} \emph{Diluvian}\ae{}\emph{, or Proofs of a Universal
Deluge}.

Both these authorities supposed the creatures whose remains they studied
to have perished suddenly in the mighty flood whose awful current,
as they supposed, gouged out the modern valleys and hurled great blocks
of granite broadcast over the land. And they invoked similar floods
for the extermination of previous populations.

It is true these scientific citations had met with only qualified
approval at the time of their utterance, because then the conservative
majority of mankind did not concede that there had been a plurality
of populations or revolutions; but now that the belief in past geologic
ages had ceased to be a heresy, the recurring catastrophes of the
great paleontologists were accepted with acclaim. For the moment science
and tradition were at one, and there was a truce to controversy, except
indeed in those outlying skirmish-lines of thought whither news from
headquarters does not permeate till it has become ancient history
at its source.

The truce, however, was not for long. Hardly had contemporary thought
begun to adjust itself to the conception of past ages of incomprehensible
extent, each terminated by a catastrophe of the Noachian type, when
a man appeared who made the utterly bewildering assertion that the
geological record, instead of proving numerous catastrophic revolutions
in the earth's past history, gives no warrant to the pretensions of
any universal catastrophe whatever, near or remote.

This iconoclast was Charles Lyell, the Scotchman, who was soon to
be famous as the greatest geologist of his time. As a young man he
had become imbued with the force of the Huttonian proposition, that
present causes are one with those that produced the past changes of
the globe, and he carried that idea to what he conceived to be its
logical conclusion. To his mind this excluded the thought of catastrophic
changes in either inorganic or organic worlds.

But to deny catastrophism was to suggest a revolution in current thought.
Needless to say, such revolution could not be effected without a long
contest. For a score of years the matter was argued pro and con.,
often with most unscientific ardor. A mere outline of the controversy
would fill a volume; yet the essential facts with which Lyell at last
established his proposition, in its bearings on the organic world,
may be epitomized in a few words. The evidence which seems to tell
of past revolutions is the apparently sudden change of fossils from
one stratum to another of the rocks. But Lyell showed that this change
is not always complete. Some species live on from one alleged epoch
into the next. By no means all the contemporaries of the mammoth are
extinct, and numerous marine forms vastly more ancient still have
living representatives.

Moreover, the blanks between strata in any particular vertical series
are amply filled in with records in the form of thick strata in some
geographically distant series. For example, in some regions Silurian
rocks are directly overlaid by the coal measures; but elsewhere this
sudden break is filled in with the Devonian rocks that tell of a great
{}``age of fishes.'' So commonly are breaks in the strata in one
region filled up in another that we are forced to conclude that the
record shown by any single vertical series is of but local significance---telling,
perhaps, of a time when that particular sea-bed oscillated above the
water-line, and so ceased to receive sediment until some future age
when it had oscillated back again. But if this be the real significance
of the seemingly sudden change from stratum to stratum, then the whole
case for catastrophism is hopelessly lost; for such breaks in the
strata furnish the only suggestion geology can offer of sudden and
catastrophic changes of wide extent.

Let us see how Lyell elaborates these ideas, particularly with reference
to the rotation of species.%
\footnote{Charles Lyell, \emph{Principles of Geology} (4 vols.), London, 1834.
(p.\ 92). %
}

\begin{quotation}
{}``I have deduced as a corollary,''\ he says, {}``that the species
existing at any particular period must, in the course of ages, become
extinct, one after the other. `They must die out,'\ to borrow an
emphatic expression from Buffon, `because Time fights against them.'
If the views which I have taken are just, there will be no difficulty
in explaining why the habitations of so many species are now restrained
within exceeding narrow limits. Every local revolution tends to circumscribe
the range of some species, while it enlarges that of others; and if
we are led to infer that new species originate in one spot only, each
must require time to diffuse itself over a wide area. It will follow,
therefore, from the adoption of our hypothesis that the recent origin
of some species and the high antiquity of others are equally consistent
with the general fact of their limited distribution, some being local
because they have not existed long enough to admit of their wide dissemination;
others, because circumstances in the animate or inanimate world have
occurred to restrict the range within which they may once have obtained\ldots{}.

{}``If the reader should infer, from the facts laid before him, that
the successive extinction of animals and plants may be part of the
constant and regular course of nature, he will naturally inquire whether
there are any means provided for the repair of these losses? Is it
possible as a part of the economy of our system that the habitable
globe should to a certain extent become depopulated, both in the ocean
and on the land, or that the variety of species should diminish until
some new era arrives when a new and extraordinary effort of creative
energy is to be displayed? Or is it possible that new species can
be called into being from time to time, and yet that so astonishing
a phenomenon can escape the naturalist?

{}``In the first place, it is obviously more easy to prove that a
species once numerously represented in a given district has ceased
to be than that some other which did not pre-exist had made its appearance---assuming
always, for reasons before stated, that single stocks only of each
animal and plant are originally created, and that individuals of new
species did not suddenly start up in many different places at once.

{}``So imperfect has the science of natural history remained down
to our own times that, within the memory of persons now living, the
numbers of known animals and plants have doubled, or even quadrupled,
in many classes. New and often conspicuous species are annually discovered
in parts of the old continent long inhabited by the most civilized
nations. Conscious, therefore, of the limited extent of our information,
we always infer, when such discoveries are made, that the beings in
question had previously eluded our research, or had at least existed
elsewhere, and only migrated at a recent period into the territories
where we now find them.

{}``What kind of proofs, therefore, could we reasonably expect to
find of the origin at a particular period of a new species?

{}``Perhaps, it may be said in reply, that within the last two or
three centuries some forest tree or new quadruped might have been
observed to appear suddenly in those parts of England or France which
had been most thoroughly investigated---that naturalists might have
been able to show that no such being inhabited any other region of
the globe, and that there was no tradition of anything similar having
been observed in the district where it had made its appearance.

{}``Now, although this objection may seem plausible, yet its force
will be found to depend entirely on the rate of fluctuation which
we suppose to prevail in the animal world, and on the proportions
which such conspicuous subjects of the animal and vegetable kingdoms
bear to those which are less known and escape our observation. There
are perhaps more than a million species of plants and animals, exclusive
of the microscopic and infusory animalcules, now inhabiting the terraqueous
globe, so that if only one of these were to become extinct annually,
and one new one were to be every year called into being, much more
than a million of years might be required to bring about a complete
revolution of organic life.

{}``I am not hazarding at present any hypothesis as to the probable
rate of change, but none will deny that when the annual birth and
the annual death of one species on the globe is proposed as a mere
speculation, this, at least, is to imagine no slight degree of instability
in the animate creation. If we divide the surface of the earth into
twenty regions of equal area, one of these might comprehend a space
of land and water about equal in dimensions to Europe, and might contain
a twentieth part of the million of species which may be assumed to
exist in the animal kingdom. In this region one species only could,
according to the rate of mortality before assumed, perish in twenty
years, or only five out of fifty thousand in the course of a century.
But as a considerable portion of the whole world belongs to the aquatic
classes, with which we have a very imperfect acquaintance, we must
exclude them from our consideration, and, if they constitute half
of the entire number, then one species only might be lost in forty
years among the terrestrial tribes. Now the mammalia, whether terrestrial
or aquatic, bear so small a proportion to other classes of animals,
forming less, perhaps, than a thousandth part of a whole, that, if
the longevity of species in the different orders were equal, a vast
period must elapse before it would come to the turn of this conspicuous
class to lose one of their number. If one species only of the whole
animal kingdom died out in forty years, no more than one mammifer
might disappear in forty thousand years, in a region of the dimensions
of Europe.

{}``It is easy, therefore, to see that in a small portion of such
an area, in countries, for example, of the size of England and France,
periods of much greater duration must elapse before it would be possible
to authenticate the first appearance of one of the larger plants or
animals, assuming the annual birth and death of one species to be
the rate of vicissitude in the animal creation throughout the world.''%
\footnote{\emph{Ibid}., vol. III., pp.\ 596-598. %
}
\end{quotation}
{}

In a word, then, said Lyell, it becomes clear that the numberless
species that have been exterminated in the past have died out one
by one, just as individuals of a species die, not in vast shoals;
if whole populations have passed away, it has been not by instantaneous
extermination, but by the elimination of a species now here, now there,
much as one generation succeeds another in the life history of any
single species. The causes which have brought about such gradual exterminations,
and in the long lapse of ages have resulted in rotations of population,
are the same natural causes that are still in operation. Species have
died out in the past as they are dying out in the present, under influence
of changed surroundings, such as altered climate, or the migration
into their territory of more masterful species. Past and present causes
are one---natural law is changeless and eternal.

Such was the essence of the Huttonian doctrine, which Lyell adopted
and extended, and with which his name will always be associated. Largely
through his efforts, though of course not without the aid of many
other workers after a time, this idea---the doctrine of uniformitarianism,
it came to be called---became the accepted dogma of the geologic world
not long after the middle of the nineteenth century. The catastrophists,
after clinging madly to their phantom for a generation, at last capitulated
without terms: the old heresy became the new orthodoxy, and the way
was paved for a fresh controversy.


\section*{\raggedright THE ORIGIN OF SPECIES}

\addcontentsline{toc}{section}{THE ORIGIN OF SPECIES}

The fresh controversy followed quite as a matter of course. For the
idea of catastrophism had not concerned the destruction of species
merely, but their introduction as well. If whole faunas had been extirpated
suddenly, new faunas had presumably been introduced with equal suddenness
by special creation; but if species die out gradually, the introduction
of new species may be presumed to be correspondingly gradual. Then
may not the new species of a later geological epoch be the modified
lineal descendants of the extinct population of an earlier epoch?

The idea that such might be the case was not new. It had been suggested
when fossils first began to attract conspicuous attention; and such
sagacious thinkers as Buffon and Kant and Goethe and Erasmus Darwin
had been disposed to accept it in the closing days of the eighteenth
century. Then, in 1809, it had been contended for by one of the early
workers in systematic paleontology---Jean Baptiste Lamarck, who had
studied the fossil shells about Paris while Cuvier studied the vertebrates,
and who had been led by these studies to conclude that there had been
not merely a rotation but a progression of life on the globe. He found
the fossil shells---the fossils of invertebrates, as he himself had
christened them---in deeper strata than Cuvier's vertebrates; and
he believed that there had been long ages when no higher forms than
these were in existence, and that in successive ages fishes, and then
reptiles, had been the highest of animate creatures, before mammals,
including man, appeared. Looking beyond the pale of his bare facts,
as genius sometimes will, he had insisted that these progressive populations
had developed one from another, under influence of changed surroundings,
in unbroken series.

Of course such a thought as this was hopelessly misplaced in a generation
that doubted the existence of extinct species, and hardly less so
in the generation that accepted catastrophism; but it had been kept
alive by here and there an advocate like Geoffrey Saint-Hilaire, and
now the banishment of catastrophism opened the way for its more respectful
consideration. Respectful consideration was given it by Lyell in each
recurring edition of his \emph{Principles}, but such consideration
led to its unqualified rejection. In its place Lyell put forward a
modified hypothesis of special creation. He assumed that from time
to time, as the extirpation of a species had left room, so to speak,
for a new species, such new species had been created \emph{de novo};
and he supposed that such intermittent, spasmodic impulses of creation
manifest themselves nowadays quite as frequently as at any time in
the past. He did not say in so many words that no one need be surprised
to-day were he to see a new species of deer, for example, come up
out of the ground before him, {}``pawing to get free,''\ like Milton's
lion, but his theory implied as much. And that theory, let it be noted,
was not the theory of Lyell alone, but of nearly all his associates
in the geologic world. There is perhaps no other fact that will bring
home to one so vividly the advance in thought of our own generation
as the recollection that so crude, so almost unthinkable a conception
could have been the current doctrine of science less than half a century
ago.

This theory of special creation, moreover, excluded the current doctrine
of uniformitarianism as night excludes day, though most thinkers of
the time did not seem to be aware of the incompatibility of the two
ideas. It may be doubted whether even Lyell himself fully realized
it. If he did, he saw no escape from the dilemma, for it seemed to
him that the record in the rocks clearly disproved the alternative
Lamarckian hypothesis. And almost with one accord the paleontologists
of the time sustained the verdict. Owen, Agassiz, Falconer, Barrande,
Pictet, Forbes, repudiated the idea as unqualifiedly as their great
predecessor Cuvier had done in the earlier generation. Some of them
did, indeed, come to believe that there is evidence of a progressive
development of life in the successive ages, but no such graded series
of fossils had been discovered as would give countenance to the idea
that one species had ever been transformed into another. And to nearly
every one this objection seemed insuperable.

But in 1859 appeared a book which, though not dealing primarily with
paleontology, yet contained a chapter that revealed the geological
record in an altogether new light. The book was Charles Darwin's \emph{Origin
of Species}, the chapter that wonderful citation of the {}``Imperfections
of the Geological Record.'' In this epoch-making chapter Darwin shows
what conditions must prevail in any given place in order that fossils
shall be formed, how unusual such conditions are, and how probable
it is that fossils once imbedded in sediment of a sea-bed will be
destroyed by metamorphosis of the rocks, or by denudation when the
strata are raised above the water-level. Add to this the fact that
only small territories of the earth have been explored geologically,
he says, and it becomes clear that the paleontological record as we
now possess it shows but a mere fragment of the past history of organisms
on the earth. It is a history {}``imperfectly kept and written in
a changing dialect. Of this history we possess the last volume alone,
relating only to two or three countries. Of this volume only here
and there a short chapter has been preserved, and of each page only
here and there a few lines.'' For a paleontologist to dogmatize from
such a record would be as rash, he thinks, as {}``for a naturalist
to land for five minutes on a barren point of Australia and then discuss
the number and range of its productions.''

This citation of observations, which when once pointed out seemed
almost self-evident, came as a revelation to the geological world.
In the clarified view now possible old facts took on a new meaning.
It was recalled that Cuvier had been obliged to establish a new order
for some of the first fossil creatures he examined, and that Buckland
had noted that the nondescript forms were intermediate in structure
between allied existing orders. More recently such intermediate forms
had been discovered over and over; so that, to name but one example,
Owen had been able, with the aid of extinct species, to {}``dissolve
by gradations the apparently wide interval between the pig and the
camel.'' Owen, moreover, had been led to speak repeatedly of the
{}``generalized forms''\ of extinct animals, and Agassiz had called
them {}``synthetic or prophetic types,''\ these terms clearly implying
{}``that such forms are in fact intermediate or connecting links.''
Darwin himself had shown some years before that the fossil animals
of any continent are closely related to the existing animals of that
continent---edentates predominating, for example, in South America,
and marsupials in Australia. Many observers had noted that recent
strata everywhere show a fossil \emph{fauna} more nearly like the
existing one than do more ancient strata; and that fossils from any
two consecutive strata are far more closely related to each other
than are the fossils of two remote formations, the \emph{fauna} of
each geological formation being, indeed, in a wide view, intermediate
between preceding and succeeding faunas.

So suggestive were all these observations that Lyell, the admitted
leader of the geological world, after reading Darwin's citations,
felt able to drop his own crass explanation of the introduction of
species and adopt the transmutation hypothesis, thus rounding out
the doctrine of uniformitarianism to the full proportions in which
Lamarck had conceived it half a century before. Not all paleontologists
could follow him at once, of course; the proof was not yet sufficiently
demonstrative for that; but all were shaken in the seeming security
of their former position, which is always a necessary stage in the
progress of thought. And popular interest in the matter was raised
to white heat in a twinkling.

So, for the third time in this first century of its existence, paleontology
was called upon to play a leading r\^{o}le in a controversy whose
interest extended far beyond the bounds of staid truth-seeking science.
And the controversy waged over the age of the earth had not been more
bitter, that over catastrophism not more acrimonious, than that which
now raged over the question of the transmutation of species. The question
had implications far beyond the bounds of paleontology, of course.
The main evidence yet presented had been drawn from quite other fields,
but by common consent the record in the rocks might furnish a crucial
test of the truth or falsity of the hypothesis. {}``He who rejects
this view of the imperfections of the geological record,''\ said
Darwin, {}``will rightly reject the whole theory.''

With something more than mere scientific zeal, therefore, paleontologists
turned anew to the records in the rocks, to inquire what evidence
in proof or refutation might be found in unread pages of the {}``great
stone book.'' And, as might have been expected, many minds being
thus prepared to receive new evidence, such evidence was not long
withheld.


\section*{\raggedright FOSSIL MAN}

\addcontentsline{toc}{section}{FOSSIL MAN}

Indeed, at the moment of Darwin's writing a new and very instructive
chapter of the geologic record was being presented to the public---a
chapter which for the first time brought man into the story. In 1859
Dr.\ Falconer, the distinguished British paleontologist, made a visit
to Abbeville, in the valley of the Somme, incited by reports that
for a decade before had been sent out from there by M.\ Boucher de
Perthes. These reports had to do with the alleged finding of flint
implements, clearly the work of man, in undisturbed gravel-beds, in
the midst of fossil remains of the mammoth and other extinct animals.
What Falconer saw there and what came of his visit may best be told
in his own words:\ 

\begin{quotation}
{}``In September of 1856 I made the acquaintance of my distinguished
friend M.\ Boucher de Perthes,'' wrote Dr.\ Falconer, {}``on the
introduction of M.\ Desnoyers at Paris, when he presented to me the
earlier volume of his \emph{Antiquit\'{e}s celtiques}, \textit{etc}.,
with which I thus became acquainted for the first time. I was then
fresh from the examination of the Indian fossil remains of the valley
of the Jumna; and the antiquity of the human race being a subject
of interest to both, we conversed freely about it, each from a different
point of view. M.\ de Perthes invited me to visit Abbeville, in order
to examine his antediluvian collection, fossil and geological, gleaned
from the valley of the Somme. This I was unable to accomplish then,
but I reserved it for a future occasion.

{}``In October, 1856, having determined to proceed to Sicily, I arranged
by correspondence with M.\ Boucher de Perthes to visit Abbeville
on my journey through France. I was at the time in constant communication
with Mr.\ Prestwich about the proofs of the antiquity of the human
race yielded by the Broxham Cave, in which he took a lively interest;
and I engaged to communicate to him the opinions at which I should
arrive, after my examination of the Abbeville collection. M.\ de
Perthes gave me the freest access to his materials, with unreserved
explanations of all the facts of the case that had come under his
observation; and having considered his Menchecourt Section, taken
with such scrupulous care, and identified the molars of \emph{elephas
primigenius}, which he had exhumed with his own hands deep in that
section, along with flint weapons, presenting the same character as
some of those found in the Broxham Cave, I arrived at the conviction
that they were of contemporaneous age, although I was not prepared
to go along with M.\ de Perthes in all his inferences regarding the
hieroglyphics and in an industrial interpretation of the various other
objects which he had met with.''%
\footnote{Hugh Falconer, in \emph{Paleontological Memoirs}, vol.\ II., p.\ 596. %
}
\end{quotation}
{}

That Dr.\ Falconer was much impressed by the collection of M.\ de
Perthes is shown in a communication which he sent at once to his friend
Prestwich:\ 

\begin{quote}
{}``I have been richly rewarded,''\ he exclaims. {}``His collection
of wrought flint implements, and of the objects of every description
associated with them, far exceeds everything I expected to have seen,
especially from a single locality. He has made great additions, since
the publication of his first volume, in the second, which I now have
by me. He showed me flint hatchets which \textit{he} \textit{had}
\textit{dug} \textit{up} with his own hands, mixed \textit{indiscriminately}
with molars of \emph{elephas primigenius}. I examined and identified
plates of the molars and the flint objects which were got along with
them. Abbeville is an out-of-the-way place, very little visited; and
the French savants who meet him in Paris laugh at Monsieur de Perthes
and his researches. But after devoting the greater part of a day to
his vast collection, I am perfectly satisfied that there is a great
deal of fair presumptive evidence in favor of many of his speculations
regarding the remote antiquity of these industrial objects and their
association with animals now extinct. M.\ Boucher's hotel is, from
the ground floor to garret, a continued museum, filled with pictures,
medi\ae{}val art, and Gaulish antiquities, including antediluvian
flint-knives, fossil-bones, \textit{etc}. If, during next summer,
you should happen to be paying a visit to France, let me strongly
recommend you to come to Abbeville. I am sure you would be richly
rewarded.''%
\footnote{\emph{Ibid}., p.\ 598. %
}
\end{quote}
{}

This letter aroused the interest of the English geologists, and in
the spring of 1859 Prestwich and Mr.\ (afterwards Sir John)\ Evans
made a visit to Abbeville to see the specimens and examine at first
hand the evidences as pointed out by Dr.\ Falconer. 

\begin{quotation}
{}``The evidence yielded by the valley of the Somme,''\ continues
Falconer, in speaking of this visit, {}``was gone into with the scrupulous
care and severe and exhaustive analysis which are characteristic of
Mr.\ Prestwich's researches. The conclusions to which he was conducted
were communicated to the Royal Society on May 12, 1859, in his celebrated
memoir, read on May 26th and published in the \emph{Philosophical
Transactions} of 1860, which, in addition to researches made in the
valley of the Somme, contained an account of similar phenomena presented
by the valley of the Waveney, near Hoxne, in Suffolk. Mr.\ Evans
communicated to the Society of Antiquaries a memoir on the character
and geological position of the `Flint Implements in the Drift,'\ which
appeared in the \emph{Arch}\ae{}\emph{ologia} for 1860. The results
arrived at by Mr.\ Prestwich were expressed as follows:\ 

{}``First. That the flint implements are the result of design and
the work of man.

{}``Second. That they are found in beds of gravel, sand, and clay,
which have never been artificially disturbed.

{}``Third. That they occur associated with the remains of land, fresh-water,
and marine testacea, of species now living, and most of them still
common in the same neighborhood, and also with the remains of various
mammalia---a few species now living, but more of extinct forms.

{}``Fourth. That the period at which their entombment took place
was subsequent to the bowlder-clay period, and to that extent post-glacial;
and also that it was among the latest in geological time---one apparently
anterior to the surface assuming its present form, so far as it regards
some of the minor features.''%
\footnote{\emph{Ibid}., p.\ 599. %
}
\end{quotation}
{}

These reports brought the subject of the very significant human fossils
at Abbeville prominently before the public; whereas the publications
of the original discoverer, Boucher de Perthes, bearing date of 1847,
had been altogether ignored. A new aspect was thus given to the current
controversy.

As Dr.\ Falconer remarked, geology was now passing through the same
ordeal that astronomy passed in the age of Galileo. But the times
were changed since the day when the author of the \emph{Dialogues}
was humbled before the Congregation of the Index, and now no Index
Librorum Prohibitorum could avail to hide from eager human eyes such
pages of the geologic story as Nature herself had spared. Eager searchers
were turning the leaves with renewed zeal everywhere, and with no
small measure of success. In particular, interest attached just at
this time to a human skull which Dr.\ Fuhlrott had discovered in
a cave at Neanderthal two or three years before---a cranium which
has ever since been famous as the Neanderthal skull, the type specimen
of what modern zoologists are disposed to regard as a distinct species
of man, \emph{Homo neanderthalensis}. Like others of the same type
since discovered at Spy, it is singularly simian in character---low-arched,
with receding forehead and enormous, protuberant eyebrows. When it
was first exhibited to the scientists at Berlin by Dr.\ Fuhlrott,
in 1857, its human character was doubted by some of the witnesses;
of that, however, there is no present question.

This interesting find served to recall with fresh significance some
observations that had been made in France and Belgium a long generation
earlier, but whose bearings had hitherto been ignored. In 1826 MM.\ Tournal
and Christol had made independent discoveries of what they believed
to be human fossils in the caves of the south of France; and in 1827
Dr.\ Schmerling had found in the cave of Engis, in Westphalia, fossil
bones of even greater significance. Schmerling's explorations had
been made with the utmost care, and patience. At Engis he had found
human bones, including skulls, intermingled with those of extinct
mammals of the mammoth period in a way that left no doubt in his mind
that all dated from the same geological epoch. He had published a
full account of his discoveries in an elaborate monograph issued in
1833.

But at that time, as it chanced, human fossils were under a ban as
effectual as any ever pronounced by canonical index, though of far
different origin. The oracular voice of Cuvier had declared against
the authenticity of all human fossils. Some of the bones brought him
for examination the great anatomist had pettishly pitched out of the
window, declaring them fit only for a cemetery, and that had settled
the matter for a generation: the evidence gathered by lesser workers
could avail nothing against the decision rendered at the Delphi of
Science. But no ban, scientific or canonical, can longer resist the
germinative power of a fact, and so now, after three decades of suppression,
the truth which Cuvier had buried beneath the weight of his ridicule
burst its bonds, and fossil man stood revealed, if not as a flesh-and-blood,
at least as a skeletal entity.

The reception now accorded our prehistoric ancestor by the progressive
portion of the scientific world amounted to an ovation; but the unscientific
masses, on the other hand, notwithstanding their usual fondness for
tracing remote genealogies, still gave the men of Engis and Neanderthal
the cold shoulder. Nor were all of the geologists quite agreed that
the contemporaneity of these human fossils with the animals whose
remains had been mingled with them had been fully established. The
bare possibility that the bones of man and of animals that long preceded
him had been swept together into the eaves in successive ages, and
in some mysterious way intermingled there, was clung to by the conservatives
as a last refuge. But even this small measure of security was soon
to be denied them, for in 1865 two associated workers, M.\ Edouard
Lartet and Mr.\ Henry Christy, in exploring the caves of Dordogne,
unearthed a bit of evidence against which no such objection could
be urged. This momentous exhibit was a bit of ivory, a fragment of
the tusk of a mammoth, on which was scratched a rude but unmistakable
outline portrait of the mammoth itself. If all the evidence as to
man's antiquity before presented was suggestive merely, here at last
was demonstration; for the cave-dwelling man could not well have drawn
the picture of the mammoth unless he had seen that animal, and to
admit that man and the mammoth had been contemporaries was to concede
the entire case. So soon, therefore, as the full import of this most
instructive work of art came to be realized, scepticism as to man's
antiquity was silenced for all time to come.

In the generation that has elapsed since the first drawing of the
cave-dweller artist was discovered, evidences of the wide-spread existence
of man in an early epoch have multiplied indefinitely, and to-day
the paleontologist traces the history of our race back beyond the
iron and bronze ages, through a neolithic or polished-stone age, to
a paleolithic or rough-stone age, with confidence born of unequivocal
knowledge. And he looks confidently to the future explorer of the
earth's fossil records to extend the history back into vastly more
remote epochs, for it is little doubted that paleolithic man, the
most ancient of our recognized progenitors, is a modern compared to
those generations that represented the real childhood of our race.


\section*{\raggedright THE FOSSIL-BEDS OF AMERICA}

\addcontentsline{toc}{section}{THE FOSSIL-BEDS OF AMERICA}

Coincidently with the discovery of these highly suggestive pages of
the geologic story, other still more instructive chapters were being
brought to light in America. It was found that in the Rocky Mountain
region, in strata found in ancient lake beds, records of the tertiary
period, or age of mammals, had been made and preserved with fulness
not approached in any other region hitherto geologically explored.
These records were made known mainly by Professors Joseph Leidy, O.\ C.
Marsh, and E.\ D.\ Cope, working independently, and more recently
by numerous younger paleontologists.

The profusion of vertebrate remains thus brought to light quite beggars
all previous exhibits in point of mere numbers. Professor Marsh, for
example, who was first in the field, found three hundred new tertiary
species between the years 1870 and 1876. Meanwhile, in cretaceous
strata, he unearthed remains of about two hundred birds with teeth,
six hundred pterodactyls, or flying dragons, some with a spread of
wings of twenty-five feet, and one thousand five hundred mosasaurs
of the sea-serpent type, some of them sixty feet or more in length.
In a single bed of Jurassic rock, not larger than a good-sized lecture-room,
he found the remains of one hundred and sixty individuals of mammals,
representing twenty species and nine genera; while beds of the same
age have yielded three hundred reptiles, varying from the size of
a rabbit to sixty or eighty feet in length.

But the chief interest of these fossils from the West is not their
number but their nature; for among them are numerous illustrations
of just such intermediate types of organisms as must have existed
in the past if the succession of life on the globe has been an unbroken
lineal succession. Here are reptiles with bat-like wings, and others
with bird-like pelves and legs adapted for bipedal locomotion. Here
are birds with teeth, and other reptilian characters. In short, what
with reptilian birds and birdlike reptiles, the gap between modern
reptiles and birds is quite bridged over. In a similar way, various
diverse mammalian forms, as the tapir, the rhinoceros, and the horse,
are linked together by fossil progenitors. And, most important of
all, Professor Marsh has discovered a series of mammalian remains,
occurring in successive geological epochs, which are held to represent
beyond cavil the actual line of descent of the modern horse; tracing
the lineage of our one-toed species back through two and three toed
forms, to an ancestor in the eocene or early tertiary that had four
functional toes and the rudiment of a fifth. This discovery is too
interesting and too important not to be detailed at length in the
words of the discoverer.


\subsection*{\raggedright Marsh Describes the Fossil Horse}

\addcontentsline{toc}{subsection}{Marsh Describes the Fossil Horse}

\begin{quotation}
{}``It is a well-known fact,''\ says Professor Marsh, {}``that
the Spanish discoverers of America discovered no horses on this continent,
and that the modern horse (\emph{Equus caballus}, Linn.)\ was subsequently
introduced from the Old World. It is, however, not so generally known
that these animals had formerly been abundant here, and that long
before, in tertiary time, near relatives of the horse, and probably
his ancestors, existed in the far West in countless numbers and in
a marvellous variety of forms. The remains of equine mammals, now
known from the tertiary and quaternary deposits of this country, already
represent more than double the number of genera and species hitherto
found in the strata of the eastern hemisphere, and hence afford most
important aid in tracing out the genealogy of the horses still existing.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth,
  height=0.80\paperwidth,
  keepaspectratio]{3hsci10-Wil3S108}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small The Evolution of a Horse's
Foot and of a Horse's Head}\end{center}{\small \par}

\noindent \emph{\footnotesize (The ancestral horse on the bottom,
the modern horse on the top. In the American Museum of Natural History.)}
\end{figure}
{}``The animals of this group which lived in America during the three
diversions of the tertiary period were especially numerous in the
Rocky Mountain regions, and their remains are well preserved in the
old lake basins which then covered so much of that country. The most
ancient of these lakes---which extended over a considerable part of
the present territories of Wyoming and Utah---remained so long in
eocene times that the mud and sand, slowly deposited in it, accumulated
to more than a mile in vertical thickness. In these deposits vast
numbers of tropical animals were entombed, and here the oldest equine
remains occur, four species of which have been described. These belong
to the genus \emph{Orohippus} (Marsh), and are all of a diminutive
size, hardly bigger than a fox. The skeletons of these animals resemble
that of the horse in many respects, much more indeed than any other
existing species, but, instead of the single toe on each foot, so
characteristic of all modern equines, the various species of \emph{Orohippus}
had four toes before and three behind, all of which reached the ground.
The skull, too, was proportionately shorter, and the orbit was not
enclosed behind by a bridge of bone. There were fifty four teeth in
all, and the premolars were larger than the molars. The crowns of
these teeth were very short. The canine teeth were developed in both
sexes, and the incisors did not have the {}``mark''\ which indicates
the age of the modern horse. The radius and ulna were separate, and
the latter was entire through the whole length. The tibia and fibula
were distinct. In the forefoot all the digits except the pollex, or
first, were well developed. The third digit is the largest, and its
close resemblance to that of the horse is clearly marked. The terminal
phalanx, or coffin-bone, has a shallow median bone in front, as in
many species of this group in the later tertiary. The fourth digit
exceeds the second in size, and the second is much the shortest of
all. Its metacarpal bone is considerably curved outward. In the hind-foot
of this genus there are but three digits. The fourth metatarsal is
much larger than the second.

{}``The larger number of equine mammals now known from the tertiary
deposits of this country, and their regular distributions through
the subdivisions of this formation, afford a good opportunity to ascertain
the probable descent of the modern horse. The American representative
of the latter is the extinct \emph{Equus fraternus} (Leidy), a species
almost, if not wholly, identical with the Old World \emph{Equus caballus}
(Linn\ae{}us), to which our recent horse belongs. Huxley has traced
successfully the later genealogy of the horse through European extinct
forms, but the line in America was probably a more direct one, and
the record is more complete. Taking, then, as the extreme of a series,
\emph{Orohippus agilis} (Marsh), from the eocene, and \emph{Equus
fraternus} (Leidy), from the quaternary, intermediate forms may be
intercalated with considerable certainty from thirty or more well-marked
species that lived in the intervening periods. The natural line of
descent would seem to be through the following genera: \emph{Orohippus},
of the eocene; \emph{Miohippus} and \emph{Anchitherium}, of the miocene;
\emph{Anchippus}, \emph{Hipparion}, \emph{Protohippus}, \emph{Phohippus},
of the pliocene; and \emph{Equus}, quaternary and recent.

The most marked changes undergone by the successive equine genera
are as follows: First, increase in size; second, increase in speed,
through concentration of limb bones; third, elongation of head and
neck, and modifications of skull. The eocene \emph{Orohippus} was
the size of a fox. \emph{Miohippus} and \emph{Anchitherium}, from
the miocene, were about as large as a sheep. \emph{Hipparion} and
\emph{Pliohippus}, of the pliocene, equalled the ass in height; while
the size of the quaternary \emph{Equus} was fully up to that of a
modern horse.

{}``The increase of speed was equally well marked, and was a direct
result of the gradual formation of the limbs. The latter were slowly
concentrated by the reduction of their lateral elements and enlargement
of the axial bone, until the force exerted by each limb came to act
directly through its axis in the line of motion. This concentration
is well seen---e.g., in the fore-limb. There was, first, a change
in the scapula and humerus, especially in the latter, which facilitated
motion in one line only; second, an expansion of the radius and reduction
of the ulna, until the former alone remained entire and effective;
third, a shortening of all the carpal bones and enlargement of the
median ones, insuring a firmer wrist; fourth, an increase of size
of the third digit, at the expense of those of each side, until the
former alone supported the limb.

{}``Such is, in brief, a general outline of the more marked changes
that seemed to have produced in America the highly specialized modern
\emph{Equus} from his diminutive four-toed predecessor, the eocene
\emph{Orohippus}. The line of descent appears to have been direct,
and the remains now known supply every important intermediate form.
It is, of course, impossible to say with certainty through which of
the three-toed genera of the pliocene that lived together the succession
came. It is not impossible that the latter species, which appear generically
identical, are the descendants of more distinct pliocene types, as
the persistent tendency in all the earlier forms was in the same direction.
Considering the remarkable development of the group through the tertiary
period, and its existence even later, it seems very strange that none
of the species should have survived, and that we are indebted for
our present horse to the Old World.''%
\footnote{{}``Fossil Horses in America'' (reprinted from \emph{American Naturalist},
vol.\ VIII., May, 1874), by O.\ C.\ Marsh, pp.\ 288, 289.%
}
\end{quotation}

\section*{\raggedright PALEONTOLOGY OF EVOLUTION}

\addcontentsline{toc}{section}{PALEONTOLOGY OF EVOLUTION}

These and such-like revelations have come to light in our own time---are,
indeed, still being disclosed. Needless to say, no index of any sort
now attempts to conceal them; yet something has been accomplished
towards the same end by the publication of the discoveries in Smithsonian
bulletins and in technical memoirs of government surveys. Fortunately,
however, the results have been rescued from that partial oblivion
by such interpreters as Professors Huxley and Cope, so the unscientific
public has been allowed to gain at least an inkling of the wonderful
progress of paleontology in our generation.

The writings of Huxley in particular epitomize the record. In 1862
he admitted candidly that the paleontological record as then known,
so far as it bears on the doctrine of progressive development, negatives
that doctrine. In 1870 he was able to {}``soften somewhat the Brutus-like
severity''\ of his former verdict, and to assert that the results
of recent researches seem {}``to leave a clear balance in favor of
the doctrine of the evolution of living forms one from another.''
Six years later, when reviewing the work of Marsh in America and of
Gaudry in Pikermi, he declared that, {}``on the evidence of paleontology,
the evolution of many existing forms of animal life from their predecessors
is no longer an hypothesis, but an historical fact.'' In 1881 he
asserted that the evidence gathered in the previous decade had been
so unequivocal that, had the transmutation hypothesis not existed,
{}``the paleontologist would have had to invent it.''

Since then the delvers after fossils have piled proof on proof in
bewildering profusion. The fossil-beds in the {}``bad lands''\ of
western America seem inexhaustible. And in the Connecticut River Valley
near relatives of the great reptiles which Professor Marsh and others
have found in such profusion in the West left their tracks on the
mud-flats---since turned to sandstone; and a few skeletons also have
been found. The bodies of a race of great reptiles that were the lords
of creation of their day have been dissipated to their elements, while
the chance indentations of their feet as they raced along the shores,
mere footprints on the sands, have been preserved among the most imperishable
of the memory-tablets of the world.

Of the other vertebrate fossils that have been found in the eastern
portions of America, among the most abundant and interesting are the
skeletons of mastodons. Of these one of the largest and most complete
is that which was unearthed in the bed of a drained lake near Newburg,
New York, in 1845. This specimen was larger than the existing elephants,
and had tusks eleven feet in length. It was mounted and described
by Dr.\ John C.\ Warren, of Boston, and has been famous for half
a century as the {}``Warren mastodon.''

But to the student of racial development as recorded by the fossils
all these sporadic finds have but incidental interest as compared
with the rich Western fossil-beds to which we have already referred.
From records here unearthed, the racial evolution of many mammals
has in the past few years been made out in greater or less detail.
Professor Cope has traced the ancestry of the camels (which, like
the rhinoceroses, hippopotami, and sundry other forms now spoken of
as {}``Old World,'' seem to have had their origin here)\ with much
completeness.

A lemuroid form of mammal, believed to be of the type from which man
has descended, has also been found in these beds. It is thought that
the descendants of this creature, and of the other {}``Old-World''
forms above referred to, found their way to Asia, probably, as suggested
by Professor Marsh, across a bridge at Bering Strait, to continue
their evolution on the other hemisphere, becoming extinct in the land
of their nativity. The ape-man fossil found in the tertiary strata
of the island of Java in 1891 by the Dutch surgeon Dr.\ Eugene Dubois,
and named \emph{Pithecanthropus erectus}, may have been a direct descendant
of the American tribe of primitive lemurs, though this is only a conjecture.

Not all the strange beasts which have left their remains in our {}``bad
lands''\ are represented by living descendants. The titanotheres,
or brontotherid\ae{}, for example, a gigantic tribe, offshoots of
the same stock which produced the horse and rhinoceros, represented
the culmination of a line of descent. They developed rapidly in a
geological sense, and flourished about the middle of the tertiary
period; then, to use Agassiz's phrase,''\ time fought against them.''
The story of their evolution has been worked out by Professors Leidy,
Marsh, Cope, and H.\ F.\ Osborne.

A recent bit of paleontological evidence bearing on the question of
the introduction of species is that presented by Dr.\ J.\ L.\ Wortman
in connection with the fossil lineage of the edentates. It was suggested
by Marsh, in 1877, that these creatures, whose modern representatives
are all South American, originated in North America long before the
two continents had any land connection. The stages of degeneration
by which these animals gradually lost the enamel from their teeth,
coming finally to the unique condition of their modern descendants
of the sloth tribe, are illustrated by strikingly graded specimens
now preserved in the American Museum of Natural History, as shown
by Dr.\ Wortman.

All these and a multitude of other recent observations that cannot
be even outlined here tell the same story. With one accord paleontologists
of our time regard the question of the introduction of new species
as solved. As Professor Marsh has said, {}``to doubt evolution today
is to doubt science; and science is only another name for truth.''

Thus the third great battle over the meaning of the fossil records
has come to a conclusion. Again there is a truce to controversy, and
it may seem to the casual observer that the present stand of the science
of fossils is final and impregnable. But does this really mean that
a full synopsis of the story of paleontology has been told? Or do
we only await the coming of the twentieth-century Lamarck or Darwin,
who shall attack the fortified knowledge of to-day with the batteries
of a new generalization?


\chapter*{\raggedright IV. THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY}

\addcontentsline{toc}{chapter}{IV. THE ORIGIN AND DEVELOPMENT OF
MODERN GEOLOGY}

\markboth{A HISTORY OF SCIENCE, BOOK III}{IV. MODERN GEOLOGY}


\section*{\raggedright JAMES HUTTON}

\addcontentsline{toc}{section}{JAMES HUTTON}

One might naturally suppose that the science of the earth which lies
at man's feet would at least have kept pace with the science of the
distant stars. But perhaps the very obviousness of the phenomena delayed
the study of the crust of the earth. It is the unattainable that allures
and mystifies and enchants the developing mind. The proverbial child
spurns its toys and cries for the moon.

So in those closing days of the eighteenth century, when astronomers
had gone so far towards explaining the mysteries of the distant portions
of the universe, we find a chaos of opinion regarding the structure
and formation of the earth. Guesses were not wanting to explain the
formation of the world, it is true, but, with one or two exceptions,
these are bizarre indeed. One theory supposed the earth to have been
at first a solid mass of ice, which became animated only after a comet
had dashed against it. Other theories conceived the original globe
as a mass of water, over which floated vapors containing the solid
elements, which in due time were precipitated as a crust upon the
waters. In a word, the various schemes supposed the original mass
to have been ice, or water, or a conglomerate of water and solids,
according to the random fancies of the theorists; and the final separation
into land and water was conceived to have taken place in all the ways
which fancy, quite unchecked by any tenable data, could invent.

Whatever important changes in the general character of the surface
of the globe were conceived to have taken place since its creation
were generally associated with the Mosaic: deluge, and the theories
which attempted to explain this catastrophe were quite on a par with
those which dealt with a remoter period of the earth's history. Some
speculators, holding that the interior of the globe is a great abyss
of waters, conceived that the crust had dropped into this chasm and
had thus been inundated. Others held that the earth had originally
revolved on a vertical axis, and that the sudden change to its present
position had caused the catastrophic shifting of its oceans. But perhaps
the favorite theory was that which supposed a comet to have wandered
near the earth, and in whirling about it to have carried the waters,
through gravitation, in a vast tide over the continents.

Thus blindly groped the majority of eighteenth-century philosophers
in their attempts to study what we now term geology. Deluded by the
old deductive methods, they founded not a science, but the ghost of
a science, as immaterial and as unlike anything in nature as any other
phantom that could be conjured from the depths of the speculative
imagination. And all the while the beckoning earth lay beneath the
feet of these visionaries; but their eyes were fixed in air.

At last, however, there came a man who had the penetration to see
that the phantom science of geology needed before all else a body
corporeal, and who took to himself the task of supplying it. This
was Dr.\ James Hutton, of Edinburgh, physician, farmer, and manufacturing
chemist---patient, enthusiastic, level-headed devotee of science.
Inspired by his love of chemistry to study the character of rocks
and soils, Hutton had not gone far before the earth stood revealed
to him in a new light. He saw, what generations of predecessors had
blindly refused to see, that the face of nature everywhere, instead
of being rigid and immutable, is perennially plastic, and year by
year is undergoing metamorphic changes. The solidest rocks are day
by day disintegrated slowly, but none the less surely, by wind and
rain and frost, by mechanical attrition and chemical decomposition,
to form the pulverized earth and clay. This soil is being swept away
by perennial showers, and carried off to the oceans. The oceans themselves
beat on their shores, and eat insidiously into the structure of sands
and rocks. Everywhere, slowly but surely, the surface of the land
is being worn away; its substance is being carried to burial in the
seas.

Should this denudation continue long enough, thinks Hutton, the entire
surface of the continents must be worn away. Should it be continued
\textit{long} \textit{enough}! And with that thought there flashes
on his mind an inspiring conception---the idea that solar time is
long, indefinitely long. That seems a simple enough thought---almost
a truism---to the twentieth-century mind; but it required genius to
conceive it in the eighteenth. Hutton pondered it, grasped its full
import, and made it the basis of his hypothesis, his {}``theory of
the earth.''


\section*{\raggedright MODERN GEOLOGY}

\addcontentsline{toc}{section}{MODERN GEOLOGY}

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{3hsci10-Wil3S118}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small James Hutton}\end{center}
\end{figure}
The hypothesis is this---that the observed changes of the surface
of the earth, continued through indefinite lapses of time, must result
in conveying all the land at last to the sea; in wearing continents
away till the oceans overflow them. What then? Why, as the continents
wear down, the oceans are filling up. Along their bottoms the detritus
of wasted continents is deposited in strata, together with the bodies
of marine animals and vegetables. Why might not this debris solidify
to form layers of rocks---the basis of new continents? Why not, indeed?

But have we any proof that such formation of rocks in an ocean-bed
has, in fact, occurred? To be sure we have. It is furnished by every
bed of limestone, every outcropping fragment of fossil-bearing rock,
every stratified cliff. How else than through such formation in an
ocean-bed came these rocks to be stratified? How else came they to
contain the shells of once living organisms imbedded in their depths?
The ancients, finding fossil shells imbedded in the rocks, explained
them as mere freaks of {}``nature and the stars.'' Less superstitious
generations had repudiated this explanation, but had failed to give
a tenable solution of the mystery. To Hutton it is a mystery no longer.
To him it seems clear that the basis of the present continents was
laid in ancient sea-beds, formed of the detritus of continents yet
more ancient.

But two links are still wanting to complete the chain of Hutton's
hypothesis. Through what agency has the ooze of the ocean-bed been
transformed into solid rock? and through what agency has this rock
been lifted above the surface of the water to form new continents?
Hutton looks about him for a clew, and soon he finds it. Everywhere
about us there are outcropping rocks that are not stratified, but
which give evidence to the observant eye of having once been in a
molten state. Different minerals are mixed together; pebbles are scattered
through masses of rock like plums in a pudding; irregular crevices
in otherwise solid masses of rock---so-called veinings---are seen
to be filled with equally solid granite of a different variety, which
can have gotten there in no conceivable way, so Hutton thinks, but
by running in while molten, as liquid metal is run into the moulds
of the founder. Even the stratified rocks, though they seemingly have
not been melted, give evidence in some instances of having been subjected
to the action of heat. Marble, for example, is clearly nothing but
calcined limestone.

With such evidence before him, Hutton is at no loss to complete his
hypothesis. The agency which has solidified the ocean-beds, he says,
is subterranean heat. The same agency, acting excessively, has produced
volcanic cataclysms, upheaving ocean-beds to form continents. The
rugged and uneven surfaces of mountains, the tilted and broken character
of stratified rocks everywhere, are the standing witnesses of these
gigantic upheavals.

And with this the imagined cycle is complete. The continents, worn
away and carried to the sea by the action of the elements, have been
made over into rocks again in the ocean-beds, and then raised once
more into continents. And this massive cycle, In Hutton's scheme,
is supposed to have occurred not once only, but over and over again,
times without number. In this unique view ours is indeed a world without
beginning and without end; its continents have been making and unmaking
in endless series since time began.

Hutton formulated his hypothesis while yet a young man, not long after
the middle of the century. He first gave it publicity in 1781, in
a paper before the Royal Society of Edinburgh:\ 

\begin{quotation}
{}``A solid body of land could not have answered the purpose of a
habitable world,''\ said Hutton, {}``for a soil is necessary to
the growth of plants, and a soil is nothing but the material collected
from the destruction of the solid land. Therefore the surface of this
land inhabited by man, and covered by plants and animals, is made
by nature to decay, in dissolving from that hard and compact state
in which it is found; and this soil is necessarily washed away by
the continual circulation of the water running from the summits of
the mountains towards the general receptacle of that fluid.

{}``The heights of our land are thus levelled with our shores, our
fertile plains are formed from the ruins of the mountains; and those
travelling materials are still pursued by the moving water, and propelled
along the inclined surface of the earth. These movable materials,
delivered into the sea, cannot, for a long continuance, rest upon
the shore, for by the agitation of the winds, the tides, and the currents
every movable thing is carried farther and farther along the shelving
bottom of the sea, towards the unfathomable regions of the ocean.

{}``If the vegetable soil is thus constantly removed from the surface
of the land, and if its place is then to be supplied from the dissolution
of the solid earth as here represented, we may perceive an end to
this beautiful machine; an end arising from no error in its constitution
as a world, but from that destructibility of its land which is so
necessary in the system of the globe, in the economy of life and vegetation.

{}``The immense time necessarily required for the total destruction
of the land must not be opposed to that view of future events which
is indicated by the surest facts and most approved principles. Time,
which measures everything in our idea, and is often deficient to our
schemes, is to nature endless and as nothing; it cannot limit that
by which alone it has existence; and as the natural course of time,
which to us seems infinite, cannot be bounded by any operation that
may have an end, the progress of things upon this globe that in the
course of nature cannot be limited by time must proceed in a continual
succession. We are, therefore, to consider as inevitable the destruction
of our land, so far as effected by those operations which are necessary
in the purpose of the globe, considered as a habitable world, and
so far as we have not examined any other part of the economy of nature,
in which other operations and a different intention might appear.

{}``We have now considered the globe of this earth as a machine,
constructed upon chemical as well as mechanical principles, by which
its different parts are all adapted, in form, in quality, and quantity,
to a certain end---an end attained with certainty of success, and
an end from which we may perceive wisdom in contemplating the means
employed.

{}``But is this world to be considered thus merely as a machine,
to last no longer than its parts retain their present position, their
proper forms and qualities? Or may it not be also considered as an
organized body such as has a constitution, in which the necessary
decay of the machine is naturally repaired in the exertion of those
productive powers by which it has been formed?

{}``This is the view in which we are now to examine the globe; to
see if there be, in the constitution of the world, a reproductive
operation by which a ruined constitution may be again repaired and
a duration of stability thus procured to the machine considered as
a world containing plants and animals.

{}``If no such reproductive power, or reforming operation, after
due inquiry, is to be found in the constitution of this world, we
should have reason to conclude that the system of this earth has either
been intentionally made imperfect or has not been the work of infinite
power and wisdom.''%
\footnote{James Hutton, from \emph{Transactions of the Royal Society of Edinburgh},
1788, vol.\ I., p.\ 214. A paper on the {}``Theory of the Earth,''\ read
before the Society in 1781. %
}
\end{quotation}
{}

This, then, was the important question to be answered---the question
of the constitution of the globe. To accomplish this, it was necessary,
first of all, to examine without prejudice the material already in
hand, adding such new discoveries from time to time as might be made,
but always applying to the whole unvarying scientific principles and
inductive methods of reasoning.

\begin{quotation}
{}``If we are to take the written history of man for the rule by
which we should judge of the time when the species first began,''\ said
Hutton, {}``that period would be but little removed from the present
state of things. The Mosaic history places this beginning of man at
no great distance; and there has not been found, in natural history,
any document by which high antiquity might be attributed to the human
race. But this is not the case with regard to the inferior species
of animals, particularly those which inhabit the ocean and its shores.
We find in natural history monuments which prove that those animals
had long existed; and we thus procure a measure for the computation
of a period of time extremely remote, though far from being precisely
ascertained.

{}``In examining things present, we have data from which to reason
with regard to what has been; and from what actually has been we have
data for concluding with regard to that which is to happen hereafter.
Therefore, upon the supposition that the operations of nature are
equable and steady, we find, in natural appearances, means for concluding
a certain portion of time to have necessarily elapsed in the production
of those events of which we see the effects.

{}``It is thus that, in finding the relics of sea animals of every
kind in the solid body of our earth, a natural history of those animals
is formed, which includes a certain portion of time; and for the ascertaining
this portion of time we must again have recourse to the regular operations
of this world. We shall thus arrive at facts which indicate a period
to which no other species of chronology is able to remount.

{}``We find the marks of marine animals in the most solid parts of
the earth, consequently those solid parts have been formed after the
ocean was inhabited by those animals which are proper to that fluid
medium. If, therefore, we knew the natural history of these solid
parts, and could trace the operations of the globe by which they have
been formed, we would have some means for computing the time through
which those species of animals have continued to live. But how shall
we describe a process which nobody has seen performed and of which
no written history gives any account? This is only to be investigated,
first, in examining the nature of those solid bodies the history of
which we want to know; and, secondly, in examining the natural operations
of the globe, in order to see if there now exist such operations as,
from the nature of the solid bodies, appear to have been necessary
for their formation.

{}``There are few beds of marble or limestone in which may not be
found some of those objects which indicate the marine object of the
mass. If, for example, in a mass of marble taken from a quarry upon
the top of the Alps or Andes there shall be found one cockle-shell
or piece of coral, it must be concluded that this bed of stone has
been originally formed at the bottom of the sea, as much as another
bed which is evidently composed almost altogether of cockle-shells
and coral. If one bed of limestone is thus found to have been of marine
origin, every concomitant bed of the same kind must be also concluded
to have been formed in the same manner.

{}``In those calcareous strata, which are evidently of marine origin,
there are many parts which are of sparry structure---that is to say,
the original texture of those beds in such places has been dissolved,
and a new structure has been assumed which is peculiar to a certain
state of the calcareous earth. This change is produced by crystallization,
in consequence of a previous state of fluidity, which has so disposed
the concerting parts as to allow them to assume a regular shape and
structure proper to that substance. A body whose external form has
been modified by this process is called a \textit{Crystal}; one whose
internal arrangement of parts is determined by it is said to be of
a \textit{sparry} \textit{structure}, and this is known from its fracture.

{}``There are, in all the regions of the earth, huge masses of calcareous
matter in that crystalline form or sparry state in which, perhaps,
no vestige can be found of any organized body, nor any indication
that such calcareous matter has belonged to animals; but as in other
masses this sparry structure or crystalline state is evidently assumed
by the marine calcareous substances in operations which are natural
to the globe, and which are necessary to the consolidation of the
strata, it does not appear that the sparry masses in which no figured
body is formed have been originally different from other masses, which,
being only crystallized in part, and in part still retaining their
original form, have ample evidence of their marine origin.

{}``We are led, in this manner, to conclude that all the strata of
the earth, not only those consisting of such calcareous masses, but
others superincumbent upon these, have had their origin at the bottom
of the sea.

{}``The general amount of our reasoning is this, that nine-tenths,
perhaps, or ninety-nine-hundredths, of this earth, so far as we see,
have been formed by natural operations of the globe in collecting
loose materials and depositing them at the bottom of the sea; consolidating
those collections in various degrees, and either elevating those consolidated
masses above the level on which they were formed or lowering the level
of that sea.

{}``Let us now consider how far the other proposition of strata being
elevated by the power of heat above the level of the sea may be confirmed
from the examination of natural appearances. The strata formed at
the bottom of the ocean are necessarily horizontal in their position,
or nearly so, and continuous in their horizontal direction or extent.
They may be changed and gradually assume the nature of each other,
so far as concerns the materials of which they are formed, but there
cannot be any sudden change, fracture, or displacement naturally in
the body of a stratum. But if the strata are cemented by the heat
of fusion, and erected with an expansive power acting below, we may
expect to find every species of fracture, dislocation, and contortion
in those bodies and every degree of departure from a horizontal towards
a vertical position.

{}``The strata of the globe are actually found in every possible
position: for from horizontal they are frequently found vertical;
from continuous they are broken and separated in every possible direction;
and from a plane they are bent and doubled. It is impossible that
they could have originally been formed, by the known laws of nature,
in their present state and position; and the power that has been necessarily
required for their change has not been inferior to that which might
have been required for their elevation from the place in which they
have been formed.''%
\footnote{\emph{Ibid}., p.\ 216. %
}
\end{quotation}
{}

From all this, therefore, Hutton reached the conclusion that the elevation
of the bodies of land above the water on the earth's surface had been
effected by the same force which had acted in consolidating the strata
and giving them stability. This force he conceived to be exerted by
the expansion of heated matter.

\begin{quotation}
{}``We have,''\ he said, {}``been now supposing that the beginning
of our present earth had been laid in the bottom of the ocean, at
the completion of the former land, but this was only for the sake
of distinctness. The just view is this, that when the former land
of the globe had been complete, so as to begin to waste and be impaired
by the encroachment of the sea, the present land began to appear above
the surface of the ocean. In this manner we suppose a due proportion
to be always preserved of land and water upon the surface of the globe,
for the purpose of a habitable world such as this which we possess.
We thus also allow time and opportunity for the translation of animals
and plants to occupy the earth.

{}``But if the earth on which we live began to appear in the ocean
at the time when the \textit{last} began to be resolved, it could
not be from the materials of the continent immediately preceding this
which we examine that the present earth has been constructed; for
the bottom of the ocean must have been filled with materials before
land could be made to appear above its surface.

{}``Let us suppose that the continent which is to succeed our land
is at present beginning to appear above the water in the middle of
the Pacific Ocean; it must be evident that the materials of this great
body, which is formed and ready to be brought forth, must have been
collected from the destruction of an earth which does not now appear.
Consequently, in this true statement of the case there is necessarily
required the destruction of an animal and vegetable earth prior to
the former land; and the materials of that earth which is first in
our account must have been collected at the bottom of the ocean, and
begun to be concocted for the production of the present earth, when
the land immediately preceding the present had arrived at its full
extent.

{}``We have now got to the end of our reasoning; we have no data
further to conclude immediately from that which actually is; but we
have got enough; we have the satisfaction to find that in nature there
are wisdom, system, and consistency. For having in the natural history
of the earth seen a succession of worlds, we may from this conclude
that there is a system in nature; in like manner as, from seeing revolutions
of the planets, it is concluded that there is a system by which they
are intended to continue those revolutions. But if the succession
of worlds is established in the system of nature, it is in vain to
look for anything higher in the origin of the earth. The result, therefore,
of our present inquiry is that we find no vestige of a beginning---no
prospect of an end.''
\end{quotation}
{}

Altogether remarkable as this paper seems in the light of later knowledge,
neither friend nor foe deigned to notice it at the moment. It was
not published in book form until the last decade of the century, when
Hutton had lived with and worked over his theory for almost fifty
years. Then it caught the eye of the world. A school of followers
expounded the Huttonian doctrines; a rival school under Werner in
Germany opposed some details of the hypothesis, and the educated world
as a whole viewed the disputants askance. The very novelty of the
new views forbade their immediate acceptance. Bitter attacks were
made upon the {}``heresies,''\ and that was meant to be a soberly
tempered judgment which in 1800 pronounced Hutton's theories {}``not
only hostile to sacred history, but equally hostile to the principles
of probability, to the results of the ablest observations on the mineral
kingdom, and to the dictates of rational philosophy.'' And all this
because Hutton's theory presupposed the earth to have been in existence
more than six thousand years.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth,
  height=0.90\paperwidth,
  keepaspectratio]{3hsci10-Wil3S130}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small A Landscape and Mammal of the
Tertiary Age}\end{center}
\end{figure}
Thus it appears that though the thoughts of men had widened, in those
closing days of the eighteenth century, to include the stars, they
had not as yet expanded to receive the most patent records that are
written everywhere on the surface of the earth. Before Hutton's views
could be accepted, his pivotal conception that time is long must be
established by convincing proofs. The evidence was being gathered
by William Smith, Cuvier, and other devotees of the budding science
of paleontology in the last days of the century, but their labors
were not brought to completion till a subsequent epoch.


\section*{\raggedright NEPTUNISTS VERSUS PLUTONISTS}

\addcontentsline{toc}{section}{NEPTUNISTS VERSUS PLUTONISTS}

In the mean time, James Hutton's theory that continents wear away
and are replaced by volcanic upheaval gained comparatively few adherents.
Even the lucid \emph{Illustrations of the Huttonian Theory}, which
Playfair, the pupil and friend of the great Scotchman, published in
1802, did not at once prove convincing. The world had become enamoured
of the rival theory of Hutton's famous contemporary, Werner of Saxony---the
theory which taught that {}``in the beginning''\ all the solids
of the earth's present crust were dissolved in the heated waters of
a universal sea. Werner affirmed that all rocks, of whatever character,
had been formed by precipitation from this sea as the waters cooled;
that even veins have originated in this way; and that mountains are
gigantic crystals, not upheaved masses. In a word, he practically
ignored volcanic action, and denied \emph{in toto} the theory of metamorphosis
of rocks through the agency of heat.

The followers of Werner came to be known as Neptunists; the Huttonians
as Plutonists. The history of geology during the first quarter of
the nineteenth century is mainly a recital of the intemperate controversy
between these opposing schools; though it should not be forgotten
that, meantime, the members of the Geological Society of London were
making an effort to hunt for facts and avoid compromising theories.
Fact and theory, however, were too closely linked to be thus divorced.

The brunt of the controversy settled about the unstratified rocks---granites
and their allies---which the Plutonists claimed as of igneous origin.
This contention had the theoretical support of the nebular hypothesis,
then gaining ground, which supposed the earth to be a cooling globe.
The Plutonists laid great stress, too, on the observed fact that the
temperature of the earth increases at a pretty constant ratio as descent
towards its centre is made in mines. But in particular they appealed
to the phenomena of volcanoes.

The evidence from this source was gathered and elaborated by Mr.\ G.\ Poulett
Scrope, secretary of the Geological Society of England, who, in 1823,
published a classical work on volcanoes in which he claimed that volcanic
mountains, including some of the highest-known peaks, are merely accumulated
masses of lava belched forth from a crevice in the earth's crust.

\begin{quotation}
{}``Supposing the globe to have had any irregular shape when detached
from the sun,''\ said Scrope, {}``the vaporization of its surface,
and, of course, of its projecting angles, together with its rotatory
motion on its axis and the liquefaction of its outer envelope, would
necessarily occasion its actual figure of an oblate spheroid. As the
process of expansion proceeded in depth, the original granitic beds
were first partially disaggregated, next disintegrated, and more or
less liquefied, the crystals being merged in the elastic vehicle produced
by the vaporization of the water contained between the lamin\ae{}.

{}``Where this fluid was produced in abundance by great dilatation---that
is, in the outer and highly disintegrated strata, the superior specific
gravity of the crystals forced it to ooze upward, and thus a great
quantity of aqueous vapor was produced on the surface of the globe.
As this elastic fluid rose into outer space, its continually increasing
expansion must have proportionately lowered its temperature; and,
in consequence, a part was recondensed into water and sank back towards
the more solid surface of the globe.

{}``And in this manner, for a certain time, a violent reciprocation
of atmospheric phenomena must have continued---torrents of vapor rising
outwardly, while equally tremendous torrents of condensed vapor, or
rain, fell towards the earth. The accumulation of the latter on the
yet unstable and unconsolidated surface of the globe constituted the
primeval ocean. The surface of this ocean was exposed to continued
vaporization owing to intense heat; but this process, abstracting
caloric from the stratum of the water below, by partially cooling
it, tended to preserve the remainder in a liquid form. The ocean will
have contained, both in solution and suspension, many of the matters
carried upward from the granitic bed in which the vapors from whose
condensation it proceeded were produced, and which they had traversed
in their rise. The dissolved matters will have been silex, carbonates,
and sulphates of lime, and those other mineral substances which water
at an intense temperature and under such circumstances was enabled
to hold in solution. The suspended substances will have been all the
lighter and finer particles of the upper beds where the disintegration
had been extreme; and particularly their mica, which, owing to the
tenuity of its plate-shaped crystals, would be most readily carried
up by the ascending fluid, and will have remained longest in suspension.

{}``But as the torrents of vapor, holding these various matters in
solution and suspension, were forced upward, the greater part of the
disintegrated crystals by degrees subsided; those of felspar and quartz
first, the mica being, as observed above, from the form of its plates,
of peculiar buoyancy, and therefore held longest in suspension.

{}``The crystals of felspar and quartz as they subsided, together
with a small proportion of mica, would naturally arrange themselves
so as to have their longest dimensions more or less parallel to the
surface on which they rest; and this parallelism would be subsequently
increased, as we shall see hereafter, by the pressure of these beds
sustained between the weight of the supported column of matter and
the expansive force beneath them. These beds I conceive, when consolidated,
to constitute the gneiss formation.

{}``The farther the process of expansion proceeded in depth, the
more was the column of liquid matter lengthened, which, gravitating
towards the centre of the globe, tended to check any further expansion.
It is, therefore, obvious that after the globe settled into its actual
orbit, and thenceforward lost little of its enveloping matter, the
whole of which began from that moment to gravitate towards its centre,
the progress of expansion inwardly would continually increase in rapidity;
and a moment must have at length arrived when the forces of expansion
and repression had reached an equilibrium and the process was stopped
from progressing farther inwardly by the great pressure of the gravitating
column of liquid.

{}``This column may be considered as consisting of different strata,
though the passage from one extremity of complete solidity to the
other of complete expansion, in reality, must have been perfectly
gradual. The lowest stratum, immediately above the extreme limit of
expansion, will have been granite barely \textit{disaggregated}, and
rendered imperfectly liquid by the partial vaporization of its contained
water.

{}``The second stratum was granite \textit{disintegrated}; aqueous
vapor, having been produced in such abundance as to be enabled to
rise upward, partially disintegrating the crystals of felspar and
mica, and superficially dissolving those of quartz. This mass would
reconsolidate into granite, though of a smaller grain than the preceding
rock.

{}``The third stratum was so disintegrated that a greater part of
the mica had been carried up by the escaping vapor \textit{in} \textit{suspension},
and that of quartz in solution; the felspar crystals, with the remaining
quartz and mica, \textit{subsiding} by their specific gravity and
arranging themselves in horizontal planes.

{}``The consolidation of this stratum produced the gneiss formation.

{}``The fourth zone will have been composed of the ocean of turbid
and heated water, holding mica, \textit{etc}., in suspension, and
quartz, carbonate of lime, \textit{etc}., in solution, and continually
traversed by reciprocating bodies of heated water rising from below,
and of cold fluid sinking from the surface, by reason of their specific
gravities.

{}``The disturbance thus occasioned will have long retarded the deposition
of the suspended particles. But this must by degrees have taken place,
the quartz grains and the larger and coarser plates of mica subsiding
first and the finest last.

{}``But the fragments of quartz and mica were not deposited alone;
a great proportion of the quartz held in \textit{solution} must have
been precipitated at the same time as the water cooled, and therefore
by degrees lost its faculty of so much in solution. Thus was gradually
produced the formation of mica-schist, the mica imperfectly recrystallizing
or being merely aggregated together in horizontal plates, between
which the quartz either spread itself generally in minute grains or
unified into crystalline nuclei. On other spots, instead of silex,
carbonate of lime was precipitated, together with more or less of
the nucaceous sediment, and gave rise to saccharoidal limestones.
At a later period, when the ocean was yet further cooled down, rock-salt
and sulphate of lime were locally precipitated in a similar mode.

{}``The fifth stratum was aeriform, and consisted in great part of
aqueous vapors; the remainder being a compound of other elastic fluids
(permanent gases) which had been formed probably from the volatilization
of some of the substances contained in the primitive granite and carried
upward with the aqueous vapor from below. These gases will have been
either mixed together or otherwise disposed, according to their different
specific gravities or chemical affinities, and this stratum constituted
the atmosphere or aerial envelope of the globe.

{}``When, in this manner, the general and positive expansion of the
globe, occasioned by the sudden reduction of outward pressure, had
ceased (in consequence of the \textit{repressive} \textit{force},
consisting of the weight of its fluid envelope, having reached an
equilibrium with the \textit{expansive} \textit{force}, consisting
of the caloric of the heated nucleus), the rapid superficial evaporation
of the ocean continued; and, by gradually reducing its temperature,
occasioned the precipitation of a proportionate quantity of the minerals
it held in solution, particularly its silex. These substances falling
to the bottom, accompanied by a large proportion of the matters held
in solution, particularly the mica, in consequence of the greater
comparative tranquillity of the ocean, agglomerated these into more
or less compact beds of rock (the mica-schist formation), producing
the first crust or solid envelope of the globe. Upon this, other stratified
rocks, composed sometimes of a mixture, sometimes of an alternation
of precipitations, sediments, and occasionally of conglomerates, were
by degrees deposited, giving rise to the \textit{transition} formations.

{}``Beneath this crust a new process now commenced. The outer zones
of crystalline matter having been suddenly refrigerated by the rapid
vaporization and partial escape of the water they contained, abstracted
caloric from the intensely heated nucleus of the globe. These crystalline
zones were of unequal density, the expansion they had suffered diminishing
from above downward.

{}``Their expansive force was, however, equal at all points, their
temperature everywhere bearing an inverse ratio to their density.
But when by the accession of caloric from the inner and unliquefied
nucleus the temperature, and consequently the expansive force of the
lower strata of dilated crystalline matter, was augmented, it acted
upon the upper and more liquefied strata. These being prevented from
yielding \textit{outwardly} by the tenacity and weight of the solid
involucrum of precipitated and sedimental deposits which overspread
them, sustained a pressure out of proportion to their expansive force,
and were in consequence proportionately condensed, and by the continuance
of the process, where the overlying strata were sufficiently resistant,
finally consolidated.

{}``This process of consolidation must have progressed from above
downward, with the increase of the expansive force in the lower strata,
commencing from the upper surface, which, its temperature being lowest,
offered the least resistance to the force of compression.

{}``By this process the upper zone of crystalline matter, which had
intumesced so far as to allow of the escape of its aqueous vapor and
of much of its mica and quartz, was resolidified, the component crystals
arranging themselves in planes perpendicular to the direction of the
pressure by which the mass was consolidated---that is, to the radius
of the globe. The gneiss formation, as already observed, was the result.

{}``The inferior zone of barely disintegrated granite, from which
only a part of the steam and quartz and none of the mica had escaped,
reconsolidated in a confused or granitoidal manner; but exhibits marks
of the process it had undergone in its broken crystals of felspar
and mica, its rounded and superficially dissolved grains of quartz,
its imbedded fragments (broken from the more solid parts of the mass,
as it rose, and enveloped by the softer parts), its concretionary
nodules and new minerals, \textit{etc}.

{}``Beneath this, the granite which had been simply disintegrated
was again solidified, and returned in all respects to its former condition.
The temperature, however, and with it the expansive force of the inferior
zone, was continually on the increase, the caloric of the interior
of the globe still endeavoring to put itself \emph{in equilibrio}
by passing off towards the less-intensely heated crust.

{}``This continually increasing expansive force must at length have
overcome the resistance opposed by the tenacity and weight of the
overlying consolidated strata. It is reasonable to suppose that this
result took place contemporaneously, or nearly so, on many spots,
wherever accidental circumstances in the texture or composition of
the oceanic deposits led them to yield more readily; and in this manner
were produced those original fissures in the primeval crust of the
earth through some of which (fissures of elevation)\ were intruded
portions of interior crystalline zones in a solid or nearly solid
state, together with more or less of the intumescent granite, in the
manner above described; while others (fissures of eruption)\ gave
rise to extravasations of the heated crystalline matter, in the form
of lavas---that is, still further liquefied by the greater comparative
reduction of the pressure they endured.''%
\footnote{\emph{Consideration on Volcanoes}, by G.\ Poulett Scrope, Esq., pp.\ 228-234. %
}
\end{quotation}
{}

The Neptunists stoutly contended for the aqueous origin of volcanic
as of other mountains. But the facts were with Scrope, and as time
went on it came to be admitted that not merely volcanoes, but many
{}``trap''\ formations not taking the form of craters, had been
made by the obtrusion of molten rock through fissures in overlying
strata. Such, for example, to cite familiar illustrations, are Mount
Holyoke, in Massachusetts, and the well-known formation of the Palisades
along the Hudson.

But to admit the {}``Plutonic''\ origin of such widespread formations
was practically to abandon the Neptunian hypothesis. So gradually
the Huttonian explanation of the origin of granites and other {}``igneous''
rocks, whether massed or in veins, came to be accepted. Most geologists
then came to think of the earth as a molten mass, on which the crust
rests as a mere film. Some, indeed, with Lyell, preferred to believe
that the molten areas exist only as lakes in a solid crust, heated
to melting, perhaps, by electrical or chemical action, as Davy suggested.
More recently a popular theory attempts to reconcile geological facts
with the claim of the physicists, that the earth's entire mass is
at least as rigid as steel, by supposing that a molten film rests
between the observed solid crust and the alleged solid nucleus. But
be that as it may, the theory that subterranean heat has been instrumental
in determining the condition of {}``primary''\ rocks, and in producing
many other phenomena of the earth's crust, has never been in dispute
since the long controversy between the Neptunists and the Plutonists
led to its establishment.


\section*{\raggedright LYELL AND UNIFORMITARIANISM}

\addcontentsline{toc}{section}{LYELL AND UNIFORMITARIANISM}

If molten matter exists beneath the crust of the earth, it must contract
in cooling, and in so doing it must disturb the level of the portion
of the crust already solidified. So a plausible explanation of the
upheaval of continents and mountains was supplied by the Plutonian
theory, as Hutton had from the first alleged. But now an important
difference of opinion arose as to the exact rationale of such upheavals.
Hutton himself, and practically every one else who accepted his theory,
had supposed that there are long periods of relative repose, during
which the level of the crust is undisturbed, followed by short periods
of active stress, when continents are thrown up with volcanic suddenness,
as by the throes of a gigantic earthquake. But now came Charles Lyell
with his famous extension of the {}``uniformitarian''\ doctrine,
claiming that past changes of the earth's surface have been like present
changes in degree as well as in kind. The making of continents and
mountains, he said, is going on as rapidly to-day as at any time in
the past. There have been no gigantic cataclysmic upheavals at any
time, but all changes in level of the strata as a whole have been
gradual, by slow oscillation, or at most by repeated earthquake shocks
such as are still often experienced.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics{3hsci10-CharlesLyell}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Charles Lyell}\end{center}
\end{figure}
In support of this very startling contention Lyell gathered a mass
of evidence of the recent changes in level of continental areas. He
corroborated by personal inspection the claim which had been made
by Playfair in 1802, and by von Buch in 1807, that the coast-line
of Sweden is rising at the rate of from a few inches to several feet
in a century. He cited Darwin's observations going to prove that Patagonia
is similarly rising, and Pingel's claim that Greenland is slowly sinking.
Proof as to sudden changes of level of several feet, over large areas,
due to earthquakes, was brought forward in abundance. Cumulative evidence
left it no longer open to question that such oscillatory changes of
level, either upward or downward, are quite the rule, and it could
not be denied that these observed changes, if continued long enough
in one direction, would produce the highest elevations. The possibility
that the making of even the highest ranges of mountains had been accomplished
without exaggerated catastrophic action came to be freely admitted.

It became clear that the supposedly stable land surfaces are in reality
much more variable than the surface of the {}``shifting sea''; that
continental masses, seemingly so fixed, are really rising and falling
in billows thousands of feet in height, ages instead of moments being
consumed in the sweep between crest and hollow.

These slow oscillations of land surfaces being understood, many geological
enigmas were made clear---such as the alternation of marine and fresh-water
formations in a vertical series, which Cuvier and Brongniart had observed
near Paris; or the sandwiching of layers of coal, of subaerial formation,
between layers of subaqueous clay or sandstone, which may be observed
everywhere in the coal measures. In particular, the extreme thickness
of the sedimentary strata as a whole, many times exceeding the depth
of the deepest known sea, was for the first time explicable when it
was understood that such strata had formed in slowly sinking ocean-beds.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth,
  height=0.80\paperwidth]{3hsci10-Wil3S142}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small A Landscape and Terrestrial
Reptile of the Mesozoic Time}\end{center}
\end{figure}
All doubt as to the mode of origin of stratified rocks being thus
removed, the way was opened for a more favorable consideration of
that other Huttonian doctrine of the extremely slow denudation of
land surfaces. The enormous amount of land erosion will be patent
to any one who uses his eyes intelligently in a mountain district.
It will be evident in any region where the strata are tilted---as,
for example, the Alleghanies---that great folds of strata which must
once have risen miles in height have in many cases been worn entirely
away, so that now a valley marks the location of the former eminence.
Where the strata are level, as in the case of the mountains of Sicily,
the Scotch Highlands, and the familiar Catskills, the evidence of
denudation is, if possible, even more marked; for here it is clear
that elevation and valley have been carved by the elements out of
land that rose from the sea as level plateaus.

But that this herculean labor of land-sculpturing could have been
accomplished by the slow action of wind and frost and shower was an
idea few men could grasp within the first half-century after Hutton
propounded it; nor did it begin to gain general currency until Lyell's
crusade against catastrophism, begun about 1830, had for a quarter
of a century accustomed geologists to the thought of slow, continuous
changes producing final results of colossal proportions. And even
long after that it was combated by such men as Murchison, Director-General
of the Geological Survey of Great Britain, then accounted the foremost
field-geologist of his time, who continued to believe that the existing
valleys owe their main features to subterranean forces of upheaval.
Even Murchison, however, made some recession from the belief of the
Continental authorities, Elie de Beaumont and Leopold von Buch, who
contended that the mountains had sprung up like veritable jacks-in-the-box.
Von Buch, whom his friend and fellow-pupil von Humboldt considered
the foremost geologist of the time, died in 1853, still firm in his
early faith that the erratic bowlders found high on the Jura had been
hurled there, like cannon-balls, across the valley of Geneva by the
sudden upheaval of a neighboring mountain-range.


\section*{\raggedright AGASSIZ AND THE GLACIAL THEORY}

\addcontentsline{toc}{section}{AGASSIZ AND THE GLACIAL THEORY}

The bowlders whose presence on the crags of the Jura the old German
accounted for in a manner so theatrical had long been a source of
contention among geologists. They are found not merely on the Jura,
but on numberless other mountains in all north-temperate latitudes,
and often far out in the open country, as many a farmer who has broken
his plough against them might testify. The early geologists accounted
for them, as for nearly everything else, with their supposititious
Deluge. Brongniart and Cuvier and Buckland and their contemporaries
appeared to have no difficulty in conceiving that masses of granite
weighing hundreds of tons had been swept by this current scores or
hundreds of miles from their source. But, of course, the uniformitarian
faith permitted no such explanation, nor could it countenance the
projection idea; so Lyell was bound to find some other means of transportation
for the puzzling erratics.

The only available medium was ice, but, fortunately, this one seemed
quite sufficient. Icebergs, said Lyell, are observed to carry all
manner of debris, and deposit it in the sea-bottoms. Present land
surfaces have often been submerged beneath the sea. During the latest
of these submergences icebergs deposited the bowlders now scattered
here and there over the land. Nothing could be simpler or more clearly
uniformitarian. And even the catastrophists, though they met Lyell
amicably on almost no other theoretical ground, were inclined to admit
the plausibility of his theory of erratics. Indeed, of all Lyell's
nonconformist doctrines, this seemed the one most likely to meet with
general acceptance.

Yet, even as this iceberg theory loomed large and larger before the
geological world, observations were making in a different field that
were destined to show its fallacy. As early as 1815 a sharp-eyed chamois-hunter
of the Alps, Perraudin by name, had noted the existence of the erratics,
and, unlike most of his companion hunters, had puzzled his head as
to how the bowlders got where he saw them. He knew nothing of submerged
continents or of icebergs, still less of upheaving mountains; and
though he doubtless had heard of the Flood, he had no experience of
heavy rocks floating like corks in water. Moreover, he had never observed
stones rolling uphill and perching themselves on mountain-tops, and
he was a good enough uniformitarian (though he would have been puzzled
indeed had any one told him so)\ to disbelieve that stones in past
times had disported themselves differently in this regard from stones
of the present. Yet there the stones are. How did they get there?

The mountaineer thought that he could answer that question. He saw
about him those gigantic serpent-like streams of ice called glaciers,
{}``from their far fountains slow rolling on,''\ carrying with
them blocks of granite and other debris to form moraine deposits.
If these glaciers had once been much more extensive than they now
are, they might have carried the bowlders and left them where we find
them. On the other hand, no other natural agency within the sphere
of the chamois-hunter's knowledge could have accomplished this, ergo
the glaciers must once have been more extensive. Perraudin would probably
have said that common-sense drove him to this conclusion; but be that
as it may, he had conceived one of the few truly original and novel
ideas of which the nineteenth century can boast.

Perraudin announced his idea to the greatest scientist in his little
world---Jean de Charpentier, director of the mines at Bex, a skilled
geologist who had been a fellow-pupil of von Buch and von Humboldt
under Werner at the Freiberg School of Mines. Charpentier laughed
at the mountaineer's grotesque idea, and thought no more about it.
And ten years elapsed before Perraudin could find any one who treated
his notion with greater respect. Then he found a listener in M.\ Venetz,
a civil engineer, who read a paper on the novel glacial theory before
a local society in 1823. This brought the matter once more to the
attention of de Charpentier, who now felt that there might be something
in it worth investigation.

A survey of the field in the light of the new theory soon convinced
Charpentier that the chamois-hunter had all along been right. He became
an enthusiastic supporter of the idea that the Alps had once been
imbedded in a mass of ice, and in 1836 he brought the notion to the
attention of Louis Agassiz, who was spending the summer in the Alps.
Agassiz was sceptical at first, but soon became a convert.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics{3hsci10-LouisJeanRudolphAgassiz}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Louis Jean Rudolph Agassiz}\end{center}
\end{figure}
In 1840 Agassiz published a paper in which the results of his Alpine
studies were elaborated.

\begin{quotation}
{}``Let us consider,''\ he says, {}``those more considerable changes
to which glaciers are subject, or rather, the immense extent which
they had in the prehistoric period. This former immense extension,
greater than any that tradition has preserved, is proved, in the case
of nearly every valley in the Alps, by facts which are both many and
well established. The study of these facts is even easy if the student
is looking out for them, and if he will seize the least indication
of their presence; and, if it were a long time before they were observed
and connected with glacial action, it is because the evidences are
often isolated and occur at places more or less removed from the glacier
which originated them. If it be true that it is the prerogative of
the scientific observer to group in the field of his mental vision
those facts which appear to be without connection to the vulgar herd,
it is, above all, in such a case as this that he is called upon to
do so. I have often compared these feeble effects, produced by the
glacial action of former ages, with the appearance of the markings
upon a lithographic stone, prepared for the purpose of preservation,
and upon which one cannot see the lines of the draughtsman's work
unless it is known beforehand where and how to search for them.

{}``The fact of the former existence of glaciers which have now disappeared
is proved by the survival of the various phenomena which always accompany
them, and which continue to exist even after the ice has melted. These
phenomena are as follows:\ 

{}``1. Moraines.---The disposition and composition of moraines enable
them to be always recognized, even when they are no longer adjacent
to a glacier nor immediately surround its lower extremities. I may
remark that lateral and terminal moraines alone enable us to recognize
with certainty the limits of glacial extension, because they can be
easily distinguished from the dikes and irregularly distributed stones
carried down by the Alpine torrents, The lateral moraines deposited
upon the sides of valleys are rarely affected by the larger torrents,
but they are, however, often cut by the small streams which fall down
the side of a mountain, and which, by interfering with their continuity,
make them so much more difficult to recognize.

{}``2. The Perched Bowlders.---It often happens that glaciers encounter
projecting points of rock, the sides of which become rounded, and
around which funnel-like cavities are formed with more or less profundity.
When glaciers diminish and retire, the blocks which have fallen into
these funnels often remain perched upon the top of the projecting
rocky point within it, in such a state of equilibrium that any idea
of a current of water as the cause of their transportation is completely
inadmissible on account of their position. When such points of rock
project above the surface of the glacier or appear as a more considerable
islet in the midst of its mass (such as is the case in the Jardin
of the Mer de Glace, above Montavert), such projections become surrounded
on all sides by stones which ultimately form a sort of crown around
the summit whenever the glaciers decrease or retire completely. Water
currents never produce anything like this; but, on the contrary, whenever
a stream breaks itself against a projecting rock, the stones which
it carries down are turned aside and form a more or less regular trail.
Never, under such circumstances, can the stones remain either at the
top or at the sides of the rock, for, if such a thing were possible,
the rapidity of the current would be accelerated by the increased
resistance, and the moving bowlders would be carried beyond the obstruction
before they were finally deposited.

{}``3. The polished and striated rocks, such as have been described
in Chapter XIV., afford yet further evidence of the presence of a
glacier; for, as has been said already, neither a current nor the
action of waves upon an extensive beach produces such effects. The
general direction of the channels and furrows indicates the direction
of the general movement of the glacier, and the streaks which vary
more or less from this direction are produced by the local effects
of oscillation and retreat, as we shall presently see.

{}``4. The Lapiaz, or Lapiz, which the inhabitants of German Switzerland
call \emph{Karrenfelder}, cannot always be distinguished from erosions,
because, both produced as they are by water, they do not differ in
their exterior characteristics, but only in their positions. Erosions
due to torrents are always found in places more or less depressed,
and never occur upon large inclined surfaces. The Lapiaz, on the contrary,
are frequently found upon the projecting parts of the sides of valleys
in places where it is not possible to suppose that water has ever
formed a current. Some geologists, in their embarrassment to explain
these phenomena, have supposed that they were due to the infiltration
of acidulated water, but this hypothesis is purely gratuitous.

{}``We will now describe the remains of these various phenomena as
they are found in the Alps outside the actual glacial limits, in order
to prove that at a certain epoch glaciers were much larger than they
are to-day.

{}``The ancient moraines, situated as they are at a great distance
from those of the present day, are nowhere so distinct or so frequent
as in Valais, where MM.\ Venetz and J.\ de Charpentier noticed them
for the first time; but as their observations are as yet unpublished,
and they themselves gave me the information, it would be an appropriation
of their discovery if I were to describe them here in detail. I will
limit myself to say that there can be found traces, more or less distinct,
of ancient terminal moraines in the form of vaulted dikes at the foot
of every glacier, at a distance of a few minutes'\ walk, a quarter
of an hour, a half-hour, an hour, and even of several leagues from
their present extremities. These traces become less distinct in proportion
to their distance from the glacier, and, since they are also often
traversed by torrents, they are not as continuous as the moraines
which are nearer to the glaciers. The farther these ancient moraines
are removed from the termination of a glacier, the higher up they
reach upon the sides of the valley, which proves to us that the thickness
of the glacier must have been greater when its size was larger. At
the same time, their number indicates so many stopping-places in the
retreat of the glacier, or so many extreme limits of its extension---limits
which were never reached again after it had retired. I insist upon
this point, because if it is true that all these moraines demonstrate
a larger extent of the glacier, they also prove that their retreat
into their present boundaries, far from having been catastrophic,
was marked on the contrary by periods of repose more or less frequent,
which caused the formation of a series of concentric moraines which
even now indicate their retrogression.

{}``The remains of longitudinal moraines are less frequent, less
distinct, and more difficult to investigate, because, indicating as
they do the levels to which the edges of the glacier reached at different
epochs, it is generally necessary to look for them above the line
of the paths along the escarpments of the valleys, and hence it is
not always possible to follow them along a valley. Often, also, the
sides of a valley which enclosed a glacier are so steep that it is
only here and there that the stones have remained in place. They are,
nevertheless, very distinct in the lower part of the valley of the
Rhone, between Martigny and the Lake of Geneva, where several parallel
ridges can be observed, one above the other, at a height of one thousand,
one thousand two hundred, and even one thousand five hundred feet
above the Rhone. It is between St.\ Maurice and the cascade of Pissevache,
close to the hamlet of Chaux-Fleurie, that they are most accessible,
for at this place the sides of the valley at different levels ascend
in little terraces, upon which the moraines have been preserved. They
are also very distinct above the Bains de Lavey, and above the village
of Monthey at the entrance of the Val d'Illiers, where the sides of
the valley are less inclined than in many other places.

{}``The perched bowlders which are found in the Alpine valleys, at
considerable distances from the glaciers, occupy at times positions
so extraordinary that they excite in a high degree the curiosity of
those who see them. For instance, when one sees an angular stone perched
upon the top of an isolated pyramid, or resting in some way in a very
steep locality, the first inquiry of the mind is, When and how have
these stones been placed in such positions, where the least shock
would seem to turn them over? But this phenomenon is not in the least
astonishing when it is seen to occur also within the limits of actual
glaciers, and it is recalled by what circumstances it is occasioned.

{}``The most curious examples of perched stones which can be cited
are those which command the northern part of the cascade of Pissevache,
close to Chaux-Fleurie, and those above the Bains de Lavey, close
to the village of Morcles; and those, even more curious, which I have
seen in the valley of St.\ Nicolas and Oberhasli. At Kirchet, near
Meiringen, can be seen some very remarkable crowns of bowlders around
several domes of rock which appear to have been projected above the
surface of the glacier which surrounded them. Something very similar
can be seen around the top of the rock of St.\ Triphon.

{}``The extraordinary phenomenon of perched stones could not escape
the observing eye of de Saussure, who noticed several at Saleve, of
which he described the positions in the following manner: `One sees,'
said he, `upon the slope of an inclined meadow, two of these great
bowlders of granite, elevated one upon the other, above the grass
at a height of two or three feet, upon a base of limestone rock on
which both rest. This base is a continuation of the horizontal strata
of the mountain, and is even united with it visibly on its lower face,
being cut perpendicularly upon the other sides, and is not larger
than the stone which it supports.' But seeing that the entire mountain
is composed of the same limestone, de Saussure naturally concluded
that it would be absurd to think that it was elevated precisely and
only beneath the blocks of granite. But, on the other hand, since
he did not know the manner in which these perched stones are deposited
in our days by glacial action, he had recourse to another explanation:
He supposes that the rock was worn away around its base by the continual
erosion of water and air, while the portion of the rock which served
as the base for the granite had been protected by it. This explanation,
although very ingenious, could no longer be admitted after the researches
of M.\ Elie de Beaumont had proved that the action of atmospheric
agencies was not by a good deal so destructive as was theretofore
supposed. De Saussure speaks also of a detached bowlder, situated
upon the opposite side of the T\^{e}te-Noire, `which is,'\ he says,
`of so great a size that one is tempted to believe that it was formed
in the place it occupies; and it is called \emph{B\"{a}rme russe},
because it is worn away beneath in the form of a cave which can afford
accommodation for more than thirty persons at a time.''%
\footnote{L.\ Agassiz, \emph{\'{E}tudes sur les glaciers}, Neufchatel, 1840,
p.\ 240.%
}
\end{quotation}
{}

But the implications of the theory of glaciers extend, so Agassiz
has come to believe, far beyond the Alps. If the Alps had been covered
with an ice sheet, so had many other regions of the northern hemisphere.
Casting abroad for evidences of glacial action, Agassiz found them
everywhere in the form of transported erratics, scratched and polished
outcropping rocks, and moraine-like deposits. Finally, he became convinced
that the ice sheet that covered the Alps had spread over the whole
of the higher latitudes of the northern hemisphere, forming an ice
cap over the globe. Thus the common-sense induction of the chamois-hunter
blossomed in the mind of Agassiz into the conception of a universal
ice age.

In 1837 Agassiz had introduced his theory to the world, in a paper
read at Neuchatel, and three years later he published his famous \emph{Etudes
sur les Glaciers}, from which we have just quoted. Never did idea
make a more profound disturbance in the scientific world. Von Buch
treated it with alternate ridicule, contempt, and rage; Murchison
opposed it with customary vigor; even Lyell, whose most remarkable
mental endowment was an unfailing receptiveness to new truths, could
not at once discard his iceberg theory in favor of the new claimant.
Dr.\ Buckland, however, after Agassiz had shown him evidence of former
glacial action in his own Scotland, became a convert---the more readily,
perhaps, as it seemed to him to oppose the uniformitarian idea. Gradually
others fell in line, and after the usual imbittered controversy and
the inevitable full generation of probation, the idea of an ice age
took its place among the accepted tenets of geology. All manner of
moot points still demanded attention---the cause of the ice age, the
exact extent of the ice sheet, the precise manner in which it produced
its effects, and the exact nature of these effects; and not all of
these have even yet been determined. But, details aside, the ice age
now has full recognition from geologists as an historical period.
There may have been many ice ages, as Dr.\ Croll contends; there
was surely one; and the conception of such a period is one of the
very few ideas of our century that no previous century had even so
much as faintly adumbrated.


\section*{\raggedright THE GEOLOGICAL AGES}

\addcontentsline{toc}{section}{THE GEOLOGICAL AGES}

But, for that matter, the entire subject of historical geology is
one that had but the barest beginning before our century. Until the
paleontologist found out the key to the earth's chronology, no one---not
even Hutton---could have any definite idea as to the true story of
the earth's past. The only conspicuous attempt to classify the strata
was that made by Werner, who divided the rocks into three systems,
based on their supposed order of deposition, and called primary, transition,
and secondary.

Though Werner's observations were confined to the small province of
Saxony, he did not hesitate to affirm that all over the world the
succession of strata would be found the same as there, the concentric
layers, according to this conception, being arranged about the earth
with the regularity of layers on an onion. But in this Werner was
as mistaken as in his theoretical explanation of the origin of the
{}``primary''\ rocks. It required but little observation to show
that the exact succession of strata is never precisely the same in
any widely separated regions. Nevertheless, there was a germ of truth
in Werner's system. It contained the idea, however faultily interpreted,
of a chronological succession of strata; and it furnished a working
outline for the observers who were to make out the true story of geological
development. But the correct interpretation of the observed facts
could only be made after the Huttonian view as to the origin of strata
had gained complete acceptance.

When William Smith, having found the true key to this story, attempted
to apply it, the territory with which he had to deal chanced to be
one where the surface rocks are of that later series which Werner
termed secondary. He made numerous subdivisions within this system,
based mainly on the fossils. Meantime it was found that, judged by
the fossils, the strata that Brongniart and Cuvier studied near Paris
were of a still more recent period (presumed at first to be due to
the latest deluge), which came to be spoken of as tertiary. It was
in these beds, some of which seemed to have been formed in fresh-water
lakes, that many of the strange mammals which Cuvier first described
were found.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics{3hsci10-AdamSedgwick}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Adam Sedgwick}\end{center}
\end{figure}
But the {}``transition''\ rocks, underlying the {}``secondary''
system that Smith studied, were still practically unexplored when,
along in the thirties, they were taken in hand by Roderick Impey Murchison,
the reformed fox-hunter and ex-captain, who had turned geologist to
such notable advantage, and Adam Sedgwick, the brilliant Woodwardian
professor at Cambridge.

Working together, these two friends classified the transition rocks
into chronological groups, since familiar to every one in the larger
outlines as the Silurian system (age of invertebrates)\ and the Devonian
system (age of fishes)---names derived respectively from the country
of the ancient Silures, in Wales and Devonshire, England. It was subsequently
discovered that these systems of strata, which crop out from beneath
newer rocks in restricted areas in Britain, are spread out into broad,
undisturbed sheets over thousands of miles in continental Europe and
in America. Later on Murchison studied them in Russia, and described
them, conjointly with Verneuil and von Kerserling, in a ponderous
and classical work. In America they were studied by Hall, Newberry,
Whitney, Dana, Whitfield, and other pioneer geologists, who all but
anticipated their English contemporaries.

The rocks that are of still older formation than those studied by
Murchison and Sedgwick (corresponding in location to the {}``primary''\ rocks
of Werner's conception) are the surface feature of vast areas in Canada,
and were first prominently studied there by William I. Logan, of the
Canadian Government Survey, as early as 1846, and later on by Sir
William Dawson. These rocks---comprising the Laurentian system---were
formerly supposed to represent parts of the original crust of the
earth, formed on first cooling from a molten state; but they are now
more generally regarded as once-stratified deposits metamorphosed
by the action of heat.

Whether {}``primitive''\ or metamorphic, however, these Canadian
rocks, and analogous ones beneath the fossiliferous strata of other
countries, are the oldest portions of the earth's crust of which geology
has any present knowledge. Mountains of this formation, as the Adirondacks
and the Storm King range, overlooking the Hudson near West Point,
are the patriarchs of their kind, beside which Alleghanies and Sierra
Nevadas are recent upstarts, and Rockies, Alps, and Andes are mere
parvenus of yesterday.

The Laurentian rocks were at first spoken of as representing {}``Azoic''\ time;
but in 1846 Dawson found a formation deep in their midst which was
believed to be the fossil relic of a very low form of life, and after
that it became customary to speak of the system as {}``Eozoic.''
Still more recently the title of Dawson's supposed fossil to rank
as such has been questioned, and Dana's suggestion that the early
rocks be termed merely Archman has met with general favor. Murchison
and Sedgwick's Silurian, Devonian, and Carboniferous groups (the ages
of invertebrates, of fishes, and of coal plants, respectively)\ are
together spoken of as representing Paleozoic time. William Smith's
system of strata, next above these, once called {}``secondary,''\ represents
Mesozoic time, or the age of reptiles. Still higher, or more recent,
are Cuvier and Brongniart's tertiary rocks, representing the age of
mammals. Lastly, the most recent formations, dating back, however,
to a period far enough from recent in any but a geological sense,
are classed as quaternary, representing the age of man.

It must not be supposed, however, that the successive {}``ages''\ of
the geologist are shut off from one another in any such arbitrary
way as this verbal classification might seem to suggest. In point
of fact, these {}``ages'' have no better warrant for existence than
have the {}``centuries''\ and the {}``weeks''\ of every-day
computation. They are convenient, and they may even stand for local
divisions in the strata, but they are bounded by no actual gaps in
the sweep of terrestrial events.

Moreover, it must be understood that the {}``ages''\ of different
continents, though described under the same name, are not necessarily
of exact contemporaneity. There is no sure test available by which
it could be shown that the Devonian age, for instance, as outlined
in the strata of Europe, did not begin millions of years earlier or
later than the period whose records are said to represent the Devonian
age in America. In attempting to decide such details as this, mineralogical
data fail us utterly. Even in rocks of adjoining regions identity
of structure is no proof of contemporaneous origin; for the veritable
substance of the rock of one age is ground up to build the rocks of
subsequent ages. Furthermore, in seas where conditions change but
little the same form of rock may be made age after age. It is believed
that chalk-beds still forming in some of our present seas may form
one continuous mass dating back to earliest geologic ages. On the
other hand, rocks different in character may be formed at the same
time in regions not far apart---say a sandstone along shore, a coral
limestone farther seaward, and a chalk-bed beyond. This continuous
stratum, broken in the process of upheaval, might seem the record
of three different epochs.

Paleontology, of course, supplies far better chronological tests,
but even these have their limitations. There has been no time since
rocks now in existence were formed, if ever, when the earth had a
uniform climate and a single undiversified \emph{fauna} over its entire
land surface, as the early paleontologists supposed. Speaking broadly,
the same general stages have attended the evolution of organic forms
everywhere, but there is nothing to show that equal periods of time
witnessed corresponding changes in diverse regions, but quite the
contrary. To cite but a single illustration, the marsupial order,
which is the dominant mammalian type of the living \emph{fauna} of
Australia to-day, existed in Europe and died out there in the tertiary
age. Hence a future geologist might think the Australia of to-day
contemporaneous with a period in Europe which in reality antedated
it by perhaps millions of years.

All these puzzling features unite to render the subject of historical
geology anything but the simple matter the fathers of the science
esteemed it. No one would now attempt to trace the exact sequence
of formation of all the mountains of the globe, as Elie de Beaumont
did a half-century ago. Even within the limits of a single continent,
the geologist must proceed with much caution in attempting to chronicle
the order in which its various parts rose from the matrix of the sea.
The key to this story is found in the identification of the strata
that are the surface feature in each territory. If Devonian rocks
are at the surface in any given region, for example, it would appear
that this region became a land surface in the Devonian age, or just
afterwards. But a moment's consideration shows that there is an element
of uncertainty about this, due to the steady denudation that all land
surfaces undergo. The Devonian rocks may lie at the surface simply
because the thousands of feet of carboniferous strata that once lay
above them have been worn away. All that the cautious geologist dare
assert, therefore, is that the region in question did not become permanent
land surface earlier than the Devonian age.

But to know even this is much---sufficient, indeed, to establish the
chronological order of elevation, if not its exact period, for all
parts of any continent that have been geologically explored---understanding
always that there must be no scrupling about a latitude of a few millions
or perhaps tens of millions of years here and there.

Regarding our own continent, for example, we learn through the researches
of a multitude of workers that in the early day it was a mere archipelago.
Its chief island---the backbone of the future continent---was a great
V-shaped area surrounding what is now Hudson Bay, an area built tip,
perhaps, through denudation of a yet more ancient polar continent,
whose existence is only conjectured. To the southeast an island that
is now the Adirondack Mountains, and another that is now the Jersey
Highlands rose above the waste of waters, and far to the south stretched
probably a line of islands now represented by the Blue Ridge Mountains.
Far off to the westward another line of islands foreshadowed our present
Pacific border. A few minor islands in the interior completed the
archipelago.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics{3hsci10-JamesDwightDana}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small James Dwight Dana}\end{center}
\end{figure}
From this bare skeleton the continent grew, partly by the deposit
of sediment from the denudation of the original islands (which once
towered miles, perhaps, where now they rise thousands of feet), but
largely also by the deposit of organic remains, especially in the
interior sea, which teemed with life. In the Silurian ages, invertebrates---brachiopods
and crinoids and cephalopods---were the dominant types. But very early---no
one knows just when---there came fishes of many strange forms, some
of the early ones enclosed in turtle-like shells. Later yet, large
spaces within the interior sea having risen to the surface, great
marshes or forests of strange types of vegetation grew and deposited
their remains to form coal-beds. Many times over such forests were
formed, only to be destroyed by the oscillations of the land surface.
All told, the strata of this Paleozoic period aggregate several miles
in thickness, and the time consumed in their formation stands to all
later time up to the present, according to Professor Dana's estimate,
as three to one.

Towards the close of this Paleozoic era the Appalachian Mountains
were slowly upheaved in great convoluted folds, some of them probably
reaching three or four miles above the sea-level, though the tooth
of time has since gnawed them down to comparatively puny limits. The
continental areas thus enlarged were peopled during the ensuing Mesozoic
time with multitudes of strange reptiles, many of them gigantic in
size. The waters, too, still teeming with invertebrates and fishes,
had their quota of reptilian monsters; and in the air were flying
reptiles, some of which measured twenty-five feet from tip to tip
of their batlike wings. During this era the Sierra Nevada Mountains
rose. Near the eastern border of the forming continent the strata
were perhaps now too thick and stiff to bend into mountain folds,
for they were rent into great fissures, letting out floods of molten
lava, remnants of which are still in evidence after ages of denudation,
as the Palisades along the Hudson, and such elevations as Mount Holyoke
in western Massachusetts.

Still there remained a vast interior sea, which later on, in the tertiary
age, was to be divided by the slow uprising of the land, which only
yesterday---that is to say, a million, or three or five or ten million,
years ago---became the Rocky Mountains. High and erect these young
mountains stand to this day, their sharp angles and rocky contours
vouching for their youth, in strange contrast with the shrunken forms
of the old Adirondacks, Green Mountains, and Appalachians, whose lowered
heads and rounded shoulders attest the weight of ages. In the vast
lakes which still remained on either side of the Rocky range, tertiary
strata were slowly formed to the ultimate depth of two or three miles,
enclosing here and there those vertebrate remains which were to be
exposed again to view by denudation when the land rose still higher,
and then, in our own time, to tell so wonderful a story to the paleontologist.

Finally, the interior seas were filled, and the shore lines of the
continent assumed nearly their present outline.

Then came the long winter of the glacial epoch---perhaps of a succession
of glacial epochs. The ice sheet extended southward to about the fortieth
parallel, driving some animals before it, and destroying those that
were unable to migrate. At its fulness, the great ice mass lay almost
a mile in depth over New England, as attested by the scratched and
polished rock surfaces and deposited erratics in the White Mountains.
Such a mass presses down with a weight of about one hundred and twenty-five
tons to the square foot, according to Dr.\ Croll's estimate. It crushed
and ground everything beneath it more or less, and in some regions
planed off hilly surfaces into prairies. Creeping slowly forward,
it carried all manner of debris with it. When it melted away its terminal
moraine built up the nucleus of the land masses now known as Long
Island and Staten Island; other of its deposits formed the {}``drumlins''\ about
Boston famous as Bunker and Breed's hills; and it left a long, irregular
line of ridges of {}``till''\ or bowlder clay and scattered erratics
clear across the country at about the latitude of New York city.

As the ice sheet slowly receded it left minor moraines all along its
course. Sometimes its deposits dammed up river courses or inequalities
in the surface, to form the lakes which everywhere abound over Northern
territories. Some glacialists even hold the view first suggested by
Ramsey, of the British Geological Survey, that the great glacial sheets
scooped out the basins of many lakes, including the system that feeds
the St.\ Lawrence. At all events, it left traces of its presence
all along the line of its retreat, and its remnants exist to this
day as mountain glaciers and the polar ice cap. Indeed, we live on
the border of the last glacial epoch, for with the closing of this
period the long geologic past merges into the present.


\section*{\raggedright PAST, PRESENT, AND FUTURE}

\addcontentsline{toc}{section}{PAST, PRESENT, AND FUTURE}

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth,
  height=0.90\paperwidth]{3hsci10-Wil3S164}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Manhattan Island in the Quaternary
Age---the Mastodon}\end{center}
\end{figure}
And the present, no less than the past, is a time of change. This
is the thought which James Hutton conceived more than a century ago,
but which his contemporaries and successors were so very slow to appreciate.
Now, however, it has become axiomatic---one can hardly realize that
it was ever doubted. Every new scientific truth, says Agassiz, must
pass through three stages---first, men say it is not true; then they
declare it hostile to religion; finally, they assert that every one
has known it always. Hutton's truth that natural law is changeless
and eternal has reached this final stage. Nowhere now could you find
a scientist who would dispute the truth of that text which Lyell,
quoting from Playfair's \emph{Illustrations of the Huttonian Theory},
printed on the title-page of his \emph{Principles}: {}``Amid all
the revolutions of the globe the economy of Nature has been uniform,
and her laws are the only things that have resisted the general movement.
The rivers and the rocks, the seas and the continents, have been changed
in all their parts; but the laws which direct those changes, and the
rules to which they are subject, have remained invariably the same.''

But, on the other hand, Hutton and Playfair, and in particular Lyell,
drew inferences from this principle which the modern physicist can
by no means admit. To them it implied that the changes on the surface
of the earth have always been the same in degree as well as in kind,
and must so continue while present forces hold their sway. In other
words, they thought of the world as a great perpetual-motion machine.
But the modern physicist, given truer mechanical insight by the doctrines
of the conservation and the dissipation of energy, will have none
of that. Lord Kelvin, in particular, has urged that in the periods
of our earth's in fancy and adolescence its developmental changes
must have been, like those of any other infant organism, vastly more
rapid and pronounced than those of a later day; and to every clear
thinker this truth also must now seem axiomatic.

Whoever thinks of the earth as a cooling globe can hardly doubt that
its crust, when thinner, may have heaved under strain of the moon's
tidal pull---whether or not that body was nearer---into great billows,
daily rising and falling, like waves of the present seas vastly magnified.

Under stress of that same lateral pressure from contraction which
now produces the slow depression of the Jersey coast, the slow rise
of Sweden, the occasional belching of an insignificant volcano, the
jetting of a geyser, or the trembling of an earthquake, once large
areas were rent in twain, and vast floods of lava flowed over thousands
of square miles of the earth's surface, perhaps, at a single jet;
and, for aught we know to the contrary, gigantic mountains may have
heaped up their contorted heads in cataclysms as spasmodic as even
the most ardent catastrophist of the elder day of geology could have
imagined.

The atmosphere of that early day, filled with vast volumes of carbon,
oxygen, and other chemicals that have since been stored in beds of
coal, limestone, and granites, may have worn down the rocks on the
one hand and built up organic forms on the other, with a rapidity
that would now seem hardly conceivable.

And yet while all these anomalous things went on, the same laws held
sway that now are operative; and a true doctrine of uniformitarianism
would make no unwonted concession in conceding them all---though most
of the imbittered geological controversies of the middle of the nineteenth
century were due to the failure of both parties to realize that simple
fact.

And as of the past and present, so of the future. The same forces
will continue to operate; and under operation of these unchanging
forces each day will differ from every one that has preceded it. If
it be true, as every physicist believes, that the earth is a cooling
globe, then, whatever its present stage of refrigeration, the time
must come when its surface contour will assume a rigidity of level
not yet attained. Then, just as surely, the slow action of the elements
will continue to wear away the land surfaces, particle by particle,
and transport them to the ocean, as it does to-day, until, compensation
no longer being afforded by the upheaval of the continents, the last
foot of dry land will sink for the last time beneath the water, the
last mountain-peak melting away, and our globe, lapsing like any other
organism into its second childhood, will be on the surface---as presumably
it was before the first continent rose---one vast {}``waste of waters.''
As puny man conceives time and things, an awful cycle will have lapsed;
in the sweep of the cosmic life, a pulse-beat will have throbbed.


\chapter*{\raggedright V.\ THE NEW SCIENCE OF METEOROLOGY}

\addcontentsline{toc}{chapter}{V. THE NEW SCIENCE OF\\
METEOROLOGY}

\markboth{A HISTORY OF SCIENCE, BOOK III}{V. METEOROLOGY}


\section*{\raggedright METEORITES}

\addcontentsline{toc}{section}{METEORITES}

{}``An astonishing miracle has just occurred in our district,''
wrote M.\ Marais, a worthy if undistinguished citizen of France,
from his home at L'Aigle, under date of {}``the 13th Flor\'{e}al,
year 11''---a date which outside of France would be interpreted as
meaning May 3, 1803. This {}``miracle''\ was the appearance of
a {}``fireball'' in broad daylight---{}``perhaps it was wildfire,''
says the na\"{\i}ve chronicle---which {}``hung over the meadow,''
being seen by many people, and then exploded with a loud sound, scattering
thousands of stony fragments over the surface of a territory some
miles in extent.

Such a {}``miracle''\ could not have been announced at a more opportune
time. For some years the scientific world had been agog over the question
whether such a form of lightning as that reported---appearing in a
clear sky, and hurling literal thunderbolts---had real existence.
Such cases had been reported often enough, it is true. The {}``thunderbolts''\ themselves
were exhibited as sacred relics before many an altar, and those who
doubted their authenticity had been chided as having {}``an evil
heart of unbelief.'' But scientific scepticism had questioned the
evidence, and late in the eighteenth century a consensus of opinion
in the French Academy had declined to admit that such stones had been
{}``conveyed to the earth by lightning,''\ let alone any more miraculous
agency.

In 1802, however, Edward Howard had read a paper before the Royal
Society in which, after reviewing the evidence recently put forward,
he had reached the conclusion that the fall of stones from the sky,
sometimes or always accompanied by lightning, must be admitted as
an actual phenomenon, however inexplicable. So now, when the great
stone-fall at L'Aigle was announced, the French Academy made haste
to send the brilliant young physicist Jean Baptiste Biot to investigate
it, that the matter might, if possible, be set finally at rest. The
investigation was in all respects successful, and Biot's report transferred
the stony or metallic lightning-bolt---the aerolite or meteorite---from
the realm of tradition and conjecture to that of accepted science.

But how explain this strange phenomenon? At once speculation was rife.
One theory contended that the stony masses had not actually fallen,
but had been formed from the earth by the action of the lightning;
but this contention was early abandoned. The chemists were disposed
to believe that the aerolites had been formed by the combination of
elements floating in the upper atmosphere. Geologists, on the other
hand, thought them of terrestrial origin, urging that they might have
been thrown up by volcanoes. The astronomers, as represented by Olbers
and Laplace, modified this theory by suggesting that the stones might,
indeed, have been cast out by volcanoes, but by volcanoes situated
not on the earth, but on the moon.

And one speculator of the time took a step even more daring, urging
that the aerolites were neither of telluric nor selenitic origin,
nor yet children of the sun, as the old Greeks had, many of them,
contended, but that they are visitants from the depths of cosmic space.
This bold speculator was the distinguished German physicist Ernst
F.\ F.\ Chladni, a man of no small repute in his day. As early as
1794 he urged his cosmical theory of meteorites, when the very existence
of meteorites was denied by most scientists. And he did more: he declared
his belief that these falling stones were really one in origin and
kind with those flashing meteors of the upper atmosphere which are
familiar everywhere as {}``shooting-stars.''

Each of these coruscating meteors, he affirmed, must tell of the ignition
of a bit of cosmic matter entering the earth's atmosphere. Such wandering
bits of matter might be the fragments of shattered worlds, or, as
Chladni thought more probable, merely aggregations of {}``world stuff''\ never
hitherto connected with any large planetary mass.

Naturally enough, so unique a view met with very scant favor. Astronomers
at that time saw little to justify it; and the non-scientific world
rejected it with fervor as being {}``atheistic and heretical,''\ because
its acceptance would seem to imply that the universe is not a perfect
mechanism.

Some light was thrown on the moot point presently by the observations
of Brandes and Benzenberg, which tended to show that falling-stars
travel at an actual speed of from fifteen to ninety miles a second.
This observation tended to discredit the selenitic theory, since an
object, in order to acquire such speed in falling merely from the
moon, must have been projected with an initial velocity not conceivably
to be given by any lunar volcanic impulse. Moreover, there was a growing
conviction that there are no active volcanoes on the moon, and other
considerations of the same tenor led to the complete abandonment of
the selenitic theory.

But the theory of telluric origin of aerolites was by no means so
easily disposed of. This was an epoch when electrical phenomena were
exciting unbounded and universal interest, and there was a not unnatural
tendency to appeal to electricity in explanation of every obscure
phenomenon; and in this case the seeming similarity between a lightning
flash and the flash of an aerolite lent color to the explanation.
So we find Thomas Forster, a meteorologist of repute, still adhering
to the atmospheric theory of formation of aerolites in his book published
in 1823; and, indeed, the prevailing opinion of the time seemed divided
between various telluric theories, to the neglect of any cosmical
theory whatever.

But in 1833 occurred a phenomenon which set the matter finally at
rest. A great meteoric shower occurred in November of that year, and
in observing it Professor Denison Olmstead, of Yale, noted that all
the stars of the shower appeared to come from a single centre or vanishing-point
in the heavens, and that this centre shifted its position with the
stars, and hence was not telluric. The full significance of this observation
was at once recognized by astronomers; it demonstrated beyond all
cavil the cosmical origin of the shooting-stars. Some conservative
meteorologists kept up the argument for the telluric origin for some
decades to come, as a matter of course---such a band trails always
in the rear of progress. But even these doubters were silenced when
the great shower of shooting-stars appeared again in 1866, as predicted
by Olbers and Newton, radiating from the same point of the heavens
as before.

Since then the spectroscope has added its confirmatory evidence as
to the identity of meteorite and shooting-star, and, moreover, has
linked these atmospheric meteors with such distant cosmic residents
as comets and nebul\ae{}. Thus it appears that Chladni's daring hypothesis
of 1794 has been more than verified, and that the fragments of matter
dissociated from planetary connection---which he postulated and was
declared atheistic for postulating---have been shown to be billions
of times more numerous than any larger cosmic bodies of which we have
cognizance---so widely does the existing universe differ from man's
preconceived notions as to what it should be.

Thus also the {}``miracle''\ of the falling stone, against which
the scientific scepticism of yesterday presented {}``an evil heart
of unbelief,''\ turns out to be the most natural phenomena, inasmuch
as it is repeated in our atmosphere some millions of times each day.


\section*{\raggedright THE \emph{AURORA BOREALIS}}

\addcontentsline{toc}{section}{THE \emph{AURORA BOREALIS}}

If fire-balls were thought miraculous and portentous in days of yore,
what interpretation must needs have been put upon that vastly more
picturesque phenomenon, the aurora? {}``Through all the city,''\ says
the Book of Maccabees, {}``for the space of almost forty days, there
were seen horsemen running in the air, in cloth of gold, armed with
lances, like a band of soldiers: and troops of horsemen in array encountering
and running one against another, with shaking of shields and multitude
of pikes, and drawing of swords, and casting of darts, and glittering
of golden ornaments and harness.'' Dire omens these; and hardly less
ominous the aurora seemed to all succeeding generations that observed
it down well into the eighteenth century---as witness the popular
excitement in England in 1716 over the brilliant aurora of that year,
which became famous through Halley's description.

But after 1752, when Franklin dethroned the lightning, all spectacular
meteors came to be regarded as natural phenomena, the aurora among
the rest. Franklin explained the aurora---which was seen commonly
enough in the eighteenth century, though only recorded once in the
seventeenth---as due to the accumulation of electricity on the surface
of polar snows, and its discharge to the equator through the upper
atmosphere. Erasmus Darwin suggested that the luminosity might be
due to the ignition of hydrogen, which was supposed by many philosophers
to form the upper atmosphere. Dalton, who first measured the height
of the aurora, estimating it at about one hundred miles, thought the
phenomenon due to magnetism acting on ferruginous particles in the
air, and his explanation was perhaps the most popular one at the beginning
of the last century.

Since then a multitude of observers have studied the aurora, but the
scientific grasp has found it as elusive in fact as it seems to casual
observation, and its exact nature is as undetermined to-day as it
was a hundred years ago. There has been no dearth of theories concerning
it, however. Blot, who studied it in the Shetland Islands in 1817,
thought it due to electrified ferruginous dust, the origin of which
he ascribed to Icelandic volcanoes. Much more recently the idea of
ferruginous particles has been revived, their presence being ascribed
not to volcanoes, but to the meteorites constantly being dissipated
in the upper atmosphere. Ferruginous dust, presumably of such origin,
has been found on the polar snows, as well as on the snows of mountain-tops,
but whether it could produce the phenomena of auroras is at least
an open question.

Other theorists have explained the aurora as due to the accumulation
of electricity on clouds or on spicules of ice in the upper air. Yet
others think it due merely to the passage of electricity through rarefied
air itself. Humboldt considered the matter settled in yet another
way when Faraday showed, in 1831, that magnetism may produce luminous
effects. But perhaps the prevailing theory of to-day assumes that
the aurora is due to a current of electricity generated at the equator
and passing through upper regions of space, to enter the earth at
the magnetic poles---simply reversing the course which Franklin assumed.

The similarity of the auroral light to that generated in a vacuum
bulb by the passage of electricity lends support to the long-standing
supposition that the aurora is of electrical origin, but the subject
still awaits complete elucidation. For once even that mystery-solver
the spectroscope has been baffled, for the line it sifts from the
aurora is not matched by that of any recognized substance. A like
line is found in the zodiacal light, it is true, but this is of little
aid, for the zodiacal light, though thought by some astronomers to
be due to meteor swarms about the sun, is held to be, on the whole,
as mysterious as the aurora itself.

Whatever the exact nature of the aurora, it has long been known to
be intimately associated with the phenomena of terrestrial magnetism.
Whenever a brilliant aurora is visible, the world is sure to be visited
with what Humboldt called a magnetic storm---a {}``storm''\ which
manifests itself to human senses in no way whatsoever except by deflecting
the magnetic needle and conjuring with the electric wire. Such magnetic
storms are curiously associated also with spots on the sun---just
how no one has explained, though the fact itself is unquestioned.
Sun-spots, too, seem directly linked with auroras, each of these phenomena
passing through periods of greatest and least frequency in corresponding
cycles of about eleven years'\ duration.

It was suspected a full century ago by Herschel that the variations
in the number of sun-spots had a direct effect upon terrestrial weather,
and he attempted to demonstrate it by using the price of wheat as
a criterion of climatic conditions, meantime making careful observation
of the sun-spots. Nothing very definite came of his efforts in this
direction, the subject being far too complex to be determined without
long periods of observation. Latterly, however, meteorologists, particularly
in the tropics, are disposed to think they find evidence of some such
connection between sun-spots and the weather as Herschel suspected.
Indeed, Mr.\ Meldrum declares that there is a positive coincidence
between periods of numerous sun-spots and seasons of excessive rain
in India.

That some such connection does exist seems intrinsically probable.
But the modern meteorologist, learning wisdom of the past, is extremely
cautious about ascribing casual effects to astronomical phenomena.
He finds it hard to forget that until recently all manner of climatic
conditions were associated with phases of the moon; that not so very
long ago showers of falling-stars were considered {}``prognostic''\ of
certain kinds of weather; and that the {}``equinoctial storm'' had
been accepted as a verity by every one, until the unfeeling hand of
statistics banished it from the earth.

Yet, on the other hand, it is easily within the possibilities that
the science of the future may reveal associations between the weather
and sun-spots, auroras, and terrestrial magnetism that as yet are
hardly dreamed of. Until such time, however, these phenomena must
feel themselves very grudgingly admitted to the inner circle of meteorology.
More and more this science concerns itself, in our age of concentration
and specialization, with weather and climate. Its votaries no longer
concern themselves with stars or planets or comets or shooting-stars---once
thought the very essence of guides to weather wisdom; and they are
even looking askance at the moon, and asking her to show cause why
she also should not be excluded from their domain. Equally little
do they care for the interior of the earth, since they have learned
that the central emanations of heat which Mairan imagined as a main
source of aerial warmth can claim no such distinction. Even such problems
as why the magnetic pole does not coincide with the geographical,
and why the force of terrestrial magnetism decreases from the magnetic
poles to the magnetic equator, as Humboldt first discovered that it
does, excite them only to lukewarm interest; for magnetism, they say,
is not known to have any connection whatever with climate or weather.


\section*{\raggedright EVAPORATION, CLOUD FORMATION, AND DEW}

\addcontentsline{toc}{section}{EVAPORATION, CLOUD FORMATION, AND
DEW}

There is at least one form of meteor, however, of those that interested
our forebears whose meteorological importance they did not overestimate.
This is the vapor of water. How great was the interest in this familiar
meteor at the beginning of the century is attested by the number of
theories then extant regarding it; and these conflicting theories
bear witness also to the difficulty with which the familiar phenomenon
of the evaporation of water was explained.

Franklin had suggested that air dissolves water much as water dissolves
salt, and this theory was still popular, though Deluc had disproved
it by showing that water evaporates even more rapidly in a vacuum
than in air. Deluc's own theory, borrowed from earlier chemists, was
that evaporation is the chemical union of particles of water with
particles of the supposititious element heat. Erasmus Darwin combined
the two theories, suggesting that the air might hold a variable quantity
of vapor in mere solution, and in addition a permanent moiety in chemical
combination with caloric.

Undisturbed by these conflicting views, that strangely original genius,
John Dalton, afterwards to be known as perhaps the greatest of theoretical
chemists, took the question in hand, and solved it by showing that
water exists in the air as an utterly independent gas. He reached
a partial insight into the matter in 1793, when his first volume of
meteorological essays was published; but the full elucidation of the
problem came to him in 1801. The merit of his studies was at once
recognized, but the tenability of his hypothesis was long and ardently
disputed.

While the nature of evaporation was in dispute, as a matter of course
the question of precipitation must be equally undetermined. The most
famous theory of the period was that formulated by Dr.\ Hutton in
a paper read before the Royal Society of Edinburgh, and published
in the volume of transactions which contained also the same author's
epoch-making paper on geology. This {}``theory of rain''\ explained
precipitation as due to the cooling of a current of saturated air
by contact with a colder current, the assumption being that the surplusage
of moisture was precipitated in a chemical sense, just as the excess
of salt dissolved in hot water is precipitated when the water cools.
The idea that the cooling of the saturated air causes the precipitation
of its moisture is the germ of truth that renders this paper of Hutton's
important. All correct later theories build on this foundation.

\begin{quotation}
{}``Let us suppose the surface of this earth wholly covered with
water,''\ said Hutton, {}``and that the sun were stationary, being
always vertical in one place; then, from the laws of heat and rarefaction,
there would be formed a circulation in the atmosphere, flowing from
the dark and cold hemisphere to the heated and illuminated place,
in all directions, towards the place of the greatest cold.

{}``As there is for the atmosphere of this earth a constant cooling
cause, this fluid body could only arrive at a certain degree of heat;
and this would be regularly decreasing from the centre of illumination
to the opposite point of the globe, most distant from the light and
heat. Between these two regions of extreme heat and cold there would,
in every place, be found two streams of air following in opposite
directions. If those streams of air, therefore, shall be supposed
as both sufficiently saturated with humidity, then, as they are of
different temperatures, there would be formed a continual condensation
of aqueous vapor, in some middle region of the atmosphere, by the
commixtion of part of those two opposite streams.

{}``Hence there is reason to believe that in this supposed case there
would be formed upon the surface of the globe three different regions---the
torrid region, the temperate, and the frigid. These three regions
would continue stationary; and the operations of each would be continual.
In the torrid region, nothing but evaporation and heat would take
place; no cloud could be formed, because in changing the transparency
of the atmosphere to opacity it would be heated immediately by the
operation of light, and thus the condensed water would be again evaporated.
But this power of the sun would have a termination; and it is these
that would begin the region of temperate heat and of continual rain.
It is not probable that the region of temperance would reach far beyond
the region of light; and in the hemisphere of darkness there would
be found a region of extreme cold and perfect dryness.

{}``Let us now suppose the earth as turning on its axis in the equinoctial
situation. The torrid region would thus be changed into a zone, in
which there would be night and day; consequently, here would be much
temperance, compared with the torrid region now considered; and here
perhaps there would be formed periodical condensation and evaporation
of humidity, corresponding to the seasons of night and day. As temperance
would thus be introduced into the region of torrid extremity, so would
the effect of this change be felt over all the globe, every part of
which would now be illuminated, consequently heated in some degree.
Thus we would have a line of great heat and evaporation, graduating
each way into a point of great cold and congelation. Between these
two extremes of heat and cold there would be found in each hemisphere
a region of much temperance, in relation to heat, but of much humidity
in the atmosphere, perhaps of continual rain and condensation.

{}``The supposition now formed must appear extremely unfit for making
this globe a habitable world in every part; but having thus seen the
effect of night and day in temperating the effects of heat and cold
in every place, we are now prepared to contemplate the effects of
supposing this globe to revolve around the sun with a certain inclination
of its axis. By this beautiful contrivance, that comparatively uninhabited
globe is now divided into two hemispheres, each of which is thus provided
with a summer and a winter season. But our present view is limited
to the evaporation and condensation of humidity; and, in this contrivance
of the seasons, there must appear an ample provision for those alternate
operations in every part; for as the place of the vertical sun is
moved alternately from one tropic to the other, heat and cold, the
original causes of evaporation and condensation, must be carried over
all the globe, producing either annual seasons of rain or diurnal
seasons of condensation and evaporation, or both these seasons, more
or less---that is, in some degree.

{}``The original cause of motion in the atmosphere is the influence
of the sun heating the surface of the earth exposed to that luminary.
We have not supposed that surface to have been of one uniform shape
and similar substance; from whence it has followed that the annual
propers of the sun, perhaps also the diurnal propers, would produce
a regular condensation of rain in certain regions, and the evaporation
of humidity in others; and this would have a regular progress in certain
determined seasons, and would not vary. But nothing can be more distant
from this supposition, that is the natural constitution of the earth;
for the globe is composed of sea and land, in no regular shape or
mixture, while the surface of the land is also irregular with respect
to its elevations and depressions, and various with regard to the
humidity and dryness of that part which is exposed to heat as the
cause of evaporation. Hence a source of the most valuable motions
in the fluid atmosphere with aqueous vapor, more or less, so far as
other natural operations will admit; and hence a source of the most
irregular commixture of the several parts of this elastic fluid, whether
saturated or not with aqueous vapor.

{}``According to the theory, nothing is required for the production
of rain besides the mixture of portions of the atmosphere with humidity,
and of mixing the parts that are in different degrees of heat. But
we have seen the causes of saturating every portion of the atmosphere
with humidity and of mixing the parts which are in different degrees
of heat. Consequently, over all the surface of the globe there should
happen occasionally rain and evaporation, more or less; and also,
in every place, those vicissitudes should be observed to take place
with some tendency to regularity, which, however, may be so disturbed
as to be hardly distinguishable upon many occasions. Variable winds
and variable rains should be found in proportion as each place is
situated in an irregular mixture of land and water; whereas regular
winds should be found in proportion to the uniformity of the surface;
and regular rains in proportion to the regular changes of those winds
by which the mixture of the atmosphere necessary to the rain may be
produced. But as it will be acknowledged that this is the case in
almost all this earth where rain appears according to the conditions
here specified, the theory is found to be thus in conformity with
nature, and natural appearances are thus explained by the theory.''%
\footnote{{}``Theory of Rain,'' by James Hutton, in \emph{Transactions of
the Royal Society of Edinburgh}, 1788, vol.\ 1 , pp.\ 53-56. %
}
\end{quotation}
{}

The next ambitious attempt to explain the phenomena of aqueous meteors
was made by Luke Howard, in his remarkable paper on clouds, published
in the \emph{Philosophical Magazine} in 1803---the paper in which
the names cirrus, cumulus, stratus, \textit{etc}., afterwards so universally
adopted, were first proposed. In this paper Howard acknowledges his
indebtedness to Dalton for the theory of evaporation; yet he still
clings to the idea that the vapor, though independent of the air,
is combined with particles of caloric. He holds that clouds are composed
of vapor that has previously risen from the earth, combating the opinions
of those who believe that they are formed by the union of hydrogen
and oxygen existing independently in the air; though he agrees with
these theorists that electricity has entered largely into the \emph{modus
operandi} of cloud formation. He opposes the opinion of Deluc and
de Saussure that clouds are composed of particles of water in the
form of hollow vesicles (miniature balloons, in short, perhaps filled
with hydrogen), which untenable opinion was a revival of the theory
as to the formation of all vapor which Dr.\ Halley had advocated
early in the eighteenth century.

Of particular interest are Howard's views as to the formation of dew,
which he explains as caused by the particles of caloric forsaking
the vapor to enter the cool body, leaving the water on the surface.
This comes as near the truth, perhaps, as could be expected while
the old idea as to the materiality of heat held sway. Howard believed,
however, that dew is usually formed in the air at some height, and
that it settles to the surface, opposing the opinion, which had gained
vogue in France and in America (where Noah Webster prominently advocated
it), that dew ascends from the earth.

The complete solution of the problem of dew formation---which really
involved also the entire question of precipitation of watery vapor
in any form---was made by Dr.\ W.\ C.\ Wells, a man of American
birth, whose life, however, after boyhood, was spent in Scotland (where
as a young man he enjoyed the friendship of David Hume)\ and in London.
Inspired, no doubt, by the researches of Mack, Hutton, and their \emph{confreres}
of that Edinburgh school, Wells made observations on evaporation and
precipitation as early as 1784, but other things claimed his attention;
and though he asserts that the subject was often in his mind, he did
not take it up again in earnest until about 1812.

Meantime the observations on heat of Rumford and Davy and Leslie had
cleared the way for a proper interpretation of the facts---about the
facts themselves there had long been practical unanimity of opinion.
Dr.\ Black, with his latent-heat observations, had really given the
clew to all subsequent discussions of the subject of precipitation
of vapor; and from this time on it had been known that heat is taken
up when water evaporates, and given out again when it condenses. Dr.\ Darwin
had shown in 1788, in a paper before the Royal Society, that air gives
off heat on contracting and takes it up on expanding; and Dalton,
in his essay of 1793, had explained this phenomenon as due to the
condensation and vaporization of the water contained in the air.

But some curious and puzzling observations which Professor Patrick
Wilson, professor of astronomy in the University of Glasgow, had communicated
to the Royal Society of Edinburgh in 1784, and some similar ones made
by Mr.\ Six, of Canterbury, a few years later, had remained unexplained.
Both these gentlemen observed that the air is cooler where dew is
forming than the air a few feet higher, and they inferred that the
dew in forming had taken up heat, in apparent violation of established
physical principles.

It remained for Wells, in his memorable paper of 1816, to show that
these observers had simply placed the cart before the horse. He made
it clear that the air is not cooler because the dew is formed, but
that the dew is formed because the air is cooler---having become so
through radiation of heat from the solids on which the dew forms.
The dew itself, in forming, gives out its latent heat, and so tends
to equalize the temperature.

Wells's paper is so admirable an illustration of the lucid presentation
of clearly conceived experiments and logical conclusions that we should
do it injustice not to present it entire. The author's mention of
the observations of Six and Wilson gives added value to his own presentation.


\section*{\raggedright Dr.\ Wells's Essay on Dew}

\addcontentsline{toc}{subsection}{Dr.\ Wells's Essay on Dew}

\begin{quotation}
{}``I was led in the autumn of 1784, by the event of a rude experiment,
to think it probable that the formation of dew is attended with the
production of cold. In 1788, a paper on hoar-frost, by Mr.\ Patrick
Wilson, of Glasgow, was published in the first volume of the \emph{Transactions}
of the Royal Society of Edinburgh, by which it appeared that this
opinion had been entertained by that gentleman before it had occurred
to myself. In the course of the same year, Mr.\ Six, of Canterbury,
mentioned in a paper communicated to the Royal Society that on clear
and dewy nights he always found the mercury lower in a thermometer
laid upon the ground in a meadow in his neighborhood than it was in
a similar thermometer suspended in the air six feet above the former;
and that upon one night the difference amounted to five degrees of
Fahrenheit's scale. Mr.\ Six, however, did not suppose, agreeably
to the opinion of Mr.\ Wilson and myself, that the cold was occasioned
by the formation of dew, but imagined that it proceeded partly from
the low temperature of the air, through which the dew, already formed
in the atmosphere, had descended, and partly from the evaporation
of moisture from the ground, on which his thermometer had been placed.
The conjecture of Mr.\ Wilson and the observations of Mr.\ Six,
together with many facts which I afterwards learned in the course
of reading, strengthened my opinion; but I made no attempt, before
the autumn of 1811, to ascertain by experiment if it were just, though
it had in the mean time almost daily occurred to my thoughts. Happening,
in that season, to be in that country in a clear and calm night, I
laid a thermometer upon grass wet with dew, and suspended a second
in the air, two feet above the other. An hour afterwards the thermometer
on the grass was found to be eight degrees lower, by Fahrenheit's
division, than the one in the air. Similar results having been obtained
from several similar experiments, made during the same autumn, I determined
in the next spring to prosecute the subject with some degree of steadiness,
and with that view went frequently to the house of one of my friends
who lives in Surrey.

At the end of two months I fancied that I had collected information
worthy of being published; but, fortunately, while preparing an account
of it I met by accident with a small posthumous work by Mr.\ Six,
printed at Canterbury in 1794, in which are related differences observed
on dewy nights between thermometers placed upon grass and others in
the air that are much greater than those mentioned in the paper presented
by him to the Royal Society in 1788. In this work, too, the cold of
the grass is attributed, in agreement with the opinion of Mr.\ Wilson,
altogether to the dew deposited upon it. The value of my own observations
appearing to me now much diminished, though they embraced many points
left untouched by Mr.\ Six, I gave up my intentions of making them
known. Shortly after, however, upon considering the subject more closely,
I began to suspect that Mr.\ Wilson, Mr.\ Six, and myself had all
committed an error regarding the cold which accompanies dew as an
effect of the formation of that fluid. I therefore resumed my experiments,
and having by means of them, I think, not only established the justness
of my suspicions, but ascertained the real cause both of dew and of
several other natural appearances which have hitherto received no
sufficient explanation, I venture now to submit to the consideration
of the learned an account of some of my labors, without regard to
the order of time in which they were performed, and of various conclusions
which may be drawn from them, mixed with facts and opinions already
published by others:\ 

{}``There are various occurrences in nature which seem to me strictly
allied to dew, though their relation to it be not always at first
sight perceivable. The statement and explanation of several of these
will form the concluding part of the present essay.

{}``1. I observed one morning, in winter, that the insides of the
panes of glass in the windows of my bedchamber were all of them moist,
but that those which had been covered by an inside shutter during
the night were much more so than the others which had been uncovered.
Supposing that this diversity of appearance depended upon a difference
of temperature, I applied the naked bulbs of two delicate thermometers
to a covered and uncovered pane; on which I found that the former
was three degrees colder than the latter. The air of the chamber,
though no fire was kept in it, was at this time eleven and one-half
degrees warmer than that without. Similar experiments were made on
many other mornings, the results of which were that the warmth of
the internal air exceeded that of the external from eight to eighteen
degrees, the temperature of the covered panes would be from one to
five degrees less than the uncovered; that the covered were sometimes
dewed, while the uncovered were dry; that at other times both were
free from moisture; that the outsides of the covered and uncovered
panes had similar differences with respect to heat, though not so
great as those of the inner surfaces; and that no variation in the
quantity of these differences was occasioned by the weather's being
cloudy or fair, provided the heat of the internal air exceeded that
of the external equally in both of those states of the atmosphere.

{}``The remote reason of these differences did not immediately present
itself. I soon, however, saw that the closed shutter shielded the
glass which it covered from the heat that was radiated to the windows
by the walls and furniture of the room, and thus kept it nearer to
the temperature of the external air than those parts could be which,
from being uncovered, received the heat emitted to them by the bodies
just mentioned.

{}``In making these experiments, I seldom observed the inside of
any pane to be more than a little damped, though it might be from
eight to twelve degrees colder than the general mass of the air in
the room; while, in the open air, I had often found a great dew to
form on substances only three or four degrees colder than the atmosphere.
This at first surprised me; but the cause now seems plain. The air
of the chamber had once been a portion of the external atmosphere,
and had afterwards been heated, when it could receive little accessories
to its original moisture. It constantly required being cooled considerably
before it was even brought back to its former nearness to repletion
with water; whereas the whole external air is commonly, at night,
nearly replete with moisture, and therefore readily precipitates dew
on bodies only a little colder than itself.

{}``When the air of a room is warmer than the external atmosphere,
the effect of an outside shutter on the temperature of the glass of
the window will be directly opposite to what has just been stated;
since it must prevent the radiation, into the atmosphere, of the heat
of the chamber transmitted through the glass.

{}``2. Count Rumford appears to have rightly conjectured that the
inhabitants of certain hot countries, who sleep at nights on the tops
of their houses, are cooled during this exposure by the radiation
of their heat to the sky; or, according to his manner of expression,
by receiving frigorific rays from the heavens. Another fact of this
kind seems to be the greater chill which we often experience upon
passing at night from the cover of a house into the air than might
have been expected from the cold of the external atmosphere. The cause,
indeed, is said to be the quickness of transition from one situation
to another. But if this were the whole reason, an equal chill would
be felt in the day, when the difference, in point of heat, between
the internal and external air was the same as at night, which is not
the case. Besides, if I can trust my own observation, the feeling
of cold from this cause is more remarkable in a clear than in a cloudy
night, and in the country than in towns. The following appears to
be the manner in which these things are chiefly to be explained:\ 

{}``During the day our bodies while in the open air, although not
immediately exposed to the sun's rays, are yet constantly deriving
heat from them by means of the reflection of the atmosphere. This
heat, though it produces little change on the temperature of the air
which it traverses, affords us some compensation for the heat which
we radiate to the heavens. At night, also, if the sky be overcast,
some compensation will be made to us, both in the town and in the
country, though in a less degree than during the day, as the clouds
will remit towards the earth no inconsiderable quantity of heat. But
on a clear night, in an open part of the country, nothing almost can
be returned to us from above in place of the heat which we radiate
upward. In towns, however, some compensation will be afforded even
on the clearest nights for the heat which we lose in the open air
by that which is radiated to us from the sun round buildings.

{}``To our loss of heat by radiation at times that we derive little
compensation from the radiation of other bodies is probably to be
attributed a great part of the hurtful effects of the night air. Descartes
says that these are not owing to dew, as was the common opinion of
his contemporaries, but to the descent of certain noxious vapors which
have been exhaled from the earth during the heat of the day, and are
afterwards condensed by the cold of a serene night. The effects in
question certainly cannot be occasioned by dew, since that fluid does
not form upon a healthy human body in temperate climates; but they
may, notwithstanding, arise from the same cause that produces dew
on those substances which do not, like the human body, possess the
power of generating heat for the supply of what they lose by radiation
or any other means.''%
\footnote{\emph{Essay on Dew}, by W.\ C.\ Wells, M.D., F.R.S., London, 1818,
pp.\ 124 f.%
}
\end{quotation}
{}

This explanation made it plain why dew forms on a clear night, when
there are no clouds to reflect the radiant heat. Combined with Dalton's
theory that vapor is an independent gas, limited in quantity in any
given space by the temperature of that space, it solved the problem
of the formation of clouds, rain, snow, and hoar-frost. Thus this
paper of Wells's closed the epoch of speculation regarding this field
of meteorology, as Hutton's paper of 1784 had opened it. The fact
that the volume containing Hutton's paper contained also his epoch-making
paper on geology finds curiously a duplication in the fact that Wells's
volume contained also his essay on Albinism, in which the doctrine
of natural selection was for the first time formulated, as Charles
Darwin freely admitted after his own efforts had made the doctrine
famous.


\section*{\raggedright ISOTHERMS AND OCEAN CURRENTS}

\addcontentsline{toc}{section}{ISOTHERMS AND OCEAN CURRENTS}

The very next year after Dr.\ Wells's paper was published there appeared
in France the third volume of the \emph{M\'{e}moires de Physique
et de Chimie de la Soci\'{e}t\'{e} d'Arcueil}, and a new epoch in
meteorology was inaugurated. The society in question was numerically
an inconsequential band, listing only a dozen members; but every name
was a famous one: Arago, Berard, Berthollet, Biot, Chaptal, de Candolle,
Dulong, Gay-Lussac, Humboldt, Laplace, Poisson, and Thenard---rare
spirits every one. Little danger that the memoirs of such a band would
be relegated to the dusty shelves where most proceedings of societies
belong---no milk-for-babes fare would be served to such a company.

The particular paper which here interests us closes this third and
last volume of memoirs. It is entitled {}``\emph{Des Lignes Isothermes
et de la Distribution de la Chaleursurle Globe}.'' The author is
Alexander Humboldt. Needless to say, the topic is handled in a masterly
manner. The distribution of heat on the surface of the globe, on the
mountain-sides, in the interior of the earth; the causes that regulate
such distribution; the climatic results---these are the topics discussed.
But what gives epochal character to the paper is the introduction
of those isothermal lines circling the earth in irregular course,
joining together places having the same mean annual temperature, and
thus laying the foundation for a science of comparative climatology.

It is true the attempt to study climates comparatively was not new.
Mairan had attempted it in those papers in which he developed his
bizarre ideas as to central emanations of heat. Euler had brought
his profound mathematical genius to bear on the topic, evolving the
{}``extraordinary conclusion that under the equator at midnight the
cold ought to be more rigorous than at the poles in winter.'' And
in particular Richard Kirwan, the English chemist, had combined the
mathematical and the empirical methods and calculated temperatures
for all latitudes. But Humboldt differs from all these predecessors
in that he grasps the idea that the basis of all such computations
should be not theory, but fact. He drew his isothermal lines not where
some occult calculation would locate them on an ideal globe, but where
practical tests with the thermometer locate them on our globe as it
is. London, for example, lies in the same latitude as the southern
extremity of Hudson Bay; but the isotherm of London, as Humboldt outlines
it, passes through Cincinnati.

Of course such deviations of climatic conditions between places in
the same latitude had long been known. As Humboldt himself observes,
the earliest settlers of America were astonished to find themselves
subjected to rigors of climate for which their European experience
had not at all prepared them. Moreover, sagacious travellers, in particular
Cook's companion on his second voyage, young George Forster, had noted
as a general principle that the western borders of continents in temperate
regions are always warmer than corresponding latitudes of their eastern
borders; and of course the general truth of temperatures being milder
in the vicinity of the sea than in the interior of continents had
long been familiar. But Humboldt's isothermal lines for the first
time gave tangibility to these ideas, and made practicable a truly
scientific study of comparative climatology.

In studying these lines, particularly as elaborated by further observations,
it became clear that they are by no means haphazard in arrangement,
but are dependent upon geographical conditions which in most cases
are not difficult to determine. Humboldt himself pointed out very
clearly the main causes that tend to produce deviations from the average---or,
as Dove later on called it, the normal---temperature of any given
latitude. For example, the mean annual temperature of a region (referring
mainly to the northern hemisphere) is raised by the proximity of a
western coast; by a divided configuration of the continent into peninsulas;
by the existence of open seas to the north or of radiating continental
surfaces to the south; by mountain ranges to shield from cold winds;
by the infrequency of swamps to become congealed; by the absence of
woods in a dry, sandy soil; and by the serenity of sky in the summer
months and the vicinity of an ocean current bringing water which is
of a higher temperature than that of the surrounding sea.

Conditions opposite to these tend, of course, correspondingly to lower
the temperature. In a word, Humboldt says the climatic distribution
of heat depends on the relative distribution of land and sea, and
on the {}``hypsometrical configuration of the continents''; and
he urges that {}``great meteorological phenomena cannot be comprehended
when considered independently of geognostic relations''---a truth
which, like most other general principles, seems simple enough once
it is pointed out.

With that broad sweep of imagination which characterized him, Humboldt
speaks of the atmosphere as the {}``aerial ocean, in the lower strata
and on the shoals of which we live,''\ and he studies the atmospheric
phenomena always in relation to those of that other ocean of water.
In each of these oceans there are vast permanent currents, flowing
always in determinate directions, which enormously modify the climatic
conditions of every zone. The ocean of air is a vast maelstrom, boiling
up always under the influence of the sun's heat at the equator, and
flowing as an upper current towards either pole, while an undercurrent
from the poles, which becomes the trade-winds, flows towards the equator
to supply its place.

But the superheated equatorial air, becoming chilled, descends to
the surface in temperate latitudes, and continues its poleward journey
as the anti-trade-winds. The trade-winds are deflected towards the
west, because in approaching the equator they constantly pass over
surfaces of the earth having a greater and greater velocity of rotation,
and so, as it were, tend to lag behind---an explanation which Hadley
pointed out in 1735, but which was not accepted until Dalton independently
worked it out and promulgated it in 1793. For the opposite reason,
the anti-trades are deflected towards the east; hence it is that the
western, borders of continents in temperate zones are bathed in moist
sea-breezes, while their eastern borders lack this cold-dispelling
influence.

In the ocean of water the main currents run as more sharply circumscribed
streams---veritable rivers in the sea. Of these the best known and
most sharply circumscribed is the familiar Gulf Stream, which has
its origin in an equatorial current, impelled westward by trade-winds,
which is deflected northward in the main at Cape St.\ Roque, entering
the Caribbean Sea and Gulf of Mexico, to emerge finally through the
Strait of Florida, and journey off across the Atlantic to warm the
shores of Europe.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth,
  height=0.90\paperwidth,
  keepaspectratio]{3hsci10-Wil3S196}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Alexander von Humboldt}\end{center}
\end{figure}
Such, at least, is the Gulf Stream as Humboldt understood it. Since
his time, however, ocean currents in general, and this one in particular,
have been the subject of no end of controversy, it being hotly disputed
whether either causes or effects of the Gulf Stream are just what
Humboldt, in common with others of his time, conceived them to be.
About the middle of the century Lieutenant M.\ F.\ Maury, the distinguished
American hydrographer and meteorologist, advocated a theory of gravitation
as the chief cause of the currents, claiming that difference in density,
due to difference in temperature and saltness, would sufficiently
account for the oceanic circulation. This theory gained great popularity
through the wide circulation of Maury's \emph{Physical Geography of
the Sea}, which is said to have passed through more editions than
any other scientific book of the period; but it was ably and vigorously
combated by Dr.\ James Croll, the Scottish geologist, in his \emph{Climate
and Time}, and latterly the old theory that ocean currents are due
to the trade-winds has again come into favor. Indeed, very recently
a model has been constructed, with the aid of which it is said to
have been demonstrated that prevailing winds in the direction of the
actual trade-winds would produce such a current as the Gulf Stream.

Meantime, however, it is by no means sure that gravitation does not
enter into the case to the extent of producing an insensible general
oceanic circulation, independent of the Gulf Stream and similar marked
currents, and similar in its larger outlines to the polar-equatorial
circulation of the air. The idea of such oceanic circulation was first
suggested in detail by Professor Lenz, of St.\ Petersburg, in 1845,
but it was not generally recognized until Dr.\ Carpenter independently
hit upon the idea more than twenty years later. The plausibility of
the conception is obvious; yet the alleged fact of such circulation
has been hotly disputed, and the question is still \emph{sub judice}.

But whether or not such general circulation of ocean water takes place,
it is beyond dispute that the recognized currents carry an enormous
quantity of heat from the tropics towards the poles. Dr.\ Croll,
who has perhaps given more attention to the physics of the subject
than almost any other person, computes that the Gulf Stream conveys
to the North Atlantic one-fourth as much heat as that body receives
directly from the sun, and he argues that were it not for the transportation
of heat by this and similar Pacific currents, only a narrow tropical
region of the globe would be warm enough for habitation by the existing
faunas. Dr.\ Croll argues that a slight change in the relative values
of northern and southern trade-winds (such as he believes has taken
place at various periods in the past)\ would suffice to so alter
the equatorial current which now feeds the Gulf Stream that its main
bulk would be deflected southward instead of northward, by the angle
of Cape St.\ Roque. Thus the Gulf Stream would be nipped in the bud,
and, according to Dr.\ Croll's estimates, the results would be disastrous
for the northern hemisphere. The anti-trades, which now are warmed
by the Gulf Stream, would then blow as cold winds across the shores
of western Europe, and in all probability a glacial epoch would supervene
throughout the northern hemisphere.

The same consequences, so far as Europe is concerned at least, would
apparently ensue were the Isthmus of Panama to settle into the sea,
allowing the Caribbean current to pass into the Pacific. But the geologist
tells us that this isthmus rose at a comparatively recent geological
period, though it is hinted that there had been some time previously
a temporary land connection between the two continents. Are we to
infer, then, that the two Americas in their unions and disunions have
juggled with the climate of the other hemisphere? Apparently so, if
the estimates made of the influence of the Gulf Stream be tenable.
It is a far cry from Panama to Russia. Yet it seems within the possibilities
that the meteorologist may learn from the geologist of Central America
something that will enable him to explain to the paleontologist of
Europe how it chanced that at one time the mammoth and rhinoceros
roamed across northern Siberia, while at another time the reindeer
and musk-ox browsed along the shores of the Mediterranean.

Possibilities, I said, not probabilities. Yet even the faint glimmer
of so alluring a possibility brings home to one with vividness the
truth of Humboldt's perspicuous observation that meteorology can be
properly comprehended only when studied in connection with the companion
sciences. There are no isolated phenomena in nature.


\section*{\raggedright CYCLONES AND ANTI-CYCLONES}

\addcontentsline{toc}{section}{CYCLONES AND ANTI-CYCLONES}

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth,
  height=0.90\paperwidth,
  keepaspectratio]{3hsci10-Wil3S154}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Water-Spouts in Mid-Atlantic}\end{center}
\end{figure}
Yet, after all, it is not to be denied that the chief concern of the
meteorologist must be with that other medium, the {}``ocean of air,
on the shoals of which we live.'' For whatever may be accomplished
by water currents in the way of conveying heat, it is the wind currents
that effect the final distribution of that heat. As Dr.\ Croll has
urged, the waters of the Gulf Stream do not warm the shores of Europe
by direct contact, but by warming the anti-trade-winds, which subsequently
blow across the continent. And everywhere the heat accumulated by
water becomes effectual in modifying climate, not so much by direct
radiation as by diffusion through the medium of the air.

This very obvious importance of aerial currents led to their practical
study long before meteorology had any title to the rank of science,
and Dalton's explanation of the trade-winds had laid the foundation
for a science of wind dynamics before the beginning of the nineteenth
century. But no substantial further advance in this direction was
effected until about 1827, when Heinrich W.\ Dove, of K\"{o}nigsberg,
afterwards to be known as perhaps the foremost meteorologist of his
generation, included the winds among the subjects of his elaborate
statistical studies in climatology.

Dove classified the winds as permanent, periodical, and variable.
His great discovery was that all winds, of whatever character, and
not merely the permanent winds, come under the influence of the earth's
rotation in such a way as to be deflected from their course, and hence
to take on a gyratory motion---that, in short, all local winds are
minor eddies in the great polar-equatorial whirl, and tend to reproduce
in miniature the character of that vast maelstrom. For the first time,
then, temporary or variable winds were seen to lie within the province
of law.

A generation later, Professor William Ferrel, the American meteorologist,
who had been led to take up the subject by a perusal of Maury's discourse
on ocean winds, formulated a general mathematical law, to the effect
that any body moving in a right line along the surface of the earth
in any direction tends to have its course deflected, owing to the
earth's rotation, to the right hand in the northern and to the left
hand in the southern hemisphere. This law had indeed been stated as
early as 1835 by the French physicist Poisson, but no one then thought
of it as other than a mathematical curiosity; its true significance
was only understood after Professor Ferrel had independently rediscovered
it (just as Dalton rediscovered Hadley's forgotten law of the trade-winds)\ and
applied it to the motion of wind currents.

Then it became clear that here is a key to the phenomena of atmospheric
circulation, from the great polar-equatorial maelstrom which manifests
itself in the trade-winds to the most circumscribed riffle which is
announced as a local storm. And the more the phenomena were studied,
the more striking seemed the parallel between the greater maelstrom
and these lesser eddies. Just as the entire atmospheric mass of each
hemisphere is seen, when viewed as a whole, to be carried in a great
whirl about the pole of that hemisphere, so the local disturbances
within this great tide are found always to take the form of whirls
about a local storm-centre---which storm-centre, meantime, is carried
along in the major current, as one often sees a little whirlpool in
the water swept along with the main current of the stream. Sometimes,
indeed, the local eddy, caught as it were in an ancillary current
of the great polar stream, is deflected from its normal course and
may seem to travel against the stream; but such deviations are departures
from the rule. In the great majority of cases, for example, in the
north temperate zone, a storm-centre (with its attendant local whirl)
travels to the northeast, along the main current of the anti-trade-wind,
of which it is a part; and though exceptionally its course may be
to the southeast instead, it almost never departs so widely from the
main channel as to progress to the westward. Thus it is that storms
sweeping over the United States can be announced, as a rule, at the
seaboard in advance of their coming by telegraphic communication from
the interior, while similar storms come to Europe off the ocean unannounced.
Hence the more practical availability of the forecasts of weather
bureaus in the former country.

But these local whirls, it must be understood, are local only in a
very general sense of the word, inasmuch as a single one may be more
than a thousand miles in diameter, and a small one is two or three
hundred miles across. But quite without regard to the size of the
whirl, the air composing it conducts itself always in one of two ways.
It never whirls in concentric circles; it always either rushes in
towards the centre in a descending spiral, in which case it is called
a cyclone, or it spreads out from the centre in a widening spiral,
in which case it is called an anti-cyclone. The word cyclone is associated
in popular phraseology with a terrific storm, but it has no such restriction
in technical usage. A gentle zephyr flowing towards a {}``storm-centre''\ is
just as much a cyclone to the meteorologist as is the whirl constituting
a West-Indian hurricane. Indeed, it is not properly the wind itself
that is called the cyclone in either case, but the entire system of
whirls---including the storm-centre itself, where there may be no
wind at all.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth,
  height=0.90\paperwidth,
  keepaspectratio]{3hsci10-Wil3S202}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small A Sandstorm on the Mojave Desert}\end{center}
\end{figure}
What, then, is this storm-centre? Merely an area of low barometric
pressure---an area where the air has become lighter than the air of
surrounding regions. Under influence of gravitation the air seeks
its level just as water does; so the heavy air comes flowing in from
all sides towards the low-pressure area, which thus becomes a {}``storm-centre.''
But the inrushing currents never come straight to their mark. In accordance
with Ferrel's law, they are deflected to the right, and the result,
as will readily be seen, must be a vortex current, which whirls always
in one direction---namely, from left to right, or in the direction
opposite to that of the hands of a watch held with its face upward.
The velocity of the cyclonic currents will depend largely upon the
difference in barometric pressure between the storm-centre and the
confines of the cyclone system. And the velocity of the currents will
determine to some extent the degree of deflection, and hence the exact
path of the descending spiral in which the wind approaches the centre.
But in every case and in every part of the cyclone system it is true,
as Buys Ballot's famous rule first pointed out, that a person standing
with his back to the wind has the storm-centre at his left.

The primary cause of the low barometric pressure which marks the storm-centre
and establishes the cyclone is expansion of the air through excess
of temperature. The heated air, rising into cold upper regions, has
a portion of its vapor condensed into clouds, and now a new dynamic
factor is added, for each particle of vapor, in condensing, gives
up its modicum of latent heat. Each pound of vapor thus liberates,
according to Professor Tyndall's estimate, enough heat to melt five
pounds of cast iron; so the amount given out where large masses of
cloud are forming must enormously add to the convection currents of
the air, and hence to the storm-developing power of the forming cyclone.
Indeed, one school of meteorologists, of whom Professor Espy was the
leader, has held that, without such added increment of energy constantly
augmenting the dynamic effects, no storm could long continue in violent
action. And it is doubted whether any storm could ever attain, much
less continue, the terrific force of that most dreaded of winds of
temperate zones, the tornado---a storm which obeys all the laws of
cyclones, but differs from ordinary cyclones in having a vortex core
only a few feet or yards in diameter---without the aid of those great
masses of condensing vapor which always accompany it in the form of
storm-clouds.

The anti-cyclone simply reverses the conditions of the cyclone. Its
centre is an area of high pressure, and the air rushes out from it
in all directions towards surrounding regions of low pressure. As
before, all parts of the current will be deflected towards the right,
and the result, clearly, is a whirl opposite in direction to that
of the cyclone. But here there is a tendency to dissipation rather
than to concentration of energy, hence, considered as a storm-generator,
the anti-cyclone is of relative insignificance.

In particular the professional meteorologist who conducts a {}``weather
bureau''---as, for example, the chief of the United States signal-service
station in New York---is so preoccupied with the observation of this
phenomenon that cyclone-hunting might be said to be his chief pursuit.
It is for this purpose, in the main, that government weather bureaus
or signal-service departments have been established all over the world.
Their chief work is to follow up cyclones, with the aid of telegraphic
reports, mapping their course and recording the attendant meteorological
conditions. Their so-called predictions or forecasts are essentially
predications, gaining locally the effect of predictions because the
telegraph outstrips the wind.

At only one place on the globe has it been possible as yet for the
meteorologist to make long-time forecasts meriting the title of predictions.
This is in the middle Ganges Valley of northern India. In this country
the climatic conditions are largely dependent upon the periodical
winds called monsoons, which blow steadily landward from April to
October, and seaward from October to April. The summer monsoons bring
the all-essential rains; if they are delayed or restricted in extent,
there will be drought and consequent famine. And such restriction
of the monsoon is likely to result when there has been an unusually
deep or very late snowfall on the Himalayas, because of the lowering
of spring temperature by the melting snow. Thus here it is possible,
by observing the snowfall in the mountains, to predict with some measure
of success the average rainfall of the following summer. The drought
of 1896, with the consequent famine and plague that devastated India
the following winter, was thus predicted some months in advance.

This is the greatest present triumph of practical meteorology. Nothing
like it is yet possible anywhere in temperate zones. But no one can
say what may not be possible in times to come, when the data now being
gathered all over the world shall at last be co-ordinated, classified,
and made the basis of broad inductions. Meteorology is pre-eminently
a science of the future.


\chapter*{\raggedright VI. MODERN THEORIES OF HEAT AND LIGHT}

\addcontentsline{toc}{chapter}{VI. MODERN THEORIES OF HEAT AND\\
LIGHT}

\markboth{A HISTORY OF SCIENCE, BOOK III}{VI. HEAT AND LIGHT}

\textit{\emph{The}} eighteenth-century philosopher made great strides
in his studies of the physical properties of matter and the application
of these properties in mechanics, as the steam-engine, the balloon,
the optic telegraph, the spinning-jenny, the cotton-gin, the chronometer,
the perfected compass, the Leyden jar, the lightning-rod, and a host
of minor inventions testify. In a speculative way he had thought out
more or less tenable conceptions as to the ultimate nature of matter,
as witness the theories of Leibnitz and Boscovich and Davy, to which
we may recur. But he had not as yet conceived the notion of a distinction
between matter and energy, which is so fundamental to the physics
of a later epoch. He did not speak of heat, light, electricity, as
forms of energy or {}``force''; he conceived them as subtile forms
of matter---as highly attenuated yet tangible fluids, subject to gravitation
and chemical attraction; though he had learned to measure none of
them but heat with accuracy, and this one he could test only within
narrow limits until late in the century, when Josiah Wedgwood, the
famous potter, taught him to gauge the highest temperatures with the
clay pyrometer.

He spoke of the matter of heat as being the most universally distributed
fluid in nature; as entering in some degree into the composition of
nearly all other substances; as being sometimes liquid, sometimes
condensed or solid, and as having weight that could be detected with
the balance. Following Newton, he spoke of light as a {}``corpuscular
emanation''\ or fluid, composed of shining particles which possibly
are transmutable into particles of heat, and which enter into chemical
combination with the particles of other forms of matter. Electricity
he considered a still more subtile kind of matter---perhaps an attenuated
form of light. Magnetism, {}``vital fluid,''\ and by some even
a {}``gravic fluid,''\ and a fluid of sound were placed in the
same scale; and, taken together, all these supposed subtile forms
of matter were classed as {}``imponderables.''

This view of the nature of the {}``imponderables''\ was in some
measure a retrogression, for many seventeenth-century philosophers,
notably Hooke and Huygens and Boyle, had held more correct views;
but the materialistic conception accorded so well with the eighteenth-century
tendencies of thought that only here and there a philosopher like
Euler called it in question, until well on towards the close of the
century. Current speech referred to the materiality of the {}``imponderables''
unquestioningly. Students of meteorology---a science that was just
dawning---explained atmospheric phenomena on the supposition that
heat, the heaviest imponderable, predominated in the lower atmosphere,
and that light, electricity, and magnetism prevailed in successively
higher strata. And Lavoisier, the most philosophical chemist of the
century, retained heat and light on a par with oxygen, hydrogen, iron,
and the rest, in his list of elementary substances.


\section*{\raggedright COUNT RUMFORD AND THE VIBRATORY THEORY OF HEAT}

\addcontentsline{toc}{section}{COUNT RUMFORD AND THE\\
VIBRATORY THEORY OF HEAT}

But just at the close of the century the confidence in the status
of the imponderables was rudely shaken in the minds of philosophers
by the revival of the old idea of Fra Paolo and Bacon and Boyle, that
heat, at any rate, is not a material fluid, but merely a mode of motion
or vibration among the particles of {}``ponderable'' matter. The
new champion of the old doctrine as to the nature of heat was a very
distinguished philosopher and diplomatist of the time, who, it may
be worth recalling, was an American. He was a sadly expatriated American,
it is true, as his name, given all the official appendages, will amply
testify; but he had been born and reared in a Massachusetts village
none the less, and he seems always to have retained a kindly interest
in the land of his nativity, even though he lived abroad in the service
of other powers during all the later years of his life, and was knighted
by England, ennobled by Bavaria, and honored by the most distinguished
scientific bodies of Europe. The American, then, who championed the
vibratory theory of heat, in opposition to all current opinion, in
this closing era of the eighteenth century, was Lieutenant-General
Sir Benjamin Thompson, Count Rumford, F.R.S.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{3hsci10-Wil3S208}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Benjamin Thompson (Count Rumford)}\end{center}
\end{figure}
Rumford showed that heat may be produced in indefinite quantities
by friction of bodies that do not themselves lose any appreciable
matter in the process, and claimed that this proves the immateriality
of heat. Later on he added force to the argument by proving, in refutation
of the experiments of Bowditch, that no body either gains or loses
weight in virtue of being heated or cooled. He thought he had proved
that heat is only a form of motion.

His experiment for producing indefinite quantities of heat by friction
is recorded by him in his paper entitled, {}``Inquiry Concerning
the Source of Heat Excited by Friction.''

\begin{quotation}
{}``Being engaged, lately, in superintending the boring of cannon
in the workshops of the military arsenal at Munich,''\ he says,
{}``I was struck with the very considerable degree of heat which
a brass gun acquires in a short time in being bored; and with the
still more intense heat (much greater than that of boiling water,
as I found by experiment)\ of the metallic chips separated from it
by the borer.

{}``Taking a cannon (a brass six-pounder), cast solid, and rough,
as it came from the foundry, and fixing it horizontally in a machine
used for boring, and at the same time finishing the outside of the
cannon by turning, I caused its extremity to be cut off; and by turning
down the metal in that part, a solid cylinder was formed, 7$\frac{3}{4}$
inches in diameter and 9$\frac{8}{10}$ inches long; which, when finished,
remained joined to the rest of the metal (that which, properly speaking,
constituted the cannon)\ by a small cylindrical neck, only 2$\frac{1}{5}$
inches in diameter and 3$\frac{8}{10}$ inches long.

{}``This short cylinder, which was supported in its horizontal position,
and turned round its axis by means of the neck by which it remained
united to the cannon, was now bored with the horizontal borer used
in boring cannon.

{}``This cylinder being designed for the express purpose of generating
heat by friction, by having a blunt borer forced against its solid
bottom at the same time that it should be turned round its axis by
the force of horses, in order that the heat accumulated in the cylinder
might from time to time be measured, a small, round hole 0.37 of an
inch only in diameter and 4.2 inches in depth, for the purpose of
introducing a small cylindrical mercurial thermometer, was made in
it, on one side, in a direction perpendicular to the axis of the cylinder,
and ending in the middle of the solid part of the metal which formed
the bottom of the bore.

{}``At the beginning of the experiment, the temperature of the air
in the shade, as also in the cylinder, was just sixty degrees Fahrenheit.
At the end of thirty minutes, when the cylinder had made 960 revolutions
about its axis, the horses being stopped, a cylindrical mercury thermometer,
whose bulb was $\frac{32}{100}$ of an inch in diameter and 3$\frac{1}{4}$
inches in length, was introduced into the hole made to receive it
in the side of the cylinder, when the mercury rose almost instantly
to one hundred and thirty degrees.

{}``In order, by one decisive experiment, to determine whether the
air of the atmosphere had any part or not in the generation of the
heat, I contrived to repeat the experiment under circumstances in
which it was evidently impossible for it to produce any effect whatever.
By means of a piston exactly fitted to the mouth of the bore of the
cylinder, through the middle of which piston the square iron bar,
to the end of which the blunt steel borer was fixed, passed in a square
hole made perfectly air-tight, the excess of the external air, to
the inside of the bore of the cylinder, was effectually prevented.
I did not find, however, by this experiment that the exclusion of
the air diminished in the smallest degree the quantity of heat excited
by the friction.

{}``There still remained one doubt, which, though it appeared to
me to be so slight as hardly to deserve any attention, I was, however,
desirous to remove. The piston which choked the mouth of the bore
of the cylinder, in order that it might be air-tight, was fitted into
it with so much nicety, by means of its collars of leather, and pressed
against it with so much force, that, notwithstanding its being oiled,
it occasioned a considerable degree of friction when the hollow cylinder
was turned round its axis. Was not the heat produced, or at least
some part of it, occasioned by this friction of the piston?\ and,
as the external air had free access to the extremity of the bore,
where it came into contact with the piston, is it not possible that
this air may have had some share in the generation of the heat produced?

{}``A quadrangular oblong deal box, water-tight, being provided with
holes or slits in the middle of each of its ends, just large enough
to receive, the one the square iron rod to the end of which the blunt
steel borer was fastened, the other the small cylindrical neck which
joined the hollow cylinder to the cannon; when this box (which was
occasionally closed above by a wooden cover or lid moving on hinges)\ was
put into its place---that is to say, when, by means of the two vertical
opening or slits in its two ends, the box was fixed to the machinery
in such a manner that its bottom being in the plane of the horizon,
its axis coincided with the axis of the hollow metallic cylinder,
it is evident, from the description, that the hollow, metallic cylinder
would occupy the middle of the box, without touching it on either
side; and that, on pouring water into the box and filling it to the
brim, the cylinder would be completely covered and surrounded on every
side by that fluid. And, further, as the box was held fast by the
strong, square iron rod which passed in a square hole in the centre
of one of its ends, while the round or cylindrical neck which joined
the hollow cylinder to the end of the cannon could turn round freely
on its axis in the round hole in the centre of the other end of it,
it is evident that the machinery could be put in motion without the
least danger of forcing the box out of its place, throwing the water
out of it, or deranging any part of the apparatus.''
\end{quotation}
{}

Everything being thus ready, the box was filled with cold water, having
been made water-tight by means of leather collars, and the machinery
put in motion. 

\begin{quotation}
{}``The result of this beautiful experiment,''\ says Rumford, {}``was
very striking, and the pleasure it afforded me amply repaid me for
all the trouble I had had in contriving and arranging the complicated
machinery used in making it. The cylinder, revolving at the rate of
thirty-two times in a minute, had been in motion but a short time
when I perceived, by putting my hand into the water and touching the
outside of the cylinder, that heat was generated, and it was not long
before the water which surrounded the cylinder began to be sensibly
warm.

{}``At the end of one hour I found, by plunging a thermometer into
the box,\ldots{}\ that its temperature had been raised no less than
forty-seven degrees Fahrenheit, being now one hundred and seven degrees
Fahrenheit\ldots{}. One hour and thirty minutes after the machinery
had been put in motion the heat of the water in the box was one hundred
and forty-two degrees. At the end of two hours\ \ldots{}\ it was
raised to one hundred and seventy-eight degrees; and at two hours
and thirty minutes it \textit{actually} \textit{boiled}!

{}``It would be difficult to describe the surprise and astonishment
expressed in the countenances of the bystanders on seeing so large
a quantity of cold water heated, and actually made to boil, without
any fire. Though there was, in fact, nothing that could justly be
considered as a surprise in this event, yet I acknowledge fairly that
it afforded me a degree of childish pleasure which, were I ambitious
of the reputation of a \textit{grave} \textit{philosopher}, I ought
most certainly rather to hide than to discover\ldots{}.''
\end{quotation}
{}

Having thus dwelt in detail on these experiments, Rumford comes now
to the all-important discussion as to the significance of them---the
subject that had been the source of so much speculation among the
philosophers---the question as to what heat really is, and if there
really is any such thing (as many believed)\ as an igneous fluid,
or a something called caloric.

\begin{quotation}
{}``From whence came this heat which was continually given off in
this manner, in the foregoing experiments?'' asks Rumford. {}``Was
it furnished by the small particles of metal detached from the larger
solid masses on their being rubbed together? This, as we have already
seen, could not possibly have been the case.

{}``Was it furnished by the air? This could not have been the case;
for, in three of the experiments, the machinery being kept immersed
in water, the access of the air of the atmosphere was completely prevented.

{}``Was it furnished by the water which surrounded the machinery?
That this could not have been the case is evident: first, because
this water was continually \textit{receiving} heat from the machinery,
and could not, at the same time, be \textit{giving} \textit{to} and
\textit{receiving} \textit{heat} \textit{from} the same body; and,
secondly, because there was no chemical decomposition of any part
of this water. Had any such decomposition taken place (which, indeed,
could not reasonably have been expected), one of its component elastic
fluids (most probably hydrogen)\ must, at the same time, have been
set at liberty, and, in making its escape into the atmosphere, would
have been detected; but, though I frequently examined the water to
see if any air-bubbles rose up through it, and had even made preparations
for catching them if they should appear, I could perceive none; nor
was there any sign of decomposition of any kind whatever, or other
chemical process, going on in the water.

{}``Is it possible that the heat could have been supplied by means
of the iron bar to the end of which the blunt steel borer was fixed?
Or by the small neck of gun-metal by which the hollow cylinder was
united to the cannon? These suppositions seem more improbable even
than either of the before-mentioned; for heat was continually going
off, or \textit{out} \textit{of} \textit{the} \textit{machinery},
by both these passages during the whole time the experiment lasted.

{}``And in reasoning on this subject we must not forget to consider
that most remarkable circumstance, that the source of the heat generated
by friction in these experiments appeared evidently to be \textit{inexhaustible}.

{}``It is hardly necessary to add that anything which any \textit{insulated}
body, or system of bodies, can continue to furnish \textit{without}
\textit{limitation} cannot possibly be a \textit{material} substance;
and it appears to me to be extremely difficult, if not quite impossible,
to form any distinct idea of anything capable of being excited and
communicated, in the manner the heat was excited and communicated
in these experiments, except in \textit{motion}.''%
\footnote{\emph{Essays Political, Economical, and Philosophical}, by Benjamin
Thompson, Count of Rumford (2 vols.), Vol. II., pp.\ 470-493, London;
T.\ Cadell, Jr., and W.\ Davies, 1797. %
}
\end{quotation}

\section*{\raggedright THOMAS YOUNG AND THE WAVE THEORY OF LIGHT}

\addcontentsline{toc}{section}{THOMAS YOUNG AND THE WAVE THEORY OF
LIGHT}

But contemporary judgment, while it listened respectfully to Rumford,
was little minded to accept his verdict. The cherished beliefs of
a generation are not to be put down with a single blow. Where many
minds have a similar drift, however, the first blow may precipitate
a general conflict; and so it was here. Young Humphry Davy had duplicated
Rumford's experiments, and reached similar conclusions; and soon others
fell into line. Then, in 1800, Dr.\ Thomas Young---{}``Phenomenon
Young''\ they called him at Cambridge, because he was reputed to
know everything---took up the cudgels for the vibratory theory of
light, and it began to be clear that the two {}``imponderables,''\ heat
and light, must stand or fall together; but no one as yet made a claim
against the fluidity of electricity.

Before we take up the details of the assault made by Young upon the
old doctrine of the materiality of light, we must pause to consider
the personality of Young himself. For it chanced that this Quaker
physician was one of those prodigies who come but few times in a century,
and the full list of whom in the records of history could be told
on one's thumbs and fingers. His biographers tell us things about
him that read like the most patent fairy-tales. As a mere infant in
arms he had been able to read fluently. Before his fourth birthday
came he had read the Bible twice through, as well as Watts's \emph{Hymns}---poor
child!---and when seven or eight he had shown a propensity to absorb
languages much as other children absorb nursery tattle and Mother
Goose rhymes. When he was fourteen, a young lady visiting the household
of his tutor patronized the pretty boy by asking to see a specimen
of his penmanship. The pretty boy complied readily enough, and mildly
rebuked his interrogator by rapidly writing some sentences for her
in fourteen languages, including such as, Arabian, Persian, and Ethiopic.

Meantime languages had been but an incident in the education of the
lad. He seems to have entered every available field of thought---mathematics,
physics, botany, literature, music, painting, languages, philosophy,
arch\ae{}ology, and so on to tiresome lengths---and once he had entered
any field he seldom turned aside until he had reached the confines
of the subject as then known and added something new from the recesses
of his own genius. He was as versatile as Priestley, as profound as
Newton himself. He had the range of a mere dilettante, but everywhere
the full grasp of the master. He took early for his motto the saying
that what one man has done, another man may do. Granting that the
other man has the brain of a Thomas Young, it is a true motto.

Such, then, was the young Quaker who came to London to follow out
the humdrum life of a practitioner of medicine in the year 1801. But
incidentally the young physician was prevailed upon to occupy the
interims of early practice by fulfilling the duties of the chair of
Natural Philosophy at the Royal Institution, which Count Rumford had
founded, and of which Davy was then Professor of Chemistry---the institution
whose glories have been perpetuated by such names as Faraday and Tyndall,
and which the Briton of to-day speaks of as the {}``Pantheon of Science.''
Here it was that Thomas Young made those studies which have insured
him a niche in the temple of fame not far removed from that of Isaac
Newton.

As early as 1793, when he was only twenty, Young had begun to Communicate
papers to the Royal Society of London, which were adjudged worthy
to be printed in full in the \emph{Philosophical Transactions}; so
it is not strange that he should have been asked to deliver the Bakerian
lecture before that learned body the very first year after he came
to London. The lecture was delivered November 12, 1801. Its subject
was {}``The Theory of Light and Colors,''\ and its reading marks
an epoch in physical science; for here was brought forward for the
first time convincing proof of that undulatory theory of light with
which every student of modern physics is familiar---the theory which
holds that light is not a corporeal entity, but a mere pulsation in
the substance of an all-pervading ether, just as sound is a pulsation
in the air, or in liquids or solids.

Young had, indeed, advocated this theory at an earlier date, but it
was not until 1801 that he hit upon the idea which enabled him to
bring it to anything approaching a demonstration. It was while pondering
over the familiar but puzzling phenomena of colored rings into which
white light is broken when reflected from thin films---Newton's rings,
so called---that an explanation occurred to him which at once put
the entire undulatory theory on a new footing. With that sagacity
of insight which we call genius, he saw of a sudden that the phenomena
could be explained by supposing that when rays of light fall on a
thin glass, part of the rays being reflected from the upper surface,
other rays, reflected from the lower surface, might be so retarded
in their course through the glass that the two sets would interfere
with one another, the forward pulsation of one ray corresponding to
the backward pulsation of another, thus quite neutralizing the effect.
Some of the component pulsations of the light being thus effaced by
mutual interference, the remaining rays would no longer give the optical
effect of white light; hence the puzzling colors.

Here is Young's exposition of the subject:\ 


\subsection*{\noindent \raggedright{}Of the Colors of Thin Plates}

\addcontentsline{toc}{subsection}{Of the Colors of Thin Plates}

\begin{quotation}
{}``When a beam of light falls upon two refracting surfaces, the
partial reflections coincide perfectly in direction; and in this case
the interval of retardation taken between the surfaces is to their
radius as twice the cosine of the angle of refraction to the radius.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth,
  height=0.95\columnwidth,
  keepaspectratio]{3hsci10-Wil3S218}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Thomas Young}\end{center}{\small \par}

\noindent \emph{\footnotesize (From Peacock's} {\footnotesize Life
of Young}\emph{\footnotesize , by permission of John Murray, publisher,
London.)}
\end{figure}
{}``Let the medium between the surfaces be rarer than the surrounding
mediums; then the impulse reflected at the second surface, meeting
a subsequent undulation at the first, will render the particles of
the rarer medium capable of wholly stopping the motion of the denser
and destroying the reflection, while they themselves will be more
strongly propelled than if they had been at rest, and the transmitted
light will be increased. So that the colors by reflection will be
destroyed, and those by transmission rendered more vivid, when the
double thickness or intervals of retardation are any multiples of
the whole breadth of the undulations; and at intermediate thicknesses
the effects will be reversed according to the Newtonian observation.

{}``If the same proportions be found to hold good with respect to
thin plates of a denser medium, which is, indeed, not improbable,
it will be necessary to adopt the connected demonstrations of Prop.
IV., but, at any rate, if a thin plate be interposed between a rarer
and a denser medium, the colors by reflection and transmission may
be expected to change places.''
\end{quotation}

\subsection*{\noindent \raggedright{}Of the Colors of Thick Plates}

\addcontentsline{toc}{subsection}{Of the Colors of Thick Plates}

\begin{quotation}
{}``When a beam of light passes through a refracting surface, especially
if imperfectly polished, a portion of it is irregularly scattered,
and makes the surface visible in all directions, but most conspicuously
in directions not far distant from that of the light itself; and if
a reflecting surface be placed parallel to the refracting surface,
this scattered light, as well as the principal beam, will be reflected,
and there will be also a new dissipation of light, at the return of
the beam through the refracting surface. These two portions of scattered
light will coincide in direction; and if the surfaces be of such a
form as to collect the similar effects, will exhibit rings of colors.
The interval of retardation is here the difference between the paths
of the principal beam and of the scattered light between the two surfaces;
of course, wherever the inclination of the scattered light is equal
to that of the beam, although in different planes, the interval will
vanish and all the undulations will conspire. At other inclinations,
the interval will be the difference of the secants from the secant
of the inclination, or angle of refraction of the principal beam.
From these causes, all the colors of concave mirrors observed by Newton
and others are necessary consequences; and it appears that their production,
though somewhat similar, is by no means as Newton imagined, identical
with the production of thin plates.''%
\footnote{Thomas Young, \emph{Phil. Trans}., 1802, p.\ 35. %
}
\end{quotation}
{}

By following up this clew with mathematical precision, measuring the
exact thickness of the plate and the space between the different rings
of color, Young was able to show mathematically what must be the length
of pulsation for each of the different colors of the spectrum. He
estimated that the undulations of red light, at the extreme lower
end of the visible spectrum, must number about thirty-seven thousand
six hundred and forty to the inch, and pass any given spot at a rate
of four hundred and sixty-three millions of millions of undulations
in a second, while the extreme violet numbers fifty-nine thousand
seven hundred and fifty undulations to the inch, or seven hundred
and thirty-five millions of millions to the second.


\subsection*{\raggedright The Colors of Striated Surfaces}

\addcontentsline{toc}{subsection}{The Colors of Striated Surfaces}

Young similarly examined the colors that are produced by scratches
on a smooth surface, in particular testing the light from {}``Mr.\ Coventry's
exquisite micrometers,'' which consist of lines scratched on glass
at measured intervals. These microscopic tests brought the same results
as the other experiments. The colors were produced at certain definite
and measurable angles, and the theory of interference of undulations
explained them perfectly, while, as Young affirmed with confidence,
no other hypothesis hitherto advanced would explain them at all. Here
are his words:\ 

\begin{quotation}
{}``Let there be in a given plane two reflecting points very near
each other, and let the plane be so situated that the reflected image
of a luminous object seen in it may appear to coincide with the points;
then it is obvious that the length of the incident and reflected ray,
taken together, is equal with respect to both points, considering
them as capable of reflecting in all directions. Let one of the points
be now depressed below the given plane; then the whole path of the
light reflected from it will be lengthened by a line which is to the
depression of the point as twice the cosine of incidence to the radius.

{}``If, therefore, equal undulations of given dimensions be reflected
from two points, situated near enough to appear to the eye but as
one, whenever this line is equal to half the breadth of a whole undulation
the reflection from the depressed point will so interfere with the
reflection from the fixed point that the progressive motion of the
one will coincide with the retrograde motion of the other, and they
will both be destroyed; but when this line is equal to the whole breadth
of an undulation, the effect will be doubled, and when to a breadth
and a half, again destroyed; and thus for a considerable number of
alternations, and if the reflected undulations be of a different kind,
they will be variously affected, according to their proportions to
the various length of the line which is the difference between the
lengths of their two paths, and which may be denominated the interval
of a retardation.

{}``In order that the effect may be the more perceptible, a number
of pairs of points must be united into two parallel lines; and if
several such pairs of lines be placed near each other, they will facilitate
the observation. If one of the lines be made to revolve round the
other as an axis, the depression below the given plane will be as
the sine of the inclination; and while the eye and the luminous object
remain fixed the difference of the length of the paths will vary as
this sine.

{}``The best subjects for the experiment are Mr.\ Coventry's exquisite
micrometers; such of them as consist of parallel lines drawn on glass,
at a distance of one-five-hundredth of an inch, are the most convenient.
Each of these lines appears under a microscope to consist of two or
more finer lines, exactly parallel, and at a distance of somewhat
more than a twentieth more than the adjacent lines. I placed one of
these so as to reflect the sun's light at an angle of forty-five degrees,
and fixed it in such a manner that while it revolved round one of
the lines as an axis, I could measure its angular motion; I found
that the longest red color occurred at the inclination 10$\frac{1}{4}$
degrees, 20$\frac{3}{4}$ degrees, 32 degrees, and 45 degrees; of
which the sines are as the numbers 1, 2, 3, and 4. At all other angles
also, when the sun's light was reflected from the surface, the color
vanished with the inclination, and was equal at equal inclinations
on either side.

{}``This experiment affords a very strong confirmation of the theory.
It is impossible to deduce any explanation of it from any hypothesis
hitherto advanced; and I believe it would be difficult to invent any
other that would account for it. There is a striking analogy between
this separation of colors and the production of a musical note by
successive echoes from equidistant iron palisades, which I have found
to correspond pretty accurately with the known velocity of sound and
the distances of the surfaces.

{}``It is not improbable that the colors of the integuments of some
insects, and of some other natural bodies, exhibiting in different
lights the most beautiful versatility, may be found to be of this
description, and not to be derived from thin plates. In some cases
a single scratch or furrow may produce similar effects, by the reflection
of its opposite edges.''%
\footnote{\emph{Ibid}., p.\ 36.%
}
\end{quotation}
{}

This doctrine of interference of undulations was the absolutely novel
part of Young's theory. The all-compassing genius of Robert Hooke
had, indeed, very nearly apprehended it more than a century before,
as Young himself points out, but no one else had so much as vaguely
conceived it; and even with the sagacious Hooke it was only a happy
guess, never distinctly outlined in his own mind, and utterly ignored
by all others. Young did not know of Hooke's guess until he himself
had fully formulated the theory, but he hastened then to give his
predecessor all the credit that could possibly be adjudged his due
by the most disinterested observer. To Hooke's contemporary, Huygens,
who was the originator of the general doctrine of undulation as the
explanation of light, Young renders full justice also. For himself
he claims only the merit of having demonstrated the theory which these
and a few others of his predecessors had advocated without full proof.

The following year Dr.\ Young detailed before the Royal Society other
experiments, which threw additional light on the doctrine of interference;
and in 1803 he cited still others, which, he affirmed, brought the
doctrine to complete demonstration. In applying this demonstration
to the general theory of light, he made the striking suggestion that
{}``the luminiferous ether pervades the substance of all material
bodies with little or no resistance, as freely, perhaps, as the wind
passes through a grove of trees.'' He asserted his belief also that
the chemical rays which Ritter had discovered beyond the violet end
of the visible spectrum are but still more rapid undulations of the
same character as those which produce light. In his earlier lecture
he had affirmed a like affinity between the light rays and the rays
of radiant heat which Herschel detected below the red end of the spectrum,
suggesting that {}``light differs from heat only in the frequency
of its undulations or vibrations---those undulations which are within
certain limits with respect to frequency affecting the optic nerve
and constituting light, and those which are slower and probably stronger
constituting heat only.'' From the very outset he had recognized
the affinity between sound and light; indeed, it had been this affinity
that led him on to an appreciation of the undulatory theory of light.

But while all these affinities seemed so clear to the great co-ordinating
brain of Young, they made no such impression on the minds of his contemporaries.
The immateriality of light had been substantially demonstrated, but
practically no one save its author accepted the demonstration. Newton's
doctrine of the emission of corpuscles was too firmly rooted to be
readily dislodged, and Dr.\ Young had too many other interests to
continue the assault unceasingly. He occasionally wrote something
touching on his theory, mostly papers contributed to the \emph{Quarterly
Review} and similar periodicals, anonymously or under pseudonym, for
he had conceived the notion that too great conspicuousness in fields
outside of medicine would injure his practice as a physician. His
views regarding light (including the original papers from the \emph{Philosophical
Transactions of the Royal Society})\ were again given publicity in
full in his celebrated volume on natural philosophy, consisting in
part of his lectures before the Royal Institution, published in 1807;
but even then they failed to bring conviction to the philosophic world.
Indeed, they did not even arouse a controversial spirit, as his first
papers had done.


\section*{\raggedright ARAGO AND FRESNEL CHAMPION THE WAVE THEORY}

\addcontentsline{toc}{section}{ARAGO AND FRESNEL CHAMPION THE WAVE
THEORY}

So it chanced that when, in 1815, a young French military engineer,
named Augustin Jean Fresnel, returning from the Napoleonic wars, became
interested in the phenomena of light, and made some experiments concerning
diffraction which seemed to him to controvert the accepted notions
of the materiality of light, he was quite unaware that his experiments
had been anticipated by a philosopher across the Channel. He communicated
his experiments and results to the French Institute, supposing them
to be absolutely novel. That body referred them to a committee, of
which, as good fortune would have it, the dominating member was Dominique
Francois Arago, a man as versatile as Young himself, and hardly less
profound, if perhaps not quite so original. Arago at once recognized
the merit of Fresnel's work, and soon became a convert to the theory.
He told Fresnel that Young had anticipated him as regards the general
theory, but that much remained to be done, and he offered to associate
himself with Fresnel in prosecuting the investigation. Fresnel was
not a little dashed to learn that his original ideas had been worked
out by another while he was a lad, but he bowed gracefully to the
situation and went ahead with unabated zeal.

The championship of Arago insured the undulatory theory a hearing
before the French Institute, but by no means sufficed to bring about
its general acceptance. On the contrary, a bitter feud ensued, in
which Arago was opposed by the {}``Jupiter Olympus of the Academy,''
Laplace, by the only less famous Poisson, and by the younger but hardly
less able Biot. So bitterly raged the feud that a life-long friendship
between Arago and Biot was ruptured forever. The opposition managed
to delay the publication of Fresnel's papers, but Arago continued
to fight with his customary enthusiasm and pertinacity, and at last,
in 1823, the Academy yielded, and voted Fresnel into its ranks, thus
implicitly admitting the value of his work.

It is a humiliating thought that such controversies as this must mar
the progress of scientific truth; but fortunately the story of the
introduction of the undulatory theory has a more pleasant side. Three
men, great both in character and in intellect, were concerned in pressing
its claims---Young, Fresnel, and Arago---and the relations of these
men form a picture unmarred by any of those petty jealousies that
so often dim the lustre of great names. Fresnel freely acknowledged
Young's priority so soon as his attention was called to it; and Young
applauded the work of the Frenchman, and aided with his counsel in
the application of the undulatory theory to the problems of polarization
of light, which still demanded explanation, and which Fresnel's fertility
of experimental resource and profundity of mathematical insight sufficed
in the end to conquer.

After Fresnel's admission to the Institute in 1823 the opposition
weakened, and gradually the philosophers came to realize the merits
of a theory which Young had vainly called to their attention a full
quarter-century before. Now, thanks largely to Arago, both Young and
Fresnel received their full meed of appreciation. Fresnel was given
the Rumford medal of the Royal Society of England in 1825, and chosen
one of the foreign members of the society two years later, while Young
in turn was elected one of the eight foreign members of the French
Academy. As a fitting culmination of the chapter of felicities between
the three friends, it fell to the lot of Young, as Foreign Secretary
of the Royal Society, to notify Fresnel of the honors shown him by
England's representative body of scientists; while Arago, as Perpetual
Secretary of the French Institute, conveyed to Young in the same year
the notification that he had been similarly honored by the savants
of France.

A few months later Fresnel was dead, and Young survived him only two
years. Both died prematurely, but their great work was done, and the
world will remember always and link together these two names in connection
with a theory which in its implications and importance ranks little
below the theory of universal gravitation.


\chapter*{\raggedright VII. THE MODERN DEVELOPMENT OF ELECTRICITY AND MAGNETISM}

\addcontentsline{toc}{chapter}{VII. THE MODERN DEVELOPMENT OF ELECTRICITY
AND MAGNETISM}

\markboth{A HISTORY OF SCIENCE, BOOK III}{VII. ELECTRICITY AND MAGNETISM}


\section*{\raggedright GALVANI AND VOLTA}

\addcontentsline{toc}{section}{GALVANI AND VOLTA}

The full importance of Young's studies of light might perhaps have
gained earlier recognition had it not chanced that, at the time when
they were made, the attention of the philosophic world was turned
with the fixity and fascination of a hypnotic stare upon another field,
which for a time brooked no rival. How could the old, familiar phenomenon,
light, interest any one when the new agent, galvanism, was in view?
As well ask one to fix attention on a star while a meteorite blazes
across the sky.

Galvanism was so called precisely as the Roentgen ray was christened
at a later day---as a safe means of begging the question as to the
nature of the phenomena involved. The initial fact in galvanism was
the discovery of Luigi Galvani (1737-1798), a physician of Bologna,
in 1791, that by bringing metals in contact with the nerves of a frog's
leg violent muscular contractions are produced. As this simple little
experiment led eventually to the discovery of galvanic electricity
and the invention of the galvanic battery, it may be regarded as the
beginning of modern electricity.

The story is told that Galvani was led to his discovery while preparing
frogs'\ legs to make a broth for his invalid wife. As the story runs,
he had removed the skins from several frogs'\ legs, when, happening
to touch the exposed muscles with a scalpel which had lain in close
proximity to an electrical machine, violent muscular action was produced.
Impressed with this phenomenon, he began a series of experiments which
finally resulted in his great discovery. But be this story authentic
or not, it is certain that Galvani experimented for several years
upon frogs'\ legs suspended upon wires and hooks, until he finally
constructed his arc of two different metals, which, when arranged
so that one was placed in contact with a nerve and the other with
a muscle, produced violent contractions.

These two pieces of metal form the basic principle of the modern galvanic
battery, and led directly to Alessandro Volta's invention of his {}``voltaic
pile,''\ the immediate ancestor of the modern galvanic battery.
Volta's experiments were carried on at the same time as those of Galvani,
and his invention of his pile followed close upon Galvani's discovery
of the new form of electricity. From these facts the new form of electricity
was sometimes called {}``galvanic''\ and sometimes {}``voltaic''\ electricity,
but in recent years the term {}``galvanism''\ and {}``galvanic
current''\ have almost entirely supplanted the use of the term voltaic.

It was Volta who made the report of Galvani's wonderful discovery
to the Royal Society of London, read on January 31, 1793. In this
letter he describes Galvani's experiments in detail and refers to
them in glowing terms of praise. He calls it one of the {}``most
beautiful and important discoveries,''\ and regarded it as the germ
or foundation upon which other discoveries were to be made. The prediction
proved entirely correct, Volta himself being the chief discoverer.

Working along lines suggested by Galvani's discovery, Volta constructed
an apparatus made up of a number of disks of two different kinds of
metal, such as tin and silver, arranged alternately, a piece of some
moist, porous substance, like paper or felt, being interposed between
each pair of disks. With this {}``pile,'' as it was called, electricity
was generated, and by linking together several such piles an electric
battery could be formed.

This invention took the world by storm. Nothing like the enthusiasm
it created in the philosophic world had been known since the invention
of the Leyden jar, more than half a century before. Within a few weeks
after Volta's announcement, batteries made according to his plan were
being experimented with in every important laboratory in Europe.

As the century closed, half the philosophic world was speculating
as to whether {}``galvanic influence'' were a new imponderable,
or only a form of electricity; and the other half was eagerly seeking
to discover what new marvels the battery might reveal. The least imaginative
man could see that here was an invention that would be epoch-making,
but the most visionary dreamer could not even vaguely adumbrate the
real measure of its importance.

It was evident at once that almost any form of galvanic battery, despite
imperfections, was a more satisfactory instrument for generating electricity
than the frictional machine hitherto in use, the advantage lying in
the fact that the current from the galvanic battery could be controlled
practically at will, and that the apparatus itself was inexpensive
and required comparatively little attention. These advantages were
soon made apparent by the practical application of the electric current
in several fields.

It will be recalled that despite the energetic endeavors of such philosophers
as Watson, Franklin, Galvani, and many others, the field of practical
application of electricity was very limited at the close of the eighteenth
century. The lightning-rod had come into general use, to be sure,
and its value as an invention can hardly be overestimated. But while
it was the result of extensive electrical discoveries, and is a most
practical instrument, it can hardly be called one that puts electricity
to practical use, but simply acts as a means of warding off the evil
effects of a natural manifestation of electricity. The invention,
however, had all the effects of a mechanism which turned electricity
to practical account. But with the advent of the new kind of electricity
the age of practical application began.


\section*{\raggedright DAVY AND ELECTRIC LIGHT}

\addcontentsline{toc}{section}{DAVY AND ELECTRIC LIGHT}

Volta's announcement of his pile was scarcely two months old when
two Englishmen, Messrs.\ Nicholson and Carlisle, made the discovery
that the current from the galvanic battery had a decided effect upon
certain chemicals, among other things decomposing water into its elements,
hydrogen and oxygen. On May 7, 1800, these investigators arranged
the ends of two brass wires connected with the poles of a voltaic
pile, composed of alternate silver and zinc plates, so that the current
coming from the pile was discharged through a small quantity of {}``New
River water.'' {}``A fine stream of minute bubbles immediately began
to flow from the point of the lower wire in the tube which communicated
with the silver,''\ wrote Nicholson, {}``and the opposite point
of the upper wire became tarnished, first deep orange and then black\ldots{}.''
The product of gas during two hours and a half was two-thirtieths
of a cubic inch. {}``It was then mixed with an equal quantity of
common air,''\ continues Nicholson, {}``and exploded by the application
of a lighted waxen thread.''

This demonstration was the beginning of the very important science
of electro-chemistry.

The importance of this discovery was at once recognized by Sir Humphry
Davy, who began experimenting immediately in this new field. He constructed
a series of batteries in various combinations, with which he attacked
the {}``fixed alkalies,''\ the composition of which was then unknown.
Very shortly he was able to decompose potash into bright metallic
globules, resembling quicksilver. This new substance he named {}``potassium.''
Then in rapid succession the elementary substances sodium, calcium,
strontium, and magnesium were isolated.

It was soon discovered, also, that the new electricity, like the old,
possessed heating power under certain conditions, even to the fusing
of pieces of wire. This observation was probably first made by Frommsdorff,
but it was elaborated by Davy, who constructed a battery of two thousand
cells with which he produced a bright light from points of carbon---the
prototype of the modern arc lamp. He made this demonstration before
the members of the Royal Institution in 1810. But the practical utility
of such a light for illuminating purposes was still a thing of the
future. The expense of constructing and maintaining such an elaborate
battery, and the rapid internal destruction of its plates, together
with the constant polarization, rendered its use in practical illumination
out of the question. It was not until another method of generating
electricity was discovered that Davy's demonstration could be turned
to practical account.

In Davy's own account of his experiment he says:\ 

\begin{quote}
%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{3hsci10-Wil3S234}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Sir Humphry Davy}\end{center}
\end{figure}
{}``When pieces of charcoal about an inch long and one-sixth of an
inch in diameter were brought near each other (within the thirtieth
or fortieth of an inch), a bright spark was produced, and more than
half the volume of the charcoal became ignited to whiteness; and,
by withdrawing the points from each other, a constant discharge took
place through the heated air, in a space equal to at least four inches,
producing a most brilliant ascending arch of light, broad and conical
in form in the middle. When any substance was introduced into this
arch, it instantly became ignited; platina melted as readily in it
as wax in a common candle; quartz, the sapphire, magnesia, lime, all
entered into fusion; fragments of diamond and points of charcoal and
plumbago seemed to evaporate in it, even when the connection was made
in the receiver of an air-pump; but there was no evidence of their
having previously undergone fusion. When the communication between
the points positively and negatively electrified was made in the air
rarefied in the receiver of the air-pump, the distance at which the
discharge took place increased as the exhaustion was made; and when
the atmosphere in the vessel supported only one-fourth of an inch
of mercury in the barometrical gauge, the sparks passed through a
space of nearly half an inch; and, by withdrawing the points from
each other, the discharge was made through six or seven inches, producing
a most brilliant coruscation of purple light; the charcoal became
intensely ignited, and some platina wire attached to it fused with
brilliant scintillations and fell in large globules upon the plate
of the pump. All the phenomena of chemical decomposition were produced
with intense rapidity by this combination.''%
\footnote{Davy's paper before Royal Institution, 1810. %
}
\end{quote}
{}

But this experiment demonstrated another thing besides the possibility
of producing electric light and chemical decomposition, this being
the heating power capable of being produced by the electric current.
Thus Davy's experiment of fusing substances laid the foundation of
the modern electric furnaces, which are of paramount importance in
several great commercial industries.

While some of the results obtained with Davy's batteries were practically
as satisfactory as could be obtained with modern cell batteries, the
batteries themselves were anything but satisfactory. They were expensive,
required constant care and attention, and, what was more important
from an experimental standpoint at least, were not constant in their
action except for a very limited period of time, the current soon
{}``running down.'' Numerous experimenters, therefore, set about
devising a satisfactory battery, and when, in 1836, John Frederick
Daniell produced the cell that bears his name, his invention was epoch-making
in the history of electrical progress. The Royal Society considered
it of sufficient importance to bestow the Copley medal upon the inventor,
whose device is the direct parent of all modern galvanic cells. From
the time of the advent of the Daniell cell experiments in electricity
were rendered comparatively easy. In the mean while, however, another
great discovery was made.


\section*{\raggedright ELECTRICITY AND MAGNETISM}

\addcontentsline{toc}{section}{ELECTRICITY AND MAGNETISM}

For many years there had been a growing suspicion, amounting in many
instances to belief in the close relationship existing between electricity
and magnetism. Before the winter of 1815, however, it was a belief
that was surmised but not demonstrated. But in that year it occurred
to Jean Christian Oersted, of Denmark, to pass a current of electricity
through a wire held parallel with, but not quite touching, a suspended
magnetic needle. The needle was instantly deflected and swung out
of its position.

\begin{quotation}
{}``The first experiments in connection with the subject which I
am undertaking to explain,''\ wrote Oersted, {}``were made during
the course of lectures which I held last winter on electricity and
magnetism. From those experiments it appeared that the magnetic needle
could be moved from its position by means of a galvanic battery---one
with a closed galvanic circuit. Since, however, those experiments
were made with an apparatus of small power, I undertook to repeat
and increase them with a large galvanic battery.

{}``Let us suppose that the two opposite ends of the galvanic apparatus
are joined by a metal wire. This I shall always call the conductor
for the sake of brevity. Place a rectilinear piece of this conductor
in a horizontal position over an ordinary magnetic needle so that
it is parallel to it. The magnetic needle will be set in motion and
will deviate towards the west under that part of the conductor which
comes from the negative pole of the galvanic battery. If the wire
is not more than four-fifths of an inch distant from the middle of
this needle, this deviation will be about forty-five degrees. At a
greater distance the angle of deviation becomes less. Moreover, the
deviation varies according to the strength of the battery. The conductor
can be moved towards the east or west, so long as it remains parallel
to the needle, without producing any other result than to make the
deviation smaller.

{}``The conductor can consist of several combined wires or metal
coils. The nature of the metal does not alter the result except, perhaps,
to make it greater or less. We have used wires of platinum, gold,
silver, brass, and iron, and coils of lead, tin, and quicksilver with
the same result. If the conductor is interrupted by water, all effect
is not cut off, unless the stretch of water is several inches long.

{}``The conductor works on the magnetic needle through glass, metals,
wood, water, and resin, through clay vessels and through stone, for
when we placed a glass plate, a metal plate, or a board between the
conductor and the needle the effect was not cut off; even the three
together seemed hardly to weaken the effect, and the same was the
case with an earthen vessel, even when it was full of water. Our experiments
also demonstrated that the said effects were not altered when we used
a magnetic needle which was in a brass case full of water.

{}``When the conductor is placed in a horizontal plane under the
magnetic needle all the effects we have described take place in precisely
the same way, but in the opposite direction to what took place when
the conductor was in a horizontal plane above the needle.

{}``If the conductor is moved in a horizontal plane so that it gradually
makes ever-increasing angles with the magnetic meridian, the deviation
of the magnetic needle from the magnetic meridian is increased when
the wire is turned towards the place of the needle; it decreases,
on the other hand, when it is turned away from that place.

{}``A needle of brass which is hung in the same way as the magnetic
needle is not set in motion by the influence of the conductor. A needle
of glass or rubber likewise remains static under similar experiments.
Hence the electrical conductor affects only the magnetic parts of
a substance. That the electrical current is not confined to the conducting
wire, but is comparatively widely diffused in the surrounding space,
is sufficiently demonstrated from the foregoing observations.''%
\footnote{Hans Christian Oersted, \emph{Experiments with the Effects of the
Electric Current on the Magnetic Needle}, 1815. %
}
\end{quotation}
{}

The effect of Oersted's demonstration is almost incomprehensible.
By it was shown the close relationship between magnetism and electricity.
It showed the way to the establishment of the science of electrodynamics;
although it was by the French savant Andre Marie Amp\`{e}re (1775-1836)\ that
the science was actually created, and this within the space of one
week after hearing of Oersted's experiment in deflecting the needle.
Amp\`{e}re first received the news of Oersted's experiment on September
11, 1820, and on the 18th of the same month he announced to the Academy
the fundamental principles of the science of electro-dynamics---seven
days of rapid progress perhaps unequalled in the history of science.

Amp\`{e}re's distinguished countryman, Ar\-a\-go, a few months
later, gave the finishing touches to Oersted's and Amp\`{e}re's discoveries,
by demonstrating conclusively that electricity not only influenced
a magnet, but actually produced magnetism under proper circumstances---a
complemental fact most essential in practical mechanics

Some four years after Arago's discovery, Sturgeon made the first {}``electro-magnet''\ by
winding a soft iron core with wire through which a current of electricity
was passed. This study of electro-magnets was taken up by Professor
Joseph Henry, of Albany, New York, who succeeded in making magnets
of enormous lifting power by winding the iron core with several coils
of wire. One of these magnets, excited by a single galvanic cell of
less than half a square foot of surface, and containing only half
a pint of dilute acids, sustained a weight of six hundred and fifty
pounds.

Thus by Oersted's great discovery of the intimate relationship of
magnetism and electricity, with further elaborations and discoveries
by Amp\`{e}re, Volta, and Henry, and with the invention of Daniell's
cell, the way was laid for putting electricity to practical use. Soon
followed the invention and perfection of the electro-magnetic telegraph
and a host of other but little less important devices.


\section*{\raggedright FARADAY AND ELECTRO-MAGNETIC INDUCTION}

\addcontentsline{toc}{section}{FARADAY AND ELECTRO-MAGNETIC INDUCTION}

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{3hsci10-Wil3S227}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Michael Faraday}\end{center}
\end{figure}
With these great discoveries and inventions at hand, electricity became
no longer a toy or a {}``plaything for philosophers,''\ but of
enormous and growing importance commercially. Still, electricity generated
by chemical action, even in a very perfect cell, was both feeble and
expensive, and, withal, only applicable in a comparatively limited
field. Another important scientific discovery was necessary before
such things as electric traction and electric lighting on a large
scale were to become possible; but that discovery was soon made by
Sir Michael Faraday.

Faraday, the son of a blacksmith and a bookbinder by trade, had interested
Sir Humphry Davy by his admirable notes on four of Davy's lectures,
which he had been able to attend. Although advised by the great scientist
to {}``stick to his bookbinding''\ rather than enter the field
of science, Faraday became, at twenty-two years of age, Davy's assistant
in the Royal Institution. There, for several years, he devoted all
his spare hours to scientific investigations and experiments, perfecting
himself in scientific technique.

A few years later he became interested, like all the scientists of
the time, in Arago's experiment of rotating a copper disk underneath
a suspended compass-needle. When this disk was rotated rapidly, the
needle was deflected, or even rotated about its axis, in a manner
quite inexplicable. Faraday at once conceived the idea that the cause
of this rotation was due to electricity, induced in the revolving
disk---not only conceived it, but put his belief in writing. For several
years, however, he was unable to demonstrate the truth of his assumption,
although he made repeated experiments to prove it. But in 1831 he
began a series of experiments that established forever the fact of
electro-magnetic induction.

In his famous paper, read before the Royal Society in 1831, Faraday
describes the method by which he first demonstrated electro-magnetic
induction, and then explained the phenomenon of Arago's revolving
disk.

\begin{quotation}
{}``About twenty-six feet of copper wire, one-twentieth of an inch
in diameter, were wound round a cylinder of wood as a helix,''\ he
said, {}``the different spires of which were prevented from touching
by a thin interposed twine. This helix was covered with calico, and
then a second wire applied in the same manner. In this way twelve
helices were superposed, each containing an average length of wire
of twenty-seven feet, and all in the same direction. The first, third,
fifth, seventh, ninth, and eleventh of these helices were connected
at their extremities end to end so as to form one helix; the others
were connected in a similar manner; and thus two principal helices
were produced, closely interposed, having the same direction, not
touching anywhere, and each containing one hundred and fifty-five
feet in length of wire.

{}``One of these helices was connected with a galvanometer, the other
with a voltaic battery of ten pairs of plates four inches square,
with double coppers and well charged; yet not the slightest sensible
deflection of the galvanometer needle could be observed.

{}``A similar compound helix, consisting of six lengths of copper
and six of soft iron wire, was constructed. The resulting iron helix
contained two hundred and eight feet; but whether the current from
the trough was passed through the copper or the iron helix, no effect
upon the other could be perceived at the galvanometer.

{}``In these and many similar experiments no difference in action
of any kind appeared between iron and other metals.

{}``Two hundred and three feet of copper wire in one length were
passed round a large block of wood; other two hundred and three feet
of similar wire were interposed as a spiral between the turns of the
first, and metallic contact everywhere prevented by twine. One of
these helices was connected with a galvanometer and the other with
a battery of a hundred pairs of plates four inches square, with double
coppers and well charged. When the contact was made, there was a sudden
and very slight effect at the galvanometer, and there was also a similar
slight effect when the contact with the battery was broken. But whilst
the voltaic current was continuing to pass through the one helix,
no galvanometrical appearances of any effect like induction upon the
other helix could be perceived, although the active power of the battery
was proved to be great by its heating the whole of its own helix,
and by the brilliancy of the discharge when made through charcoal.

{}``Repetition of the experiments with a battery of one hundred and
twenty pairs of plates produced no other effects; but it was ascertained,
both at this and at the former time, that the slight deflection of
the needle occurring at the moment of completing the connection was
always in one direction, and that the equally slight deflection produced
when the contact was broken was in the other direction; and, also,
that these effects occurred when the first helices were used.

{}``The results which I had by this time obtained with magnets led
me to believe that the battery current through one wire did, in reality,
induce a similar current through the other wire, but that it continued
for an instant only, and partook more of the nature of the electrical
wave passed through from the shock of a common Leyden jar than of
that from a voltaic battery, and, therefore, might magnetize a steel
needle although it scarcely affected the galvanometer.

{}``This expectation was confirmed; for on substituting a small hollow
helix, formed round a glass tube, for the galvanometer, introducing
a steel needle, making contact as before between the battery and the
inducing wire, and then removing the needle before the battery contact
was broken, it was found magnetized.

{}``When the battery contact was first made, then an unmagnetized
needle introduced, and lastly the battery contact broken, the needle
was found magnetized to an equal degree apparently with the first;
but the poles were of the contrary kinds.''%
\footnote{{}``On the Induction of Electric Currents,'' by Michael Faraday,
F.R.S., \emph{Phil.\ Trans.\ of Royal Society of London} for 1832,
pp.\ 126-128. %
}
\end{quotation}
{}

To Faraday these experiments explained the phenomenon of Arago's rotating
disk, the disk inducing the current from the magnet, and, in reacting,
deflecting the needle. To prove this, he constructed a disk that revolved
between the poles of an electro-magnet, connecting the axis and the
edge of the disk with a galvanometer. 

\begin{quotation}
{}``\ldots{}\ A disk of copper, twelve inches in diameter, fixed
upon a brass axis,''\ he says, {}``was mounted in frames so as
to be revolved either vertically or horizontally, its edge being at
the same time introduced more or less between the magnetic poles.
The edge of the plate was well amalgamated for the purpose of obtaining
good but movable contact; a part round the axis was also prepared
in a similar manner.

{}``Conductors or collectors of copper and lead were constructed
so as to come in contact with the edge of the copper disk, or with
other forms of plates hereafter to be described. These conductors
we're about four inches long, one-third of an inch wide, and one-fifth
of an inch thick; one end of each was slightly grooved, to allow of
more exact adaptation to the somewhat convex edge of the plates, and
then amalgamated. Copper wires, one-sixteenth of an inch in thickness,
attached in the ordinary manner by convolutions to the other ends
of these conductors, passed away to the galvanometer.

{}``All these arrangements being made, the copper disk was adjusted,
the small magnetic poles being about one-half an inch apart, and the
edge of the plate inserted about half their width between them. One
of the galvanometer wires was passed twice or thrice loosely round
the brass axis of the plate, and the other attached to a conductor,
which itself was retained by the hand in contact with the amalgamated
edge of the disk at the part immediately between the magnetic poles.
Under these circumstances all was quiescent, and the galvanometer
exhibited no effect. But the instant the plate moved the galvanometer
was influenced, and by revolving the plate quickly the needle could
be deflected ninety degrees or more.''%
\footnote{{}``Explication of Arago's Magnetic Phenomena,'' by Michael Faraday,
F.R.S., \emph{Phil.\ Trans.\ Royal Society of London} for 1832,
pp.\ 146-149.%
}
\end{quotation}
{}

This rotating disk was really a dynamo electric machine in miniature,
the first ever constructed, but whose direct descendants are the ordinary
dynamos. Modern dynamos range in power from little machines operating
machinery requiring only fractions of a horsepower to great dynamos
operating street-car lines and lighting cities; but all are built
on the same principle as Faraday's rotating disk. By this discovery
the use of electricity as a practical and economical motive power
became possible.


\section*{\raggedright STORAGE BATTERIES}

\addcontentsline{toc}{section}{STORAGE BATTERIES}

When the discoveries of Faraday of electro-magnetic induction had
made possible the means of easily generating electricity, the next
natural step was to find a means of storing it or accumulating it.
This, however, proved no easy matter, and as yet a practical storage
or secondary battery that is neither too cumbersome, too fragile,
nor too weak in its action has not been invented. If a satisfactory
storage battery could be made, it is obvious that its revolutionary
effects could scarcely be overestimated. In the single field of aeronautics,
it would probably solve the question of aerial navigation. Little
wonder, then, that inventors have sought so eagerly for the invention
of satisfactory storage batteries. As early as 1803 Ritter had attempted
to make such a secondary battery. In 1843 Grove also attempted it.
But it was not until 1859, when Gaston Planche produced his invention,
that anything like a reasonably satisfactory storage battery was made.
Planche discovered that sheets of lead immersed in dilute sulphuric
acid were very satisfactory for the production of polarization effects.
He constructed a battery of sheets of lead immersed in sulphuric acid,
and, after charging these for several hours from the cells of an ordinary
Bunsen battery, was able to get currents of great strength and considerable
duration. This battery, however, from its construction of lead, was
necessarily heavy and cumbersome. Faure improved it somewhat by coating
the lead plates with red-lead, thus increasing the capacity of the
cell. Faure's invention gave a fresh impetus to inventors, and shortly
after the market was filled with storage batteries of various kinds,
most of them modifications of Planche's or Faure's. The ardor of enthusiastic
inventors soon flagged, however, for all these storage batteries proved
of little practical account in the end, as compared with other known
methods of generating power.

Three methods of generating electricity are in general use: static
or frictional electricity is generated by {}``plate''\ or {}``static''\ machines;
galvanic, generated by batteries based on Volta's discovery; and induced,
or faradic, generated either by chemical or mechanical action. There
is still another kind, thermo-electricity, that may be generated in
a most simple manner. In 1821 Seebecle, of Berlin, discovered that
when a circuit was formed of two wires of different metals, if there
be a difference in temperature at the juncture of these two metals
an electrical current will be established. In this way heat may be
transmitted directly into the energy of the current without the interposition
of the steam-engine. Batteries constructed in this way are of low
resistance, however, although by arranging several of them in {}``series,''\ currents
of considerable strength can be generated. As yet, however, they are
of little practical importance.

About the middle of the century Clerk-Maxwell advanced the idea that
light waves were really electro-magnetic waves. If this were true
and light proved to be simply one form of electrical energy, then
the same would be true of radiant heat. Maxwell advanced this theory,
but failed to substantiate it by experimental confirmation. But Dr.\ Heinrich
Hertz, a few years later, by a series of experiments, demonstrated
the correctness of Maxwell's surmises. What are now called {}``Hertzian
waves''\ are waves apparently identical with light waves, but of
much lower pitch or period. In his experiments Hertz showed that,
under proper conditions, electric sparks between polished balls were
attended by ether waves of the same nature as those of light, but
of a pitch of several millions of vibrations per second. These waves
could be dealt with as if they were light waves---reflected, refracted,
and polarized. These are the waves that are utilized in wireless telegraphy.


\section*{\raggedright ROENTGEN RAYS, OR X-RAYS}

\addcontentsline{toc}{section}{ROENTGEN RAYS, OR X-RAYS}

In December of 1895 word came out of Germany of a scientific discovery
that startled the world. It came first as a rumor, little credited;
then as a pronounced report; at last as a demonstration. It told of
a new manifestation of energy, in virtue of which the interior of
opaque objects is made visible to human eyes. One had only to look
into a tube containing a screen of a certain composition, and directed
towards a peculiar electrical apparatus, to acquire clairvoyant vision
more wonderful than the discredited second-sight of the medium. Coins
within a purse, nails driven into wood, spectacles within a leather
case, became clearly visible when subjected to the influence of this
magic tube; and when a human hand was held before the tube, its bones
stood revealed in weird simplicity, as if the living, palpitating
flesh about them were but the shadowy substance of a ghost.

Not only could the human eye see these astounding revelations, but
the impartial evidence of inanimate chemicals could be brought forward
to prove that the mind harbored no illusion. The photographic film
recorded the things that the eye might see, and ghostly pictures galore
soon gave a quietus to the doubts of the most sceptical. Within a
month of the announcement of Professor Roentgen's experiments comment
upon the {}``X-ray''\ and the {}``new photography''\ had become
a part of the current gossip of all Christendom.

It is hardly necessary to say that such a revolutionary thing as the
discovery of a process whereby opaque objects became transparent,
or translucent, was not achieved at a single bound with no intermediate
discoveries. In 1859 the German physicist Julius Pl\"{u}cker (1801-1868)\ noticed
that when there was an electrical discharge through an exhausted tube
at a low pressure, on the surrounding walls of the tube near the negative
pole, or cathode, appeared a greenish phosphorescence. This discovery
was soon being investigated by a number of other scientists, among
others Hittorf, Goldstein, and Professor (now Sir William)\ Crookes.
The explanations given of this phenomenon by Professor Crookes concern
us here more particularly, inasmuch as his views did not accord exactly
with those held by the other two scientists, and as his researches
were more directly concerned in the discovery of the Roentgen rays.
He held that the heat and phosphorescence produced in a low-pressure
tube were caused by streams of particles, projected from the cathode
with great velocity, striking the sides of the glass tube. The composition
of the glass seemed to enter into this phosphorescence also, for while
lead glass produced blue phosphorescence, soda glass produced a yellowish
green. The composition of the glass seemed to be changed by a long-continued
pelting of these particles, the phosphorescence after a time losing
its initial brilliancy, caused by the glass becoming {}``tired,''\ as
Professor Crookes said. Thus when some opaque substance, such as iron,
is placed between the cathode and the sides of the glass tube so that
it casts a shadow in a certain spot on the glass for some little time,
it is found on removing the opaque substance or changing its position
that the area of glass at first covered by the shadow now responded
to the rays in a different manner from the surrounding glass.

The peculiar rays, now known as the cathode rays, not only cast a
shadow, but are deflected by a magnet, so that the position of the
phosphorescence on the sides of the tube may be altered by the proximity
of a powerful magnet. From this it would seem that the rays are composed
of particles charged with negative electricity, and Professor J.\ J.\ Thomson
has modified the experiment of Perrin to show that negative electricity
is actually associated with the rays. There is reason for believing,
therefore, that the cathode rays are rapidly moving charges of negative
electricity. It is possible, also, to determine the velocity at which
these particles are moving by measuring the deflection produced by
the magnetic field.

From the fact that opaque substances cast a shadow in these rays it
was thought at first that all solids were absolutely opaque to them.
Hertz, however, discovered that a small amount of phosphorescence
occurred on the glass even when such opaque substances as gold-leaf
or aluminium foil were interposed between the cathode and the sides
of the tube. Shortly afterwards Lenard discovered that the cathode
rays can be made to pass from the inside of a discharge tube to the
outside air. For convenience these rays outside the tube have since
been known as {}``Lenard rays.''

In the closing days of December, 1895, Professor Wilhelm Konrad Roentgen,
of W\"{u}rzburg, announced that he had made the discovery of the
remarkable effect arising from the cathode rays to which reference
was made above. He found that if a plate covered with a phosphorescent
substance is placed near a discharge tube exhausted so highly that
the cathode rays produced a green phosphorescence, this plate is made
to glow in a peculiar manner. The rays producing this glow were not
the cathode rays, although apparently arising from them, and are what
have since been called the Roentgen rays, or X-rays.

Roentgen found that a shadow is thrown upon the screen by substances
held between it and the exhausted tube, the character of the shadow
depending upon the density of the substance. Thus metals are almost
completely opaque to the rays; such substances as bone much less so,
and ordinary flesh hardly so at all. If a coin were held in the hand
that had been interposed between the tube and the screen the picture
formed showed the coin as a black shadow; and the bones of the hand,
while casting a distinct shadow, showed distinctly lighter; while
the soft tissues produced scarcely any shadow at all. The value of
such a discovery was obvious from the first; and was still further
enhanced by the discovery made shortly that, photographic plates are
affected by the rays, thus making it possible to make permanent photographic
records of pictures through what we know as opaque substances.

What adds materially to the practical value of Roentgen's discovery
is the fact that the apparatus for producing the X-rays is now so
simple and relatively inexpensive that it is within the reach even
of amateur scientists. It consists essentially of an induction coil
attached either to cells or a street-current plug for generating the
electricity, a focus tube, and a phosphorescence screen. These focus
tubes are made in various shapes, but perhaps the most popular are
in the form of a glass globe, not unlike an ordinary small-sized water-bottle,
this tube being closed and exhausted, and having the two poles (anode
and cathode)\ sealed into the glass walls, but protruding at either
end for attachment to the conducting wires from the induction coil.
This tube may be mounted on a stand at a height convenient for manipulation.
The phosphorescence screen is usually a plate covered with some platino-cyanide
and mounted in the end of a box of convenient size, the opposite end
of which is so shaped that it fits the contour of the face, shutting
out the light and allowing the eyes of the observer to focalize on
the screen at the end. For making observations the operator has simply
to turn on the current of electricity and apply the screen to his
eyes, pointing it towards the glowing tube, when the shadow of any
substance interposed between the tube and the screen will appear upon
the phosphorescence plate.

The wonderful shadow pictures produced on the phosphorescence screen,
or the photographic plate, would seem to come from some peculiar form
of light, but the exact nature of these rays is still an open question.
Whether the Roentgen rays are really a form of light---that is, a
form of {}``electro-magnetic disturbance propagated through ether,''\ is
not fully determined. Numerous experiments have been undertaken to
determine this, but as yet no proof has been found that the rays are
a form of light, although there appears to be nothing in their properties
inconsistent with their being so. For the moment most investigators
are content to admit that the term X-ray virtually begs the question
as to the intimate nature of the form of energy involved.


\chapter*{\raggedright VIII. THE CONSERVATION OF ENERGY}

\addcontentsline{toc}{chapter}{VIII. THE CONSERVATION OF ENERGY}

\markboth{A HISTORY OF SCIENCE, BOOK III}{VIII. CONSERVATION OF ENERGY}

As we have seen, it was in 1831 that Faraday opened up the field of
magneto-electricity. Reversing the experiments of his predecessors,
who had found that electric currents may generate magnetism, he showed
that magnets have power under certain circumstances to generate electricity;
he proved, indeed, the interconvertibility of electricity and magnetism.
Then he showed that all bodies are more or less subject to the influence
of magnetism, and that even light may be affected by magnetism as
to its phenomena of polarization. He satisfied himself completely
of the true identity of all the various forms of electricity, and
of the convertibility of electricity and chemical action. Thus he
linked together light, chemical affinity, magnetism, and electricity.
And, moreover, he knew full well that no one of these can be produced
in indefinite supply from another. {}``Nowhere,''\ he says, {}``is
there a pure creation or production of power without a corresponding
exhaustion of something to supply it.''

When Faraday wrote those words in 1840 he was treading on the very
heels of a greater generalization than any which he actually formulated;
nay, he had it fairly within his reach. He saw a great truth without
fully realizing its import; it was left for others, approaching the
same truth along another path, to point out its full significance.

The great generalization which Faraday so narrowly missed is the truth
which since then has become familiar as the doctrine of the conservation
of energy---the law that in transforming energy from one condition
to another we can never secure more than an equivalent quantity; that,
in short, {}``to create or annihilate energy is as impossible as
to create or annihilate matter; and that all the phenomena of the
material universe consist in transformations of energy alone.'' Some
philosophers think this the greatest generalization ever conceived
by the mind of man. Be that as it may, it is surely one of the great
intellectual landmarks of the nineteenth century. It stands apart,
so stupendous and so far-reaching in its implications that the generation
which first saw the law developed could little appreciate it; only
now, through the vista of half a century, do we begin to see it in
its true proportions.

A vast generalization such as this is never a mushroom growth, nor
does it usually spring full grown from the mind of any single man.
Always a number of minds are very near a truth before any one mind
fully grasps it. Pre-eminently true is this of the doctrine of the
conservation of energy. Not Faraday alone, but half a dozen different
men had an inkling of it before it gained full expression; indeed,
every man who advocated the undulatory theory of light and heat was
verging towards the goal. The doctrine of Young and Fresnel was as
a highway leading surely on to the wide plain of conservation. The
phenomena of electro-magnetism furnished another such highway. But
there was yet another road which led just as surely and even more
readily to the same goal. This was the road furnished by the phenomena
of heat, and the men who travelled it were destined to outstrip their
fellow-workers; though, as we have seen, wayfarers on other roads
were within hailing distance when the leaders passed the mark.

In order to do even approximate justice to the men who entered into
the great achievement, we must recall that just at the close of the
eighteenth century Count Rumford and Humphry Davy independently showed
that labor may be transformed into heat; and correctly interpreted
this fact as meaning the transformation of molar into molecular motion.
We can hardly doubt that each of these men of genius realized---vaguely,
at any rate---that there must be a close correspondence between the
amount of the molar and the molecular motions; hence that each of
them was in sight of the law of the mechanical equivalent of heat.
But neither of them quite grasped or explicitly stated what each must
vaguely have seen; and for just a quarter of a century no one else
even came abreast their line of thought, let alone passing it.

But then, in 1824, a French philosopher, Sadi Carnot, caught step
with the great Englishmen, and took a long leap ahead by explicitly
stating his belief that a definite quantity of work could be transformed
into a definite quantity of heat, no more, no less. Carnot did not,
indeed, reach the clear view of his predecessors as to the nature
of heat, for he still thought it a form of {}``imponderable''\ fluid;
but he reasoned none the less clearly as to its mutual convertibility
with mechanical work. But important as his conclusions seem now that
we look back upon them with clearer vision, they made no impression
whatever upon his contemporaries. Carnot's work in this line was an
isolated phenomenon of historical interest, but it did not enter into
the scheme of the completed narrative in any such way as did the work
of Rumford and Davy.

The man who really took up the broken thread where Rumford and Davy
had dropped it, and wove it into a completed texture, came upon the
scene in 1840. His home was in Manchester, England; his occupation
that of a manufacturer. He was a friend and pupil of the great Dr.\ Dalton.
His name was James Prescott Joule. When posterity has done its final
juggling with the names of the nineteenth century, it is not unlikely
that the name of this Manchester philosopher will be a household word,
like the names of Aristotle, Copernicus, and Newton.

For Joule's work it was, done in the fifth decade of the century,
which demonstrated beyond all cavil that there is a precise and absolute
equivalence between mechanical work and heat; that whatever the form
of manifestation of molar motion, it can generate a definite and measurable
amount of heat, and no more. Joule found, for example, that at the
sea-level in Manchester a pound weight falling through seven hundred
and seventy-two feet could generate enough heat to raise the temperature
of a pound of water one degree Fahrenheit. There was nothing haphazard,
nothing accidental, about this; it bore the stamp of unalterable law.
And Joule himself saw, what others in time were made to see, that
this truth is merely a particular case within a more general law.
If heat cannot be in any sense created, but only made manifest as
a transformation of another kind of motion, then must not the same
thing be true of all those other forms of {}``force''---light, electricity,
magnetism---which had been shown to be so closely associated, so mutually
convertible, with heat? All analogy seemed to urge the truth of this
inference; all experiment tended to confirm it. The law of the mechanical
equivalent of heat then became the main corner-stone of the greater
law of the conservation of energy.

But while this citation is fresh in mind, we must turn our attention
with all haste to a country across the Channel---to Denmark, in short---and
learn that even as Joule experimented with the transformation of heat,
a philosopher of Copenhagen, Colding by name, had hit upon the same
idea, and carried it far towards a demonstration. And then, without
pausing, we must shift yet again, this time to Germany, and consider
the work of three other men, who independently were on the track of
the same truth, and two of whom, it must be admitted, reached it earlier
than either Joule or Colding, if neither brought it to quite so clear
a demonstration. The names of these three Germans are Mohr, Mayer,
and Helmholtz. Their share in establishing the great doctrine of conservation
must now claim our attention.

As to Karl Friedrich Mohr, it may be said that his statement of the
doctrine preceded that of any of his fellows, yet that otherwise it
was perhaps least important. In 1837 this thoughtful German had grasped
the main truth, and given it expression in an article published in
the \emph{Zeitschrift f\"{u}r Physik}, \textit{etc}. But the article
attracted no attention whatever, even from Mohr's own countrymen.
Still, Mohr's title to rank as one who independently conceived the
great truth, and perhaps conceived it before any other man in the
world saw it as clearly, even though he did not demonstrate its validity,
is not to be disputed.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics{3hsci10-JuliusRobertMayer}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Julius Robert Mayer}\end{center}
\end{figure}
It was just five years later, in 1842, that Dr.\ Julius Robert Mayer,
practising physician in the little German town of Heilbronn, published
a paper in Liebig's \emph{Annalen} on {}``The Forces of Inorganic
Nature,''\ in which not merely the mechanical theory of heat, but
the entire doctrine of the conservation of energy, is explicitly if
briefly stated. Two years earlier Dr.\ Mayer, while surgeon to a
Dutch India vessel cruising in the tropics, had observed that the
venous blood of a patient seemed redder than venous blood usually
is observed to be in temperate climates. He pondered over this seemingly
insignificant fact, and at last reached the conclusion that the cause
must be the lesser amount of oxidation required to keep up the body
temperature in the tropics. Led by this reflection to consider the
body as a machine dependent on outside forces for its capacity to
act, he passed on into a novel realm of thought, which brought him
at last to independent discovery of the mechanical theory of heat,
and to the first full and comprehensive appreciation of the great
law of conservation. Blood-letting, the modern physician holds, was
a practice of very doubtful benefit, as a rule, to the subject; but
once, at least, it led to marvellous results. No straw is go small
that it may not point the receptive mind of genius to new and wonderful
truths.


\section*{\raggedright MAYER'S PAPER OF 1842}

\addcontentsline{toc}{section}{MAYER'S PAPER OF 1842}

The paper in which Mayer first gave expression to his revolutionary
ideas bore the title of {}``The Forces of Inorganic Nature,''\ and
was published in 1842. It is one of the gems of scientific literature,
and fortunately it is not too long to be quoted in its entirety. Seldom
if ever was a great revolutionary doctrine expounded in briefer compass:

\begin{quotation}
{}``What are we to understand by `forces'?\ and how are different
forces related to each other? The term force conveys for the most
part the idea of something unknown, unsearchable, and hypothetical;
while the term matter, on the other hand, implies the possession,
by the object in question, of such definite properties as weight and
extension. An attempt, therefore, to render the idea of force equally
exact with that of matter is one which should be welcomed by all those
who desire to have their views of nature clear and unencumbered by
hypothesis.

{}``Forces are causes; and accordingly we may make full application
in relation to them of the principle \emph{causa aequat effectum}.
If the cause $c$ has the effect $e$, then $c=e$; if, in its turn,
$e$ is the cause of a second effect of $f$, we have $e=f$, and
so on: $c=e=f=...=c$. In a series of causes and effects, a term or
a part of a term can never, as is apparent from the nature of an equation,
become equal to nothing. This first property of all causes we call
their indestructibility.

{}``If the given cause $c$ has produced an effect $e$ equal to
itself, it has in that very act ceased to be---$c$ has become $e$.
If, after the production of $e$, $c$ still remained in the whole
or in part, there must be still further effects corresponding to this
remaining cause: the total effect of $c$ would thus be $>e$, which
would be contrary to the supposition $c=e$. Accordingly, since $c$
becomes $e$, and $e$ becomes $f$, \textit{etc}., we must regard
these various magnitudes as different forms under which one and the
same object makes its appearance. This capability of assuming various
forms is the second essential property of all causes. Taking both
properties together, we may say, causes are \textit{indestructible}
quantitatively, and quantitatively \textit{convertible} objects.

{}``There occur in nature two causes which apparently never pass
one into the other,''\ said Mayer. {}``The first class consists
of such causes as possess the properties of weight and impenetrability.
These are kinds of matter. The other class is composed of causes which
are wanting in the properties just mentioned---namely, forces, called
also imponderables, from the negative property that has been indicated.
Forces are therefore \textit{indestructible}, \textit{convertible},
\textit{imponderable} \textit{objects}.

{}``As an example of causes and effects, take matter: explosive gas,
H +\ O, and water, \textit{Ho}, are related to each other as cause
and effect; therefore H +\ O = HO. But if H +\ O becomes HO, heat,
cal., makes its appearance as well as water; this heat must likewise
have a cause, $x$, and we have therefore H +\ O +\ $x$ = HO +\ cal.
It might be asked, however, whether H +\ O is really =\ HO and $x$
=\ cal., and not perhaps H +\ O = cal., and $x$ =\ HO, whence
the above equation could equally be deduced; and so in many other
cases. The phlogistic chemists recognized the equation between cal.\ and
$x$, or phlogiston as they called it, and in so doing made a great
step in advance; but they involved themselves again in a system of
mistakes by putting $x$ in place of O.\ In this way they obtained
H = HO +\ $x$.

{}``Chemistry teaches us that matter, as a cause, has matter for
its effect; but we may say with equal justification that to force
as a cause corresponds force as effect. Since $c=e$, and $e=c$,
it is natural to call one term of an equation a force, and the other
an effect of force, or phenomenon, and to attach different notions
to the expression force and phenomenon. In brief, then, if the cause
is matter, the effect is matter; if the cause is a force, the effect
is also a force.

{}``The cause that brings about the raising of a weight is a force.
The effect of the raised weight is, therefore, also a force; or, expressed
in a more general form, \textit{separation} \textit{in} \textit{space}
\textit{of} \textit{ponderable} \textit{objects} \textit{is} \textit{a
force}; and since this force causes the fall of bodies, we call it
\textit{falling} \textit{force}. Falling force and fall, or, still
more generally, falling force and motion, are forces related to each
other as cause and effect---forces convertible into each other---two
different forms of one and the same object. For example, a weight
resting on the ground is not a force: it is neither the cause of motion
nor of the lifting of another weight. It becomes so, however, in proportion
as it is raised above the ground. The cause---that is, the distance
between a weight and the earth, and the effect, or the quantity of
motion produced, bear to each other, as shown by mechanics, a constant
relation.

{}``Gravity being regarded as the cause of the falling of bodies,
a gravitating force is spoken of; and thus the ideas of \textit{property}
and of \textit{force} are confounded with each other. Precisely that
which is the essential attribute of every force---that is, the \textit{union}
of indestructibility with convertibility---is wanting in every property:
between a property and a force, between gravity and motion, it is
therefore impossible to establish the equation required for a rightly
conceived causal relation. If gravity be called a force, a cause is
supposed which produces effects without itself diminishing, and incorrect
conceptions of the causal connections of things are thereby fostered.
In order that a body may fall, it is just as necessary that it be
lifted up as that it should be heavy or possess gravity. The fall
of bodies, therefore, ought not to be ascribed to their gravity alone.
The problem of mechanics is to develop the equations which subsist
between falling force and motion, motion and falling force, and between
different motions. Here is a case in point: The magnitude of the falling
force $v$ is directly proportional (the earth's radius being assumed
$\infty $)\ to the magnitude of the mass $m$, and the height $d$,
to which it is raised---that is, $v=md$. If the height $d=1$, to
which the mass m is raised, is transformed into the final velocity
$c=1$ of this mass, we have also $v=mc$; but from the known relations
existing between $d$ and $c$, it results that, for other values
of $d$ or of $c$, the measure of the force $v$ is $mc^{2}$; accordingly
$v=md=mc^{2}$. The law of the conservation of \emph{vis viva} is
thus found to be based on the general law of the indestructibility
of causes.

{}``In many cases we see motion cease without having caused another
motion or the lifting of a weight. But a force once in existence cannot
be annihilated---it can only change its form. And the question therefore
arises, what other forms is force, which we have become acquainted
with as falling force and motion, capable of assuming? Experience
alone can lead us to a conclusion on this point. That we may experiment
to advantage, we must select implements which, besides causing a real
cessation of motion, are as little as possible altered by the objects
to be examined. For example, if we rub together two metal plates,
we see motion disappear, and heat, on the other hand, make its appearance,
and there remains to be determined only whether \textit{motion} is
the cause of heat. In order to reach a decision on this point, we
must discuss the question whether, in the numberless cases in which
the expenditure of motion is accompanied by the appearance of heat,
the motion has not some other effect than the production of heat,
and the heat some other cause than the motion.

{}``A serious attempt to ascertain the effects of ceasing motion
has never been made. Without wishing to exclude \emph{a priori} the
hypothesis which it may be possible to establish, therefore, we observe
only that, as a rule, this effect cannot be supposed to be an alteration
in the state of aggregation of the moved (that is, rubbing, \textit{etc}.)\ bodies.
If we assume that a certain quantity of motion $v$ is expended in
the conversion of a rubbing substance $m$ into $n$, we must then
have $m+v=n$, and $n=m+v$; and when $n$ is reconverted into $m$,
$v$ must appear again in some form or other.

{}``By the friction of two metallic plates continued for a very long
time, we can gradually cause the cessation of an immense quantity
of movement; but would it ever occur to us to look for even the smallest
trace of the force which has disappeared in the metallic dust that
we could collect, and to try to regain it thence? We repeat, the motion
cannot have been annihilated; and contrary, or positive and negative,
motions cannot be regarded as $=0$ any more than contrary motions
can come out of nothing, or a weight can raise itself.

{}``Without the recognition of a causal relation between motion and
heat, it is just as difficult to explain the production of heat as
it is to give any account of the motion that disappears. The heat
cannot be derived from the diminution of the volume of the rubbing
substances. It is well known that two pieces of ice may be melted
by rubbing them together \emph{in vacuo}; but let any one try to convert
ice into water by pressure, however enormous. The author has found
that water undergoes a rise of temperature when shaken violently.
The water so heated (from twelve to thirteen degrees centigrade)\ has
a greater bulk after being shaken than it had before. Whence now comes
this quantity of heat, which by repeated shaking may be called into
existence in the same apparatus as often as we please? The vibratory
hypothesis of heat is an approach towards the doctrine of heat being
the effect of motion, but it does not favor the admission of this
causal relation in its full generality. It rather lays the chief stress
on restless oscillations.

{}``If it be considered as now established that in many cases no
other effect of motion can be traced except heat, and that no other
cause than motion can be found for the heat that is produced, we prefer
the assumption that heat proceeds from motion to the assumption of
a cause without effect and of an effect without a cause. Just as the
chemist, instead of allowing oxygen and hydrogen to disappear without
further investigation, and water to be produced in some inexplicable
manner, establishes a connection between oxygen and hydrogen on the
one hand, and water on the other.

{}``We may conceive the natural connection existing between falling
force, motion, and heat as follows: We know that heat makes its appearance
when the separate particles of a body approach nearer to each other;
condensation produces heat. And what applies to the smallest particles
of matter, and the smallest intervals between them, must also apply
to large masses and to measurable distances. The falling of a weight
is a diminution of the bulk of the earth, and must therefore without
doubt be related to the quantity of heat thereby developed; this quantity
of heat must be proportional to the greatness of the weight and its
distance from the ground. From this point of view we are easily led
to the equations between falling force, motion, and heat that have
already been discussed.

{}``But just as little as the connection between falling force and
motion authorizes the conclusion that the essence of falling force
is motion, can such a conclusion be adopted in the case of heat. We
are, on the contrary, rather inclined to infer that, before it can
become heat, motion must cease to exist as motion, whether simple,
or vibratory, as in the case of light and radiant heat, \textit{etc}.

{}``If falling force and motion are equivalent to heat, heat must
also naturally be equivalent to motion and falling force. Just as
heat appears as an \textit{effect} of the diminution of bulk and of
the cessation of motion, so also does heat disappear as a \textit{cause}
when its effects are produced in the shape of motion, expansion, or
raising of weight.

{}``In water-mills the continual diminution in bulk which the earth
undergoes, owing to the fall of the water, gives rise to motion, which
afterwards disappears again, calling forth unceasingly a great quantity
of heat; and, inversely, the steam-engine serves to decompose heat
again into motion or the raising of weights. A locomotive with its
train may be compared to a distilling apparatus; the heat applied
under the boiler passes off as motion, and this is deposited again
as heat at the axles of the wheels.''
\end{quotation}
{}

Mayer then closes his paper with the following deduction: 

\begin{quotation}
{}``The solution of the equations subsisting between falling force
and motion requires that the space fallen through in a given time---e.g.,
the first second---should be experimentally determined. In like manner,
the solution of the equations subsisting between falling force and
motion on the one hand and heat on the other requires an answer to
the question, How great is the quantity of heat which corresponds
to a given quantity of motion or falling force? For instance, we must
ascertain how high a given weight requires to be raised above the
ground in order that its falling force maybe equivalent to the raising
of the temperature of an equal weight of water from 0$^\circ$ to
1$^\circ$ centigrade. The attempt to show that such an equation is
the expression of a physical truth may be regarded as the substance
of the foregoing remarks.

{}``By applying the principles that have been set forth to the relations
subsisting between the temperature and the volume of gases, we find
that the sinking of a mercury column by which a gas is compressed
is equivalent to the quantity of heat set free by the compression;
and hence it follows, the ratio between the capacity for heat of air
under constant pressure and its capacity under constant volume being
taken as $=1.421$, that the warming of a given weight of water from
0$^\circ$ to 1$^\circ$ centigrade corresponds to the fall of an
equal weight from the height of about three hundred and sixty-five
metres. If we compare with this result the working of our best steam-engines,
we see how small a part only of the heat applied under the boiler
is really transformed into motion or the raising of weights; and this
may serve as justification for the attempts at the profitable production
of motion by some other method than the expenditure of the chemical
difference between carbon and oxygen---more particularly by the transformation
into motion of electricity obtained by chemical means.''%
\footnote{{}``The Forces of Inorganic Nature,'' a paper by Dr.\ Julius Robert
Mayer, Liebig's \emph{Annalen}, 1842. %
}
\end{quotation}

\section*{\raggedright MAYER AND HELMHOLTZ}

\addcontentsline{toc}{section}{MAYER AND HELMHOLTZ}

Here, then, was this obscure German physician, leading the humdrum
life of a village practitioner, yet seeing such visions as no human
being in the world had ever seen before.

The great principle he had discovered became the dominating thought
of his life, and filled all his leisure hours. He applied it far and
wide, amid all the phenomena of the inorganic and organic worlds.
It taught him that both vegetables and animals are machines, bound
by the same laws that hold sway over inorganic matter, transforming
energy, but creating nothing. Then his mind reached out into space
and met a universe made up of questions. Each star that blinked down
at him as he rode in answer to a night-call seemed an interrogation-point
asking, How do I exist? Why have I not long since burned out if your
theory of conservation be true? No one had hitherto even tried to
answer that question; few had so much as realized that it demanded
an answer. But the Heilbronn physician understood the question and
found an answer. His meteoric hypothesis, published in 1848, gave
for the first time a tenable explanation of the persistent light and
heat of our sun and the myriad other suns---an explanation to which
we shall recur in another connection.

All this time our isolated philosopher, his brain aflame with the
glow of creative thought, was quite unaware that any one else in the
world was working along the same lines. And the outside world was
equally heedless of the work of the Heilbronn physician. There was
no friend to inspire enthusiasm and give courage, no kindred spirit
to react on this masterful but lonely mind. And this is the more remarkable
because there are few other cases where a master-originator in science
has come upon the scene except as the pupil or friend of some other
master-originator. Of the men we have noticed in the present connection,
Young was the friend and \emph{confrere} of Davy; Davy, the prot\'{e}g\'{e}
of Rumford; Faraday, the pupil of Davy; Fresnel, the co-worker with
Arago; Colding, the \emph{confrere} of Oersted; Joule, the pupil of
Dalton. But Mayer is an isolated phenomenon---one of the lone mountain-peak
intellects of the century. That estimate may be exaggerated which
has called him the Galileo of the nineteenth century, but surely no
lukewarm praise can do him justice.

Yet for a long time his work attracted no attention whatever. In 1847,
when another German physician, Hermann von Helmholtz, one of the most
massive and towering intellects of any age, had been independently
led to comprehension of the doctrine of the conservation of energy
and published his treatise on the subject, he had hardly heard of
his countryman Mayer. When he did hear of him, however, he hastened
to renounce all claim to the doctrine of conservation, though the
world at large gives him credit of independent even though subsequent
discovery.


\section*{\raggedright JOULE'S PAPER OF 1843}

\addcontentsline{toc}{section}{JOULE'S PAPER OF 1843}

Meantime, in England, Joule was going on from one experimental demonstration
to another, oblivious of his German competitors and almost as little
noticed by his own countrymen. He read his first paper before the
chemical section of the British Association for the Advancement of
Science in 1843, and no one heeded it in the least. It is well worth
our while, however, to consider it at length. It bears the title,
{}``On the Calorific Effects of Magneto-Electricity, and the Mechanical
Value of Heat.'' The full text, as published in the \emph{Report}
of the British Association, is as follows:\ 

\begin{quotation}
%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics{3hsci10-JamesPrescottJoule}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small James Prescott Joule}\end{center}
\end{figure}
{}``Although it has been long known that fine platinum wire can be
ignited by magneto-electricity, it still remained a matter of doubt
whether heat was evolved by the \textit{coils} in which the magneto-electricity
was generated; and it seemed indeed not unreasonable to suppose that
\textit{cold} was produced there in order to make up for the heat
evolved by the other part of the circuit. The author therefore has
endeavored to clear up this uncertainty by experiment. His apparatus
consisted of a small compound electro-magnet, immersed in water, revolving
between the poles of a powerful stationary magnet. The magneto-electricity
developed in the coils of the revolving electro-magnet was measured
by an accurate galvanometer; and the temperature of the water was
taken before and after each experiment by a very delicate thermometer.
The influence of the temperature of the surrounding atmospheric air
was guarded against by covering the revolving tube with flannel, \textit{etc}.,
and by the adoption of a system of interpolation. By an extensive
series of experiments with the above apparatus the author succeeded
in proving that heat is evolved by the coils of the magneto-electrical
machine, as well as by any other part of the circuit, in proportion
to the resistance to conduction of the wire and the square of the
current; the magneto having, under comparable circumstances, the same
calorific power as the voltaic electricity.

{}``Professor Jacobi, of St.\ Petersburg, had shown that the motion
of an electro-magnetic machine generates magneto-electricity in opposition
to the voltaic current of the battery. The author had observed the
same phenomenon on arranging his apparatus as an electro-magnetic
machine; but had found that no additional heat was evolved on account
of the conflict of forces in the coil of the electro-magnet, and that
the heat evolved by the coil remained, as before, proportional to
the square of the current. Again, by turning the machine contrary
to the direction of the attractive forces, so as to increase the intensity
of the voltaic current by the assistance of the magneto-electricity,
he found that the evolution of heat was still proportional to the
square of the current. The author discovered, therefore, that the
heat evolved by the voltaic current is invariably proportional to
the square of the current, however the intensity of the current may
be varied by magnetic induction. But Dr.\ Faraday has shown that
the chemical effects of the current are simply as its quantity. Therefore
he concluded that in the electro-magnetic engine a part of the heat
due to the chemical actions of the battery is lost by the circuit,
and converted into mechanical power; and that when the electro-magnetic
engine is turned \textit{contrary} to the direction of the attractive
forces, a greater quantity of heat is evolved by the circuit than
is due to the chemical reactions of the battery, the over-plus quantity
being produced by the conversion of the mechanical force exerted in
turning the machine. By a dynamometrical apparatus attached to his
machine, the author has ascertained that, in all the above cases,
a quantity of heat, capable of increasing the temperature of a pound
of water by one degree of Fahrenheit's scale, is equal to the mechanical
force capable of raising a weight of about eight hundred and thirty
pounds to the height of one foot.''%
\footnote{{}``On the Calorific Effects of Magneto-Electricity and the Mechanical
Value of Heat,'' by J.\ P.\ Joule, in \emph{Report of the British
Association for the Advancement of Science}, vol.\ XII., p.\ 33.%
}
\end{quotation}

\section*{\raggedright JOULE OR MAYER?}

\addcontentsline{toc}{section}{JOULE OR MAYER?}

Two years later Joule wished to read another paper, but the chairman
hinted that time was limited, and asked him to confine himself to
a brief verbal synopsis of the results of his experiments. Had the
chairman but known it, he was curtailing a paper vastly more important
than all the other papers of the meeting put together. However, the
synopsis was given, and one man was there to hear it who had the genius
to appreciate its importance. This was William Thomson, the present
Lord Kelvin, now known to all the world as among the greatest of natural
philosophers, but then only a novitiate in science. He came to Joule's
aid, started rolling the ball of controversy, and subsequently associated
himself with the Manchester experimenter in pursuing his investigations.

But meantime the acknowledged leaders of British science viewed the
new doctrine askance. Faraday, Brewster, Herschel---those were the
great names in physics at that day, and no one of them could quite
accept the new views regarding energy. For several years no older
physicist, speaking with recognized authority, came forward in support
of the doctrine of conservation. This culminating thought of the first
half of the nineteenth century came silently into the world, unheralded
and unopposed. The fifth decade of the century had seen it elaborated
and substantially demonstrated in at least three different countries,
yet even the leaders of thought did not so much as know of its existence.
In 1853 Whewell, the historian of the inductive sciences, published
a second edition of his history, and, as Huxley has pointed out, he
did not so much as refer to the revolutionizing thought which even
then was a full decade old.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics{3hsci10-JohnTyndall}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small John Tyndall}\end{center}
\end{figure}
By this time, however, the battle was brewing. The rising generation
saw the importance of a law which their elders could not appreciate,
and soon it was noised abroad that there were more than one claimant
to the honor of discovery. Chiefly through the efforts of Professor
Tyndall, the work of Mayer became known to the British public, and
a most regrettable controversy ensued between the partisans of Mayer
and those of Joule---a bitter controversy, in which Davy's contention
that science knows no country was not always regarded, and which left
its scars upon the hearts and minds of the great men whose personal
interests were involved.

And so to this day the question who is the chief discoverer of the
law of the conservation of energy is not susceptible of a categorical
answer that would satisfy all philosophers. It is generally held that
the first choice lies between Joule and Mayer. Professor Tyndall has
expressed the belief that in future each of these men will be equally
remembered in connection with this work. But history gives us no warrant
for such a hope. Posterity in the long run demands always that its
heroes shall stand alone. Who remembers now that Robert Hooke contested
with Newton the discovery of the doctrine of universal gravitation?
The judgment of posterity is unjust, but it is inexorable. And so
we can little doubt that a century from now one name will be mentioned
as that of the originator of the great doctrine of the conservation
of energy. The man whose name is thus remembered will perhaps be spoken
of as the Galileo, the Newton, of the nineteenth century; but whether
the name thus dignified by the final verdict of history will be that
of Colding, Mohr, Mayer, Helmholtz, or Joule, is not as, yet decided.


\section*{\raggedright LORD KELVIN AND THE DISSIPATION OF ENERGY}

\addcontentsline{toc}{section}{LORD KELVIN AND THE\\
DISSIPATION OF ENERGY}

The gradual permeation of the field by the great doctrine of conservation
simply repeated the history of the introduction of every novel and
revolutionary thought. Necessarily the elder generation, to whom all
forms of energy were imponderable fluids, must pass away before the
new conception could claim the field. Even the word energy, though
Young had introduced it in 1807, did not come into general use till
some time after the middle of the century. To the generality of philosophers
(the word physicist was even less in favor at this time)\ the various
forms of energy were still subtile fluids, and never was idea relinquished
with greater unwillingness than this. The experiments of Young and
Fresnel had convinced a large number of philosophers that light is
a vibration and not a substance; but so great an authority as Biot
clung to the old emission idea to the end of his life, in 1862, and
held a following.

Meantime, however, the company of brilliant young men who had just
served their apprenticeship when the doctrine of conservation came
upon the scene had grown into authoritative positions, and were battling
actively for the new ideas. Confirmatory evidence that energy is a
molecular motion and not an {}``imponderable''\ form of matter
accumulated day by day. The experiments of two Frenchmen, Hippolyte
L. Fizeau and Leon Foucault, served finally to convince the last lingering
sceptics that light is an undulation; and by implication brought heat
into the same category, since James David Forbes, the Scotch physicist,
had shown in 1837 that radiant heat conforms to the same laws of polarization
and double refraction that govern light. But, for that matter, the
experiments that had established the mechanical equivalent of heat
hardly left room for doubt as to the immateriality of this {}``imponderable.''
Doubters had indeed, expressed scepticism as to the validity of Joule's
experiments, but the further researches, experimental and mathematical,
of such workers as Thomson (Lord Kelvin), Rankine, and Tyndall in
Great Britain, of Helmholtz and Clausius in Germany, and of Regnault
in France, dealing with various manifestations of heat, placed the
evidence beyond the reach of criticism.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics{3hsci10-WilliamThomson-LordKelvin}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small William Thomson (Lord Kelvin)}\end{center}
\end{figure}
Out of these studies, just at the middle of the century, to which
the experiments of Mayer and Joule had led, grew the new science of
thermodynamics. Out of them also grew in the mind of one of the investigators
a new generalization, only second in importance to the doctrine of
conservation itself. Professor William Thomson (Lord Kelvin)\ in
his studies in thermodynamics was early impressed with the fact that
whereas all the molar motion developed through labor or gravity could
be converted into heat, the process is not fully reversible. Heat
can, indeed, be converted into molar motion or work, but in the process
a certain amount of the heat is radiated into space and lost. The
same thing happens whenever any other form of energy is converted
into molar motion. Indeed, every transmutation of energy, of whatever
character, seems complicated by a tendency to develop heat, part of
which is lost. This observation led Professor Thomson to his doctrine
of the dissipation of energy, which he formulated before the Royal
Society of Edinburgh in 1852, and published also in the \emph{Philosophical
Magazine} the same year, the title borne being, {}``On a Universal
Tendency in Nature to the Dissipation of Mechanical Energy.''

From the principle here expressed Professor Thomson drew the startling
conclusion that, {}``since any restoration of this mechanical energy
without more than an equivalent dissipation is impossible,''\ the
universe, as known to us, must be in the condition of a machine gradually
running down; and in particular that the world we live on has been
within a finite time unfit for human habitation, and must again become
so within a finite future. This thought seems such a commonplace to-day
that it is difficult to realize how startling it appeared half a century
ago. A generation trained, as ours has been, in the doctrines of the
conservation and dissipation of energy as the very alphabet of physical
science can but ill appreciate the mental attitude of a generation
which for the most part had not even thought it problematical whether
the sun could continue to give out heat and light forever. But those
advance thinkers who had grasped the import of the doctrine of conservation
could at once appreciate the force of Thomson's doctrine of dissipation,
and realize the complementary character of the two conceptions.

Here and there a thinker like Rankine did, indeed, attempt to fancy
conditions under which the energy lost through dissipation might be
restored to availability, but no such effort has met with success,
and in time Professor Thomson's generalization and his conclusions
as to the consequences of the law involved came to be universally
accepted.

The introduction of the new views regarding the nature of energy followed,
as I have said, the course of every other growth of new ideas. Young
and imaginative men could accept the new point of view; older philosophers,
their minds channelled by preconceptions, could not get into the new
groove. So strikingly true is this in the particular case now before
us that it is worth while to note the ages at the time of the revolutionary
experiments of the men whose work has been mentioned as entering into
the scheme of evolution of the idea that energy is merely a manifestation
of matter in motion. Such a list will tell the story better than a
volume of commentary.

Observe, then, that Davy made his epochal experiment of melting ice
by friction when he was a youth of twenty. Young was no older when
he made his first communication to the Royal Society, and was in his
twenty-seventh year when he first actively espoused the undulatory
theory. Fresnel was twenty-six when he made his first important discoveries
in the same field; and Arago, who at once became his champion, was
then but two years his senior, though for a decade he had been so
famous that one involuntarily thinks of him as belonging to an elder
generation.

Forbes was under thirty when he discovered the polarization of heat,
which pointed the way to Mohr, then thirty-one, to the mechanical
equivalent. Joule was twenty-two in 1840, when his great work was
begun; and Mayer, whose discoveries date from the same year, was then
twenty-six, which was also the age of Helmholtz when he published
his independent discovery of the same law. William Thomson was a youth
just past his majority when he came to the aid of Joule before the
British Society, and but seven years older when he formulated his
own doctrine of the dissipation of energy. And Clausius and Rankine,
who are usually mentioned with Thomson as the great developers of
thermo-dynamics, were both far advanced with their novel studies before
they were thirty. With such a list in mind, we may well agree with
the father of inductive science that {}``the man who is young in
years may be old in hours.''

Yet we must not forget that the shield has a reverse side. For was
not the greatest of observing astronomers, Herschel, past thirty-five
before he ever saw a telescope, and past fifty before he discovered
the heat rays of the spectrum? And had not Faraday reached middle
life before he turned his attention especially to electricity? Clearly,
then, to make this phrase complete, Bacon should have added that {}``the
man who is old in years may be young in imagination.'' Here, however,
even more appropriate than in the other case---more's the pity---would
have been the application of his qualifying clause: {}``but that
happeneth rarely.''


\section*{\raggedright THE FINAL UNIFICATION}

\addcontentsline{toc}{section}{THE FINAL UNIFICATION}

There are only a few great generalizations as yet thought out in any
single field of science. Naturally, then, after a great generalization
has found definitive expression, there is a period of lull before
another forward move. In the case of the doctrines of energy, the
lull has lasted half a century. Throughout this period, it is true,
a multitude of workers have been delving in the field, and to the
casual observer it might seem as if their activity had been boundless,
while the practical applications of their ideas---as exemplified,
for example, in the telephone, phonograph, electric light, and so
on---have been little less than revolutionary. Yet the most competent
of living authorities, Lord Kelvin, could assert in 1895 that in fifty
years he had learned nothing new regarding the nature of energy.

This, however, must not be interpreted as meaning that the world has
stood still during these two generations. It means rather that the
rank and file have been moving forward along the road the leaders
had already travelled. Only a few men in the world had the range of
thought regarding the new doctrine of energy that Lord Kelvin had
at the middle of the century. The few leaders then saw clearly enough
that if one form of energy is in reality merely an undulation or vibration
among the particles of {}``ponderable''\ matter or of ether, all
other manifestations of energy must be of the same nature. But the
rank and file were not even within sight of this truth for a long
time after they had partly grasped the meaning of the doctrine of
conservation. When, late in the fifties, that marvellous young Scotchman,
James Clerk-Maxwell, formulating in other words an idea of Faraday's,
expressed his belief that electricity and magnetism are but manifestations
of various conditions of stress and motion in the ethereal medium
(electricity a displacement of strain, magnetism a whirl in the ether),
the idea met with no immediate popularity. And even less cordial was
the reception given the same thinker's theory, put forward in 1863,
that the ethereal undulations producing the phenomenon we call light
differ in no respect except in their wave-length from the pulsations
of electro-magnetism.

At about the same time Helmholtz formulated a somewhat similar electro-magnetic
theory of light; but even the weight of this combined authority could
not give the doctrine vogue until very recently, when the experiments
of Heinrich Hertz, the pupil of Helmholtz, have shown that a condition
of electrical strain may be developed into a wave system by recurrent
interruptions of the electric state in the generator, and that such
waves travel through the ether with the rapidity of light. Since then
the electro-magnetic theory of light has been enthusiastically referred
to as the greatest generalization of the century; but the sober thinker
must see that it is really only what Hertz himself called it---one
pier beneath the great arch of conservation. It is an interesting
detail of the architecture, but the part cannot equal the size of
the whole.

More than that, this particular pier is as yet by no means a very
firm one. It has, indeed, been demonstrated that waves of electro-magnetism
pass through space with the speed of light, but as yet no one has
developed electric waves even remotely approximating the shortness
of the visual rays. The most that can positively be asserted, therefore,
is that all the known forms of radiant energy-heat, light, electro-magnetism---travel
through space at the same rate of speed, and consist of traverse vibrations---{}``lateral
quivers,'' as Fresnel said of light---known to differ in length,
and not positively known to differ otherwise. It has, indeed, been
suggested that the newest form of radiant energy, the famous X-ray
of Professor Roentgen's discovery, is a longitudinal vibration, but
this is a mere surmise. Be that as it may, there is no one now to
question that all forms of radiant energy, whatever their exact affinities,
consist essentially of undulatory motions of one uniform medium.

A full century of experiment, calculation, and controversy has thus
sufficed to correlate the {}``imponderable fluids''\ of our forebears,
and reduce them all to manifestations of motion among particles of
matter. At first glimpse that seems an enormous change of view. And
yet, when closely considered, that change in thought is not so radical
as the change in phrase might seem to imply. For the nineteenth-century
physicist, in displacing the {}``imponderable fluids''\ of many
kinds---one each for light, heat, electricity, magnetism---has been
obliged to substitute for them one all-pervading fluid, whose various
quivers, waves, ripples, whirls or strains produce the manifestations
which in popular parlance are termed forms of force. This all-pervading
fluid the physicist terms the ether, and he thinks of it as having
no weight. In effect, then, the physicist has dispossessed the many
imponderables in favor of a single imponderable---though the word
imponderable has been banished from his vocabulary. In this view the
ether---which, considered as a recognized scientific verity, is essentially
a nineteenth-century discovery---is about the most interesting thing
in the universe. Something more as to its properties, real or assumed,
we shall have occasion to examine as we turn to the obverse side of
physics, which demands our attention in the next chapter.


\chapter*{\raggedright IX. THE ETHER AND PONDERABLE MATTER}

\addcontentsline{toc}{chapter}{IX. THE ETHER AND PONDERABLE MATTER}

\markboth{A HISTORY OF SCIENCE, BOOK III}{IX. ETHER AND MATTER}

\begin{quote}
{}``Whatever difficulties we may have in forming a consistent idea
of the constitution of the ether, there can be no doubt that the interplanetary
and interstellar spaces are not empty, but are occupied by a material
substance or body which is certainly the largest and probably the
most uniform body of which we have any knowledge.''
\end{quote}
{}

Such was the verdict pronounced some thirty years ago by James Clerk-Maxwell,
one of the very greatest of nineteenth-century physicists, regarding
the existence of an all-pervading plenum in the universe, in which
every particle of tangible matter is immersed. And this verdict may
be said to express the attitude of the entire philosophical world
of our day. Without exception, the authoritative physicists of our
time accept this plenum as a verity, and reason about it with something
of the same confidence they manifest in speaking of {}``ponderable''\ matter
or of energy. It is true there are those among them who are disposed
to deny that this all-pervading plenum merits the name of matter.
But that it is a something, and a vastly important something at that,
all are agreed. Without it, they allege, we should know nothing of
light, of radiant heat, of electricity or magnetism; without it there
would probably be no such thing as gravitation; nay, they even hint
that without this strange something, ether, there would be no such
thing as matter in the universe. If these contentions of the modern
physicist are justified, then this intangible ether is incomparably
the most important as well as the {}``largest and most uniform substance
or body''\ in the universe. Its discovery may well be looked upon
as one of the most important feats of the nineteenth century.

For a discovery of that century it surely is, in the sense that all
the known evidences of its existence were gathered in that epoch.
True dreamers of all ages have, for metaphysical reasons, imagined
the existence of intangible fluids in space---they had, indeed, peopled
space several times over with different kinds of ethers, as Maxwell
remarks---but such vague dreamings no more constituted the discovery
of the modern ether than the dream of some pre-Columbian visionary
that land might lie beyond the unknown waters constituted the discovery
of America. In justice it must be admitted that Huyghens, the seventeenth-century
originator of the undulatory theory of light, caught a glimpse of
the true ether; but his contemporaries and some eight generations
of his successors were utterly deaf to his claims; so he bears practically
the same relation to the nineteenth-century discoverers of ether that
the Norseman bears to Columbus.

The true Columbus of the ether was Thomas Young. His discovery was
consummated in the early days of the nineteenth century, when he brought
forward the first, conclusive proofs of the undulatory theory of light.
To say that light consists of undulations is to postulate something
that undulates; and this something could not be air, for air exists
only in infinitesimal quantity, if at all, in the interstellar spaces,
through which light freely penetrates. But if not air, what then?
Why, clearly, something more intangible than air; something supersensible,
evading all direct efforts to detect it, yet existing everywhere in
seemingly vacant space, and also interpenetrating the substance of
all transparent liquids and solids, if not, indeed, of all tangible
substances. This intangible something Young rechristened the Luminiferous
Ether.

In the early days of his discovery Young thought of the undulations
which produce light and radiant heat as being longitudinal---a forward
and backward pulsation, corresponding to the pulsations of sound---and
as such pulsations can be transmitted by a fluid medium with the properties
of ordinary fluids, he was justified in thinking of the ether as being
like a fluid in its properties, except for its extreme intangibility.
But about 1818 the experiments of Fresnel and Arago with polarization
of light made it seem very doubtful whether the theory of longitudinal
vibrations is sufficient, and it was suggested by Young, and independently
conceived and demonstrated by Fresnel, that the luminiferous undulations
are not longitudinal, but transverse; and all the more recent experiments
have tended to confirm this view. But it happens that ordinary fluids---gases
and liquids---cannot transmit lateral vibrations; only rigid bodies
are capable of such a vibration. So it became necessary to assume
that the luminiferous ether is a body possessing elastic rigidity---a
familiar property of tangible solids, but one quite unknown among
fluids.

The idea of transverse vibrations carried with it another puzzle.
Why does not the ether, when set aquiver with the vibration which
gives us the sensation we call light, have produced in its substance
subordinate quivers, setting out at right angles from the path of
the original quiver? Such perpendicular vibrations seem not to exist,
else we might see around a corner; how explain their absence? The
physicist could think of but one way: they must assume that the ether
is incompressible. It must fill all space---at any rate, all space
with which human knowledge deals---perfectly full.

These properties of the ether, incompressibility and elastic rigidity,
are quite conceivable by themselves; but difficulties of thought appear
when we reflect upon another quality which the ether clearly must
possess---namely, frictionlessness. By hypothesis this rigid, incompressible
body pervades all space, imbedding every particle of tangible matter;
yet it seems not to retard the movements of this matter in the slightest
degree. This is undoubtedly the most difficult to comprehend of the
alleged properties of the ether. The physicist explains it as due
to the perfect elasticity of the ether, in virtue of which it closes
in behind a moving particle with a push exactly counterbalancing the
stress required to penetrate it in front.

To a person unaccustomed to think of seemingly solid matter as really
composed of particles relatively wide apart, it is hard to understand
the claim that ether penetrates the substance of solids---of glass,
for example---and, to use Young's expression, which we have previously
quoted, moves among them as freely as the wind moves through a grove
of trees. This thought, however, presents few difficulties to the
mind accustomed to philosophical speculation. But the question early
arose in the mind of Fresnel whether the ether is not considerably
affected by contact with the particles of solids. Some of his experiments
led him to believe that a portion of the ether which penetrates among
the molecules of tangible matter is held captive, so to speak, and
made to move along with these particles. He spoke of such portions
of the ether as {}``bound''\ ether, in contradistinction to the
great mass of {}``free''\ ether. Half a century after Fresnel's
death, when the ether hypothesis had become an accepted tenet of science,
experiments were undertaken by Fizeau in France, and by Clerk-Maxwell
in England, to ascertain whether any portion of ether is really thus
bound to particles of matter; but the results of the experiments were
negative, and the question is still undetermined.

While the undulatory theory of light was still fighting its way, another
kind of evidence favoring the existence of an ether was put forward
by Michael Faraday, who, in the course of his experiments in electrical
and magnetic induction, was led more and more to perceive definite
lines or channels of force in the medium subject to electro-magnetic
influence. Faraday's mind, like that of Newton and many other philosophers,
rejected the idea of action at a distance, and he felt convinced that
the phenomena of magnetism and of electric induction told strongly
for the existence of an invisible plenum everywhere in space, which
might very probably be the same plenum that carries the undulations
of light and radiant heat.

Then, about the middle of the century, came that final revolution
of thought regarding the nature of energy which we have already outlined
in the preceding chapter, and with that the case for ether was considered
to be fully established. The idea that energy is merely a {}``mode
of motion''\ (to adopt Tyndall's familiar phrase), combined with
the universal rejection of the notion of action at a distance, made
the acceptance of a plenum throughout space a necessity of thought---so,
at any rate, it has seemed to most physicists of recent decades. The
proof that all known forms of radiant energy move through space at
the same rate of speed is regarded as practically a demonstration
that but one plenum---one ether---is concerned in their transmission.
It has, indeed, been tentatively suggested, by Professor J.\ Oliver
Lodge, that there may be two ethers, representing the two opposite
kinds of electricity, but even the author of this hypothesis would
hardly claim for it a high degree of probability.

The most recent speculations regarding the properties of the ether
have departed but little from the early ideas of Young and Fresnel.
It is assumed on all sides that the ether is a continuous, incompressible
body, possessing rigidity and elasticity. Lord Kelvin has even calculated
the probable density of this ether, and its coefficient of rigidity.
As might be supposed, it is all but infinitely tenuous as compared
with any tangible solid, and its rigidity is but infinitesimal as
compared with that of steel. In a word, it combines properties of
tangible matter in a way not known in any tangible substance. Therefore
we cannot possibly conceive its true condition correctly. The nearest
approximation, according to Lord Kelvin, is furnished by a mould of
transparent jelly. It is a crude, inaccurate analogy, of course, the
density and resistance of jelly in particular being utterly different
from those of the ether; but the quivers that run through the jelly
when it is shaken, and the elastic tension under which it is placed
when its mass is twisted about, furnish some analogy to the quivers
and strains in the ether, which are held to constitute radiant energy,
magnetism, and electricity.

The great physicists of the day being at one regarding the existence
of this all-pervading ether, it would be a manifest presumption for
any one standing without the pale to challenge so firmly rooted a
belief. And, indeed, in any event, there seems little ground on which
to base such a challenge. Yet it may not be altogether amiss to reflect
that the physicist of to-day is no more certain of his ether than
was his predecessor of the eighteenth century of the existence of
certain alleged substances which he called phlogiston, caloric, corpuscles
of light, and magnetic and electric fluids. It would be but the repetition
of history should it chance that before the close of another century
the ether should have taken its place along with these discarded creations
of the scientific imagination of earlier generations. The philosopher
of to-day feels very sure that an ether exists; but when he says there
is {}``no doubt''\ of its existence he speaks incautiously, and
steps beyond the bounds of demonstration. He does not \textit{know}
that action cannot take place at a distance; he does not \textit{know}
that empty space itself may not perform the functions which he ascribes
to his space-filling ether.

Meantime, however, the ether, be it substance or be it only dream-stuff,
is serving an admirable purpose in furnishing a fulcrum for modern
physics. Not alone to the student of energy has it proved invaluable,
but to the student of matter itself as well. Out of its hypothetical
mistiness has been reared the most tenable theory of the constitution
of ponderable matter which has yet been suggested---or, at any rate,
the one that will stand as the definitive nineteenth-century guess
at this {}``riddle of the ages.'' I mean, of course, the vortex
theory of atoms---that profound and fascinating doctrine which suggests
that matter, in all its multiform phases, is neither more nor less
than ether in motion.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{3hsci10-Wil3S251}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Hermann Ludwig Ferdinand Helmholtz}\end{center}{\small \par}

\noindent \begin{center}\emph{\footnotesize (From a photograph by
Loescher \& Petsch, Berlin.)}\end{center}
\end{figure}
The author of this wonderful conception is Lord Kelvin. The idea was
born in his mind of a happy union of mathematical calculations with
concrete experiments. The mathematical calculations were largely the
work of Hermann von Helmholtz, who, about the year 1858, had undertaken
to solve some unique problems in vortex motions. Helmholtz found that
a vortex whirl, once established in a frictionless medium, must go
on, theoretically, unchanged forever. In a limited medium such a whirl
may be V-shaped, with its ends at the surface of the medium. We may
imitate such a vortex by drawing the bowl of a spoon quickly through
a cup of water. But in a limitless medium the vortex whirl must always
be a closed ring, which may take the simple form of a hoop or circle,
or which may be indefinitely contorted, looped, or, so to speak, knotted.
Whether simple or contorted, this endless chain of whirling matter
(the particles revolving about the axis of the loop as the particles
of a string revolve when the string is rolled between the fingers)
must, in a frictionless medium, retain its form and whirl on with
undiminished speed forever.

While these theoretical calculations of Helmholtz were fresh in his
mind, Lord Kelvin (then Sir William Thomson)\ was shown by Professor
P.\ G.\ Tait, of Edinburgh, an apparatus constructed for the purpose
of creating vortex rings in air. The apparatus, which any one may
duplicate, consisted simply of a box with a hole bored in one side,
and a piece of canvas stretched across the opposite side in lieu of
boards. Fumes of chloride of ammonia are generated within the box,
merely to render the air visible. By tapping with the hand on the
canvas side of the box, vortex rings of the clouded air are driven
out, precisely similar in appearance to those smoke-rings which some
expert tobacco-smokers can produce by tapping on their cheeks, or
to those larger ones which we sometimes see blown out from the funnel
of a locomotive.

The advantage of Professor Tait's apparatus is its manageableness
and the certainty with which the desired result can be produced. Before
Lord Kelvin's interested observation it threw out rings of various
sizes, which moved straight across the room at varying rates of speed,
according to the initial impulse, and which behaved very strangely
when coming in contact with one another. If, for example, a rapidly
moving ring overtook another moving in the same path, the one in advance
seemed to pause, and to spread out its periphery like an elastic band,
while the pursuer seemed to contract, till it actually slid through
the orifice of the other, after which each ring resumed its original
size, and continued its course as if nothing had happened. When, on
the other hand, two rings moving in slightly different directions
came near each other, they seemed to have an attraction for each other;
yet if they impinged, they bounded away, quivering like elastic solids.
If an effort were made to grasp or to cut one of these rings, the
subtle thing shrank from the contact, and slipped away as if it were
alive.

And all the while the body which thus conducted itself consisted simply
of a whirl in the air, made visible, but not otherwise influenced,
by smoky fumes. Presently the friction of the surrounding air wore
the ring away, and it faded into the general atmosphere---often, however,
not until it had persisted for many seconds, and passed clear across
a large room. Clearly, if there were no friction, the ring's inertia
must make it a permanent structure. Only the frictionless medium was
lacking to fulfil all the conditions of Helmholtz's indestructible
vortices. And at once Lord Kelvin bethought him of the frictionless
medium which physicists had now begun to accept---the all-pervading
ether. What if vortex rings were started in this ether, must they
not have the properties which the vortex rings in air had exhibited---inertia,
attraction, elasticity? And are not these the properties of ordinary
tangible matter? Is it not probable, then, that what we call matter
consists merely of aggregations of infinitesimal vortex rings in the
ether?

Thus the vortex theory of atoms took form in Lord Kelvin's mind, and
its expression gave the world what many philosophers of our time regard
as the most plausible conception of the constitution of matter hitherto
formulated. It is only a theory, to be sure; its author would be the
last person to claim finality for it. {}``It is only a dream,''\ Lord
Kelvin said to me, in referring to it not long ago. But it has a basis
in mathematical calculation and in analogical experiment such as no
other theory of matter can lay claim to, and it has a unifying or
monistic tendency that makes it, for the philosophical mind, little
less than fascinating. True or false, it is the definitive theory
of matter of the twentieth century.

Quite aside from the question of the exact constitution of the ultimate
particles of matter, questions as to the distribution of such particles,
their mutual relations, properties, and actions, came in for a full
share of attention during the nineteenth century, though the foundations
for the modern speculations were furnished in a previous epoch. The
most popular eighteenth-century speculation as to the ultimate constitution
of matter was that of the learned Italian priest, Roger Joseph Boscovich,
published in 1758, in his \emph{Theoria Philosophi}\ae{} \emph{Naturalis}.
{}``In this theory,''\ according to an early commentator, {}``the
whole mass of which the bodies of the universe are composed is supposed
to consist of an exceedingly great yet finite number of simple, indivisible,
inextended atoms. These atoms are endued by the Creator with \textit{repulsive}
and \textit{attractive} forces, which vary according to the distance.
At very small distances the particles of matter repel each other;
and this repulsive force increases beyond all limits as the distances
are diminished, and will consequently forever prevent actual contact.
When the particles of matter are removed to sensible distances, the
repulsive is exchanged for an attractive force, which decreases in
inverse ratio with the squares of the distances, and extends beyond
the spheres of the most remote comets.''

This conception of the atom as a mere centre of force was hardly such
as could satisfy any mind other than the metaphysical. No one made
a conspicuous attempt to improve upon the idea, however, till just
at the close of the century, when Humphry Davy was led, in the course
of his studies of heat, to speculate as to the changes that occur
in the intimate substance of matter under altered conditions of temperature.
Davy, as we have seen, regarded heat as a manifestation of motion
among the particles of matter. As all bodies with which we come in
contact have some temperature, Davy inferred that the intimate particles
of every substance must be perpetually in a state of vibration. Such
vibrations, he believed, produced the {}``repulsive force''\ which
(in common with Boscovich)\ he admitted as holding the particles
of matter at a distance from one another. To heat a substance means
merely to increase the rate of vibration of its particles; thus also,
plainly, increasing the repulsive forces and expanding the bulk of
the mass as a whole. If the degree of heat applied be sufficient,
the repulsive force may become strong enough quite to overcome the
attractive force, and the particles will separate and tend to fly
away from one another, the solid then becoming a gas.

Not much attention was paid to these very suggestive ideas of Davy,
because they were founded on the idea that heat is merely a motion,
which the scientific world then repudiated; but half a century later,
when the new theories of energy had made their way, there came a revival
of practically the same ideas of the particles of matter (molecules
they were now called) which Davy had advocated. Then it was that Clausius
in Germany and Clerk-Maxwell in England took up the investigation
of what came to be known as the kinetic theory of gases---the now
familiar conception that all the phenomena of gases are due to the
helter-skelter flight of the showers of widely separated molecules
of which they are composed. The specific idea that the pressure or
{}``spring''\ of gases is due to such molecular impacts was due
to Daniel Bournelli, who advanced it early in the eighteenth century.
The idea, then little noticed, had been revived about a century later
by William Herapath, and again with some success by J.\ J.\ Waterston,
of Bombay, about 1846; but it gained no distinct footing until taken
in hand by Clausius in 1857 and by Clerk-Maxwell in 1859.

The considerations that led Clerk-Maxwell to take up the computations
may be stated in his own words, as formulated in a paper {}``On the
Motions and Collisions of Perfectly Elastic Spheres.''

\begin{quotation}
{}``So many of the properties of matter, especially when in the gaseous
form,''\ he says, {}``can be deduced from the hypothesis that their
minute parts are in rapid motion, the velocity increasing with the
temperature, that the precise nature of this motion becomes a subject
of rational curiosity. Daniel Bournelli, Herapath, Joule, Kronig,
Clausius, \textit{etc}., have shown that the relations between pressure,
temperature, and density in a perfect gas can be explained by supposing
the particles to move with uniform velocities in straight lines, striking
against the sides of the containing vessel and thus producing pressure.
It is not necessary to suppose each particle to travel to any great
distance in the same straight line; for the effect in producing pressure
will be the same if the particles strike against each other; so that
the straight line described may be very short. M.\ Clausius has determined
the mean length of path in terms of the average of the particles,
and the distance between the centres of two particles when the collision
takes place. We have at present no means of ascertaining either of
these distances; but certain phenomena, such as the internal friction
of gases, the conduction of heat through a gas, and the diffusion
of one gas through another, seem to indicate the possibility of determining
accurately the mean length of path which a particle describes between
two successive collisions. In order to lay the foundation of such
investigations on strict mechanical principles, I shall demonstrate
the laws of motion of an indefinite number of small, hard, and perfectly
elastic spheres acting on one another only during impact. If the properties
of such a system of bodies are found to correspond to those of gases,
an important physical analogy will be established, which may lead
to more accurate knowledge of the properties of matter. If experiments
on gases are inconsistent with the hypothesis of these propositions,
then our theory, though consistent with itself, is proved to be incapable
of explaining the phenomena of gases. In either case it is necessary
to follow out these consequences of the hypothesis.

{}``Instead of saying that the particles are hard, spherical, and
elastic, we may, if we please, say the particles are centres of force,
of which the action is insensible except at a certain very small distance,
when it suddenly appears as a repulsive force of very great intensity.
It is evident that either assumption will lead to the same results.
For the sake of avoiding the repetition of a long phrase about these
repulsive bodies, I shall proceed upon the assumption of perfectly
elastic spherical bodies. If we suppose those aggregate molecules
which move together to have a bounding surface which is not spherical,
then the rotatory motion of the system will close up a certain proportion
of the whole \emph{vis viva}, as has been shown by Clausius, and in
this way we may account for the value of the specific heat being greater
than on the more simple hypothesis.''%
\footnote{James Clerk-Maxwell, \emph{Philosophical Magazine} for January and
July, 1860.%
}
\end{quotation}
{}

The elaborate investigations of Clerk-Maxwell served not merely to
substantiate the doctrine, but threw a flood of light upon the entire
subject of molecular dynamics. Soon the physicists came to feel as
certain of the existence of these showers of flying molecules making
up a gas as if they could actually see and watch their individual
actions. Through study of the viscosity of gases---that is to say,
of the degree of frictional opposition they show to an object moving
through them or to another current of gas---an idea was gained, with
the aid of mathematics, of the rate of speed at which the particles
of the gas are moving, and the number of collisions which each particle
must experience in a given time, and of the length of the average
free path traversed by the molecule between collisions, These measurements
were confirmed by study of the rate of diffusion at which different
gases mix together, and also by the rate of diffusion of heat through
a gas, both these phenomena being chiefly due to the helter-skelter
flight of the molecules.

It is sufficiently astonishing to be told that such measurements as
these have been made at all, but the astonishment grows when one hears
the results. It appears from Clerk-Maxwell's calculations that the
mean free path, or distance traversed by the molecules between collisions
in ordinary air, is about one-half-millionth of an inch; while the
speed of the molecules is such that each one experiences about eight
billions of collisions per second! It would be hard, perhaps, to cite
an illustration showing the refinements of modern physics better than
this; unless, indeed, one other result that followed directly from
these calculations be considered such---the feat, namely, of measuring
the size of the molecules themselves. Clausius was the first to point
out how this might be done from a knowledge of the length of free
path; and the calculations were made by Loschmidt in Germany and by
Lord Kelvin in England, independently.

The work is purely mathematical, of course, but the results are regarded
as unassailable; indeed, Lord Kelvin speaks of them as being absolutely
demonstrative within certain limits of accuracy. This does not mean,
however, that they show the exact dimensions of the molecule; it means
an estimate of the limits of size within which the actual size of
the molecule may lie. These limits, Lord Kelvin estimates, are about
the one-ten-millionth of a centimetre for the maximum, and the one-one-hundred-millionth
of a centimetre for the minimum. Such figures convey no particular
meaning to our blunt senses, but Lord Kelvin has given a tangible
illustration that aids the imagination to at least a vague comprehension
of the unthinkable smallness of the molecule. He estimates that if
a ball, say of water or glass, about {}``as large as a football,
were to be magnified up to the size of the earth, each constituent
molecule being magnified in the same proportion, the magnified structure
would be more coarse-grained than a heap of shot, but probably less
coarse-grained than a heap of footballs.''

Several other methods have been employed to estimate the size of molecules.
One of these is based upon the phenomena of contact electricity; another
upon the wave-theory of light; and another upon capillary attraction,
as shown in the tense film of a soap-bubble! No one of these methods
gives results more definite than that due to the kinetic theory of
gases, just outlined; but the important thing is that the results
obtained by these different methods (all of them due to Lord Kelvin)\ agree
with one another in fixing the dimensions of the molecule at somewhere
about the limits already mentioned. We may feel very sure indeed,
therefore, that the molecules of matter are not the unextended, formless
points which Boscovich and his followers of the eighteenth century
thought them. But all this, it must be borne in mind, refers to the
molecule, not to the ultimate particle of matter, about which we shall
have more to say in another connection. Curiously enough, we shall
find that the latest theories as to the final term of the series are
not so very far afield from the dreamings of the eighteenth-century
philosophers; the electron of J.\ J.\ Thompson shows many points
of resemblance to the formless centre of Boscovich.

Whatever the exact form of the molecule, its outline is subject to
incessant variation; for nothing in molecular science is regarded
as more firmly established than that the molecule, under all ordinary
circumstances, is in a state of intense but variable vibration. The
entire energy of a molecule of gas, for example, is not measured by
its momentum, but by this plus its energy of vibration and rotation,
due to the collisions already referred to. Clausius has even estimated
the relative importance of these two quantities, showing that the
translational motion of a molecule of gas accounts for only three-fifths
of its kinetic energy. The total energy of the molecule (which we
call {}``heat'') includes also another factor---namely, potential
energy, or energy of position, due to the work that has been done
on expanding, in overcoming external pressure, and internal attraction
between the molecules themselves. This potential energy (which will
be recovered when the gas contracts)\ is the {}``latent heat''\ of
Black, which so long puzzled the philosophers. It is latent in the
same sense that the energy of a ball thrown into the air is latent
at the moment when the ball poises at its greatest height before beginning
to fall.

It thus appears that a variety of motions, real and potential, enter
into the production of the condition we term heat. It is, however,
chiefly the translational motion which is measurable as temperature;
and this, too, which most obviously determines the physical state
of the substance that the molecules collectively compose---whether,
that is to say, it shall appear to our blunt perceptions as a gas,
a liquid, or a solid. In the gaseous state, as we have seen, the translational
motion of the molecules is relatively enormous, the molecules being
widely separated. It does not follow, as we formerly supposed, that
this is evidence of a repulsive power acting between the molecules.
The physicists of to-day, headed by Lord Kelvin, decline to recognize
any such power. They hold that the molecules of a gas fly in straight
lines by virtue of their inertia, quite independently of one another,
except at times of collision, from which they rebound by virtue of
their elasticity; or on an approach to collision, in which latter
case, coming within the range of mutual attraction, two molecules
may circle about each other, as a comet circles about the sun, then
rush apart again, as the comet rushes from the sun.

It is obvious that the length of the mean free path of the molecules
of a gas may be increased indefinitely by decreasing the number of
the molecules themselves in a circumscribed space. It has been shown
by Professors Tait and Dewar that a vacuum may be produced artificially
of such a degree of rarefaction that the mean free path of the remaining
molecules is measurable in inches. The calculation is based on experiments
made with the radiometer of Professor Crookes, an instrument which
in itself is held to demonstrate the truth of the kinetic theory of
gases. Such an attenuated gas as this is considered by Professor Crookes
as constituting a fourth state of matter, which he terms ultra-gaseous.

If, on the other hand, a gas is subjected to pressure, its molecules
are crowded closer together, and the length of their mean free path
is thus lessened. Ultimately, the pressure being sufficient, the molecules
are practically in continuous contact. Meantime the enormously increased
number of collisions has set the molecules more and more actively
vibrating, and the temperature of the gas has increased, as, indeed,
necessarily results in accordance with the law of the conservation
of energy. No amount of pressure, therefore, can suffice by itself
to reduce the gas to a liquid state. It is believed that even at the
centre of the sun, where the pressure is almost inconceivably great,
all matter is to be regarded as really gaseous, though the molecules
must be so packed together that the consistency is probably more like
that of a solid.

If, however, coincidently with the application of pressure, opportunity
be given for the excess of heat to be dissipated to a colder surrounding
medium, the molecules, giving off their excess of energy, become relatively
quiescent, and at a certain stage the gas becomes a liquid. The exact
point at which this transformation occurs, however, differs enormously
for different substances. In the case of water, for example, it is
a temperature more than four hundred degrees above zero, centigrade;
while for atmospheric air it is one hundred and ninety-four degrees
centigrade below zero, or more than a hundred and fifty degrees below
the point at which mercury freezes.

Be it high or low, the temperature above which any substance is always
a gas, regardless of pressure, is called the critical temperature,
or absolute boiling-point, of that substance. It does not follow,
however, that below this point the substance is necessarily a liquid.
This is a matter that will be determined by external conditions of
pressure. Even far below the critical temperature the molecules have
an enormous degree of activity, and tend to fly asunder, maintaining
what appears to be a gaseous, but what technically is called a vaporous,
condition---the distinction being that pressure alone suffices to
reduce the vapor to the liquid state. Thus water may change from the
gaseous to the liquid state at four hundred degrees above zero, but
under conditions of ordinary atmospheric pressure it does not do so
until the temperature is lowered three hundred degrees further. Below
four hundred degrees, however, it is technically a vapor, not a gas;
but the sole difference, it will be understood, is in the degree of
molecular activity.

It thus appeared that the prevalence of water in a vaporous and liquid
rather than in a {}``permanently'' gaseous condition here on the
globe is a mere incident of telluric evolution. Equally incidental
is the fact that the air we breathe is {}``permanently''\ gaseous
and not liquid or solid, as it might be were the earth's surface temperature
to be lowered to a degree which, in the larger view, may be regarded
as trifling. Between the atmospheric temperature in tropical and in
arctic regions there is often a variation of more than one hundred
degrees; were the temperature reduced another hundred, the point would
be reached at which oxygen gas becomes a vapor, and under increased
pressure would be a liquid. Thirty-seven degrees more would bring
us to the critical temperature of nitrogen.

Nor is this a mere theoretical assumption; it is a determination of
experimental science, quite independent of theory. The physicist in
the laboratory has produced artificial conditions of temperature enabling
him to change the state of the most persistent gases. Some fifty years
since, when the kinetic theory was in its infancy, Faraday liquefied
carbonic-acid gas, among others, and the experiments thus inaugurated
have been extended by numerous more recent investigators, notably
by Cailletet in Switzerland, by Pictet in France, and by Dr.\ Thomas
Andrews and Professor James Dewar in England. In the course of these
experiments not only has air been liquefied, but hydrogen also, the
most subtle of gases; and it has been made more and more apparent
that gas and liquid are, as Andrews long ago asserted, {}``only distant
stages of a long series of continuous physical changes.'' Of course,
if the temperature be lowered still further, the liquid becomes a
solid; and this change also has been effected in the case of some
of the most {}``permanent''\ gases, including air.

The degree of cold---that is, of absence of heat---thus produced is
enormous, relatively to anything of which we have experience in nature
here at the earth now, yet the molecules of solidified air, for example,
are not absolutely quiescent. In other words, they still have a temperature,
though so very low. But it is clearly conceivable that a stage might
be reached at which the molecules became absolutely quiescent, as
regards either translational or vibratory motion. Such a heatless
condition has been approached, but as yet not quite attained, in laboratory
experiments. It is called the absolute zero of temperature, and is
estimated to be equivalent to two hundred and seventy-three degrees
Centigrade below the freezing-point of water, or ordinary zero.

A temperature (or absence of temperature)\ closely approximating
this is believed to obtain in the ethereal ocean of interplanetary
and interstellar space, which transmits, but is thought not to absorb,
radiant energy. We here on the earth's surface are protected from
exposure to this cold, which would deprive every organic thing of
life almost instantaneously, solely by the thin blanket of atmosphere
with which the globe is coated. It would seem as if this atmosphere,
exposed to such a temperature at its surface, must there be incessantly
liquefied, and thus fall back like rain to be dissolved into gas again
while it still is many miles above the earth's surface. This may be
the reason why its scurrying molecules have not long ago wandered
off into space and left the world without protection.

But whether or not such liquefaction of the air now occurs in our
outer atmosphere, there can be no question as to what must occur in
its entire depth were we permanently shut off from the heating influence
of the sun, as the astronomers threaten that we may be in a future
age. Each molecule, not alone of the atmosphere, but of the entire
earth's substance, is kept aquiver by the energy which it receives,
or has received, directly or indirectly, from the sun. Left to itself,
each molecule would wear out its energy and fritter it off into the
space about it, ultimately running completely down, as surely as any
human-made machine whose power is not from time to time restored.
If, then, it shall come to pass in some future age that the sun's
rays fail us, the temperature of the globe must gradually sink towards
the absolute zero. That is to say, the molecules of gas which now
fly about at such inconceivable speed must drop helpless to the earth;
liquids must in turn become solids; and solids themselves, their molecular
quivers utterly stilled, may perhaps take on properties the nature
of which we cannot surmise.

Yet even then, according to the current hypothesis, the heatless molecule
will still be a thing instinct with life. Its vortex whirl will still
go on, uninfluenced by the dying-out of those subordinate quivers
that produced the transitory effect which we call temperature. For
those transitory thrills, though determining the physical state of
matter as measured by our crude organs of sense, were no more than
non-essential incidents; but the vortex whirl is the essence of matter
itself. Some estimates as to the exact character of this intramolecular
motion, together with recent theories as to the actual structure of
the molecule, will claim our attention in a later volume. We shall
also have occasion in another connection to make fuller inquiry as
to the phenomena of low temperature.
\end{document}
