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\title{A History of Science,\\
{\large Volume II,}\\
{\large The Beginnings of Modern Science}}


\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
OmniPage Professional OCR software. The Project Gutenberg edition
({}``2hsci10'') was subsequently converted to \LaTeX{} by means
of \textbf{GutenMark} software (version Jan 5 2003), and modified
by Ron Burkey to clean up formatting problems. Numbered endnotes have
been converted to footnotes for stylistic consistency with other texts
presented at sandroid.org. Illustrations missing from the Project
Gutenberg edition were scanned by S. A. Cohen; one figure has been
redrawn. Report problems to info@sandroid.org.

\noindent \begin{center}Revision: A\\
Date: 02/22/03\end{center}

\vspace{\stretch{1}}

 \frontmatter


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{\small \tableofcontents}

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\noindent \begin{center}\noun{\small Sir Isaac Newton}\end{center}
\end{figure}


\mainmatter



\chapter*{\raggedright FOREWORD}

\addcontentsline{toc}{chapter}{FOREWORD}

\markboth{A HISTORY OF SCIENCE, VOLUME II}{FOREWORD}

The studies of the present book cover the progress of science from
the close of the Roman period in the fifth century A.D.\ to about
the middle of the eighteenth century. In tracing the course of events
through so long a period, a difficulty becomes prominent which everywhere
besets the historian in less degree---a difficulty due to the conflict
between the strictly chronological and the topical method of treatment.
We must hold as closely as possible to the actual sequence of events,
since, as already pointed out, one discovery leads on to another.
But, on the other hand, progressive steps are taken contemporaneously
in the various fields of science, and if we were to attempt to introduce
these in strict chronological order we should lose all sense of topical
continuity.

Our method has been to adopt a compromise, following the course of
a single science in each great epoch to a convenient stopping-point,
and then turning back to bring forward the story of another science.
Thus, for example, we tell the story of Copernicus and Galileo, bringing
the record of cosmical and mechanical progress down to about the middle
of the seventeenth century, before turning back to take up the physiological
progress of the fifteenth and sixteenth centuries. Once the latter
stream is entered, however, we follow it without interruption to the
time of Harvey and his contemporaries in the middle of the seventeenth
century, where we leave it to return to the field of mechanics as
exploited by the successors of Galileo, who were also the predecessors
and contemporaries of Newton.

In general, it will aid the reader to recall that, so far as possible,
we hold always to the same sequences of topical treatment of contemporary
events; as a rule we treat first the cosmical, then the physical,
then the biological sciences. The same order of treatment will be
held to in succeeding volumes.

Several of the very greatest of scientific generalizations are developed
in the period covered by the present book: for example, the Copernican
theory of the solar system, the true doctrine of planetary motions,
the laws of motion, the theory of the circulation of the blood, and
the Newtonian theory of gravitation. The labors of the investigators
of the early decades of the eighteenth century, terminating with Franklin's
discovery of the nature of lightning and with the Linn\ae{}an classification
of plants and animals, bring us to the close of our second great epoch;
or, to put it otherwise, to the threshold of the modern period.


\chapter*{\raggedright I.\ SCIENCE IN THE DARK AGE}

\addcontentsline{toc}{chapter}{I. SCIENCE IN THE DARK AGE}

\markboth{A HISTORY OF SCIENCE, VOLUME II}{I. SCIENCE IN THE DARK
AGE}

An obvious distinction between the classical and medi\ae{}val epochs
may be found in the fact that the former produced, whereas the latter
failed to produce, a few great thinkers in each generation who were
imbued with that scepticism which is the foundation of the investigating
spirit; who thought for themselves and supplied more or less rational
explanations of observed phenomena. Could we eliminate the work of
some score or so of classical observers and thinkers, the classical
epoch would seem as much a dark age as does the epoch that succeeded
it.

But immediately we are met with the question: Why do no great original
investigators appear during all these later centuries? We have already
offered a part explanation in the fact that the borders of civilization,
where racial mingling naturally took place, were peopled with semi-barbarians.
But we must not forget that in the centres of civilization all along
there were many men of powerful intellect. Indeed, it would violate
the principle of historical continuity to suppose that there was any
sudden change in the level of mentality of the Roman world at the
close of the classical period. We must assume, then, that the direction
in which the great minds turned was for some reason changed. Newton
is said to have alleged that he made his discoveries by {}``intending''\ his
mind in a certain direction continuously. It is probable that the
same explanation may be given of almost every great scientific discovery.
Anaxagoras could not have thought out the theory of the moon's phases;
Aristarchus could not have found out the true mechanism of the solar
system; Eratosthenes could not have developed his plan for measuring
the earth, had not each of these investigators {}``intended''\ his
mind persistently towards the problems in question.

Nor can we doubt that men lived in every generation of the dark age
who were capable of creative thought in the field of science, had
they chosen similarly to {}``intend''\ their minds in the right
direction. The difficulty was that they did not so choose. Their minds
had a quite different bent. They were under the spell of different
ideals; all their mental efforts were directed into different channels.
What these different channels were cannot be in doubt---they were
the channels of oriental ecclesiasticism. One all-significant fact
speaks volumes here. It is the fact that, as Professor Robinson%
\footnote{James Harvey Robinson, \emph{An Introduction to the History of Western
Europe}, New York, 1898, p.\ 330.%
} points out, from the time of Boethius (died 524 or 525 A.D.)\ to
that of Dante (1265-1321 A.D.)\ there was not a single writer of
renown in western Europe who was not a professional churchman. All
the learning of the time, then, centred in the priesthood. We know
that the same condition of things pertained in Egypt, when science
became static there. But, contrariwise, we have seen that in Greece
and early Rome the scientific workers were largely physicians or professional
teachers; there was scarcely a professional theologian among them.

Similarly, as we shall see in the Arabic world, where alone there
was progress in the medi\ae{}val epoch, the learned men were, for
the most part, physicians. Now the meaning of this must be self-evident.
The physician naturally {}``intends''\ his mind towards the practicalities.
His professional studies tend to make him an investigator of the operations
of nature. He is usually a sceptic, with a spontaneous interest in
practical science. But the theologian {}``intends''\ his mind away
from practicalities and towards mysticism. He is a professional believer
in the supernatural; he discounts the value of merely {}``natural''
phenomena. His whole attitude of mind is unscientific; the fundamental
tenets of his faith are based on alleged occurrences which inductive
science cannot admit---namely, miracles. And so the minds {}``intended''\ towards
the supernatural achieved only the hazy mysticism of medi\ae{}val
thought. Instead of investigating natural laws, they paid heed (as,
for example, Thomas Aquinas does in his \textit{Summa} \textit{Theologia})\ to
the {}``acts of angels,''\ the {}``speaking of angels,''\ the
{}``subordination of angels,''\ the {}``deeds of guardian angels,''\ and
the like. They disputed such important questions as, How many angels
can stand upon the point of a needle? They argued pro and con as to
whether Christ were coeval with God, or whether he had been merely
created {}``in the beginning,''\ perhaps ages before the creation
of the world. How could it be expected that science should flourish
when the greatest minds of the age could concern themselves with problems
such as these?

Despite our preconceptions or prejudices, there can be but one answer
to that question. Oriental superstition cast its blight upon the fair
field of science, whatever compensation it may or may not have brought
in other fields. But we must be on our guard lest we overestimate
or incorrectly estimate this influence. Posterity, in glancing backward,
is always prone to stamp any given age of the past with one idea,
and to desire to characterize it with a single phrase; whereas in
reality all ages are diversified, and any generalization regarding
an epoch is sure to do that epoch something less or something more
than justice. We may be sure, then, that the ideal of ecclesiasticism
is not solely responsible for the scientific stasis of the dark age.
Indeed, there was another influence of a totally different character
that is too patent to be overlooked---the influence, namely, of the
economic condition of western Europe during this period. As I have
elsewhere pointed out,%
\footnote{Henry Smith Williams, {}``A Prefatory Characterization of The History
of Italy,'' in \textit{\emph{vol}}.\ IX.\ of \emph{The Historians'\ History
of the World}, 25 \textit{\emph{vols}}., London and New York, 1904.%
} Italy, the centre of western civilization, was at this time impoverished,
and hence could not provide the monetary stimulus so essential to
artistic and scientific no less than to material progress. There were
no patrons of science and literature such as the Ptolemies of that
elder Alexandrian day. There were no great libraries; no colleges
to supply opportunities and afford stimuli to the rising generation.
Worst of all, it became increasingly difficult to secure books.

This phase of the subject is often overlooked. Yet a moment's consideration
will show its importance. How should we fare to-day if no new scientific
books were being produced, and if the records of former generations
were destroyed? That is what actually happened in Europe during the
Middle Ages. At an earlier day books were made and distributed much
more abundantly than is sometimes supposed. Bookmaking had, indeed,
been an important profession in Rome, the actual makers of books being
slaves who worked under the direction of a publisher. It was through
the efforts of these workers that the classical works in Greek and
Latin were multiplied and disseminated. Unfortunately the climate
of Europe does not conduce to the indefinite preservation of a book;
hence very few remnants of classical works have come down to us in
the original from a remote period. The rare exceptions are certain
papyrus fragments, found in Egypt, some of which are Greek manuscripts
dating from the third century B.C. Even from these sources the output
is meagre; and the only other repository of classical books is a single
room in the buried city of Herculaneum, which contained several hundred
manuscripts, mostly in a charred condition, a considerable number
of which, however, have been unrolled and found more or less legible.
This library in the buried city was chiefly made up of philosophical
works, some of which were quite unknown to the modern world until
discovered there.

But this find, interesting as it was from an arch\ae{}ological stand-point,
had no very important bearing on our knowledge of the literature of
antiquity. Our chief dependence for our knowledge of that literature
must still be placed in such copies of books as were made in the successive
generations. Comparatively few of the extant manuscripts are older
than the tenth century of our era. It requires but a momentary consideration
of the conditions under which ancient books were produced to realize
how slow and difficult the process was before the invention of printing.
The taste of the book-buying public demanded a clearly written text,
and in the Middle Ages it became customary to produce a richly ornamented
text as well. The script employed being the prototype of the modern
printed text, it will be obvious that a scribe could produce but a
few pages at best in a day. A large work would therefore require the
labor of a scribe for many months or even for several years. We may
assume, then, that it would be a very flourishing publisher who could
produce a hundred volumes all told \emph{per annum}; and probably
there were not many publishers at any given time, even in the period
of Rome's greatest glory, who had anything like this output.

As there was a large number of authors in every generation of the
classical period, it follows that most of these authors must have
been obliged to content themselves with editions numbering very few
copies; and it goes without saying that the greater number of books
were never reproduced in what might be called a second edition. Even
books that retained their popularity for several generations would
presently fail to arouse sufficient interest to be copied; and in
due course such works would pass out of existence altogether. Doubtless
many hundreds of books were thus lost before the close of the classical
period, the names of their authors being quite forgotten, or preserved
only through a chance reference; and of course the work of elimination
went on much more rapidly during the Middle Ages, when the interest
in classical literature sank to so low an ebb in the West. Such collections
of references and quotations as the \emph{Greek Anthology} and the
famous anthologies of Stob\ae{}us and Athanasius and Eusebius give
us glimpses of a host of writers---more than seven hundred are quoted
by Stob\ae{}us---a very large proportion of whom are quite unknown
except through these brief excerpts from their lost works.

Quite naturally the scientific works suffered at least as largely
as any others in an age given over to ecclesiastical dreamings. Yet
in some regards there is matter for surprise as to the works preserved.
Thus, as we have seen, the very extensive works of Aristotle on natural
history, and the equally extensive natural history of Pliny, which
were preserved throughout this period, and are still extant, make
up relatively bulky volumes. These works seem to have interested the
monks of the Middle Ages, while many much more important scientific
books were allowed to perish. A considerable bulk of scientific literature
was also preserved through the curious channels of Arabic and Armenian
translations. Reference has already been made to the \emph{Almagest}
of Ptolemy, which, as we have seen, was translated into Arabic, and
which was at a later day brought by the Arabs into western Europe
and (at the instance of Frederick II.\ of Sicily)\ translated out
of their language into medi\ae{}val Latin.

It remains to inquire, however, through what channels the Greek works
reached the Arabs themselves. To gain an answer to this question we
must follow the stream of history from its Roman course eastward to
the new seat of the Roman empire in Byzantium. Here civilization centred
from about the fifth century A.D., and here the European came in contact
with the civilization of the Syrians, the Persians, the Armenians,
and finally of the Arabs. The Byzantines themselves, unlike the inhabitants
of western Europe, did not ignore the literature of old Greece; the
Greek language became the regular speech of the Byzantine people,
and their writers made a strenuous effort to perpetuate the idiom
and style of the classical period. Naturally they also made transcriptions
of the classical authors, and thus a great mass of literature was
preserved, while the corresponding works were quite forgotten in western
Europe.

Meantime many of these works were translated into Syriac, Armenian,
and Persian, and when later on the Byzantine civilization degenerated,
many works that were no longer to be had in the Greek originals continued
to be widely circulated in Syriac, Persian, Armenian, and, ultimately,
in Arabic translations. When the Arabs started out in their conquests,
which carried them through Egypt and along the southern coast of the
Mediterranean, until they finally invaded Europe from the west by
way of Gibraltar, they carried with them their translations of many
a Greek classical author, who was introduced anew to the western world
through this strange channel.

We are told, for example, that Averrhoes, the famous commentator of
Aristotle, who lived in Spain in the twelfth century, did not know
a word of Greek and was obliged to gain his knowledge of the master
through a Syriac translation; or, as others alleged (denying that
he knew even Syriac), through an Arabic version translated from the
Syriac. We know, too, that the famous chronology of Eusebius was preserved
through an Armenian translation; and reference has more than once
been made to the Arabic translation of Ptolemy's great work, to which
we still apply its Arabic title of \emph{Almagest}.

The familiar story that when the Arabs invaded Egypt they burned the
Alexandrian library is now regarded as an invention of later times.
It seems much more probable that the library had been largely scattered
before the coming of the Moslems. Indeed, it has even been suggested
that the Christians of an earlier day removed the records of pagan
thought. Be that as it may, the famous Alexandrian library had disappeared
long before the revival of interest in classical learning. Meanwhile,
as we have said, the Arabs, far from destroying the western literature,
were its chief preservers. Partly at least because of their regard
for the records of the creative work of earlier generations of alien
peoples, the Arabs were enabled to outstrip their contemporaries.
For it cannot be in doubt that, during that long stretch of time when
the western world was ignoring science altogether or at most contenting
itself with the casual reading of Aristotle and Pliny, the Arabs had
the unique distinction of attempting original investigations in science.
To them were due all important progressive steps which were made in
any scientific field whatever for about a thousand years after the
time of Ptolemy and Galen. The progress made even by the Arabs during
this long period seems meagre enough, yet it has some significant
features. These will now demand our attention.


\chapter*{\raggedright II. MEDI\AE{}VAL SCIENCE AMONG THE ARABIANS}

\addcontentsline{toc}{chapter}{II. MEDI\AE{}VAL SCIENCE AMONG THE\\
ARABIANS}

\markboth{A HISTORY OF SCIENCE, VOLUME II}{II. ARABIAN MEDI\AE{}VAL
SCIENCE}

The successors of Mohammed showed themselves curiously receptive of
the ideas of the western people whom they conquered. They came in
contact with the Greeks in western Asia and in Egypt, and, as has
been said, became their virtual successors in carrying forward the
torch of learning. It must not be inferred, however, that the Arabian
scholars, as a class, were comparable to their predecessors in creative
genius. On the contrary, they retained much of the conservative oriental
spirit. They were under the spell of tradition, and, in the main,
what they accepted from the Greeks they regarded as almost final in
its teaching. There were, however, a few notable exceptions among
their men of science, and to these must be ascribed several discoveries
of some importance.

The chief subjects that excited the interest and exercised the ingenuity
of the Arabian scholars were astronomy, mathematics, and medicine.
The practical phases of all these subjects were given particular attention.
Thus it is well known that our so-called Arabian numerals date from
this period. The revolutionary effect of these characters, as applied
to practical mathematics, can hardly be overestimated; but it is generally
considered, and in fact was admitted by the Arabs themselves, that
these numerals were really borrowed from the Hindoos, with whom the
Arabs came in contact on the east. Certain of the Hindoo alphabets,
notably that of the Battaks of Sumatra, give us clews to the originals
of the numerals. It does not seem certain, however, that the Hindoos
employed these characters according to the decimal system, which is
the prime element of their importance. Knowledge is not forthcoming
as to just when or by whom such application was made. If this was
an Arabic innovation, it was perhaps the most important one with which
that nation is to be credited. Another mathematical improvement was
the introduction into trigonometry of the sine---the half-chord of
the double arc---instead of the chord of the arc itself which the
Greek astronomers had employed. This improvement was due to the famous
Albategnius, whose work in other fields we shall examine in a moment.

Another evidence of practicality was shown in the Arabian method of
attempting to advance upon Eratosthenes'\ measurement of the earth.
Instead of trusting to the measurement of angles, the Arabs decided
to measure directly a degree of the earth's surface---or rather two
degrees. Selecting a level plain in Mesopotamia for the experiment,
one party of the surveyors progressed northward, another party southward,
from a given point to the distance of one degree of arc, as determined
by astronomical observations. The result found was fifty-six miles
for the northern degree, and fifty-six and two-third miles for the
southern. Unfortunately, we do not know the precise length of the
mile in question, and therefore cannot be assured as to the accuracy
of the measurement. It is interesting to note, however, that the two
degrees were found of unequal lengths, suggesting that the earth is
not a perfect sphere---a suggestion the validity of which was not
to be put to the test of conclusive measurements until about the close
of the eighteenth century. The Arab measurement was made in the time
of Caliph Abdallah \textit{\emph{al}}-Mamun, the son of the famous
Harun-\textit{\emph{al}}-Rashid. Both father and son were famous for
their interest in science. Harun-\textit{\emph{al}}-Rashid was, it
will be recalled, the friend of Charlemagne. It is said that he sent
that ruler, as a token of friendship, a marvellous clock which let
fall a metal ball to mark the hours. This mechanism, which is alleged
to have excited great wonder in the West, furnishes yet another instance
of Arabian practicality.

Perhaps the greatest of the Arabian astronomers was Mohammed \textit{\emph{ben}}
Jabir Albategnius, or El-batani, who was born at \textit{\emph{Batan}},
in Mesopotamia, about the year 850 A.D., and died in 929. Albategnius
was a student of the Ptolemaic astronomy, but he was also a practical
observer. He made the important discovery of the motion of the solar
apogee. That is to say, he found that the position of the sun among
the stars, at the time of its greatest distance from the earth, was
not what it had been in the time of Ptolemy. The Greek astronomer
placed the sun in longitude 65$^\circ$, but Albategnius found it
in longitude 82$^\circ$, a distance too great to be accounted for
by inaccuracy of measurement. The modern inference from this observation
is that the solar system is moving through space; but of course this
inference could not well be drawn while the earth was regarded as
the fixed centre of the universe.

In the eleventh century another Arabian discoverer, Arzachel, observing
the sun to be less advanced than Albategnius had found it, inferred
incorrectly that the sun had receded in the mean time. The modern
explanation of this observation is that the measurement of Albategnius
was somewhat in error, since we know that the sun's motion is steadily
progressive. Arzachel, however, accepting the measurement of his predecessor,
drew the false inference of an oscillatory motion of the stars, the
idea of the motion of the solar system not being permissible. This
assumed phenomenon, which really has no existence in point of fact,
was named the {}``trepidation of the fixed stars,''\ and was for
centuries accepted as an actual phenomenon. Arzachel explained this
supposed phenomenon by assuming that the equinoctial points, or the
points of intersection of the equator and the ecliptic, revolve in
circles of eight degrees'\ radius. The first points of Aries and
Libra were supposed to describe the circumference of these circles
in about eight hundred years. All of which illustrates how a difficult
and false explanation may take the place of a simple and correct one.
The observations of later generations have shown conclusively that
the sun's shift of position is regularly progressive, hence that there
is no {}``trepidation''\ of the stars and no revolution of the
equinoctial points.

If the Arabs were wrong as regards this supposed motion of the fixed
stars, they made at least one correct observation as to the inequality
of motion of the moon. Two inequalities of the motion of this body
were already known. A third, called the moon's variation, was discovered
by an Arabian astronomer who lived at Cairo and observed at Bagdad
in 975, and who bore the formidable name of Mohammed Aboul Wefaal-Bouzdjani.
The inequality of motion in question, in virtue of which the moon
moves quickest when she is at new or full, and slowest at the first
and third quarter, was rediscovered by Tycho Brahe six centuries later;
a fact which in itself evidences the neglect of the Arabian astronomer's
discovery by his immediate successors.

In the ninth and tenth centuries the Arabian city of Cordova, in Spain,
was another important centre of scientific influence. There was a
library of several hundred thousand volumes here, and a college where
mathematics and astronomy were taught. Granada, Toledo, and Salamanca
were also important centres, to which students flocked from western
Europe. It was the proximity of these Arabian centres that stimulated
the scientific interests of Alfonso X.\ of Castile, at whose instance
the celebrated Alfonsine tables were constructed. A familiar story
records that Alfonso, pondering the complications of the Ptolemaic
cycles and epicycles, was led to remark that, had he been consulted
at the time of creation, he could have suggested a much better and
simpler plan for the universe. Some centuries were to elapse before
Copernicus was to show that it was not the plan of the universe, but
man's interpretation of it, that was at fault.

Another royal personage who came under Arabian influence was Frederick
\textit{\emph{II}}.\ of Sicily---the {}``Wonder of the World,''\ as
he was called by his contemporaries. The \emph{Almagest} of Ptolemy
was translated into Latin at his instance, being introduced to the
Western world through this curious channel. At this time it became
quite usual for the Italian and Spanish scholars to understand Arabic
although they were totally ignorant of Greek.

In the field of physical science one of the most important of the
Arabian scientists was Alhazen. His work, published about the year
1100 A.D., had great celebrity throughout the medi\ae{}val period.
The original investigations of Alhazen had to do largely with optics.
He made particular studies of the eye itself, and the names given
by him to various parts of the eye, as the vitreous humor, the cornea,
and the retina, are still retained by anatomists. It is known that
Ptolemy had studied the refraction of light, and that he, in common
with his immediate predecessors, was aware that atmospheric refraction
affects the apparent position of stars near the horizon. Alhazen carried
forward these studies, and was led through them to make the first
recorded scientific estimate of the phenomena of twilight and of the
height of the atmosphere. The persistence of a glow in the atmosphere
after the sun has disappeared beneath the horizon is so familiar a
phenomenon that the ancient philosophers seem not to have thought
of it as requiring an explanation. Yet a moment's consideration makes
it clear that, if light travels in straight lines and the rays of
the sun were in no wise deflected, the complete darkness of night
should instantly succeed to day when the sun passes below the horizon.
That this sudden change does not occur, Alhazen explained as due to
the reflection of light by the earth's atmosphere.

Alhazen appears to have conceived the atmosphere as a sharply defined
layer, and, assuming that twilight continues only so long as rays
of the sun reflected from the outer surface of this layer can reach
the spectator at any given point, he hit upon a means of measurement
that seemed to solve the hitherto inscrutable problem as to the atmospheric
depth. Like the measurements of Aristarchus and Eratosthenes, this
calculation of Alhazen is simple enough in theory. Its defect consists
largely in the difficulty of fixing its terms with precision, combined
with the further fact that the rays of the sun, in taking the slanting
course through the earth's atmosphere, are really deflected from a
straight line in virtue of the constantly increasing density of the
air near the earth's surface. Alhazen must have been aware of this
latter fact, since it was known to the later Alexandrian astronomers,
but he takes no account of it in the present measurement. The diagram
will make the method of Alhazen clear.

%
\begin{figure}
\noindent \begin{center}\includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2Sc20}\end{center}

\noindent \begin{center}\noun{\small Diagram to Illustrate Alhazen's
Measurement of the Height of the Atmosphere}\end{center}{\small \par}

\noindent \emph{\footnotesize (For explanation refer to the text.
It will be understood, of course, that the distorted, proportions
make an angle very inaccurate. HMS, for example, as shown in the diagram,
is obviously much greater than 19$^\circ$. Perhaps it should be added
that the angle HMS would not at all serve the purpose to which it
is here put were it not that the distance of the sun makes the ray
SM virtually parallel to the imaginary line SA, which latter defines
the actual angle of the sun's position with regard to the observer
at A). }
\end{figure}
His important premises are two: first, the well-recognized fact that,
when light is reflected from any surface, the angle of incidence is
equal to the angle of reflection; and, second, the much more doubtful
observation that twilight continues until such time as the sun, according
to a simple calculation, is nineteen degrees below the horizon. Referring
to the diagram, let the inner circle represent the earth's surface,
the outer circle the limits of the atmosphere, $C$ being the earth's
centre, and $RR$ radii of the earth. Then the observer at the point
$A$ will continue to receive the reflected rays of the sun until
that body reaches the point $S$, which is, according to the hypothesis,
nineteen degrees below the horizon line of the observer at $A$. This
horizon line, being represented by $AH$, and the sun's ray by $SM$,
the angle $HMS$ is an angle of nineteen degrees. The complementary
angle $SMA$ is, obviously, an angle of (180-19)\ one hundred and
sixty-one degrees. But since $M$ is the reflecting surface and the
angle of incidence equals the angle of reflection, the angle $AMC$
is an angle of one-half of one hundred and sixty-one degrees, or eighty
degrees and thirty minutes. Now this angle $AMC$, being known, the
right-angled triangle $MAC$ is easily resolved, since the side $AC$
of that triangle, being the radius of the earth, is a known dimension.
Resolution of this triangle gives us the length of the hypotenuse
$MC$, and the difference between this and the radius ($AC$), or
$CD$, is obviously the height of the atmosphere ($h$), which was
the measurement desired. According to the calculation of Alhazen,
this $h$, or the height of the atmosphere, represents from twenty
to thirty miles. The modern computation extends this to about fifty
miles. But, considering the various ambiguities that necessarily attended
the experiment, the result was a remarkably close approximation to
the truth.

Turning from physics to chemistry, we find as perhaps the greatest
Arabian name that of Geber, who taught in the College of Seville in
the first half of the eighth century. The most important researches
of this really remarkable experimenter had to do with the acids. The
ancient world had had no knowledge of any acid more powerful than
acetic. Geber, however, vastly increased the possibilities of chemical
experiment by the discovery of sulphuric, nitric, and nitromuriatic
acids. He made use also of the processes of sublimation and filtration,
and his works describe the water bath and the chemical oven. Among
the important chemicals which he first differentiated is oxide of
mercury, and his studies of sulphur in its various compounds have
peculiar interest. In particular is this true of his observation that,
under certain conditions of oxidation, the weight of a metal was lessened.

From the record of these studies in the fields of astronomy, physics,
and chemistry, we turn to a somewhat extended survey of the Arabian
advances in the field of medicine.


\section*{\raggedright ARABIAN MEDICINE}

\addcontentsline{toc}{section}{ARABIAN MEDICINE}

The influence of Arabian physicians rested chiefly upon their use
of drugs rather than upon anatomical knowledge. Like the medi\ae{}val
Christians, they looked with horror on dissection of the human body;
yet there were always among them investigators who turned constantly
to nature herself for hidden truths, and were ready to uphold the
superiority of actual observation to mere reading. Thus the physician
Abd el-Letif, while in Egypt, made careful studies of a mound of bones
containing more than twenty thousand skeletons. While examining these
bones he discovered that the lower jaw consists of a single bone,
not of two, as had been taught by Galen. He also discovered several
other important mistakes in Galenic anatomy, and was so impressed
with his discoveries that he contemplated writing a work on anatomy
which should correct the great classical authority's mistakes.

It was the Arabs who invented the apothecary, and their pharmacop\oe{}ia,
issued from the hospital at Gondisapor, and elaborated from time to
time, formed the basis for Western pharmacop\oe{}ias. Just how many
drugs originated with them, and how many were borrowed from the Hindoos,
Jews, Syrians, and Persians, cannot be determined. It is certain,
however, that through them various new and useful drugs, such as senna,
aconite, rhubarb, camphor, and mercury, were handed down through the
Middle Ages, and that they are responsible for the introduction of
alcohol in the field of therapeutics.

In medi\ae{}val Europe, Arabian science came to be regarded with
superstitious awe, and the works of certain Arabian physicians were
exalted to a position above all the ancient writers. In modern times,
however, there has been a reaction and a tendency to depreciation
of their work. By some they are held to be mere copyists or translators
of Greek books, and in no sense original investigators in medicine.
Yet there can be little doubt that while the Arabians did copy and
translate freely, they also originated and added considerably to medical
knowledge. It is certain that in the time when Christian monarchs
in western Europe were paying little attention to science or education,
the caliphs and \textit{\emph{vizirs}} were encouraging physicians
and philosophers, building schools, and erecting libraries and hospitals.
They made at least a creditable effort to uphold and advance upon
the scientific standards of an earlier age.

The first distinguished Arabian physician was \textit{\emph{Harets}}
\emph{}\textit{\emph{ben}} Kaladah, who received his education in
the Nestonian school at Gondisapor, about the beginning of the seventh
century. Notwithstanding the fact that \textit{\emph{Harets}} was
a Christian, he was chosen by Mohammed as his chief medical adviser,
and recommended as such to his successor, the Caliph Abu Bekr. Thus,
at the very outset, the science of medicine was divorced from religion
among the Arabians; for if the prophet himself could employ the services
of an unbeliever, surely others might follow his example. And that
this example was followed is shown in the fact that many Christian
physicians were raised to honorable positions by succeeding generations
of Arabian monarchs. This broad-minded view of medicine taken by the
Arabs undoubtedly assisted as much as any one single factor in upbuilding
the science, just as the narrow and superstitious view taken by Western
nations helped to destroy it.

The education of the Arabians made it natural for them to associate
medicine with the natural sciences, rather than with religion. An
Arabian savant was supposed to be equally well educated in philosophy,
jurisprudence, theology, mathematics, and medicine, and to practise
law, theology, and medicine with equal skill upon occasion. It is
easy to understand, therefore, why these religious fanatics were willing
to employ unbelieving physicians, and their physicians themselves
to turn to the scientific works of Hippocrates and Galen for medical
instruction, rather than to religious works. Even Mohammed himself
professed some knowledge of medicine, and often relied upon this knowledge
in treating ailments rather than upon prayers or incantations. He
is said, for example, to have recommended and applied the cautery
in the case of a friend who, when suffering from angina, had sought
his aid.

The list of eminent Arabian physicians is too long to be given here,
but some of them are of such importance in their influence upon later
medicine that they cannot be entirely ignored. One of the first of
these was Honain \textit{\emph{ben}} Isaac (809-873 A.D.), a Christian
Arab of Bagdad. He made translations of the works of Hippocrates,
and practised the art along the lines indicated by his teachings and
those of Galen. He is considered the greatest translator of the ninth
century and one of the greatest philosophers of that period.

Another great Arabian physician, whose work was just beginning as
Honain's was drawing to a close, was Rhazes (850-923 A.D.), who during
his life was no less noted as a philosopher and musician than as a
physician. He continued the work of Honain, and advanced therapeutics
by introducing more extensive use of chemical remedies, such as mercurial
ointments, sulphuric acid, and \emph{aqua vitae}. He is also credited
with being the first physician to describe small-pox and measles accurately.

While Rhazes was still alive another Arabian, Haly Abbas (died about
994), was writing his famous encyclop\ae{}dia of medicine, called
\emph{The Royal Book}. But the names of all these great physicians
have been considerably obscured by the reputation of Avicenna (980-1037),
the Arabian {}``Prince of Physicians,''\ the greatest name in Arabic
medicine, and one of the most remarkable men in history. Leclerc says
that {}``he was perhaps never surpassed by any man in brilliancy
of intellect and indefatigable activity.'' His career was a most
varied one. He was at all times a boisterous reveller, but whether
flaunting gayly among the guests of an emir or biding in some obscure
apothecary cellar, his work of philosophical writing was carried on
steadily. When a friendly emir was in power, he taught and wrote and
caroused at court; but between times, when some unfriendly ruler was
supreme, he was hiding away obscurely, still pouring out his great
mass of manuscripts. In this way his entire life was spent.

By his extensive writings he revived and kept alive the best of the
teachings of the Greek physicians, adding to them such observations
as he had made in anatomy, physiology, and \textit{materia} \textit{medica}.
Among his discoveries is that of the contagiousness of pulmonary tuberculosis.
His works for several centuries continued to be looked upon as the
highest standard by physicians, and he should undoubtedly be credited
with having at least retarded the decline of medi\ae{}val medicine.

But it was not the Eastern Arabs alone who were active in the field
of medicine. Cordova, the capital of the western caliphate, became
also a great centre of learning and produced several great physicians.
One of these, Albucasis (died in 1013 A.D.), is credited with having
published the first illustrated work on surgery, this book being remarkable
in still another way, in that it was also the first book, since classical
times, written from the practical experience of the physician, and
not a mere compilation of ancient authors. A century after Albucasis
came the great physician Avenzoar (1113-1196), with whom he divides
about equally the medical honors of the western caliphate. Among Avenzoar's
discoveries was that of the cause of {}``itch''---a little parasite,
{}``so small that he is hardly visible.'' The discovery of the cause
of this common disease seems of minor importance now, but it is of
interest in medical history because, had Avenzoar's discovery been
remembered a hundred years ago, {}``itch struck in'' could hardly
have been considered the cause of three-fourths of all diseases, as
it was by the famous Hahnemann.

The illustrious pupil of Avenzoar, Averrhoes, who died in 1198 A.D.,
was the last of the great Arabian physicians who, by rational conception
of medicine, attempted to stem the flood of superstition that was
overwhelming medicine. For a time he succeeded; but at last the Moslem
theologians prevailed, and he was degraded and banished to a town
inhabited only by the despised Jews.


\section*{\raggedright ARABIAN HOSPITALS}

\addcontentsline{toc}{section}{ARABIAN HOSPITALS}

To early Christians belong the credit of having established the first
charitable institutions for caring for the sick; but their efforts
were soon eclipsed by both Eastern and Western Mohammedans. As early
as the eighth century the Arabs had begun building hospitals, but
the flourishing time of hospital building seems to have begun early
in the tenth century. Lady Seidel, in 918 A.D., opened a hospital
at Bagdad, endowed with an amount corresponding to about three hundred
pounds sterling a month. Other similar hospitals were erected in the
years immediately following, and in 977 the Emir Adad-adaula established
an enormous institution with a staff of twenty-four medical officers.
The great physician Rhazes is said to have selected the site for one
of these hospitals by hanging pieces of meat in various places about
the city, selecting the site near the place at which putrefaction
was slowest in making its appearance. By the middle of the twelfth
century there were something like sixty medical institutions in Bagdad
alone, and these institutions were free to all patients and supported
by official charity.

The Emir Nureddin, about the year 1160, founded a great hospital at
Damascus, as a thank-offering for his victories over the Crusaders.
This great institution completely overshadowed all the earlier Moslem
hospitals in size and in the completeness of its equipment. It was
furnished with facilities for teaching, and was conducted for several
centuries in a lavish manner, regardless of expense. But little over
a century after its foundation the fame of its methods of treatment
led to the establishment of a larger and still more luxurious institution---the
Mansuri hospital at Cairo. It seems that a certain sultan, having
been cured by medicines from the Damascene hospital, determined to
build one of his own at Cairo which should eclipse even the great
Damascene institution.

In a single year (1283-1284)\ this hospital was begun and completed.
No efforts were spared in hurrying on the good work, and no one was
exempt from performing labor on the building if he chanced to pass
one of the adjoining streets. It was the order of the sultan that
any person passing near could be impressed into the work, and this
order was carried out to the letter, noblemen and beggars alike being
forced to lend a hand. Very naturally, the adjacent thoroughfares
became unpopular and practically deserted, but still the holy work
progressed rapidly and was shortly completed.

This immense structure is said to have contained four courts, each
having a fountain in the centre; lecture-halls, wards for isolating
certain diseases, and a department that corresponded to the modern
hospital's {}``out-patient''\ department. The yearly endowment
amounted to something like the equivalent of one hundred and twenty-five
thousand dollars. A novel feature was a hall where musicians played
day and night, and another where story-tellers were employed, so that
persons troubled with insomnia were amused and melancholiacs cheered.
Those of a religious turn of mind could listen to readings of the
Koran, conducted continuously by a staff of some fifty chaplains.
Each patient on leaving the hospital received some gold pieces, that
he need not be obliged to attempt hard labor at once.

In considering the astonishing tales of these sumptuous Arabian institutions,
it should be borne in mind that our accounts of them are, for the
most part, from Mohammedan sources. Nevertheless, there can be little
question that they were enormous institutions, far surpassing any
similar institutions in western Europe. The so-called hospitals in
the West were, at this time, branches of monasteries under supervision
of the monks, and did not compare favorably with the Arabian hospitals.

But while the medical science of the Mohammedans greatly overshadowed
that of the Christians during this period, it did not completely obliterate
it. About the year 1000 A.D.\ came into prominence the Christian
medical school at Salerno, situated on the Italian coast, some thirty
miles southeast of Naples. Just how long this school had been in existence,
or by whom it was founded, cannot be determined, but its period of
greatest influence was the eleventh, twelfth, and thirteenth centuries.
The members of this school gradually adopted Arabic medicine, making
use of many drugs from the Arabic pharmacop\oe{}ia, and this formed
one of the stepping-stones to the introduction of Arabian medicine
all through western Europe.

It was not the adoption of Arabian medicines, however, that has made
the school at Salerno famous both in rhyme and prose, but rather the
fact that women there practised the healing art. Greatest among them
was Trotula, who lived in the eleventh century, and whose learning
is reputed to have equalled that of the greatest physicians of the
day. She is accredited with a work on \emph{Diseases of Women}, still
extant, and many of her writings on general medical subjects were
quoted through two succeeding centuries. If we may judge from these
writings, she seemed to have had many excellent ideas as to the proper
methods of treating diseases, but it is difficult to determine just
which of the writings credited to her are in reality hers. Indeed,
the uncertainty is even greater than this implies, for, according
to some writers, {}``Trotula''\ is merely the title of a book.
Such an authority as Malgaigne, however, believed that such a woman
existed, and that the works accredited to her are authentic. The truth
of the matter may perhaps never be fully established, but this at
least is certain---the tradition in regard to Trotula could never
have arisen had not women held a far different position among the
Arabians of this period from that accorded them in contemporary Christendom.


\chapter*{\raggedright III. MEDI\AE{}VAL SCIENCE IN THE WEST}

\addcontentsline{toc}{chapter}{III. MEDI\AE{}VAL SCIENCE IN THE
WEST}

\markboth{A HISTORY OF SCIENCE, VOLUME II}{III. WESTERN MEDI\AE{}VAL
SCIENCE}

We have previously referred to the influence of the Byzantine civilization
in transmitting the learning of antiquity across the abysm of the
dark age. It must be admitted, however, that the importance of that
civilization did not extend much beyond the task of the common carrier.
There were no great creative scientists in the later Roman empire
of the East any more than in the corresponding empire of the West.
There was, however, one field in which the Byzantine made respectable
progress and regarding which their efforts require a few words of
special comment. This was the field of medicine.

The Byzantines of this time could boast of two great medical men,
Aetius of \textit{\emph{Amida}} (about 502-575 A.D.)\ and Paul of
Aegina (about 620-690). The works of Aetius were of value largely
because they recorded the teachings of many of his eminent predecessors,
but he was not entirely lacking in originality, and was perhaps the
first physician to mention diphtheria, with an allusion to some observations
of the paralysis of the palate which sometimes follows this disease.

Paul of Aegina, who came from the Alexandrian school about a century
later, was one of those remarkable men whose ideas are centuries ahead
of their time. This was particularly true of Paul in regard to surgery,
and his attitude towards the supernatural in the causation and treatment
of diseases. He was essentially a surgeon, being particularly familiar
with military surgery, and some of his descriptions of complicated
and difficult operations have been little improved upon even in modern
times. In his books he describes such operations as the removal of
foreign bodies from the nose, ear, and esophagus; and he recognizes
foreign growths such as \textit{polypi} in the air-passages, and gives
the method of their removal. Such operations as tracheotomy, tonsellotomy,
bronchotomy, staphylotomy, \textit{etc}., were performed by him, and
he even advocated and described puncture of the abdominal cavity,
giving careful directions as to the location in which such punctures
should be made. He advocated amputation of the breast for the cure
of cancer, and described extirpation of the uterus. Just how successful
this last operation may have been as performed by him does not appear;
but he would hardly have recommended it if it had not been sometimes,
at least, successful. That he mentions it at all, however, is significant,
as this difficult operation is considered one of the great triumphs
of modern surgery.

But Paul of Aegina is a striking exception to the rule among Byzantine
surgeons, and as he was their greatest, so he was also their last
important surgeon. The energies of all Byzantium were so expended
in religious controversies that medicine, like the other sciences,
was soon relegated to a place among the other superstitions, and the
influence of the Byzantine school was presently replaced by that of
the conquering Arabians.


\section*{\raggedright THIRTEENTH-CENTURY MEDICINE}

\addcontentsline{toc}{section}{THIRTEENTH-CENTURY MEDICINE}

The thirteenth century marks the beginning of a gradual change in
medicine, and a tendency to leave the time-worn rut of superstitious
dogmas that so long retarded the progress of science. It is thought
that the great epidemics which raged during the Middle Ages acted
powerfully in diverting the medical thought of the times into new
and entirely different channels. It will be remembered that the teachings
of Galen were handed through medi\ae{}val times as the highest and
best authority on the subject of all diseases. When, however, the
great epidemics made their appearance, the medical men appealed to
the works of Galen in vain for enlightenment, as these works, having
been written several centuries before the time of the plagues, naturally
contained no information concerning them. It was evident, therefore,
that on this subject, at least, Galen was not infallible; and it would
naturally follow that, one fallible point having been revealed, others
would be sought for. In other words, scepticism in regard to accepted
methods would be aroused, and would lead naturally, as such scepticism
usually does, to progress. The devastating effects of these plagues,
despite prayers and incantations, would arouse doubt in the minds
of many as to the efficacy of superstitious rites and ceremonies in
curing diseases. They had seen thousands and tens of thousands of
their fellow-beings swept away by these awful scourges. They had seen
the ravages of these epidemics continue for months or even years,
notwithstanding the fact that multitudes of God-fearing people prayed
hourly that such ravages might be checked. And they must have observed
also that when even very simple rules of cleanliness and hygiene were
followed there was a diminution in the ravages of the plague, even
without the aid of incantations. Such observations as these would
have a tendency to awaken a suspicion in the minds of many of the
physicians that disease was not a manifestation of the supernatural,
but a natural phenomenon, to be treated by natural methods.

But, be the causes what they may, it is a fact that the thirteenth
century marks a turning-point, or the beginning of an attitude of
mind which resulted in bringing medicine to a much more rational position.
Among the thirteenth-century physicians, two men are deserving of
special mention. These are Arnald of Villanova (1235-1312)\ and Peter
of \textit{\emph{Abano}} (1250-1315). Both these men suffered persecution
for expressing their belief in natural, as against the supernatural,
causes of disease, and at one time Arnald was obliged to flee from
Barcelona for declaring that the {}``bulls''\ of popes were human
works, and that {}``acts of charity were dearer to God than hecatombs.''
He was also accused of alchemy. Fleeing from persecution, he finally
perished by shipwreck.

Arnald was the first great representative of the school of Montpellier.
He devoted much time to the study of chemicals, and was active in
attempting to re-establish the teachings of Hippocrates and Galen.
He was one of the first of a long line of alchemists who, for several
succeeding centuries, expended so much time and energy in attempting
to find the {}``elixir of life.'' The Arab discovery of alcohol
first deluded him into the belief that the {}``elixir''\ had at
last been found; but later he discarded it and made extensive experiments
with brandy, employing it in the treatment of certain diseases---the
first record of the administration of this liquor as a medicine. Arnald
also revived the search for some an\ae{}sthetic that would produce
insensibility to pain in surgical operations. This idea was not original
with him, for since very early times physicians had attempted to discover
such an an\ae{}sthetic, and even so early a writer as Herodotus tells
how the Scythians, by inhalation of the vapors of some kind of hemp,
produced complete insensibility. It may have been these writings that
stimulated Arnald to search for such an an\ae{}sthetic. In a book
usually credited to him, medicines are named and methods of administration
described which will make the patient insensible to pain, so that
{}``he may be cut and feel nothing, as though he were dead.'' For
this purpose a mixture of opium, mandragora, and henbane is to be
used. This mixture was held at the patient's nostrils much as ether
and chloroform are administered by the modern surgeon. The method
was modified by Hugo of Lucca (died in 1252 or 1268), who added certain
other narcotics, such as hemlock, to the mixture, and boiled a new
sponge in this decoction. After boiling for a certain time, this sponge
was dried, and when wanted for use was dipped in hot water and applied
to the nostrils.

Just how frequently patients recovered from the administration of
such a combination of powerful poisons does not appear, but the percentage
of deaths must have been very high, as the practice was generally
condemned. Insensibility could have been produced only by swallowing
large quantities of the liquid, which dripped into the nose and mouth
when the sponge was applied, and a lethal quantity might thus be swallowed.
The method was revived, with various modifications, from time to time,
but as often fell into disuse. As late as 1782 it was sometimes attempted,
and in that year the King of Poland is said to have been completely
an\ae{}sthetized and to have recovered, after a painless amputation
had been performed by the surgeons.

Peter of \textit{\emph{Abano}} was one of the first great men produced
by the University of Padua. His fate would have been even more tragic
than that of the shipwrecked Arnald had he not cheated the purifying
\textit{\emph{fagots}} of the church by dying opportunely on the eve
of his execution for heresy. But if his spirit had cheated the fanatics,
his body could not, and his bones were burned for his heresy. He had
dared to deny the existence of a devil, and had suggested that the
case of a patient who lay in a trance for three days might help to
explain some miracles, like the raising of Lazarus.

His great work was \emph{Conciliator Differentiarum}, an attempt to
reconcile physicians and philosophers. But his researches were not
confined to medicine, for he seems to have had an inkling of the hitherto
unknown fact that air possesses weight, and his calculation of the
length of the year at three hundred and sixty-five days, six hours,
and four minutes, is exceptionally accurate for the age in which he
lived. He was probably the first of the Western writers to teach that
the brain is the source of the nerves, and the heart the source of
the vessels. From this it is seen that he was groping in the direction
of an explanation of the circulation of the blood, as demonstrated
by Harvey three centuries later.

The work of Arnald and Peter of \textit{\emph{Abano}} in {}``reviving''\ medicine
was continued actively by Mondino (1276-1326)\ of Bologna, the {}``restorer
of anatomy,''\ and by Guy of Chauliac: (born about 1300), the {}``restorer
of surgery.'' All through the early Middle \textit{\emph{Ages}} \textit{\emph{dissections}}
of human bodies had been forbidden, and even dissection of the lower
animals gradually fell into disrepute because physicians detected
in such practices were sometimes accused of sorcery. Before the close
of the thirteenth century, however, a reaction had begun, physicians
were protected, and \textit{\emph{dissections}} were occasionally
sanctioned by the ruling monarch. Thus Emperor Frederick II.\ (1194-1250
A.D.)---whose services to science we have already had occasion to
mention---ordered that at least one human body should be dissected
by physicians in his kingdom every five years. By the time of Mondino
\textit{\emph{dissections}} were becoming more frequent, and he himself
is known to have dissected and demonstrated several bodies. His writings
on anatomy have been called merely plagiarisms of Galen, but in all
probability he made many discoveries independently, and on the whole,
his work may be taken as more advanced than Galen's. His description
of the heart is particularly accurate, and he seems to have come nearer
to determining the course of the blood in its circulation than any
of his predecessors. In this quest he was greatly handicapped by the
prevailing belief in the idea that blood-vessels must contain air
as well as blood, and this led him to assume that one of the cavities
of the heart contained {}``spirits,''\ or air. It is probable,
however, that his accurate observations, so far as they went, were
helpful stepping-stones to Harvey in his discovery of the circulation.

Guy of Chauliac, whose innovations in surgery reestablished that science
on a firm basis, was not only one of the most cultured, but also the
most practical surgeon of his time. He had great reverence for the
works of Galen, Albucasis, and others of his noted predecessors; but
this reverence did not blind him to their mistakes nor prevent him
from using rational methods of treatment far in advance of theirs.
His practicality is shown in some of his simple but useful inventions
for the sick-room, such as the device of a rope, suspended from the
ceiling over the bed, by which a patient may move himself about more
easily; and in some of his improvements in surgical dressings, such
as stiffening bandages by dipping them in the white of an egg so that
they are held firmly. He treated broken limbs in the suspended cradle
still in use, and introduced the method of making {}``traction''\ on
a broken limb by means of a weight and pulley, to prevent deformity
through shortening of the member. He was one of the first physicians
to recognize the utility of spectacles, and recommended them in cases
not amenable to treatment with lotions and eye-waters. In some of
his surgical operations, such as trephining for fracture of the skull,
his technique has been little improved upon even in modern times.
In one of these operations he successfully removed a portion of a
man's brain.

Surgery was undoubtedly stimulated greatly at this period by the constant
wars. Lay physicians, as a class, had been looked down upon during
the Dark Ages; but with the beginning of the return to rationalism,
the services of surgeons on the battle-field, to remove missiles from
wounds, and to care for wounds and apply dressings, came to be more
fully appreciated. In return for his labors the surgeon was thus afforded
better opportunities for observing wounds and diseases, which led
naturally to a gradual improvement in surgical methods.


\section*{\raggedright FIFTEENTH-CENTURY MEDICINE}

\addcontentsline{toc}{section}{FIFTEENTH-CENTURY MEDICINE}

The thirteenth and fourteenth centuries had seen some slight advancement
in the science of medicine; at least, certain surgeons and physicians,
if not the generality, had made advances; but it was not until the
fifteenth century that the general revival of medical learning became
assured. In this movement, naturally, the printing-press played an
all-important part. Medical books, hitherto practically inaccessible
to the great mass of physicians, now became common, and this output
of reprints of Greek and Arabic treatises revealed the fact that many
of the supposed true copies were spurious. These discoveries very
naturally aroused all manner of doubt and criticism, which in turn
helped in the development of independent thought.

A certain manuscript of the great Cornelius \textit{\emph{Celsus}},
the \emph{De Medicine}, which had been lost for many centuries, was
found in the church of St.\ Ambrose, at Milan, in 1443, and was at
once put into print. The effect of the publication of this book, which
had lain in hiding for so many centuries, was a revelation, showing
the medical profession how far most of their supposed true copies
of \textit{\emph{Celsus}} had drifted away from the original. The
indisputable authenticity of this manuscript, discovered and vouched
for by the man who shortly after became Pope Nicholas V., made its
publication the more impressive. The output in book form of other
authorities followed rapidly, and the manifest discrepancies between
such teachers as \textit{\emph{Celsus}}, Hippocrates, Galen, and Pliny
heightened still more the growing spirit of criticism.

These doubts resulted in great controversies as to the proper treatment
of certain diseases, some physicians following Hippocrates, others
Galen or \textit{\emph{Celsus}}, still others the Arabian masters.
One of the most bitter of these contests was over the question of
{}``revulsion,''\ and {}``derivation''---that is, whether in
cases of pleurisy treated by bleeding, the venesection should be made
at a point distant from the seat of the disease, as held by the {}``revulsionists,''\ or
at a point nearer and on the same side of the body, as practised by
the {}``derivationists.'' That any great point for discussion could
be raised in the fifteenth or sixteenth centuries on so simple a matter
as it seems to-day shows how necessary to the progress of medicine
was the discovery of the circulation of the blood made by Harvey two
centuries later. After Harvey's discovery no such discussion could
have been possible, because this discovery made it evident that as
far as the general effect upon the circulation is concerned, it made
little difference whether the bleeding was done near a diseased part
or remote from it. But in the sixteenth century this question was
the all-absorbing one among the doctors. At one time the faculty of
Paris condemned {}``derivation''; but the supporters of this method
carried the war still higher, and Emperor Charles V.\ himself was
appealed to. He reversed the decision of the Paris faculty, and decided
in favor of {}``derivation.'' His decision was further supported
by Pope Clement VII., although the discussion dragged on until cut
short by Harvey's discovery.

But a new form of injury now claimed the attention of the surgeons,
something that could be decided by neither Greek nor Arabian authors,
as the treatment of gun-shot wounds was, for obvious reasons, not
given in their writings. About this time, also, came the great epidemics,
{}``the sweating sickness''\ and scurvy; and upon these subjects,
also, the Greeks and Arabians were silent. John of Vigo, in his book,
the \textit{Practica} \textit{Copiosa}, published in 1514, and repeated
in many editions, became the standard authority on all these subjects,
and thus supplanted the works of the ancient writers.

According to Vigo, gun-shot wounds differed from the wounds made by
ordinary weapons---that is, spear, arrow, sword, or axe---in that
the bullet, being round, bruised rather than cut its way through the
tissues; it burned the flesh; and, worst of all, it poisoned it. Vigo
laid especial stress upon treating this last condition, recommending
the use of the cautery or the oil of elder, boiling hot. It is little
wonder that gun-shot wounds were so likely to prove fatal. Yet, after
all, here was the germ of the idea of antisepsis.


\section*{\raggedright NEW BEGINNINGS IN GENERAL SCIENCE}

\addcontentsline{toc}{section}{NEW BEGINNINGS IN GENERAL\\
SCIENCE}

We have dwelt thus at length on the subject of medical science, because
it was chiefly in this field that progress was made in the Western
world during the medi\ae{}val period, and because these studies furnished
the point of departure for the revival all along the line. It will
be understood, however, from what was stated in the preceding chapter,
that the Arabian influences in particular were to some extent making
themselves felt along other lines. The opportunity afforded a portion
of the Western world---notably Spain and Sicily---to gain access to
the scientific ideas of antiquity through Arabic translations could
not fail of influence. Of like character, and perhaps even more pronounced
in degree, was the influence wrought by the Byzantine refugees, who,
when Constantinople began to be threatened by the Turks, migrated
to the West in considerable numbers, bringing with them a knowledge
of Greek literature and a large number of precious works which for
centuries had been quite forgotten or absolutely ignored in Italy.
Now Western scholars began to take an interest in the Greek language,
which had been utterly neglected since the beginning of the Middle
Ages. Interesting stories are told of the efforts made by such men
as Cosmo de' Medici to gain possession of classical manuscripts. The
revival of learning thus brought about had its first permanent influence
in the fields of literature and art, but its effect on science could
not be long delayed. Quite independently of the Byzantine influence,
however, the striving for better intellectual things had manifested
itself in many ways before the close of the thirteenth century. An
illustration of this is found in the almost simultaneous development
of centres of teaching, which developed into the universities of Italy,
France, England, and, a little later, of Germany.

The regular list of studies that came to be adopted everywhere comprised
seven nominal branches, divided into two groups---the so-called quadrivium,
comprising music, arithmetic, geometry, and astronomy; and the trivium
comprising grammar, rhetoric, and logic. The vagueness of implication
of some of these branches gave opportunity to the teacher for the
promulgation of almost any knowledge of which he might be possessed,
but there can be no doubt that, in general, science had but meagre
share in the curriculum. In so far as it was given representation,
its chief field must have been Ptolemaic astronomy. The utter lack
of scientific thought and scientific method is illustrated most vividly
in the works of the greatest men of that period---such men as Albertus
Magnus, Thomas Aquinas, Bonaventura, and the hosts of other scholastics
of lesser rank. Yet the mental awakening implied in their efforts
was sure to extend to other fields, and in point of fact there was
at least one contemporary of these great scholastics whose mind was
intended towards scientific subjects, and who produced writings strangely
at variance in tone and in content with the others. This anachronistic
thinker was the English monk, Roger Bacon.


\section*{\raggedright ROGER BACON}

\addcontentsline{toc}{section}{ROGER BACON}

Bacon was born in 1214 and died in 1292. By some it is held that he
was not appreciated in his own time because he was really a modern
scientist living in an age two centuries before modern science or
methods of modern scientific thinking were known. Such an estimate,
however, is a manifest exaggeration of the facts, although there is
probably a grain of truth in it withal. His learning certainly brought
him into contact with the great thinkers of the time, and his writings
caused him to be imprisoned by his fellow-churchmen at different times,
from which circumstances we may gather that he was advanced thinker,
even if not a modern scientist.

Although Bacon was at various times in durance, or under surveillance,
and forbidden to write, he was nevertheless a marvellously prolific
writer, as is shown by the numerous books and unpublished manuscripts
of his still extant. His master-production was the \emph{Opus Majus}.
In Part IV.\ of this work he attempts to show that all sciences rest
ultimately on mathematics; but Part V., which treats of perspective,
is of particular interest to modern scientists, because in this he
discusses reflection and refraction, and the properties of mirrors
and lenses. In this part, also, it is evident that he is making use
of such Arabian writers as Alkindi and Alhazen, and this is of especial
interest, since it has been used by his detractors, who accuse him
of lack of originality, to prove that his seeming inventions and discoveries
were in reality adaptations of the Arab scientists. It is difficult
to determine just how fully such criticisms are justified. It is certain,
however, that in this part he describes the anatomy of the eye with
great accuracy, and discusses mirrors and lenses.

The magnifying power of the segment of a glass sphere had been noted
by Alhazen, who had observed also that the magnification was increased
by increasing the size of the segment used. Bacon took up the discussion
of the comparative advantages of segments, and in this discussion
seems to show that he understood how to trace the progress of the
rays of light through a spherical transparent body, and how to determine
the place of the image. He also described a method of constructing
a telescope, but it is by no means clear that he had ever actually
constructed such an instrument. It is also a mooted question as to
whether his instructions as to the construction of such an instrument
would have enabled any one to construct one. The vagaries of the names
of terms as he uses them allow such latitude in interpretation that
modern scientists are not agreed as to the practicability of Bacon's
suggestions. For example, he constantly refers to force under such
names as \textit{virtus}, \textit{species}, \textit{imago}, \textit{agentis},
and a score of other names, and this naturally gives rise to the great
differences in the interpretations of his writings, with corresponding
differences in estimates of them.

The claim that Bacon originated the use of lenses, in the form of
spectacles, cannot be proven. Smith has determined that as early as
the opening years of the fourteenth century such lenses were in use,
but this proves nothing as regards Bacon's connection with their invention.
The knowledge of lenses seems to be very ancient, if we may judge
from the convex lens of rock crystal found by Layard in his excavations
at Nimrud. There is nothing to show, however, that the ancients ever
thought of using them to correct defects of vision. Neither, apparently,
is it feasible to determine whether the idea of such an application
originated with Bacon.

Another mechanical discovery about which there has been a great deal
of discussion is Bacon's supposed invention of gunpowder. It appears
that in a certain passage of his work he describes the process of
making a substance that is, in effect, ordinary gunpowder; but it
is more than doubtful whether he understood the properties of the
substance he describes. It is fairly well established, however, that
in Bacon's time gunpowder was known to the Arabs, so that it should
not be surprising to find references made to it in Bacon's work, since
there is reason to believe that he constantly consulted Arabian writings.

The great merit of Bacon's work, however, depends on the principles
taught as regards experiment and the observation of nature, rather
than on any single invention. He had the all-important idea of breaking
with tradition. He championed unfettered inquiry in every field of
thought. He had the instinct of a scientific worker---a rare instinct
indeed in that age. Nor need we doubt that to the best of his opportunities
he was himself an original investigator.


\section*{\raggedright LEONARDO \textit{\emph{DA}} \emph{}\textit{\emph{VINCI}}}

\addcontentsline{toc}{section}{LEONARDO DA VINCI}

The relative infertility of Bacon's thought is shown by the fact that
he founded no school and left no trace of discipleship. The entire
century after his death shows no single European name that need claim
the attention of the historian of science. In the latter part of the
fifteenth century, however, there is evidence of a renaissance of
science no less than of art. The German Muller became famous under
the latinized named of \textit{\emph{Regio}} \emph{}\textit{\emph{Montanus}}
(1437-1472), although his actual scientific attainments would appear
to have been important only in comparison with the utter ignorance
of his contemporaries. The most distinguished worker of the new era
was the famous Italian \textit{\emph{Leonardo}} \emph{}\textit{\emph{da}}
\emph{}\textit{\emph{Vinci}}---a man who has been called by Hamerton
the most universal genius that ever lived. Leonardo's position in
the history of art is known to every one. With that, of course, we
have no present concern; but it is worth our while to inquire at some
length as to the famous painter's accomplishments as a scientist.

From a passage in the works of Leonardo, first brought to light by
Venturi,%
\footnote{Etigene Muntz, \emph{Leonardo do Vinci, Artist, Thinker, and Man of}
\textit{Science}, 2 \textit{\emph{vols}}., New York, 1892. Vol.\ II.,
p.\ 73.%
} it would seem that the great painter anticipated Copernicus in determining
the movement of the earth. He made mathematical calculations to prove
this, and appears to have reached the definite conclusion that the
earth does move---or what amounts to the same thing, that the sun
does not move. Muntz is authority for the statement that in one of
his writings he declares, {}``\textit{Il} \textit{sole} \textit{non}
\textit{si} \textit{mouve}''---the sun does not move.

Among his inventions is a dynamometer for determining the traction
power of machines and animals, and his experiments with steam have
led some of his enthusiastic partisans to claim for him priority to
Watt in the invention of the steam-engine. In these experiments, however,
Leonardo seems to have advanced little beyond Hero of Alexandria and
his steam toy. Hero's steam-engine did nothing but rotate itself by
virtue of escaping jets of steam forced from the bent tubes, while
Leonardo's {}``steam-engine''\ {}``drove a ball weighing one talent
over a distance of six stadia.'' In a manuscript now in the library
of the \textit{\emph{Institut}} \emph{}\textit{\emph{de}} \emph{}\textit{\emph{France}}\emph{,}
\textit{\emph{Da}} \emph{}\textit{\emph{Vinci}} describes this engine
minutely. The action of this machine was due to the sudden conversion
of small quantities of water into steam ({}``smoke,''\ as he called
it)\ by coming suddenly in contact with a heated surface in a proper
receptacle, the rapidly formed steam acting as a propulsive force
after the manner of an explosive. It is really a steam-gun, rather
than a steam-engine, and it is not unlikely that the study of the
action of gunpowder may have suggested it to Leonardo.

%
\begin{figure}
\noindent \begin{center}\includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2Sc48}\end{center}

\noindent \begin{center}\noun{\small Roger Bacon}\end{center}
\end{figure}
It is believed that Leonardo is the true discoverer of the \textit{camera}-\textit{obscura},
although the Neapolitan philosopher, Giambattista Porta, who was not
born until some twenty years after the death of Leonardo, is usually
credited with first describing this device. There is little doubt,
however, that \textit{\emph{Da}} \emph{}\textit{\emph{Vinci}} understood
the principle of this mechanism, for he describes how such a camera
can be made by cutting a small, round hole through the shutter of
a darkened room, the reversed image of objects outside being shown
on the opposite wall.

Like other philosophers in all ages, he had observed a great number
of facts which he was unable to explain correctly. But such accumulations
of scientific observations are always interesting, as showing how
many centuries of observation frequently precede correct explanation.
He observed many facts about sounds, among others that blows struck
upon a bell produced sympathetic sounds in a bell of the same kind;
and that striking the string of a lute produced vibration in corresponding
strings of lutes strung to the same pitch. He knew, also, that sounds
could be heard at a distance at sea by listening at one end of a tube,
the other end of which was placed in the water; and that the same
expedient worked successfully on land, the end of the tube being placed
against the ground.

The knowledge of this great number of unexplained facts is often interpreted
by the admirers of \textit{\emph{Da}} \emph{}\textit{\emph{Vinci}},
as showing an almost occult insight into science many centuries in
advance of his time. Such interpretations, however, are illusive.
The observation, for example, that a tube placed against the ground
enables one to hear movements on the earth at a distance, is not in
itself evidence of anything more than acute scientific observation,
as a similar method is in use among almost every race of savages,
notably the American Indians. On the other hand, one is inclined to
give credence to almost any story of the breadth of knowledge of the
man who came so near anticipating Hutton, Lyell, and Darwin in his
interpretation of the geological records as he found them written
on the rocks.

It is in this field of geology that Leonardo is entitled to the greatest
admiration by modern scientists. He had observed the deposit of fossil
shells in various strata of rocks, even on the tops of mountains,
and he rejected once for all the theory that they had been deposited
there by the Deluge. He rightly interpreted their presence as evidence
that they had once been deposited at the bottom of the sea. This process
he assumed had taken hundreds and thousands of centuries, thus tacitly
rejecting the biblical tradition as to the date of the creation.

Notwithstanding the obvious interest that attaches to the investigations
of Leonardo, it must be admitted that his work in science remained
almost as infertile as that of his great precursor, Bacon. The really
stimulative work of this generation was done by a man of affairs,
who knew little of theoretical science except in one line, but who
pursued that one practical line until he achieved a wonderful result.
This man was Christopher Columbus. It is not necessary here to tell
the trite story of his accomplishment. Suffice it that his practical
demonstration of the rotundity of the earth is regarded by most modern
writers as marking an epoch in history. With the year of his voyage
the epoch of the Middle Ages is usually regarded as coming to an end.
It must not be supposed that any very sudden change came over the
aspect of scholarship of the time, but the preliminaries of great
things had been achieved, and when Columbus made his famous voyage
in 1492, the man was already alive who was to bring forward the first
great vitalizing thought in the field of pure science that the Western
world had originated for more than a thousand years. This man bore
the name of Kopernik, or in its familiar Anglicized form, Copernicus.
His life work and that of his disciples will claim our attention in
the succeeding chapter.


\chapter*{\raggedright IV. THE NEW COSMOLOGY---COPERNICUS TO KEPLER AND GALILEO}

\addcontentsline{toc}{chapter}{IV. THE NEW COSMOLOGY---\\
COPERNICUS TO KEPLER AND\\
GALILEO}

\markboth{A HISTORY OF SCIENCE, VOLUME II}{IV. THE NEW COSMOLOGY}

We have seen that the Ptolemaic astronomy, which was the accepted
doctrine throughout the Middle Ages, taught that the earth is round.
Doubtless there was a popular opinion current which regarded the earth
as flat, but it must be understood that this opinion had no champions
among men of science during the Middle Ages. When, in the year 1492,
Columbus sailed out to the west on his memorable voyage, his expectation
of reaching India had full scientific warrant, however much it may
have been scouted by certain ecclesiastics and by the average man
of the period. Nevertheless, we may well suppose that the successful
voyage of Columbus, and the still more demonstrative one made about
thirty years later by Magellan, gave the theory of the earth's rotundity
a certainty it could never previously have had. Alexandrian geographers
had measured the size of the earth, and had not hesitated to assert
that by sailing westward one might reach India. But there is a wide
gap between theory and practice, and it required the voyages of Columbus
and his successors to bridge that gap.

After the companions of Magellan completed the circumnavigation of
the globe, the general shape of our earth would, obviously, never
again be called in question. But demonstration of the sphericity of
the earth had, of course, no direct bearing upon the question of the
earth's position in the universe. Therefore the voyage of Magellan
served to fortify, rather than to dispute, the Ptolemaic theory. According
to that theory, as we have seen, the earth was supposed to lie immovable
at the centre of the universe; the various heavenly bodies, including
the sun, revolving about it in eccentric circles. We have seen that
several of the ancient Greeks, notably Aristarchus, disputed this
conception, declaring for the central position of the sun in the universe,
and the motion of the earth and other planets about that body. But
this revolutionary theory seemed so opposed to the ordinary observation
that, having been discountenanced by Hipparchus and Ptolemy, it did
not find a single important champion for more than a thousand years
after the time of the last great Alexandrian astronomer.

The first man, seemingly, to hark back to the Aristarchian conception
in the new scientific era that was now dawning was the noted cardinal,
\textit{\emph{Nikolaus}} of Cusa, who lived in the first half of the
fifteenth century, and was distinguished as a philosophical writer
and mathematician. His \textit{De} \textit{Docta} \textit{Ignorantia}
expressly propounds the doctrine of the earth's motion. No one, however,
paid the slightest attention to his suggestion, which, therefore,
merely serves to furnish us with another interesting illustration
of the futility of propounding even a correct hypothesis before the
time is ripe to receive it---particularly if the hypothesis is not
fully fortified by reasoning based on experiment or observation.

The man who was destined to put forward the theory of the earth's
motion in a way to command attention was born in 1473, at the village
of Thorn, in eastern Prussia. His name was Nicholas Copernicus. There
is no more famous name in the entire annals of science than this,
yet posterity has never been able fully to establish the lineage of
the famous expositor of the true doctrine of the solar system. The
city of Thorn lies in a province of that border territory which was
then under control of Poland, but which subsequently became a part
of Prussia. It is claimed that the aspects of the city were essentially
German, and it is admitted that the mother of Copernicus belonged
to that race. The nationality of the father is more in doubt, but
it is urged that Copernicus used German as his mother-tongue. His
great work was, of course, written in Latin, according to the custom
of the time; but it is said that, when not employing that language,
he always wrote in German. The disputed nationality of Copernicus
strongly suggests that he came of a mixed racial lineage, and we are
reminded again of the influences of those ethnical minglings to which
we have previously more than once referred. The acknowledged centres
of civilization towards the close of the fifteenth century were Italy
and Spain. Therefore, the birthplace of Copernicus lay almost at the
confines of civilization, reminding us of that earlier period when
Greece was the centre of culture, but when the great Greek thinkers
were born in Asia Minor and in Italy.

%
\begin{figure}
\noindent \begin{center}\includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2Sc54}\end{center}

\noindent \begin{center}\noun{\small Nicolaus Copernicus}\end{center}{\small \par}

\noindent \emph{\footnotesize (From the painting in possession of
the Royal Society) }
\end{figure}
As a young man, Copernicus made his way to Vienna to study medicine,
and subsequently he journeyed into Italy and remained there many years,
About the year 1500 he held the chair of mathematics in a college
at Rome. Subsequently he returned to his native land and passed his
remaining years there, dying at Domkerr, in Frauenburg, East Prussia,
in the year 1543.

It would appear that Copernicus conceived the idea of the heliocentric
system of the universe while he was a comparatively young man, since
in the introduction to his great work, which he addressed to Pope
Paul III., he states that he has pondered his system not merely nine
years, in accordance with the maxim of Horace, but well into the fourth
period of nine years. Throughout a considerable portion of this period
the great work of Copernicus was in manuscript, but it was not published
until the year of his death. The reasons for the delay are not very
fully established. Copernicus undoubtedly taught his system throughout
the later decades of his life. He himself tells us that he had even
questioned whether it were not better for him to confine himself to
such verbal teaching, following thus the example of Pythagoras. Just
as his life was drawing to a close, he decided to pursue the opposite
course, and the first copy of his work is said to have been placed
in his hands as he lay on his deathbed.

The violent opposition which the new system met from ecclesiastical
sources led subsequent commentators to suppose that Copernicus had
delayed publication of his work through fear of the church authorities.
There seems, however, to be no direct evidence for this opinion. It
has been thought significant that Copernicus addressed his work to
the pope. It is, of course, quite conceivable that the aged astronomer
might wish by this means to demonstrate that he wrote in no spirit
of hostility to the church. His address to the pope might have been
considered as a desirable shield precisely because the author recognized
that his work must needs meet with ecclesiastical criticism. Be that
as it may, Copernicus was removed by death from the danger of attack,
and it remained for his disciples of a later generation to run the
gauntlet of criticism and suffer the charges of heresy.

The work of Copernicus, published thus in the year 1543 at Nuremberg,
bears the title \emph{De Orbium C}\oe{}\emph{lestium Revolutionibus}.

It is not necessary to go into details as to the cosmological system
which Copernicus advocated, since it is familiar to every one. In
a word, he supposed the sun to be the centre of all the planetary
motions, the earth taking its place among the other planets, the list
of which, as known at that time, comprised Mercury, Venus, the Earth,
Mars, Jupiter, and Saturn. The fixed stars were alleged to be stationary,
and it was necessary to suppose that they are almost infinitely distant,
inasmuch as they showed to the observers of that time no parallax;
that is to say, they preserved the same apparent position when viewed
from the opposite points of the earth's orbit.

But let us allow Copernicus to speak for himself regarding his system,
His exposition is full of interest. We quote first the introduction
just referred to, in which appeal is made directly to the pope.

\begin{quotation}
{}``I can well believe, most holy father, that certain people, when
they hear of my attributing motion to the earth in these books of
mine, will at once declare that such an opinion ought to be rejected.
Now, my own theories do not please me so much as not to consider what
others may judge of them. Accordingly, when I began to reflect upon
what those persons who accept the stability of the earth, as confirmed
by the opinion of many centuries, would say when I claimed that the
earth moves, I hesitated for a long time as to whether I should publish
that which I have written to demonstrate its motion, or whether it
would not be better to follow the example of the Pythagoreans, who
used to hand down the secrets of philosophy to their relatives and
friends only in oral form. As I well considered all this, I was almost
impelled to put the finished work wholly aside, through the scorn
I had reason to anticipate on account of the newness and apparent
contrariness to reason of my theory.

{}``My friends, however, dissuaded me from such a course and admonished
me that I ought to publish my book, which had lain concealed in my
possession not only nine years, but already into four times the ninth
year. Not a few other distinguished and very learned men asked me
to do the same thing, and told me that I ought not, on account of
my anxiety, to delay any longer in consecrating my work to the general
service of mathematicians.

{}``But your holiness will perhaps not so much wonder that I have
dared to bring the results of my night labors to the light of day,
after having taken so much care in elaborating them, but is waiting
instead to hear how it entered my mind to imagine that the earth moved,
contrary to the accepted opinion of mathematicians---nay, almost contrary
to ordinary human understanding. Therefore I will not conceal from
your holiness that what moved me to consider another way of reckoning
the motions of the heavenly bodies was nothing else than the fact
that the mathematicians do not agree with one another in their investigations.
In the first place, they are so uncertain about the motions of the
sun and moon that they cannot find out the length of a full year.
In the second place, they apply neither the same laws of cause and
effect, in determining the motions of the sun and moon and of the
five planets, nor the same proofs. Some employ only concentric circles,
others use eccentric and epicyclic ones, with which, however, they
do not fully attain the desired end. They could not even discover
nor compute the main thing---namely, the form of the universe and
the symmetry of its parts. It was with them as if some should, from
different places, take hands, feet, head, and other parts of the body,
which, although very beautiful, were not drawn in their proper relations,
and, without making them in any way correspond, should construct a
monster instead of a human being.

{}``Accordingly, when I had long reflected on this uncertainty of
mathematical tradition, I took the trouble to read again the books
of all the philosophers I could get hold of, to see if some one of
them had not once believed that there were other motions of the heavenly
bodies. First I found in Cicero that Niceties had believed in the
motion of the earth. Afterwards I found in Plutarch, likewise, that
some others had held the same opinion. This induced me also to begin
to consider the movability of the earth, and, although the theory
appeared contrary to reason, I did so because I knew that others before
me had been allowed to assume rotary movements at will, in order to
explain the phenomena of these celestial bodies. I was of the opinion
that I, too, might be permitted to see whether, by presupposing motion
in the earth, more reliable conclusions than hitherto reached could
not be discovered for the rotary motions of the spheres. And thus,
acting on the hypothesis of the motion which, in the following book,
I ascribe to the earth, and by long and continued observations, I
have finally discovered that if the motion of the other planets be
carried over to the relation of the earth and this is made the basis
for the rotation of every star, not only will the phenomena of the
planets be explained thereby, but also the laws and the size of the
stars; all their spheres and the heavens themselves will appear so
harmoniously connected that nothing could be changed in any part of
them without confusion in the remaining parts and in the whole universe.
I do not doubt that clever and learned men will agree with me if they
are willing fully to comprehend and to consider the proofs which I
advance in the book before us. In order, however, that both the learned
and the unlearned may see that I fear no man's judgment, I wanted
to dedicate these, my night labors, to your holiness, rather than
to any one else, because you, even in this remote corner of the earth
where I live, are held to be the greatest in dignity of station and
in love for all sciences and for mathematics, so that you, through
your position and judgment, can easily suppress the bites of slanderers,
although the proverb says that there is no remedy against the bite
of calumny.''
\end{quotation}
{}

In chapter X.\ of book I., {}``On the Order of the Spheres,''\ occurs
a more detailed presentation of the system, as follows:\ 

\begin{quotation}
{}``That which Martianus Cap\-el\-la, and a few other Latins, very
well knew, appears to me extremely noteworthy. He believed that Venus
and Mercury revolve about the sun as their centre and that they cannot
go farther away from it than the circles of their orbits permit, since
they do not revolve about the earth like the other planets. According
to this theory, then, Mercury's orbit would be included within that
of Venus, which is more than twice as great, and would find room enough
within it for its revolution.

{}``If, acting upon this supposition, we connect Saturn, Jupiter,
and Mars with the same centre, keeping in mind the greater extent
of their orbits, which include the earth's sphere besides those of
Mercury and Venus, we cannot fail to see the explanation of the regular
order of their motions. He is certain that Saturn, Jupiter, and Mars
are always nearest the earth when they rise in the evening---that
is, when they appear over against the sun, or the earth stands between
them and the sun---but that they are farthest from the earth when
they set in the evening---that is, when we have the sun between them
and the earth. This proves sufficiently that their centre belongs
to the sun and is the same about which the orbits of Venus and Mercury
circle. Since, however, all have one centre, it is necessary for the
space intervening between the orbits of Venus and Mars to include
the earth with her accompanying moon and all that is beneath the moon;
for the moon, which stands unquestionably nearest the earth, can in
no way be separated from her, especially as there is sufficient room
for the moon in the aforesaid space. Hence we do not hesitate to claim
that the whole system, which includes the moon with the earth for
its centre, makes the round of that great circle between the planets,
in yearly motion about the sun, and revolves about the centre of the
universe, in which the sun rests motionless, and that all which looks
like motion in the sun is explained by the motion of the earth. The
extent of the universe, however, is so great that, whereas the distance
of the earth from the sun is considerable in comparison with the size
of the other planetary orbits, it disappears when compared with the
sphere of the fixed stars. I hold this to be more easily comprehensible
than when the mind is confused by an almost endless number of circles,
which is necessarily the case with those who keep the earth in the
middle of the universe. Although this may appear incomprehensible
and contrary to the opinion of many, I shall, if God wills, make it
clearer than the sun, at least to those who are not ignorant of mathematics.

{}``The order of the spheres is as follows: The first and lightest
of all the spheres is that of the fixed stars, which includes itself
and all others, and hence is motionless as the place in the universe
to which the motion and position of all other stars is referred.

{}``Then follows the outermost planet, Saturn, which completes its
revolution around the sun in thirty years; next comes Jupiter with
a twelve years'\ revolution; then Mars, which completes its course
in two years. The fourth one in order is the yearly revolution which
includes the earth with the moon's orbit as an epicycle. In the fifth
place is Venus with a revolution of nine months. The sixth place is
taken by Mercury, which completes its course in eighty days. In the
middle of all stands the sun, and who could wish to place the lamp
of this most beautiful temple in another or better place. Thus, in
fact, the sun, seated upon the royal throne, controls the family of
the stars which circle around him. We find in their order a harmonious
connection which cannot be found elsewhere. Here the attentive observer
can see why the waxing and waning of Jupiter seems greater than with
Saturn and smaller than with Mars, and again greater with Venus than
with Mercury. Also, why Saturn, Jupiter, and Mars are nearer to the
earth when they rise in the evening than when they disappear in the
rays of the sun. More prominently, however, is it seen in the case
of Mars, which when it appears in the heavens at night, seems to equal
Jupiter in size, but soon afterwards is found among the stars of second
magnitude. All of this results from the same cause---namely, from
the earth's motion. The fact that nothing of this is to be seen in
the case of the fixed stars is a proof of their immeasurable distance,
which makes even the orbit of yearly motion or its counterpart invisible
to us.''%
\footnote{Copernicus, \textit{Uber} \textit{die} \emph{Kreisbewegungen} \textit{der}
\emph{Welfkorper}, \textit{\emph{trans}}.\ from Dannemann's \emph{Geschichle
du Naturwissenschaften}, 2 \textit{\emph{vols}}., Leipzig, 1896.%
}
\end{quotation}
{}

The fact that the stars show no parallax had been regarded as an important
argument against the motion of the earth, and it was still so considered
by the opponents of the system of Copernicus. It had, indeed, been
necessary for Aristarchus to explain the fact as due to the extreme
distance of the stars; a perfectly correct explanation, but one that
implies distances that are altogether inconceivable. It remained for
nineteenth-century astronomers to show, with the aid of instruments
of greater precision, that certain of the stars have a parallax. But
long before this demonstration had been brought forward, the system
of Copernicus had been accepted as a part of common knowledge.

While Copernicus postulated a cosmical scheme that was correct as
to its main features, he did not altogether break away from certain
defects of the Ptolemaic hypothesis. Indeed, he seems to have retained
as much of this as practicable, in deference to the prejudice of his
time. Thus he records the planetary orbits as circular, and explains
their eccentricities by resorting to the theory of epicycles, quite
after the Ptolemaic method. But now, of course, a much more simple
mechanism sufficed to explain the planetary motions, since the orbits
were correctly referred to the central sun and not to the earth.

Needless to say, the revolutionary conception of Copernicus did not
meet with immediate acceptance. A number of prominent astronomers,
however, took it up almost at once, among these being Rhaeticus, who
wrote a commentary on the evolutions; Erasmus Reinhold, the author
of the Prutenic tables; Rothmann, astronomer to the Landgrave of Hesse,
and Maestlin, the instructor of Kepler. The Prutenic tables, just
referred to, so called because of their Prussian origin, were considered
an improvement on the tables of Copernicus, and were highly esteemed
by the astronomers of the time. The commentary of Rhaeticus gives
us the interesting information that it was the observation of the
orbit of Mars and of the very great difference between his apparent
diameters at different times which first led Copernicus to conceive
the heliocentric idea. Of Reinhold it is recorded that he considered
the orbit of Mercury elliptical, and that he advocated a theory of
the moon, according to which her epicycle revolved on an elliptical
orbit, thus in a measure anticipating one of the great discoveries
of Kepler to which we shall refer presently. The Landgrave of Hesse
was a practical astronomer, who produced a catalogue of fixed stars
which has been compared with that of Tycho Brahe. He was assisted
by Rothmann and by Justus Byrgius. Maestlin, the preceptor of Kepler,
is reputed to have been the first modern observer to give a correct
explanation of the light seen on portions of the moon not directly
illumined by the sun. He explained this as not due to any proper light
of the moon itself, but as light reflected from the earth. Certain
of the Greek philosophers, however, are said to have given the same
explanation, and it is alleged also that \textit{\emph{Leonardo}}
\emph{}\textit{\emph{da}} \emph{}\textit{\emph{Vinci}} anticipated
Maestlin in this regard.

While, various astronomers of some eminence thus gave support to the
Copernican system, almost from the beginning, it unfortunately chanced
that by far the most famous of the immediate successors of Copernicus
declined to accept the theory of the earth's motion. This was Tycho
Brahe, one of the greatest observing astronomers of any age. Tycho
Brahe was a Dane, born at Knudstrup in the year 1546. He died in 1601
at Prague, in Bohemia. During a considerable portion of his life he
found a patron in Frederick, King of Denmark, who assisted him to
build a splendid observatory on the Island of Huene. On the death
of his patron Tycho moved to Germany, where, as good luck would have
it, he came in contact with the youthful Kepler, and thus, no doubt,
was instrumental in stimulating the ambitions of one who in later
years was to be known as a far greater theorist than himself. As has
been said, Tycho rejected the Copernican theory of the earth's motion.
It should be added, however, that he accepted that part of the Copernican
theory which makes the sun the centre of all the planetary motions,
the earth being excepted. He thus developed a system of his own, which
was in some sort a compromise between the Ptolemaic and the Copernican
systems. As Tycho conceived it, the sun revolves about the earth,
carrying with it the planets-Mercury, Venus, Mars, Jupiter, and Saturn,
which planets have the sun and not the earth as the centre of their
orbits. This cosmical scheme, it should be added, may be made to explain
the observed motions of the heavenly bodies, but it involves a much
more complex mechanism than is postulated by the Copernican theory.

Various explanations have been offered of the conservatism which held
the great Danish astronomer back from full acceptance of the relatively
simple and, as we now know, correct Copernican doctrine. From our
latter-day point of view, it seems so much more natural to accept
than to reject the Copernican system, that we find it difficult to
put ourselves in the place of a sixteenth-century observer. Yet if
we recall that the traditional view, having warrant of acceptance
by nearly all thinkers of every age, recorded the earth as a fixed,
immovable body, we shall see that our surprise should be excited rather
by the thinker who can break away from this view than by the one who
still tends to cling to it.

Moreover, it is useless to attempt to disguise the fact that something
more than a mere vague tradition was supposed to support the idea
of the earth's overshadowing importance in the cosmical scheme. The
sixteenth-century mind was overmastered by the tenets of ecclesiasticism,
and it was a dangerous heresy to doubt that the Hebrew writings, upon
which ecclesiasticism based its claim, contained the last word regarding
matters of science. But the writers of the Hebrew text had been under
the influence of that Babylonian conception of the universe which
accepted the earth as unqualifiedly central---which, indeed, had never
so much as conceived a contradictory hypothesis; and so the Western
world, which had come to accept these writings as actually supernatural
in origin, lay under the spell of Oriental ideas of a pre-scientific
era. In our own day, no one speaking with authority thinks of these
Hebrew writings as having any scientific weight whatever. Their interest
in this regard is purely antiquarian; hence from our changed point
of view it seems scarcely credible that Tycho Brahe can have been
in earnest when he quotes the Hebrew traditions as proof that the
sun revolves about the earth. Yet we shall see that for almost three
centuries after the time of Tycho, these same dreamings continued
to be cited in opposition to those scientific advances which new observations
made necessary; and this notwithstanding the fact that the Oriental
phrasing is, for the most part, poetically ambiguous and susceptible
of shifting interpretations, as the criticism of successive generations
has amply testified.

As we have said, Tycho Brahe, great observer as he was, could not
shake himself free from the Oriental incubus. He began his objections,
then, to the Copernican system by quoting the adverse testimony of
a Hebrew prophet who lived more than a thousand years B.C. All of
this shows sufficiently that Tycho Brahe was not a great theorist.
He was essentially an observer, but in this regard he won a secure
place in the very first rank. Indeed, he was easily the greatest observing
astronomer since Hipparchus, between whom and himself there were many
points of resemblance. Hipparchus, it will be recalled, rejected the
Aristarchian conception of the universe just as Tycho rejected the
conception of Copernicus.

But if Tycho propounded no great generalizations, the list of specific
advances due to him is a long one, and some of these were to prove
important aids in the hands of later workers to the secure demonstration
of the Copernican idea. One of his most important series of studies
had to do with comets. Regarding these bodies there had been the greatest
uncertainty in the minds of astronomers. The greatest variety of opinions
regarding them prevailed; they were thought on the one hand to be
divine messengers, and on the other to be merely igneous phenomena
of the earth's atmosphere. Tycho Brahe declared that a comet which
he observed in the year 1577 had no parallax, proving its extreme
distance. The observed course of the comet intersected the planetary
orbits, which fact gave a quietus to the long-mooted question as to
whether the Ptolemaic spheres were transparent solids or merely imaginary;
since the comet was seen to intersect these alleged spheres, it was
obvious that they could not be the solid substance that they were
commonly imagined to be, and this fact in itself went far towards
discrediting the Ptolemaic system. It should be recalled, however,
that this supposition of tangible spheres for the various planetary
and stellar orbits was a medi\ae{}val interpretation of Ptolemy's
theory rather than an interpretation of Ptolemy himself, there being
nothing to show that the Alexandrian astronomer regarded his cycles
and epicycles as other than theoretical.

%
\begin{figure}
\noindent \begin{center}\includegraphics[  width=1.0\columnwidth,
  height=0.90\paperwidth,
  keepaspectratio]{2hsci10-Wil2Sc68}\end{center}

\noindent \begin{center}\noun{\small Tycho Brahe's Quadrant}\end{center}{\small \par}

\noindent \emph{\footnotesize (From Dannemann's} {\footnotesize Geschichte
der Naturwissenschaften}\emph{\footnotesize .) }
\end{figure}
An interesting practical discovery made by Tycho was his method of
determining the latitude of a place by means of two observations made
at an interval of twelve hours. Hitherto it had been necessary to
observe the sun's angle on the equinoctial days, a period of six months
being therefore required. Tycho measured the angle of elevation of
some star situated near the pole, when on the meridian, and then,
twelve hours later, measured the angle of elevation of the same star
when it again came to the meridian at the opposite point of its apparent
circle about the polestar. Half the sum of these angles gives the
latitude of the place of observation.

As illustrating the accuracy of Tycho's observations, it may be noted
that he rediscovered a third inequality of the moon's motion at its
variation, he, in common with other European astronomers, being then
quite unaware that this inequality had been observed by an Arabian
astronomer. Tycho proved also that the angle of inclination of the
moon's orbit to the ecliptic is subject to slight variation.

The very brilliant new star which shone forth suddenly in the constellation
of Cassiopeia in the year 1572, was made the object of special studies
by Tycho, who proved that the star had no sensible parallax and consequently
was far beyond the planetary regions. The appearance of a new star
was a phenomenon not unknown to the ancients, since Pliny records
that Hipparchus was led by such an appearance to make his catalogue
of the fixed stars. But the phenomenon is sufficiently uncommon to
attract unusual attention. A similar phenomenon occurred in the year
1604, when the new star---in this case appearing in the constellation
of Serpentarius---was explained by Kepler as probably proceeding from
a vast combustion. This explanation---in which Kepler is said to have
followed Tycho---is fully in accord with the most recent theories
on the subject, as we shall see in due course. It is surprising to
hear Tycho credited with so startling a theory, but, on the other
hand, such an explanation is precisely what should be expected from
the other astronomer named. For Johann Kepler, or, as he was originally
named, Johann von Kappel, was one of the most speculative astronomers
of any age. He was forever theorizing, but such was the peculiar quality
of his mind that his theories never satisfied him for long unless
he could put them to the test of observation. Thanks to this happy
combination of qualities, Kepler became the discoverer of three famous
laws of planetary motion which lie at the very foundation of modern
astronomy, and which were to be largely instrumental in guiding Newton
to his still greater generalization. These laws of planetary motion
were vastly important as corroborating the Copernican theory of the
universe, though their position in this regard was not immediately
recognized by contemporary thinkers. Let us examine with some detail
into their discovery, meantime catching a glimpse of the life history
of the remarkable man whose name they bear.


\section*{\raggedright JOHANN KEPLER AND THE LAWS OF PLANETARY MOTION}

\addcontentsline{toc}{section}{JOHANN KEPLER AND THE LAWS OF\\
PLANETARY MOTION}

Johann Kepler was born the 27th of December, 1571, in the little town
of Weil, in Wurtemburg. He was a weak, sickly child, further enfeebled
by a severe attack of small-pox. It would seem paradoxical to assert
that the parents of such a genius were mismated, but their home was
not a happy one, the mother being of a nervous temperament, which
perhaps in some measure accounted for the genius of the child. The
father led the life of a soldier, and finally perished in the campaign
against the Turks. Young Kepler's studies were directed with an eye
to the ministry. After a preliminary training he attended the university
at \textit{\emph{Tubingen}}, where he came under the influence of
the celebrated Maestlin and became his life-long friend.

Curiously enough, it is recorded that at first Kepler had no taste
for astronomy or for mathematics. But the doors of the ministry being
presently barred to him, he turned with enthusiasm to the study of
astronomy, being from the first an ardent advocate of the Copernican
system. His teacher, Maestlin, accepted the same doctrine, though
he was obliged, for theological reasons, to teach the Ptolemaic system,
as also to oppose the Gregorian reform of the calendar.

The Gregorian calendar, it should be explained, is so called because
it was instituted by Pope Gregory XIII., who put it into effect in
the year 1582, up to which time the so-called Julian calendar, as
introduced by Julius C\ae{}sar, had been everywhere accepted in Christendom.
This Julian calendar, as we have seen, was a great improvement on
preceding ones, but still lacked something of perfection inasmuch
as its theoretical day differed appreciably from the actual day. In
the course of fifteen hundred years, since the time of C\ae{}sar,
this defect amounted to a discrepancy of about eleven days. Pope Gregory
proposed to correct this by omitting ten days from the calendar, which
was done in September, 1582. To prevent similar inaccuracies in the
future, the Gregorian calendar provided that once in four centuries
the additional day to make a leap-year should be omitted, the date
selected for such omission being the last year of every fourth century.
Thus the years 1500, 1900, and 2300, A.D., would not be leap-years.
By this arrangement an approximate rectification of the calendar was
effected, though even this does not make it absolutely exact.

Such a rectification as this was obviously desirable, but there was
really no necessity for the omission of the ten days from the calendar.
The equinoctial day had shifted so that in the year 1582 it fell on
the 10th of March and September. There was no reason why it should
not have remained there. It would greatly have simplified the task
of future historians had Gregory contented himself with providing
for the future stability of the calendar without making the needless
shift in question. We are so accustomed to think of the 21st of March
and 21st of September as the natural periods of the equinox, that
we are likely to forget that these are purely arbitrary dates for
which the 10th might have been substituted without any inconvenience
or inconsistency.

But the opposition to the new calendar, to which reference has been
made, was not based on any such considerations as these. It was due,
largely at any rate, to the fact that Germany at this time was under
sway of the Lutheran revolt against the papacy. So effective was the
opposition that the Gregorian calendar did not come into vogue in
Germany until the year 1699. It may be added that England, under stress
of the same manner of prejudice, held out against the new reckoning
until the year 1751, while Russia does not accept it even now.

%
\begin{figure}
\noindent \begin{center}\includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2Sc72}\end{center}

\noindent \begin{center}\noun{\small Johann Kepler}\end{center}
\end{figure}
As the Protestant leaders thus opposed the papal attitude in a matter
of so practical a character as the calendar, it might perhaps have
been expected that the Lutherans would have had a leaning towards
the Copernican theory of the universe, since this theory was opposed
by the papacy. Such, however, was not the case. Luther himself pointed
out with great strenuousness, as a final and demonstrative argument,
the fact that Joshua commanded the sun and not the earth to stand
still; and his followers were quite as intolerant towards the new
teaching as were their ultramontane opponents. Kepler himself was,
at various times, to feel the restraint of ecclesiastical opposition,
though he was never subjected to direct persecution, as was his friend
and contemporary, Galileo. At the very outset of Kepler's career there
was, indeed, question as to the publication of a work he had written,
because that work took for granted the truth of the Copernican doctrine.
This work appeared, however, in the year 1596. It bore the title \textit{Mysterium}
\emph{Cosmographium}, and it attempted to explain the positions of
the various planetary bodies. Copernicus had devoted much time to
observation of the planets with reference to measuring their distance,
and his efforts had been attended with considerable success. He did
not, indeed, know the actual distance of the sun, and, therefore,
was quite unable to fix the distance of any planet; but, on the other
hand, he determined the relative distance of all the planets then
known, as measured in terms of the sun's distance, with remarkable
accuracy.

With these measurements as a guide, Kepler was led to a very fanciful
theory, according to which the orbits of the five principal planets
sustain a peculiar relation to the five regular solids of geometry.
His theory was this: {}``Around the orbit of the earth describe a
dodecahedron---the circle comprising it will be that of Mars; around
Mars describe a tetrahedron---the circle comprising it will be that
of Jupiter; around Jupiter describe a cube---the circle comprising
it will be that of Saturn; now within the earth's orbit inscribe an
icosahedron---the inscribed circle will be that of Venus; in the orbit
of Venus inscribe an octahedron---the circle inscribed will be that
of Mercury.''

Though this arrangement was a fanciful one, which no one would now
recall had not the theorizer obtained subsequent fame on more substantial
grounds, yet it evidenced a philosophical spirit on the part of the
astronomer which, misdirected as it was in this instance, promised
well for the future. Tycho Brahe, to whom a copy of the work was sent,
had the acumen to recognize it as a work of genius. He summoned the
young astronomer to be his assistant at Prague, and no doubt the association
thus begun was instrumental in determining the character of Kepler's
future work. It was precisely the training in minute observation that
could avail most for a mind which, like Kepler's, tended instinctively
to the formulation of theories. When Tycho Brahe died, in 1601, Kepler
became his successor. In due time he secured access to all the unpublished
observations of his great predecessor, and these were of inestimable
value to him in the progress of his own studies.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2Sc74}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Kepler's Mechanism to Illustrate
his (Incorrect) Early Theory as to the Orbits of the Planetary Bodies}\end{center}
\end{figure}
Kepler was not only an ardent worker and an enthusiastic theorizer,
but he was an indefatigable writer, and it pleased him to take the
public fully into his confidence, not merely as to his successes,
but as to his failures. Thus his works elaborate false theories as
well as correct ones, and detail the observations through which the
incorrect guesses were refuted by their originator. Some of these
accounts are highly interesting, but they must not detain us here.
For our present purpose it must suffice to point out the three important
theories, which, as culled from among a score or so of incorrect ones,
Kepler was able to demonstrate to his own satisfaction and to that
of subsequent observers. Stated in a few words, these theories, which
have come to bear the name of Kepler's Laws, are the following:\ 

1. That the planetary orbits are not circular, but elliptical, the
sun occupying one focus of the ellipses.

2. That the speed of planetary motion varies in different parts of
the orbit in such a way that an imaginary line drawn from the sun
to the planet---that is to say, the radius vector of the planet's
orbit---always sweeps the same area in a given time.

These two laws Kepler published as early as 1609. Many years more
of patient investigation were required before he found out the secret
of the relation between planetary distances and times of revolution
which his third law expresses. In 1618, however, he was able to formulate
this relation also, as follows:\ 

3. The squares of the distance of the various planets from the sun
are proportional to the cubes of their periods of revolution about
the sun.

All these laws, it will be observed, take for granted the fact that
the sun is the centre of the planetary orbits. It must be understood,
too, that the earth is constantly regarded, in accordance with the
Copernican system, as being itself a member of the planetary system,
subject to precisely the same laws as the other planets. Long familiarity
has made these wonderful laws of Kepler seem such a matter of course
that it is difficult now to appreciate them at their full value. Yet,
as has been already pointed out, it was the knowledge of these marvellously
simple relations between the planetary orbits that laid the foundation
for the Newtonian law of universal gravitation. Contemporary judgment
could not, of course, anticipate this culmination of a later generation.
What it could understand was that the first law of Kepler attacked
one of the most time-honored of metaphysical conceptions---namely,
the Aristotelian idea that the circle is the perfect figure, and hence
that the planetary orbits must be circular. Not even Copernicus had
doubted the validity of this assumption. That Kepler dared dispute
so firmly fixed a belief, and one that seemingly had so sound a philosophical
basis, evidenced the iconoclastic nature of his genius. That he did
not rest content until he had demonstrated the validity of his revolutionary
assumption shows how truly this great theorizer made his hypotheses
subservient to the most rigid inductions.


\section*{\raggedright GALILEO \textit{\emph{GALILEI}}}

\addcontentsline{toc}{section}{GALILEO GALILEI}

While Kepler was solving these riddles of planetary motion, there
was an even more famous man in Italy whose championship of the Copernican
doctrine was destined to give the greatest possible publicity to the
new ideas. This was Galileo \textit{\emph{Galilei}}, one of the most
extraordinary scientific observers of any age. Galileo was born at
Pisa, on the 18th of February (old style), 1564. The day of his birth
is doubly memorable, since on the same day the greatest Italian of
the preceding epoch, Michael Angelo, breathed his last. Persons fond
of symbolism have found in the coincidence a forecast of the transit
from the artistic to the scientific epoch of the later Renaissance.
Galileo came of an impoverished noble family. He was educated for
the profession of medicine, but did not progress far before his natural
proclivities directed him towards the physical sciences. Meeting with
opposition in Pisa, he early accepted a call to the chair of natural
philosophy in the University of Padua, and later in life he made his
home at Florence. The mechanical and physical discoveries of Galileo
will claim our attention in another chapter. Our present concern is
with his contribution to the Copernican theory.

Galileo himself records in a letter to Kepler that he became a convert
to this theory at an early day. He was not enabled, however, to make
any marked contribution to the subject, beyond the influence of his
general teachings, until about the year 1610. The brilliant contributions
which he made were due largely to a single discovery---namely, that
of the telescope. Hitherto the astronomical observations had been
made with the unaided eye. Glass lenses had been known since the thirteenth
century, but, until now, no one had thought of their possible use
as aids to distant vision. The question of priority of discovery has
never been settled. It is admitted, however, that the chief honors
belong to the opticians of the Netherlands.

As early as the year 1590 the Dutch optician Zacharias Jensen placed
a concave and a convex lens respectively at the ends of a tube about
eighteen inches long, and used this instrument for the purpose of
magnifying small objects---producing, in short, a crude microscope.
Some years later, Johannes Lippershey, of whom not much is known except
that he died in 1619, experimented with a somewhat similar combination
of lenses, and made the startling observation that the weather-vane
on a distant church-steeple seemed to be brought much nearer when
viewed through the lens. The combination of lenses he employed is
that still used in the construction of opera-glasses; the Germans
still call such a combination a Dutch telescope.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2Sc78}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Galileo Galilei}\end{center}
\end{figure}
Doubtless a large number of experimenters took the matter up and the
fame of the new instrument spread rapidly abroad. Galileo, down in
Italy, heard rumors of this remarkable contrivance, through the use
of which it was said {}``distant objects might be seen as clearly
as those near at hand.'' He at once set to work to construct for
himself a similar instrument, and his efforts were so far successful
that at first he {}``saw objects three times as near and nine times
enlarged.'' Continuing his efforts, he presently so improved his
glass that objects were enlarged almost a thousand times and made
to appear thirty times nearer than when seen with the naked eye. Naturally
enough, Galileo turned this fascinating instrument towards the skies,
and he was almost immediately rewarded by several startling discoveries.
At the very outset, his magnifying-glass brought to view a vast number
of stars that are invisible to the naked eye, and enabled the observer
to reach the conclusion that the hazy light of the Milky Way is merely
due to the aggregation of a vast number of tiny stars.

Turning his telescope towards the moon, Galileo found that body rough
and earth-like in contour, its surface covered with mountains, whose
height could be approximately measured through study of their shadows.
This was disquieting, because the current Aristotelian doctrine supposed
the moon, in common with the planets, to be a perfectly spherical,
smooth body. The metaphysical idea of a perfect universe was sure
to be disturbed by this seemingly rough workmanship of the moon. Thus
far, however, there was nothing in the observations of Galileo to
bear directly upon the Copernican theory; but when an inspection was
made of the planets the case was quite different. With the aid of
his telescope, Galileo saw that Venus, for example, passes through
phases precisely similar to those of the moon, due, of course, to
the same cause. Here, then, was demonstrative evidence that the planets
are dark bodies reflecting the light of the sun, and an explanation
was given of the fact, hitherto urged in opposition to the Copernican
theory, that the inferior planets do not seem many times brighter
when nearer the earth than when in the most distant parts of their
orbits; the explanation being, of course, that when the planets are
between the earth and the sun only a small portion of their illumined
surfaces is visible from the earth.

On inspecting the planet Jupiter, a still more striking revelation
was made, as four tiny stars were observed to occupy an equatorial
position near that planet, and were seen, when watched night after
night, to be circling about the planet, precisely as the moon circles
about the earth. Here, obviously, was a miniature solar system---a
tangible object-lesson in the Copernican theory. In honor of the ruling
Florentine house of the period, Galileo named these moons of Jupiter,
Medicean stars.

Turning attention to the sun itself, Galileo observed on the surface
of that luminary a spot or blemish which gradually changed its shape,
suggesting that changes were taking place in the substance of the
sun---changes obviously incompatible with the perfect condition demanded
by the metaphysical theorists. But however disquieting for the conservative,
the sun's spots served a most useful purpose in enabling Galileo to
demonstrate that the sun itself revolves on its axis, since a given
spot was seen to pass across the disk and after disappearing to reappear
in due course. The period of rotation was found to be about twenty-four
days.

It must be added that various observers disputed priority of discovery
of the sun's spots with Galileo. Unquestionably a sun-spot had been
seen by earlier observers, and by them mistaken for the transit of
an inferior planet. Kepler himself had made this mistake. Before the
day of the telescope, he had viewed the image of the sun as thrown
on a screen in a \textit{camera}-\textit{obscura}, and had observed
a spot on the disk which be interpreted as representing the planet
Mercury, but which, as is now known, must have been a sun-spot, since
the planetary disk is too small to have been revealed by this method.
Such observations as these, however interesting, cannot be claimed
as discoveries of the sun-spots. It is probable, however, that several
discoverers (notably Johann Fabricius)\ made the telescopic observation
of the spots, and recognized them as having to do with the sun's surface,
almost simultaneously with Galileo. One of these claimants was a Jesuit
named Scheiner, and the jealousy of this man is said to have had a
share in bringing about that persecution to which we must now refer.

There is no more famous incident in the history of science than the
heresy trial through which Galileo was led to the nominal renunciation
of his cherished doctrines. There is scarcely another incident that
has been commented upon so variously. Each succeeding generation has
put its own interpretation on it. The facts, however, have been but
little questioned. It appears that in the year 1616 the church became
at last aroused to the implications of the heliocentric doctrine of
the universe. Apparently it seemed clear to the church authorities
that the authors of the Bible believed the world to be immovably fixed
at the centre of the universe. Such, indeed, would seem to be the
natural inference from various familiar phrases of the Hebrew text,
and what we now know of the status of Oriental science in antiquity
gives full warrant to this interpretation. There is no reason to suppose
that the conception of the subordinate place of the world in the solar
system had ever so much as occurred, even as a vague speculation,
to the authors of Genesis. In common with their contemporaries, they
believed the earth to be the all-important body in the universe, and
the sun a luminary placed in the sky for the sole purpose of giving
light to the earth. There is nothing strange, nothing anomalous, in
this view; it merely reflects the current notions of Oriental peoples
in antiquity. What is strange and anomalous is the fact that the Oriental
dreamings thus expressed could have been supposed to represent the
acme of scientific knowledge. Yet such a hold had these writings taken
upon the Western world that not even a Galileo dared contradict them
openly; and when the church fathers gravely declared the heliocentric
theory necessarily false, because contradictory to Scripture, there
were probably few people in Christendom whose mental attitude would
permit them justly to appreciate the humor of such a pronouncement.
And, indeed, if here and there a man might have risen to such an appreciation,
there were abundant reasons for the repression of the impulse, for
there was nothing humorous about the response with which the authorities
of the time were wont to meet the expression of iconoclastic opinions.
The burning at the stake of Giordano Bruno, in the year 1600, was,
for example, an object-lesson well calculated to restrain the enthusiasm
of other similarly minded teachers.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2Sc82}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Frontispiece of Galileo's {}``Systema
Cosmicum''}\end{center}{\small \par}

\noindent \begin{center}\emph{\footnotesize (Published in 1641.) }\end{center}
\end{figure}
Doubtless it was such considerations that explained the relative silence
of the champions of the Copernican theory, accounting for the otherwise
inexplicable fact that about eighty years elapsed after the death
of Copernicus himself before a single text-book expounded his theory.
The text-book which then appeared, under date of 1622, was written
by the famous Kepler, who perhaps was shielded in a measure from the
papal consequences of such hardihood by the fact of residence in a
Protestant country. Not that the Protestants of the time favored the
heliocentric doctrine---we have already quoted Luther in an adverse
sense---but of course it was characteristic of the Reformation temper
to oppose any papal pronouncement, hence the ultramontane declaration
of 1616 may indirectly have aided the doctrine which it attacked,
by making that doctrine less obnoxious to Lutheran eyes. Be that as
it may, the work of Kepler brought its author into no direct conflict
with the authorities. But the result was quite different when, in
1632, Galileo at last broke silence and gave the world, under cover
of the form of dialogue, an elaborate exposition of the Copernican
theory. Galileo, it must be explained, had previously been warned
to keep silent on the subject, hence his publication doubly offended
the authorities. To be sure, he could reply that his dialogue introduced
a champion of the Ptolemaic system to dispute with the upholder of
the opposite view, and that, both views being presented with full
array of argument, the reader was left to reach a verdict for himself,
the author having nowhere pointedly expressed an opinion. But such
an argument, of course, was specious, for no one who read the dialogue
could be in doubt as to the opinion of the author. Moreover, it was
hinted that Simplicio, the character who upheld the Ptolemaic doctrine
and who was everywhere worsted in the argument, was intended to represent
the pope himself---a suggestion which probably did no good to Galileo's
cause.

The character of Galileo's artistic presentation may best be judged
from an example, illustrating the vigorous assault of Salviati, the
champion of the new theory, and the feeble retorts of his conservative
antagonist:\ 

\begin{quotation}
{}``Salviati. Let us then begin our discussion with the consideration
that, whatever motion may be attributed to the earth, yet we, as dwellers
upon it, and hence as participators in its motion, cannot possibly
perceive anything of it, presupposing that we are to consider only
earthly things. On the other hand, it is just as necessary that this
same motion belong apparently to all other bodies and visible objects,
which, being separated from the earth, do not take part in its motion.
The correct method to discover whether one can ascribe motion to the
earth, and what kind of motion, is, therefore, to investigate and
observe whether in bodies outside the earth a perceptible motion may
be discovered which belongs to all alike. Because a movement which
is perceptible only in the moon, for instance, and has nothing to
do with Venus or Jupiter or other stars, cannot possibly be peculiar
to the earth, nor can its seat be anywhere else than in the moon.
Now there is one such universal movement which controls all others---namely,
that which the sun, moon, the other planets, the fixed stars---in
short, the whole universe, with the single exception of the earth---appears
to execute from east to west in the space of twenty-four hours. This
now, as it appears at the first glance anyway, might just as well
be a motion of the earth alone as of all the rest of the universe
with the exception of the earth, for the same phenomena would result
from either hypothesis. Beginning with the most general, I will enumerate
the reasons which seem to speak in favor of the earth's motion. When
we merely consider the immensity of the starry sphere in comparison
with the smallness of the terrestrial ball, which is contained many
million times in the former, and then think of the rapidity of the
motion which completes a whole rotation in one day and night, I cannot
persuade myself how any one can hold it to be more reasonable and
credible that it is the heavenly sphere which rotates, while the earth
stands still.

{}``Simplicio. I do not well understand how that powerful motion
may be said to as good as not exist for the sun, the moon, the other
planets, and the innumerable host of fixed stars. Do you call that
nothing when the sun goes from one meridian to another, rises up over
this horizon and sinks behind that one, brings now day, and now night;
when the moon goes through similar changes, and the other planets
and fixed stars in the same way?

{}``Salviati. All the changes you mention are such only in respect
to the earth. To convince yourself of it, only imagine the earth out
of existence. There would then be no rising and setting of the sun
or of the moon, no horizon, no meridian, no day, no night---in short,
the said motion causes no change of any sort in the relation of the
sun to the moon or to any of the other heavenly bodies, be they planets
or fixed stars. All changes are rather in respect to the earth; they
may all be reduced to the simple fact that the sun is first visible
in China, then in Persia, afterwards in Egypt, Greece, France, Spain,
America, \textit{etc}., and that the same thing happens with the moon
and the other heavenly bodies. Exactly the same thing happens and
in exactly the same way if, instead of disturbing so large a part
of the universe, you let the earth revolve about itself. The difficulty
is, however, doubled, inasmuch as a second very important problem
presents itself. If, namely, that powerful motion is ascribed to the
heavens, it is absolutely necessary to regard it as opposed to the
individual motion of all the planets, every one of which indubitably
has its own very leisurely and moderate movement from west to east.
If, on the other hand, you let the earth move about itself, this opposition
of motion disappears.

{}``The improbability is tripled by the complete overthrow of that
order which rules all the heavenly bodies in which the revolving motion
is definitely established. The greater the sphere is in such a case,
so much longer is the time required for its revolution; the smaller
the sphere the shorter the time. Saturn, whose orbit surpasses those
of all the planets in size, traverses it in thirty years. Jupiter
completes its smaller course in twelve years, Mars in two; the moon
performs its much smaller revolution within a month. Just as clearly
in the Medicean stars, we see that the one nearest Jupiter completes
its revolution in a very short time---about forty-two hours; the next
in about three and one-half days, the third in seven, and the most
distant one in sixteen days. This rule, which is followed throughout,
will still remain if we ascribe the twenty-four-hourly motion to a
rotation of the earth. If, however, the earth is left motionless,
we must go first from the very short rule of the moon to ever greater
ones---to the two-yearly rule of Mars, from that to the twelve-yearly
one of Jupiter, from here to the thirty-yearly one of Saturn, and
then suddenly to an incomparably greater sphere, to which also we
must ascribe a complete rotation in twenty-four hours. If, however,
we assume a motion of the earth, the rapidity of the periods is very
well preserved; from the slowest sphere of Saturn we come to the wholly
motionless fixed stars. We also escape thereby a fourth difficulty,
which arises as soon as we assume that there is motion in the sphere
of the stars. I mean the great unevenness in the movement of these
very stars, some of which would have to revolve with extraordinary
rapidity in immense circles, while others moved very slowly in small
circles, since some of them are at a greater, others at a less, distance
from the pole. That is likewise an inconvenience, for, on the one
hand, we see all those stars, the motion of which is indubitable,
revolve in great circles, while, on the other hand, there seems to
be little object in placing bodies, which are to move in circles,
at an enormous distance from the centre and then let them move in
very small circles. And not only are the size of the different circles
and therewith the rapidity of the movement very different in the different
fixed stars, but the same stars also change their orbits and their
rapidity of motion. Therein consists the fifth inconvenience. Those
stars, namely, which were at the equator two thousand years ago, and
hence described great circles in their revolutions, must to-day move
more slowly and in smaller circles, because they are many degrees
removed from it. It will even happen, after not so very long a time,
that one of those which have hitherto been continually in motion will
finally coincide with the pole and stand still, but after a period
of repose will again begin to move. The other stars in the mean while,
which unquestionably move, all have, as was said, a great circle for
an orbit and keep this unchangeably.

{}``The improbability is further increased---this may be considered
the sixth inconvenience---by the fact that it is impossible to conceive
what degree of solidity those immense spheres must have, in the depths
of which so many stars are fixed so enduringly that they are kept
revolving evenly in spite of such difference of motion without changing
their respective positions. Or if, according to the much more probable
theory, the heavens are fluid, and every star describes an orbit of
its own, according to what law then, or for what reason, are their
orbits so arranged that, when looked at from the earth, they appear
to be contained in one single sphere? To attain this it seems to me
much easier and more convenient to make them motionless instead of
moving, just as the paving-stones on the market-place, for instance,
remain in order more easily than the swarms of children running about
on them.

{}``Finally, the seventh difficulty: If we attribute the daily rotation
to the higher region of the heavens, we should have to endow it with
force and power sufficient to carry with it the innumerable host of
the fixed stars---every one a body of very great compass and much
larger than the earth---and all the planets, although the latter,
like the earth, move naturally in an opposite direction. In the midst
of all this the little earth, single and alone, would obstinately
and wilfully withstand such force---a supposition which, it appears
to me, has much against it. I could also not explain why the earth,
a freely poised body, balancing itself about its centre, and surrounded
on all sides by a fluid medium, should not be affected by the universal
rotation. Such difficulties, however, do not confront us if we attribute
motion to the earth---such a small, insignificant body in comparison
with the whole universe, and which for that very reason cannot exercise
any power over the latter.

{}``Simplicio. You support your arguments throughout, it seems to
me, on the greater ease and simplicity with which the said effects
are produced. You mean that as a cause the motion of the earth alone
is just as satisfactory as the motion of all the rest of the universe
with the exception of the earth; you hold the actual event to be much
easier in the former case than in the latter. For the ruler of the
universe, however, whose might is infinite, it is no less easy to
move the universe than the earth or a straw balm. But if his power
is infinite, why should not a greater, rather than a very small, part
of it be revealed to me?

{}``Salviati. If I had said that the universe does not move on account
of the impotence of its ruler, I should have been wrong and your rebuke
would have been in order. I admit that it is just as easy for an infinite
power to move a hundred thousand as to move one. What I said, however,
does not refer to him who causes the motion, but to that which is
moved. In answer to your remark that it is more fitting for an infinite
power to reveal a large part of itself rather than a little, I answer
that, in relation to the infinite, one part is not greater than another,
if both are finite. Hence it is unallowable to say that a hundred
thousand is a larger part of an infinite number than two, although
the former is fifty thousand times greater than the latter. If, therefore,
we consider the moving bodies, we must unquestionably regard the motion
of the earth as a much simpler process than that of the universe;
if, furthermore, we direct our attention to so many other simplifications
which may be reached only by this theory, the daily movement of the
earth must appear much more probable than the motion of the universe
without the earth, for, according to Aristotle's just axiom, `\textit{Frustra}
\emph{fit per plura, quod potest fieri per p auciora}'\ (It is vain
to expend many means where a few are sufficient).''%
\footnote{\textit{\emph{Galileo}}, \textit{Dialogo} \textit{dei} \textit{due}
\emph{Massimi Systemi} \textit{del} \textit{Mondo}, \textit{\emph{trans}}.\ from
Dannemann, \emph{op.\ cit.}%
}
\end{quotation}
{}

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2Sc90}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Galileo Before the Tribunal}\end{center}
\end{figure}
The work was widely circulated, and it was received with an interest
which bespeaks a wide-spread undercurrent of belief in the Copernican
doctrine. Naturally enough, it attracted immediate attention from
the church authorities. Galileo was summoned to appear at Rome to
defend his conduct. The philosopher, who was now in his seventieth
year, pleaded age and infirmity. He had no desire for personal experience
of the tribunal of the Inquisition; but the mandate was repeated,
and Galileo went to Rome. There, as every one knows, he disavowed
any intention to oppose the teachings of Scripture, and formally renounced
the heretical doctrine of the earth's motion. According to a tale
which so long passed current that every historian must still repeat
it though no one now believes it authentic, Galileo qualified his
renunciation by muttering to himself, {}``\emph{E} \textit{pur} \textit{si}
\textit{muove}''\ (It does move, none the less), as he rose to his
feet and retired from the presence of his persecutors. The tale is
one of those fictions which the dramatic sense of humanity is wont
to impose upon history, but, like most such fictions, it expresses
the spirit if not the letter of truth; for just as no one believes
that Galileo's lips uttered the phrase, so no one doubts that the
rebellious words were in his mind.

After his formal renunciation, Galileo was allowed to depart, but
with the injunction that he abstain in future from heretical teaching.
The remaining ten years of his life were devoted chiefly to mechanics,
where his experiments fortunately opposed the Aristotelian rather
than the Hebrew teachings. Galileo's death occurred in 1642, a hundred
years after the death of Copernicus. Kepler had died thirteen years
before, and there remained no astronomer in the field who is conspicuous
in the history of science as a champion of the Copernican doctrine.
But in truth it might be said that the theory no longer needed a champion.
The researches of Kepler and Galileo had produced a mass of evidence
for the Copernican theory which amounted to demonstration. A generation
or two might be required for this evidence to make itself everywhere
known among men of science, and of course the ecclesiastical authorities
must be expected to stand by their guns for a somewhat longer period.
In point of fact, the ecclesiastical ban was not technically removed
by the striking of the Copernican books from the list of the \emph{Index
Expurgatorius} until the year 1822, almost two hundred years after
the date of Galileo's dialogue. But this, of course, is in no sense
a guide to the state of general opinion regarding the theory. We shall
gain a true gauge as to this if we assume that the greater number
of important thinkers had accepted the heliocentric doctrine before
the middle of the seventeenth century, and that before the close of
that century the old Ptolemaic idea had been quite abandoned. A wonderful
revolution in man's estimate of the universe had thus been effected
within about two centuries after the birth of Copernicus.


\chapter*{\raggedright V.\ GALILEO AND THE NEW PHYSICS}

\addcontentsline{toc}{chapter}{V. GALILEO AND THE NEW PHYSICS}

\markboth{A HISTORY OF SCIENCE, VOLUME II}{V. GALILEO AND THE NEW
PHYSICS}

After Galileo had felt the strong hand of the Inquisition, in 1632,
he was careful to confine his researches, or at least his publications,
to topics that seemed free from theological implications. In doing
so he reverted to the field of his earliest studies---namely, the
field of mechanics; and the \emph{Dialoghi delle Nuove Scienze}, which
he finished in 1636, and which was printed two years later, attained
a celebrity no less than that of the heretical dialogue that had preceded
it. The later work was free from all apparent \textit{\emph{heresies}},
yet perhaps it did more towards the establishment of the Copernican
doctrine, through the teaching of correct mechanical principles, than
the other work had accomplished by a more direct method.

Galileo's astronomical discoveries were, as we have seen, in a sense
accidental; at least, they received their inception through the inventive
genius of another. His mechanical discoveries, on the other hand,
were the natural output of his own creative genius. At the very beginning
of his career, while yet a very young man, though a professor of mathematics
at Pisa, he had begun that onslaught upon the old Aristotelian ideas
which he was to continue throughout his life. At the famous leaning
tower in Pisa, the young iconoclast performed, in the year 1590, one
of the most theatrical demonstrations in the history of science. Assembling
a multitude of champions of the old ideas, he proposed to demonstrate
the falsity of the Aristotelian doctrine that the velocity of falling
bodies is proportionate to their weight. There is perhaps no fact
more strongly illustrative of the temper of the Middle Ages than the
fact that this doctrine, as taught by the Aristotelian philosopher,
should so long have gone unchallenged. Now, however, it was put to
the test; Galileo released a half-pound weight and a hundred-pound
cannon-ball from near the top of the tower, and, needless to say,
they reached the ground together. Of course, the spectators were but
little pleased with what they saw. They could not doubt the evidence
of their own senses as to the particular experiment in question; they
could suggest, however, that the experiment involved a violation of
the laws of nature through the practice of magic. To controvert so
firmly established an idea savored of heresy. The young man guilty
of such iconoclasm was naturally looked at askance by the scholarship
of his time. Instead of being applauded, he was hissed, and he found
it expedient presently to retire from Pisa.

Fortunately, however, the new spirit of progress had made itself felt
more effectively in some other portions of Italy, and so Galileo found
a refuge and a following in Padua, and afterwards in Florence; and
while, as we have seen, he was obliged to curb his enthusiasm regarding
the subject that was perhaps nearest his heart---the promulgation
of the Copernican theory---yet he was permitted in the main to carry
on his experimental observations unrestrained. These experiments gave
him a place of unquestioned authority among his contemporaries, and
they have transmitted his name to posterity as that of one of the
greatest of experimenters and the virtual founder of modern mechanical
science. The experiments in question range over a wide field; but
for the most part they have to do with moving bodies and with questions
of force, or, as we should now say, of energy. The experiment at the
leaning tower showed that the velocity of falling bodies is independent
of the weight of the bodies, provided the weight is sufficient to
overcome the resistance of the atmosphere. Later experiments with
falling bodies led to the discovery of laws regarding the accelerated
velocity of fall. Such velocities were found to bear a simple relation
to the period of time from the beginning of the fall. Other experiments,
in which balls were allowed to roll down inclined planes, corroborated
the observation that the pull of gravitation gave a velocity proportionate
to the length of fall, whether such fall were direct or in a slanting
direction.

These studies were associated with observations on projectiles, regarding
which Galileo was the first to entertain correct notions. According
to the current idea, a projectile fired, for example, from a cannon,
moved in a straight horizontal line until the propulsive force was
exhausted, and then fell to the ground in a perpendicular line. Galileo
taught that the projectile begins to fall at once on leaving the mouth
of the cannon and traverses a parabolic course. According to his idea,
which is now familiar to every one, a cannon-ball dropped from the
level of the cannon's muzzle will strike the ground simultaneously
with a ball fired horizontally from the cannon. As to the paraboloid
course pursued by the projectile, the resistance of the air is a factor
which Galileo could not accurately compute, and which interferes with
the practical realization of his theory. But this is a minor consideration.
The great importance of his idea consists in the recognition that
such a force as that of gravitation acts in precisely the same way
upon all unsupported bodies, whether or not such bodies be at the
same time acted upon by a force of translation.

Out of these studies of moving bodies was gradually developed a correct
notion of several important general laws of mechanics---laws a knowledge
of which was absolutely essential to the progress of physical science.
The belief in the rotation of the earth made necessary a clear conception
that all bodies at the surface of the earth partake of that motion
quite independently of their various observed motions in relation
to one another. This idea was hard to grasp, as an oft-repeated argument
shows. It was asserted again and again that, if the earth rotates,
a stone dropped from the top of a tower could not fall at the foot
of the tower, since the earth's motion would sweep the tower far away
from its original position while the stone is in transit.

This was one of the stock arguments against the earth's motion, yet
it was one that could be refuted with the greatest ease by reasoning
from strictly analogous experiments. It might readily be observed,
for example, that a stone dropped from a moving cart does not strike
the ground directly below the point from which it is dropped, but
partakes of the forward motion of the cart. If any one doubt this
he has but to jump from a moving cart to be given a practical demonstration
of the fact that his entire body was in some way influenced by the
motion of translation. Similarly, the simple experiment of tossing
a ball from the deck of a moving ship will convince any one that the
ball partakes of the motion of the ship, so that it can be manipulated
precisely as if the manipulator were standing on the earth. In short,
every-day experience gives us illustrations of what might be called
compound motion, which makes it seem altogether plausible that, if
the earth is in motion, objects at its surface will partake of that
motion in a way that does not interfere with any other movements to
which they may be subjected. As the Copernican doctrine made its way,
this idea of compound motion naturally received more and more attention,
and such experiments as those of Galileo prepared the way for a new
interpretation of the mechanical principles involved.

The great difficulty was that the subject of moving bodies had all
along been contemplated from a wrong point of view. Since force must
be applied to an object to put it in motion, it was perhaps not unnaturally
assumed that similar force must continue to be applied to keep the
object in motion. When, for example, a stone is thrown from the hand,
the direct force applied necessarily ceases as soon as the projectile
leaves the hand. The stone, nevertheless, flies on for a certain distance
and then falls to the ground. How is this flight of the stone to be
explained? The ancient philosophers puzzled more than a little over
this problem, and the Aristotelians reached the conclusion that the
motion of the hand had imparted a propulsive motion to the air, and
that this propulsive motion was transmitted to the stone, pushing
it on. Just how the air took on this propulsive property was not explained,
and the vagueness of thought that characterized the time did not demand
an explanation. Possibly the dying away of ripples in water may have
furnished, by analogy, an explanation of the gradual dying out of
the impulse which propels the stone.

All of this was, of course, an unfortunate maladjustment of the point
of view. As every one nowadays knows, the air \textit{\emph{retards}}
the progress of the stone, enabling the pull of gravitation to drag
it to the earth earlier than it otherwise could. Were the resistance
of the air and the pull of gravitation removed, the stone as projected
from the hand would fly on in a straight line, at an unchanged velocity,
forever. But this fact, which is expressed in what we now term the
first law of motion, was extremely difficult to grasp. The first important
step towards it was perhaps implied in Galileo's study of falling
bodies. These studies, as we have seen, demonstrated that a half-pound
weight and a hundred-pound weight fall with the same velocity. It
is, however, matter of common experience that certain bodies, as,
for example, feathers, do not fall at the same rate of speed with
these heavier bodies. This anomaly demands an explanation, and the
explanation is found in the resistance offered the relatively light
object by the air. Once the idea that the air may thus act as an impeding
force was grasped, the investigator of mechanical principles had entered
on a new and promising course.

Galileo could not demonstrate the retarding influence of air in the
way which became familiar a generation or two later; he could not
put a feather and a coin in a vacuum tube and prove that the two would
there fall with equal velocity, because, in his day, the air-pump
had not yet been invented. The experiment was made only a generation
after the time of Galileo, as we shall see; but, meantime, the great
Italian had fully grasped the idea that atmospheric resistance plays
a most important part in regard to the motion of falling and projected
bodies. Thanks largely to his own experiments, but partly also to
the efforts of others, he had come, before the end of his life, pretty
definitely to realize that the motion of a projectile, for example,
must be thought of as inherent in the projectile itself, and that
the retardation or ultimate cessation of that motion is due to the
action of antagonistic forces. In other words, he had come to grasp
the meaning of the first law of motion. It remained, however, for
the great Frenchman Descartes to give precise expression to this law
two years after Galileo's death. As Descartes expressed it in his
\emph{Principia} \textit{Philosophiae}, published in 1644, any body
once in motion tends to go on in a straight line, at a uniform rate
of speed, forever. Contrariwise, a stationary body will remain forever
at rest unless acted on by some disturbing force.

This all-important law, which lies at the very foundation of all true
conceptions of mechanics, was thus worked out during the first half
of the seventeenth century, as the outcome of numberless experiments
for which Galileo's experiments with failing bodies furnished the
foundation. So numerous and so gradual were the steps by which the
reversal of view regarding moving bodies was effected that it is impossible
to trace them in detail. We must be content to reflect that at the
beginning of the Galilean epoch utterly false notions regarding the
subject were entertained by the very greatest philosophers---by Galileo
himself, for example, and by Kepler---whereas at the close of that
epoch the correct and highly illuminative view had been attained.

We must now consider some other experiments of Galileo which led to
scarcely less-important results. The experiments in question had to
do with the movements of bodies passing down an inclined plane, and
with the allied subject of the motion of a pendulum. The elaborate
experiments of Galileo regarding the former subject were made by measuring
the velocity of a ball rolling down a plane inclined at various angles.
He found that the velocity acquired by a ball was proportional to
the height from which the ball descended regardless of the steepness
of the incline. Experiments were made also with a ball rolling down
a curved gutter, the curve representing the are of a circle. These
experiments led to the study of the curvilinear motions of a weight
suspended by a cord; in other words, of the pendulum.

Regarding the motion of the pendulum, some very curious facts were
soon ascertained. Galileo found, for example, that a pendulum of a
given length performs its oscillations with the same frequency though
the arc described by the pendulum be varied greatly.%
\footnote{Rothmann, \emph{History of Astronomy} (in the \emph{Library of Useful
Knowledge}), London, 1834.%
} He found, also, that the rate of oscillation for pendulums of different
lengths varies according to a simple law. In order that one pendulum
shall oscillate one-half as fast as another, the length of the pendulums
must be as four to one. Similarly, by lengthening the pendulums nine
times, the oscillation is reduced to one-third, In other words, the
rate of oscillation of pendulums varies inversely as the square of
their length. Here, then, is a simple relation between the motions
of swinging bodies which suggests the relation which Kepler had discovered
between the relative motions of the planets. Every such discovery
coming in this age of the rejuvenation of experimental science had
a peculiar force in teaching men the all-important lesson that simple
laws lie back of most of the diverse phenomena of nature, if only
these laws can be discovered.

Galileo further observed that his pendulum might be constructed of
any weight sufficiently heavy readily to overcome the atmospheric
resistance, and that, with this qualification, neither the weight
nor the material had any influence upon the time of oscillation, this
being solely determined by the length of the cord. Naturally, the
practical utility of these discoveries was not overlooked by Galileo.
Since a pendulum of a given length oscillates with unvarying rapidity,
here is an obvious means of measuring time. Galileo, however, appears
not to have met with any great measure of success in putting this
idea into practice. It remained for the mechanical ingenuity of Huyghens
to construct a satisfactory pendulum clock.

As a theoretical result of the studies of rolling and oscillating
bodies, there was developed what is usually spoken of as the third
law of motion---namely, the law that a given force operates upon a
moving body with an effect proportionate to its effect upon the same
body when at rest. Or, as Whewell states the law: {}``The dynamical
effect of force is as the statical effect; that is, the velocity which
any force generates in a given time, when it puts the body in motion,
is proportional to the pressure which this same force produces in
a body at rest.''%
\footnote{William Whewell, \emph{History of the Inductive Sciences}, 3 Vols.,
London, 1847, Vol.\ II., p.\ 48.%
} According to the second law of motion, each one of the different
forces, operating at the same time upon a moving body, produces the
same effect as if it operated upon the body while at rest.


\section*{\raggedright STEVINUS AND THE LAW OF EQUILIBRIUM}

\addcontentsline{toc}{section}{STEVINUS AND THE LAW OF\\
EQUILIBRIUM}

It appears, then, that the mechanical studies of Galileo, taken as
a whole, were nothing less than revolutionary. They constituted the
first great advance upon the dynamic studies of Archimedes, and then
led to the secure foundation for one of the most important of modern
sciences. We shall see that an important company of students entered
the field immediately after the time of Galileo, and carried forward
the work he had so well begun. But before passing on to the consideration
of their labors, we must consider work in allied fields of two men
who were contemporaries of Galileo and whose original labors were
in some respects scarcely less important than his own. These men are
the Dutchman Stevinus, who must always be remembered as a co-laborer
with Galileo in the foundation of the science of dynamics, and the
Englishman Gilbert, to whom is due the unqualified praise of first
subjecting the phenomenon of magnetism to a strictly scientific investigation.

Stevinus was born in the year 1548, and died in 1620. He was a man
of a practical genius, and he attracted the attention of his non-scientific
contemporaries, among other ways, by the construction of a curious
land-craft, which, mounted on wheels, was to be propelled by sails
like a boat. Not only did he write a book on this curious horseless
carriage, but he put his idea into practical application, producing
a vehicle which actually traversed the distance between Scheveningen
and Petton, with no fewer than twenty-seven passengers, one of them
being Prince Maurice of Orange. This demonstration was made about
the year 1600. It does not appear, however, that any important use
was made of the strange vehicle; but the man who invented it put his
mechanical ingenuity to other use with better effect. It was he who
solved the problem of oblique forces, and who discovered the important
hydrostatic principle that the pressure of fluids is proportionate
to their depth, without regard to the shape of the including vessel.

The study of oblique forces was made by Stevinus with the aid of inclined
planes. His most demonstrative experiment was a very simple one, in
which a chain of balls of equal weight was hung from a triangle; the
triangle being so constructed as to rest on a horizontal base, the
oblique sides bearing the relation to each other of two to one. Stevinus
found that his chain of balls just balanced when four balls were on
the longer side and two on the shorter and steeper side. The balancing
of force thus brought about constituted a stable equilibrium, Stevinus
being the first to discriminate between such a condition and the unbalanced
condition called unstable equilibrium. By this simple experiment was
laid the foundation of the science of statics. Stevinus had a full
grasp of the principle which his experiment involved, and he applied
it to the solution of oblique forces in all directions. Earlier investigations
of Stevinus were published in 1608. His collected works were published
at Leyden in 1634.

This study of the equilibrium of pressure of bodies at rest led Stevinus,
not unnaturally, to consider the allied subject of the pressure of
liquids. He is to be credited with the explanation of the so-called
hydrostatic paradox. The familiar modern experiment which illustrates
this paradox is made by inserting a long perpendicular tube of small
caliber into the top of a tight barrel. On filling the barrel and
tube with water, it is possible to produce a pressure which will burst
the barrel, though it be a strong one, and though the actual weight
of water in the tube is comparatively insignificant. This illustrates
the fact that the pressure at the bottom of a column of liquid is
proportionate to the height of the column, and not to its bulk, this
being the hydrostatic paradox in question. The explanation is that
an enclosed fluid under pressure exerts an equal force upon all parts
of the circumscribing wall; the aggregate pressure may, therefore,
be increased indefinitely by increasing the surface. It is this principle,
of course, which is utilized in the familiar hydrostatic press. Theoretical
explanations of the pressure of liquids were supplied a generation
or two later by numerous investigators, including Newton, but the
practical refoundation of the science of hydrostatics in modern times
dates from the experiments of Stevinus.


\section*{\raggedright GALILEO AND THE EQUILIBRIUM OF FLUIDS}

\addcontentsline{toc}{section}{GALILEO AND THE EQUILIBRIUM OF\\
FLUIDS}

Experiments of an allied character, having to do with the equilibrium
of fluids, exercised the ingenuity of Galileo. Some of his most interesting
experiments have to do with the subject of floating bodies. It will
be recalled that Archimedes, away back in the Alexandrian epoch, had
solved the most important problems of hydrostatic equilibrium. Now,
however, his experiments were overlooked or forgotten, and Galileo
was obliged to make experiments anew, and to combat fallacious views
that ought long since to have been abandoned. Perhaps the most illuminative
view of the spirit of the times can be gained by quoting at length
a paper of Galileo's, in which he details his own experiments with
floating bodies and controverts the views of his opponents. The paper
has further value as illustrating Galileo's methods both as experimenter
and as speculative reasoner.

The current view, which Galileo here undertakes to refute, asserts
that water offers resistance to penetration, and that this resistance
is instrumental in determining whether a body placed in water will
float or sink. Galileo contends that water is non-resistant, and that
bodies float or sink in virtue of their respective weights. This,
of course, is merely a restatement of the law of Archimedes. But it
remains to explain the fact that bodies of a certain shape will float,
while bodies of the same material and weight, but of a different shape,
will sink. We shall see what explanation Galileo finds of this anomaly
as we proceed.

In the first place, Galileo makes a cone of wood or of wax, and shows
that when it floats with either its point or its base in the water,
it displaces exactly the same amount of fluid, although the apex is
by its shape better adapted to overcome the resistance of the water,
if that were the cause of buoyancy. Again, the experiment may be varied
by tempering the wax with filings of lead till it sinks in the water,
when it will be found that in any figure the same quantity of cork
must be added to it to raise the surface.

\begin{quotation}
{}``But,''\ says Galileo, {}``this silences not my antagonists;
they say that all the discourse hitherto made by me imports little
to them, and that it serves their turn; that they have demonstrated
in one instance, and in such manner and figure as pleases them best---namely,
in a board and in a ball of ebony---that one when put into the water
sinks to the bottom, and that the other stays to swim on the top;
and the matter being the same, and the two bodies differing in nothing
but in figure, they affirm that with all perspicuity they have demonstrated
and sensibly manifested what they undertook. Nevertheless, I believe,
and think I can prove, that this very experiment proves nothing against
my theory. And first, it is false that the ball sinks and the board
not; for the board will sink, too, if you do to both the figures as
the words of our question require; that is, if you put them both in
the water; for to be in the water implies to be placed in the water,
and by Aristotle's own definition of place, to be placed imports to
be environed by the surface of the ambient body; but when my antagonists
show the floating board of ebony, they put it not into the water,
but upon the water; where, being detained by a certain impediment
(of which more anon), it is surrounded, partly with water, partly
with air, which is contrary to our agreement, for that was that bodies
should be in the water, and not part in the water, part in the air.

{}``I will not omit another reason, founded also upon experience,
and, if I deceive not myself, conclusive against the notion that figure,
and the resistance of the water to penetration, have anything to do
with the buoyancy of bodies. Choose a piece of wood or other matter,
as, for instance, walnut-wood, of which a ball rises from the bottom
of the water to the surface more slowly than a ball of ebony of the
same size sinks, so that, clearly, the ball of ebony divides the water
more readily in sinking than the ball of wood does in rising. Then
take a board of walnut-tree equal to and like the floating one of
my antagonists; and if it be true that this latter floats by reason
of the figure being unable to penetrate the water, the other of walnut-tree,
without a question, if thrust to the bottom, ought to stay there,
as having the same impeding figure, and being less apt to overcome
the said resistance of the water. But if we find by experience that
not only the thin board, but every other figure of the same walnut-tree,
will return to float, as unquestionably we shall, then I must desire
my opponents to forbear to attribute the floating of the ebony to
the figure of the board, since the resistance of the water is the
same in rising as in sinking, and the force of ascension of the walnut-tree
is less than the ebony's force for going to the bottom.

{}``Now let us return to the thin plate of gold or silver, or the
thin board of ebony, and let us lay it lightly upon the water, so
that it may stay there without sinking, and carefully observe the
effect. It will appear clearly that the plates are a considerable
matter lower than the surface of the water, which rises up and makes
a kind of rampart round them on every side. But if it has already
penetrated and overcome the continuity of the water, and is of its
own nature heavier than the water, why does it not continue to sink,
but stop and suspend itself in that little dimple that its weight
has made in the water? My answer is, because in sinking till its surface
is below the water, which rises up in a bank round it, it draws after
and carries along with it the air above it, so that that which, in
this case, descends in the water is not only the board of ebony or
the plate of iron, but a compound of ebony and air, from which composition
results a solid no longer specifically heavier than the water, as
was the ebony or gold alone. But, gentlemen, we want the same matter;
you are to alter nothing but the shape, and, therefore, have the goodness
to remove this air, which may be done simply by washing the surface
of the board, for the water having once got between the board and
the air will run together, and the ebony will go to the bottom; and
if it does not, you have won the day.

{}``But methinks I hear some of my antagonists cunningly opposing
this, and telling me that they will not on any account allow their
boards to be wetted, because the weight of the water so added, by
making it heavier than it was before, draws it to the bottom, and
that the addition of new weight is contrary to our agreement, which
was that the matter should be the same.

{}``To this I answer, first, that nobody can suppose bodies to be
put into the water without their being wet, nor do I wish to do more
to the board than you may do to the ball. Moreover, it is not true
that the board sinks on account of the weight of the water added in
the washing; for I will put ten or twenty drops on the floating board,
and so long as they stand separate it shall not sink; but if the board
be taken out and all that water wiped off, and the whole surface bathed
with one single drop, and put it again upon the water, there is no
question but it will sink, the other water running to cover it, being
no longer hindered by the air. In the next place, it is altogether
false that water can in any way increase the weight of bodies immersed
in it, for water has no weight in water, since it does not sink. Now
just as he who should say that brass by its own nature sinks, but
that when formed into the shape of a kettle it acquires from that
figure the virtue of lying in water without sinking, would say what
is false, because that is not purely brass which then is put into
the water, but a compound of brass and air; so is it neither more
nor less false that a thin plate of brass or ebony swims by virtue
of its dilated and broad figure. Also, I cannot omit to tell my opponents
that this conceit of refusing to bathe the surface of the board might
beget an opinion in a third person of a poverty of argument on their
side, especially as the conversation began about flakes of ice, in
which it would be simple to require that the surfaces should be kept
dry; not to mention that such pieces of ice, whether wet or dry, always
float, and so my antagonists say, because of their shape.

{}``Some may wonder that I affirm this power to be in the air of
keeping plate of brass or silver above water, as if in a certain sense
I would attribute to the air a kind of magnetic virtue for sustaining
heavy bodies with which it is in contact. To satisfy all these doubts
I have contrived the following experiment to demonstrate how truly
the air does support these bodies; for I have found, when one of these
bodies which floats when placed lightly on the water is thoroughly
bathed and sunk to the bottom, that by carrying down to it a little
air without otherwise touching it in the least, I am able to raise
and carry it back to the top, where it floats as before. To this effect,
I take a ball of wax, and with a little lead make it just heavy enough
to sink very slowly to the bottom, taking care that its surface be
quite smooth and even. This, if put gently into the water, submerges
almost entirely, there remaining visible only a little of the very
top, which, so long as it is joined to the air, keeps the ball afloat;
but if we take away the contact of the air by wetting this top, the
ball sinks to the bottom and remains there. Now to make it return
to the surface by virtue of the air which before sustained it, thrust
into the water a glass with the mouth downward, which will carry with
it the air it contains, and move this down towards the ball until
you see, by the transparency of the glass, that the air has reached
the top of it; then gently draw the glass upward, and you will see
the ball rise, and afterwards stay on the top of the water, if you
carefully part the glass and water without too much disturbing it.''%
\footnote{\emph{The Lives of Eminent Persons}, by Biot, Jardine, Bethune, \textit{etc}.,
London, 1833.%
}
\end{quotation}
{}

It will be seen that Galileo, while holding in the main to a correct
thesis, yet mingles with it some false ideas. At the very outset,
of course, it is not true that water has no resistance to penetration;
it is true, however, in the sense in which Galileo uses the term---that
is to say, the resistance of the water to penetration is not the determining
factor ordinarily in deciding whether a body sinks or floats. Yet
in the case of the flat body it is not altogether inappropriate to
say that the water resists penetration and thus supports the body.
The modern physicist explains the phenomenon as due to surface-tension
of the fluid. Of course, Galileo's disquisition on the mixing of air
with the floating body is utterly fanciful. His experiments were beautifully
exact; his theorizing from them was, in this instance, altogether
fallacious. Thus, as already intimated, his paper is admirably adapted
to convey a double lesson to the student of science.


\section*{\raggedright WILLIAM GILBERT AND THE STUDY OF MAGNETISM}

\addcontentsline{toc}{section}{WILLIAM GILBERT AND THE STUDY\\
OF MAGNETISM}

It will be observed that the studies of Galileo and Stevinus were
chiefly concerned with the force of gravitation. Meanwhile, there
was an English philosopher of corresponding genius, whose attention
was directed towards investigation of the equally mysterious force
of terrestrial magnetism. With the doubtful exception of Bacon, Gilbert
was the most distinguished man of science in England during the reign
of Queen Elizabeth. He was for many years court physician, and Queen
Elizabeth ultimately settled upon him a pension that enabled him to
continue his researches in pure science.

His investigations in chemistry, although supposed to be of great
importance, are mostly lost; but his great work, \textit{De} \textit{Magnete},
on which he labored for upwards of eighteen years, is a work of sufficient
importance, as Hallam says, {}``to raise a lasting reputation for
its author.'' From its first appearance it created a profound impression
upon the learned men of the continent, although in England Gilbert's
theories seem to have been somewhat less favorably received. Galileo
freely expressed his admiration for the work and its author; Bacon,
who admired the author, did not express the same admiration for his
theories; but Dr. Priestley, later, declared him to be {}``the father
of modern electricity.''

Strangely enough, Gilbert's book had never been translated into English,
or apparently into any other language, until recent years, although
at the time of its publication certain learned men, unable to read
the book in the original, had asked that it should be. By this neglect,
or oversight, a great number of general readers as well as many scientists,
through succeeding centuries, have been deprived of the benefit of
writings that contained a good share of the fundamental facts about
magnetism as known to-day.

Gilbert was the first to discover that the earth is a great magnet,
and he not only gave the name of {}``pole''\ to the extremities
of the magnetic needle, but also spoke of these {}``poles''\ as
north and south pole, although he used these names in the opposite
sense from that in which we now use them, his south pole being the
extremity which pointed towards the north, and vice versa. He was
also first to make use of the terms {}``electric force,''\ {}``electric
emanations,''\ and {}``electric attractions.''

It is hardly necessary to say that some of the views taken by Gilbert,
many of his theories, and the accuracy of some of his experiments
have in recent times been found to be erroneous. As a pioneer in an
unexplored field of science, however, his work is remarkably accurate.
{}``On the whole,''\ says Dr.\ John Robinson, {}``this performance
contains more real information than any writing of the age in which
he lived, and is scarcely exceeded by any that has appeared since.''%
\footnote{William Gilbert, \textit{De} \textit{Magnete}, translated by P. Fleury
Motteley, London, 1893. In the biographical memoir, p.\ xvi.%
}

In the preface to his work Gilbert says: {}``Since in the discovery
of secret things, and in the investigation of hidden causes, stronger
reasons are obtained from sure experiments and demonstrated arguments
than from probable conjectures and the opinions of philosophical speculators
of the common sort, therefore, to the end of that noble substance
of that great loadstone, our common mother (the earth), still quite
unknown, and also that the forces extraordinary and exalted of this
globe may the better be understood, we have decided, first, to begin
with the common stony and ferruginous matter, and magnetic bodies,
and the part of the earth that we may handle and may perceive with
senses, and then to proceed with plain magnetic experiments, and to
penetrate to the inner parts of the earth.''%
\footnote{Gilbert, \emph{op.\ cit.,} p.\ xlvii.%
}

Before taking up the demonstration that the earth is simply a giant
loadstone, Gilbert demonstrated in an ingenious way that every loadstone,
of whatever size, has definite and fixed poles. He did this by placing
the stone in a metal lathe and converting it into a sphere, and upon
this sphere demonstrated how the poles can be found. To this round
loadstone he gave the name of \emph{terrella}---that is, little earth.

{}``To find, then, poles answering to the earth,''\ he says, {}``take
in your hand the round stone, and lay on it a needle or a piece of
iron wire: the ends of the wire move round their middle point, and
suddenly come to a standstill. Now, with ochre or with chalk, mark
where the wire lies still and sticks. Then move the middle or centre
of the wire to another spot, and so to a third and fourth, always
marking the stone along the length of the wire where it stands still;
the lines so marked will exhibit meridian circles, or circles like
meridians, on the stone or terrella; and manifestly they will all
come together at the poles of the stone. The circle being continued
in this way, the poles appear, both the north and the south, and betwixt
these, midway, we may draw a large circle for an equator, as is done
by the astronomer in the heavens and on his spheres, and by the geographer
on the terrestrial globe.''%
\footnote{Gilbert, \emph{op.\ cit}., p.\ 24.%
}

Gilbert had tried the familiar experiment of placing the loadstone
on a float in water, and observed that the poles always revolved until
they pointed north and south, which he explained as due to the earth's
magnetic attraction. In this same connection he noticed that a piece
of wrought iron mounted on a cork float was attracted by other metals
to a slight degree, and he observed also that an ordinary iron bar,
if suspended horizontally by a thread, assumes invariably a north
and south direction. These, with many other experiments of a similar
nature, convinced him that the earth {}``is a magnet and a loadstone,''\ which
he says is a {}``new and till now unheard-of view of the earth.''

Fully to appreciate Gilbert's revolutionary views concerning the earth
as a magnet, it should be remembered that numberless theories to explain
the action of the electric needle had been advanced. Columbus and
Paracelsus, for example, believed that the magnet was attracted by
some point in the heavens, such as a magnetic star. Gilbert himself
tells of some of the beliefs that had been held by his predecessors,
many of whom he declares {}``wilfully falsify.'' One of his first
steps was to refute by experiment such assertions as that of \textit{\emph{Cardan}},
that {}``a wound by a magnetized needle was painless''; and also
the assertion of Fracastoni that loadstone attracts silver; or that
of Scalinger, that the diamond will attract iron; and the statement
of Matthiolus that {}``iron rubbed with garlic is no longer attracted
to the loadstone.''

Gilbert made extensive experiments to explain the dipping of the needle,
which had been first noticed by William Norman. His deduction as to
this phenomenon led him to believe that this was also explained by
the magnetic attraction of the earth, and to predict where the vertical
dip would be found. These deductions seem the more wonderful because
at the time he made them the dip had just been discovered, and had
not been studied except at London. His theory of the dip was, therefore,
a scientific prediction, based on a preconceived hypothesis. Gilbert
found the dip to be 72$^\circ$ at London; eight years later Hudson
found the dip at 75$^\circ$ 22'\ north latitude to be 89$^\circ$
30'; but it was not until over two hundred years later, in 1831, that
the vertical dip was first observed by Sir James Ross at about 70$^\circ$
5'\ north latitude, and 96$^\circ$ 43'\ west longitude. This was
not the exact point assumed by Gilbert, and his scientific predictions,
therefore, were not quite correct; but such comparatively slight and
excusable errors mar but little the excellence of his work as a whole.

A brief epitome of some of his other important discoveries suffices
to show that the exalted position in science accorded him by contemporaries,
as well as succeeding generations of scientists, was well merited.
He was first to distinguish between magnetism and electricity, giving
the latter its name. He discovered also the {}``electrical charge,''\ and
pointed the way to the discovery of insulation by showing that the
charge could be retained some time in the excited body by covering
it with some non-conducting substance, such as silk; although, of
course, electrical conduction can hardly be said to have been more
than vaguely surmised, if understood at all by him. The first electrical
instrument ever made, and known as such, was invented by him, as was
also the first magnetometer, and the first electrical indicating device.
Although three centuries have elapsed since his death, the method
of magnetizing iron first introduced by him is in common use to-day.

He made exhaustive experiments with a needle balanced on a pivot to
see how many substances he could find which, like amber, on being
rubbed affected the needle. In this way he discovered that light substances
were attracted by alum, mica, arsenic, sealing-wax, \textit{\emph{lac}}
\emph{}\textit{\emph{sulphur}}, slags, beryl, amethyst, rock-crystal,
sapphire, jet, carbuncle, diamond, opal, Bristol stone, glass, glass
of antimony, gum-mastic, hard resin, rock-salt, and, of course, amber.
He discovered also that atmospheric conditions affected the production
of electricity, dryness being unfavorable and moisture favorable.

Galileo's estimate of this first electrician is the verdict of succeeding
generations. {}``I extremely admire and envy this author,''\ he
said. {}``I think him worthy of the greatest praise for the many
new and true observations which he has made, to the disgrace of so
many vain and fabling authors.''


\section*{\raggedright STUDIES OF LIGHT, HEAT, AND ATMOSPHERIC PRESSURE}

\addcontentsline{toc}{section}{STUDIES OF LIGHT, HEAT, AND\\
ATMOSPHERIC PRESSURE}

We have seen that Gilbert was by no means lacking in versatility,
yet the investigations upon which his fame is founded were all pursued
along one line, so that the father of magnetism may be considered
one of the earliest of specialists in physical science. Most workers
of the time, on the other band, extended their investigations in many
directions. The sum total of scientific knowledge of that day had
not bulked so large as to exclude the possibility that one man might
master it all. So we find a Galileo, for example, making revolutionary
discoveries in astronomy, and performing fundamental experiments in
various fields of physics. Galileo's great contemporary, Kepler, was
almost equally versatile, though his astronomical studies were of
such pre-eminent importance that his other investigations sink into
relative insignificance. Yet he performed some notable experiments
in at least one department of physics. These experiments had to do
with the refraction of light, a subject which Kepler was led to investigate,
in part at least, through his interest in the telescope.

We have seen that Ptolemy in the Alexandrian time, and Alhazen, the
Arab, made studies of refraction. Kepler repeated their experiments,
and, striving as always to generalize his observations, he attempted
to find the law that governed the observed change of direction which
a ray of light assumes in passing from one medium to another. Kepler
measured the angle of refraction by means of a simple yet ingenious
trough-like apparatus which enabled him to compare readily the direct
and refracted rays. He discovered that when a ray of light passes
through a glass plate, if it strikes the farther surface of the glass
at an angle greater than 45$^\circ$ it will be totally refracted
instead of passing through into the air. He could not well fail to
know that different mediums refract light differently, and that for
the same medium the amount of light varies with the change in the
angle of incidence. He was not able, however, to generalize his observations
as he desired, and to the last the law that governs refraction escaped
him. It remained for Willebrord Snell, a Dutchman, about the year
1621, to discover the law in question, and for Descartes, a little
later, to formulate it. Descartes, indeed, has sometimes been supposed
to be the discoverer of the law. There is reason to believe that he
based his generalizations on the experiment of Snell, though he did
not openly acknowledge his indebtedness. The law, as Descartes expressed
it, states that the sine of the angle of incidence bears a fixed ratio
to the sine of the angle of refraction for any given medium. Here,
then, was another illustration of the fact that almost infinitely
varied phenomena may be brought within the scope of a simple law.
Once the law had been expressed, it could be tested and verified with
the greatest ease; and, as usual, the discovery being made, it seems
surprising that earlier investigators---in particular so sagacious
a guesser as Kepler---should have missed it.

Galileo himself must have been to some extent a student of light,
since, as we have seen, he made such notable contributions to practical
optics through perfecting the telescope; but he seems not to have
added anything to the theory of light. The subject of heat, however,
attracted his attention in a somewhat different way, and he was led
to the invention of the first contrivance for measuring temperatures.
His thermometer was based on the afterwards familiar principle of
the expansion of a liquid under the influence of heat; but as a practical
means of measuring temperature it was a very crude affair, because
the tube that contained the measuring liquid was exposed to the air,
hence barometric changes of pressure vitiated the experiment. It remained
for Galileo's Italian successors of the \textit{\emph{Accademia}}
\emph{}\textit{\emph{del}} \emph{}\textit{\emph{Cimento}} of Florence
to improve upon the apparatus, after the experiments of Torricelli---to
which we shall refer in a moment---had thrown new light on the question
of atmospheric pressure. Still later the celebrated Huygens hit upon
the idea of using the melting and the boiling point of water as fixed
points in a scale of measurements, which first gave definiteness to
thermometric tests.


\section*{\raggedright TORRICELLI}

\addcontentsline{toc}{section}{TORRICELLI}

In the closing years of his life Galileo took into his family, as
his adopted disciple in science, a young man, Evangelista Torricelli
(1608-1647), who proved himself, during his short lifetime, to be
a worthy follower of his great master. Not only worthy on account
of his great scientific discoveries, but grateful as well, for when
he had made the great discovery that the {}``suction''\ made by
a vacuum was really nothing but air pressure, and not suction at all,
he regretted that so important a step in science might not have been
made by his great teacher, Galileo, instead of by himself. {}``This
generosity of Torricelli,'' says Playfair, {}``was, perhaps, rarer
than his genius: there are more who might have discovered the suspension
of mercury in the barometer than who would have been willing to part
with the honor of the discovery to a master or a friend.''

Torricelli's discovery was made in 1643, less than two years after
the death of his master. Galileo had observed that water will not
rise in an exhausted tube, such as a pump, to a height greater than
thirty-three feet, but he was never able to offer a satisfactory explanation
of the principle. Torricelli was able to demonstrate that the height
at which the water stood depended upon nothing but its weight as compared
with the weight of air. If this be true, it is evident that any fluid
will be supported at a definite height, according to its relative
weight as compared with air. Thus mercury, which is about thirteen
times more dense than water, should only rise to one-thirteenth the
height of a column of water---that is, about thirty inches. Reasoning
in this way, Torricelli proceeded to prove that his theory was correct.
Filling a long tube, closed at one end, with mercury, he inverted
the tube with its open orifice in a vessel of mercury. The column
of mercury fell at once, but at a height of about thirty inches it
stopped and remained stationary, the pressure of the air on the mercury
in the vessel maintaining it at that height. This discovery was a
shattering blow to the old theory that had dominated that field of
physics for so many centuries. It was completely revolutionary to
prove that, instead of a mysterious something within the tube being
responsible for the suspension of liquids at certain heights, it was
simply the ordinary atmospheric pressure mysterious enough, it is
true---pushing upon them from without. The pressure exerted by the
atmosphere was but little understood at that time, but Torricelli's
discovery aided materially in solving the mystery. The whole class
of similar phenomena of air pressure, which had been held in the trammel
of long-established but false doctrines, was now reduced to one simple
law, and the door to a solution of a host of unsolved problems thrown
open.

It had long been suspected and believed that the density of the atmosphere
varies at certain times. That the air is sometimes {}``heavy''\ and
at other times {}``light''\ is apparent to the senses without scientific
apparatus for demonstration. It is evident, then, that Torricelli's
column of mercury should rise and fall just in proportion to the lightness
or heaviness of the air. A short series of observations proved that
it did so, and with those observations went naturally the observations
as to changes in the weather. It was only necessary, therefore, to
scratch a scale on the glass tube, indicating relative atmospheric
pressures, and the Torricellian barometer was complete.

Such a revolutionary theory and such an important discovery were,
of course, not to be accepted without controversy, but the feeble
arguments of the opponents showed how untenable the old theory had
become. In 1648 Pascal suggested that if the theory of the pressure
of air upon the mercury was correct, it could be demonstrated by ascending
a mountain with the mercury tube. As the air was known to get progressively
lighter from base to summit, the height of the column should be progressively
lessened as the ascent was made, and increase again on the descent
into the denser air. The experiment was made on the mountain called
the Puy-de-Dome, in Auvergne, and the column of mercury fell and rose
progressively through a space of about three inches as the ascent
and descent were made.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2S122}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Blaise Pascal}\end{center}{\small \par}

\noindent \begin{center}\emph{\footnotesize (From the painting by
Philippe de Champagne.) }\end{center}
\end{figure}
This experiment practically sealed the verdict on the new theory,
but it also suggested something more. If the mercury descended to
a certain mark on the scale on a mountain-top whose height was known,
why was not this a means of measuring the heights of all other elevations?
And so the beginning was made which, with certain modifications and
corrections in details, is now the basis of barometrical measurements
of heights.

In hydraulics, also, Torricelli seems to have taken one of the first
steps. He did this by showing that the water which issues from a hole
in the side or bottom of a vessel does so at the same velocity as
that which a body would acquire by falling from the level of the surface
of the water to that of the orifice. This discovery was of the greatest
importance to a correct understanding of the science of the motions
of fluids. He also discovered the valuable mechanical principle that
if any number of bodies be connected so that by their motion there
is neither ascent nor descent of their centre of gravity, these bodies
are in equilibrium.

Besides making these discoveries, he greatly improved the microscope
and the telescope, and invented a simple microscope made of a globule
of glass. In 1644 he published a tract on the properties of the cycloid
in which he suggested a solution of the problem of its quadrature.
As soon as this pamphlet appeared its author was accused by \textit{\emph{Gilles}}
\emph{}\textit{\emph{Roberval}} (1602-1675)\ of having appropriated
a solution already offered by him. This led to a long debate, during
which Torricelli was seized with a fever, from the effects of which
he died, in Florence, October 25, 1647. There is reason to believe,
however, that while Roberval's discovery was made before Torricelli's,
the latter reached his conclusions independently.


\chapter*{\raggedright VI. TWO PSEUDO-SCIENCES---ALCHEMY AND ASTROLOGY}

\addcontentsline{toc}{chapter}{VI. TWO PSEUDO-SCIENCES---\\
ALCHEMY AND ASTROLOGY}

\markboth{A HISTORY OF SCIENCE, VOLUME II}{VI. TWO PSEUDO-SCIENCES}

In recent chapters we have seen science come forward with tremendous
strides. A new era is obviously at hand. But we shall misconceive
the spirit of the times if we fail to understand that in the midst
of all this progress there was still room for medi\ae{}val superstition
and for the pursuit of fallacious ideals. Two forms of pseudo-science
were peculiarly prevalent---alchemy and astrology. Neither of these
can with full propriety be called a science, yet both were pursued
by many of the greatest scientific workers of the period. Moreover,
the studies of the alchemist may with some propriety be said to have
laid the foundation for the latter-day science of chemistry; while
astrology was closely allied to astronomy, though its relations to
that science are not as intimate as has sometimes been supposed.

Just when the study of alchemy began is undetermined. It was certainly
of very ancient origin, perhaps Egyptian, but its most flourishing
time was from about the eighth century A.D.\ to the eighteenth century.
The stories of the Old Testament formed a basis for some of the strange
beliefs regarding the properties of the magic {}``elixir,''\ or
{}``philosopher's stone.'' Alchemists believed that most of the
antediluvians, perhaps all of them, possessed a knowledge of this
stone. How, otherwise, could they have prolonged their lives to nine
and a half centuries? And Moses was surely a first-rate alchemist,
as is proved by the story of the Golden Calf.%
\footnote{Exodus xxxii, 20.%
} After Aaron had made the calf of gold, Moses performed the much more
difficult task of grinding it to powder and {}``strewing it upon
the waters,''\ thus showing that he had transmuted it into some
lighter substance.

But antediluvians and Biblical characters were not the only persons
who were thought to have discovered the coveted {}``elixir.'' Hundreds
of aged medi\ae{}val chemists were credited with having made the
discovery, and were thought to be living on through the centuries
by its means. Alaies de Lisle, for example, who died in 1298, at the
age of 110, was alleged to have been at the point of death at the
age of fifty, but just at this time he made the fortunate discovery
of the magic stone, and so continued to live in health and affluence
for sixty years more. And De Lisle was but one case among hundreds.

An aged and wealthy alchemist could claim with seeming plausibility
that he was prolonging his life by his magic; whereas a younger man
might assert that, knowing the great secret, he was keeping himself
young through the centuries. In either case such a statement, or rumor,
about a learned and wealthy alchemist was likely to be believed, particularly
among strangers; and as such a man would, of course, be the object
of much attention, the claim was frequently made by persons seeking
notoriety. One of the most celebrated of these impostors was a certain
Count de Saint-Germain, who was connected with the court of Louis
XV. His statements carried the more weight because, having apparently
no means of maintenance, he continued to live in affluence year after
year---for two thousand years, as he himself admitted---by means of
the magic stone. If at any time his statements were doubted, he was
in the habit of referring to his valet for confirmation, this valet
being also under the influence of the elixir of life.

\begin{quote}
{}``Upon one occasion his master was telling a party of ladies and
gentlemen, at dinner, some conversation he had had in Palestine, with
King Richard I., of England, whom he described as a very particular
friend of his. Signs of astonishment and incredulity were visible
on the faces of the company, upon which Saint-Germain very coolly
turned to his servant, who stood behind his chair, and asked him if
he had not spoken the truth. `I really cannot say,'\ replied the
man, without moving a muscle; `you forget, sir, I have been only five
hundred years in your service.' `Ah, true,'\ said his master, `I
remember now; it was a little before your time!'''%
\footnote{Charles Mackay, \emph{Popular Delusions}, 3 \textit{\emph{vols}}.,
London, 1850. Vol.\ II., p.\ 280.%
}
\end{quote}
{}

In the time of Saint-Germain, only a little over a century ago, belief
in alchemy had almost disappeared, and his extraordinary tales were
probably regarded in the light of amusing stories. Still there was
undoubtedly a lingering suspicion in the minds of many that this man
possessed some peculiar secret. A few centuries earlier his tales
would hardly have been questioned, for at that time the belief in
the existence of this magic something was so strong that the search
for it became almost a form of mania; and once a man was seized with
it, he gambled away health, position, and life itself in pursuing
the coveted stake. An example of this is seen in Albertus Magnus,
one of the most learned men of his time, who it is said resigned his
position as bishop of Ratisbon in order that he might pursue his researches
in alchemy.

If self-sacrifice was not sufficient to secure the prize, crime would
naturally follow, for there could be no limit to the price of the
stakes in this game. The notorious Marechal de Reys, failing to find
the coveted stone by ordinary methods of laboratory research, was
persuaded by an impostor that if he would propitiate the friendship
of the devil the secret would be revealed. To this end De Reys began
secretly capturing young children as they passed his castle and murdering
them. When he was at last brought to justice it was proved that he
had murdered something like a hundred children within a period of
three years. So, at least, runs one version of the story of this perverted
being.

Naturally monarchs, constantly in need of funds, were interested in
these alchemists. Even sober England did not escape, and Raymond Lully,
one of the most famous of the thirteenth and fourteenth century alchemists,
is said to have been secretly invited by King Edward I.\ (or \textit{\emph{II}}.)\ to
leave Milan and settle in England. According to some accounts, apartments
were assigned to his use in the Tower of London, where he is alleged
to have made some six million pounds sterling for the monarch, out
of iron, mercury, lead, and pewter.

Pope John XXII., a friend and pupil of the alchemist Arnold de Villeneuve,
is reported to have learned the secrets of alchemy from his master.
Later he issued two bulls against {}``pretenders'' in the art, which,
far from showing his disbelief, were cited by alchemists as proving
that he recognized pretenders as distinct from true masters of magic.

To moderns the attitude of mind of the alchemist is difficult to comprehend.
It is, perhaps, possible to conceive of animals or plants possessing
souls, but the early alchemist attributed the same thing---or something
kin to it---to metals also. Furthermore, just as plants germinated
from seeds, so metals were supposed to germinate also, and hence a
constant growth of metals in the ground. To prove this the alchemist
cited cases where previously exhausted gold-mines were found, after
a lapse of time, to contain fresh quantities of gold. The {}``seed''\ of
the remaining particles of gold had multiplied and increased. But
this germinating process could only take place under favorable conditions,
just as the seed of a plant must have its proper surroundings before
germinating; and it was believed that the action of the philosopher's
stone was to hasten this process, as man may hasten the growth of
plants by artificial means. Gold was looked upon as the most perfect
metal, and all other metals imperfect, because not yet {}``purified.''
By some alchemists they were regarded as lepers, who, when cured of
their leprosy, would become gold. And since nature intended that all
things should be perfect, it was the aim of the alchemist to assist
her in this purifying process, and incidentally to gain wealth and
prolong his life.

By other alchemists the process of transition from baser metals into
gold was conceived to be like a process of ripening fruit. The ripened
product was gold, while the green fruit, in various stages of maturity,
was represented by the base metals. Silver, for example, was more
nearly ripe than lead; but the difference was only one of {}``digestion,''\ and
it was thought that by further {}``digestion''\ lead might first
become silver and eventually gold. In other words, Nature had not
completed her work, and was wofully slow at it at best; but man, with
his superior faculties, was to hasten the process in his laboratories---if
he could but hit upon the right method of doing so.

It should not be inferred that the alchemist set about his task of
assisting nature in a haphazard way, and without training in the various
alchemic laboratory methods. On the contrary, he usually served a
long apprenticeship in the rudiments of his calling. He was obliged
to learn, in a general way, many of the same things that must be understood
in either chemical or alchemical laboratories. The general knowledge
that certain liquids vaporize at lower temperatures than others, and
that the melting-points of metals differ greatly, for example, was
just as necessary to alchemy as to chemistry. The knowledge of the
gross structure, or nature, of materials was much the same to the
alchemist as to the chemist, and, for that matter, many of the experiments
in calcining, distilling, \textit{etc}., were practically identical.

To the alchemist there were three principles---salt, sulphur, and
mercury---and the sources of these principles were the four elements---earth,
water, fire, and air. These four elements were accountable for every
substance in nature. Some of the experiments to prove this were so
illusive, and yet apparently so simple, that one is not surprised
that it took centuries to disprove them. That water was composed of
earth and air seemed easily proven by the simple process of boiling
it in a tea-kettle, for the residue left was obviously an earthy substance,
whereas the steam driven off was supposed to be air. The fact that
pure water leaves no residue was not demonstrated until after alchemy
had practically ceased to exist. It was possible also to demonstrate
that water could be turned into fire by thrusting a red-hot poker
under a bellglass containing a dish of water. Not only did the quantity
of water diminish, but, if a lighted candle was thrust under the glass,
the contents ignited and burned, proving, apparently, that water had
been converted into fire. These, and scores of other similar experiments,
seemed so easily explained, and to accord so well with the {}``four
elements''\ theory, that they were seldom questioned until a later
age of inductive science.

But there was one experiment to which the alchemist pinned his faith
in showing that metals could be {}``killed''\ and {}``revived,''
when proper means were employed. It had been known for many centuries
that if any metal, other than gold or silver, were calcined in an
open crucible, it turned, after a time, into a peculiar kind of ash.
This ash was thought by the alchemist to represent the death of the
metal. But if to this same ash a few grains of wheat were added and
heat again applied to the crucible, the metal was seen to {}``rise
from its ashes''\ and resume its original form---a well-known phenomenon
of reducing metals from oxides by the use of carbon, in the form of
wheat, or, for that matter, any other carbonaceous substance. Wheat
was, therefore, made the symbol of the resurrection of the life eternal.
Oats, corn, or a piece of charcoal would have {}``revived'' the
metals from the ashes equally well, but the medi\ae{}val alchemist
seems not to have known this. However, in this experiment the metal
seemed actually to be destroyed and revivified, and, as science had
not as yet explained this striking phenomenon, it is little wonder
that it deceived the alchemist.

Since the alchemists pursued their search of the magic stone in such
a methodical way, it would seem that they must have some idea of the
appearance of the substance they sought. Probably they did, each according
to his own mental bias; but, if so, they seldom committed themselves
to writing, confining their discourses largely to speculations as
to the properties of this illusive substance. Furthermore, the desire
for secrecy would prevent them from expressing so important a piece
of information. But on the subject of the properties, if not on the
appearance of the {}``essence,''\ they were voluminous writers.
It was supposed to be the only perfect substance in existence, and
to be confined in various substances, in quantities proportionate
to the state of perfection of the substance. Thus, gold being most
nearly perfect would contain more, silver less, lead still less, and
so on. The {}``essence''\ contained in the more nearly perfect
metals was thought to be more potent, a very small quantity of it
being capable of creating large quantities of gold and of prolonging
life indefinitely.

It would appear from many of the writings of the alchemists that their
conception of nature and the supernatural was so confused and entangled
in an inexplicable philosophy that they themselves did not really
understand the meaning of what they were attempting to convey. But
it should not be forgotten that alchemy was kept as much as possible
from the ignorant general public, and the alchemists themselves had
knowledge of secret words and expressions which conveyed a definite
meaning to one of their number, but which would appear a meaningless
jumble to an outsider. Some of these writers declared openly that
their writings were intended to convey an entirely erroneous impression,
and were sent out only for that purpose.

However, while it may have been true that the vagaries of their writings
were made purposely, the case is probably more correctly explained
by saying that the very nature of the art made definite statements
impossible. They were dealing with something that did not exist---could
not exist. Their attempted descriptions became, therefore, the language
of romance rather than the language of science.

But if the alchemists themselves were usually silent as to the appearance
of the actual substance of the philosopher's stone, there were numberless
other writers who were less reticent. By some it was supposed to be
a stone, by others a liquid or elixir, but more commonly it was described
as a black powder. It also possessed different degrees of efficiency
according to its degrees of purity, certain forms only possessing
the power of turning base metals into gold, while others gave eternal
youth and life or different degrees of health. Thus an alchemist,
who had made a partial discovery of this substance, could prolong
life a certain number of years only, or, possessing only a small and
inadequate amount of the magic powder, he was obliged to give up the
ghost when the effect of this small quantity had passed away.

This belief in the supernatural power of the philosopher's stone to
prolong life and heal diseases was probably a later phase of alchemy,
possibly developed by attempts to connect the power of the mysterious
essence with Biblical teachings. The early Roman alchemists, who claimed
to be able to transmute metals, seem not to have made other claims
for their magic stone.

By the fifteenth century the belief in the philosopher's stone had
become so fixed that governments began to be alarmed lest some lucky
possessor of the secret should flood the country with gold, thus rendering
the existing coin of little value. Some little consolation was found
in the thought that in case all the baser metals were converted into
gold iron would then become the {}``precious metal,''\ and would
remain so until some new philosopher's stone was found to convert
gold back into iron---a much more difficult feat, it was thought.
However, to be on the safe side, the English Parliament, in 1404,
saw fit to pass an act declaring the making of gold and silver to
be a felony. Nevertheless, in 1455, King Henry VI.\ granted permission
to several {}``knights, citizens of London, chemists, and monks''\ to
find the philosopher's stone, or elixir, that the crown might thus
be enabled to pay off its debts. The monks and ecclesiastics were
supposed to be most likely to discover the secret process, since {}``they
were such good artists in transubstantiating bread and wine.''

In Germany the emperors Maximilian I., Rudolf \textit{\emph{II}}.,
and Frederick \textit{\emph{II}}.\ gave considerable attention to
the search, and the example they set was followed by thousands of
their subjects. It is said that some noblemen developed the unpleasant
custom of inviting to their courts men who were reputed to have found
the stone, and then imprisoning the poor alchemists until they had
made a certain quantity of gold, stimulating their activity with tortures
of the most atrocious kinds. Thus this danger of being imprisoned
and held for ransom until some fabulous amount of gold should be made
became the constant menace of the alchemist. It was useless for an
alchemist to plead poverty once it was noised about that he had learned
the secret. For how could such a man be poor when, with a piece of
metal and a few grains of magic powder, he was able to provide himself
with gold? It was, therefore, a reckless alchemist indeed who dared
boast that he had made the coveted discovery.

The fate of a certain indiscreet alchemist, supposed by many to have
been Seton, a Scotchman, was not an uncommon one. Word having been
brought to the elector of Saxony that this alchemist was in Dresden
and boasting of his powers, the elector caused him to be arrested
and imprisoned. Forty guards were stationed to see that he did not
escape and that no one visited him save the elector himself. For some
time the elector tried by argument and persuasion to penetrate his
secret or to induce him to make a certain quantity of gold; but as
Seton steadily refused, the rack was tried, and for several months
he suffered torture, until finally, reduced to a mere skeleton, he
was rescued by a rival candidate of the elector, a Pole named Michael
Sendivogins, who drugged the guards. However, before Seton could be
{}``persuaded''\ by his new captor, he died of his injuries.

But Sendivogins was also ambitious in alchemy, and, since Seton was
beyond his reach, he took the next best step and married his widow.
From her, as the story goes, he received an ounce of black powder---the
veritable philosopher's stone. With this he manufactured great quantities
of gold, even inviting Emperor Rudolf \textit{\emph{II}}.\ to see
him work the miracle. That monarch was so impressed that he caused
a tablet to be inserted in the wall of the room in which he had seen
the gold made.

Sendivogins had learned discretion from the misfortune of Seton, so
that he took the precaution of concealing most of the precious powder
in a secret chamber of his carriage when he travelled, having only
a small quantity carried by his steward in a gold box. In particularly
dangerous places, he is said to have exchanged clothes with his coachman,
making the servant take his place in the carriage while he mounted
the box.

About the middle of the seventeenth century alchemy took such firm
root in the religious field that it became the basis of the sect known
as the Rosicrucians. The name was derived from the teaching of a German
philosopher, Rosenkreutz, who, having been healed of a dangerous illness
by an Arabian supposed to possess the philosopher's stone, returned
home and gathered about him a chosen band of friends, to whom he imparted
the secret. This sect came rapidly into prominence, and for a short
time at least created a sensation in Europe, and at the time were
credited with having {}``refined and spiritualized''\ alchemy.
But by the end of the seventeenth century their number had dwindled
to a mere handful, and henceforth they exerted little influence.

Another and earlier religious sect was the Aureacrucians, founded
by Jacob Bohme, a shoemaker, born in Prussia in 1575. According to
his teachings the philosopher's stone could be discovered by a diligent
search of the Old and the New Testaments, and more particularly the
Apocalypse, which contained all the secrets of alchemy. This sect
found quite a number of followers during the life of Bohme, but gradually
died out after his death; not, however, until many of its members
had been tortured for heresy, and one at least, Kuhlmann, of Moscow,
burned as a sorcerer.

The names of the different substances that at various times were thought
to contain the large quantities of the {}``essence''\ during the
many centuries of searching for it, form a list of practically all
substances that were known, discovered, or invented during the period.
Some believed that acids contained the substance; others sought it
in minerals or in animal or vegetable products; while still others
looked to find it among the distilled {}``spirits''---the alcoholic
liquors and distilled products. On the introduction of alcohol by
the Arabs that substance became of all-absorbing interest, and for
a long time allured the alchemist into believing that through it they
were soon to be rewarded. They rectified and refined it until {}``sometimes
it was so strong that it broke the vessels containing it,''\ but
still it failed in its magic power. Later, brandy was substituted
for it, and this in turn discarded for more recent discoveries.

There were always, of course, two classes of alchemists: serious investigators
whose honesty could not be questioned, and clever impostors whose
legerdemain was probably largely responsible for the extended belief
in the existence of the philosopher's stone. Sometimes an alchemist
practised both, using the profits of his sleight-of-hand to procure
the means of carrying on his serious alchemical researches. The \textit{\emph{impostures}}
of some of these jugglers deceived even the most intelligent and learned
men of the time, and so kept the flame of hope constantly burning.
The age of cold investigation had not arrived, and it is easy to understand
how an unscrupulous medi\ae{}val Hermann or Kellar might completely
deceive even the most intelligent and thoughtful scholars. In scoffing
at the credulity of such an age, it should not be forgotten that the
{}``Keely motor''\ was a late nineteenth-century illusion.

But long before the belief in the philosopher's stone had died out,
the methods of the legerdemain alchemist had been investigated and
reported upon officially by bodies of men appointed to make such investigations,
although it took several generations completely to overthrow a superstition
that had been handed down through several thousand years. In April
of 1772 Monsieur Geoffroy made a report to the Royal Academy of Sciences,
at Paris, on the alchemic cheats principally of the sixteenth and
seventeenth centuries. In this report he explains many of the seemingly
marvellous feats of the unscrupulous alchemists. A very common form
of deception was the use of a double-bottomed crucible. A copper or
brass crucible was covered on the inside with a layer of wax, cleverly
painted so as to resemble the ordinary metal. Between this layer of
wax and the bottom of the crucible, however, was a layer of gold dust
or silver. When the alchemist wished to demonstrate his power, he
had but to place some mercury or whatever substance he chose in the
crucible, heat it, throw in a grain or two of some mysterious powder,
pronounce a few equally mysterious phrases to impress his audience,
and, behold, a lump of precious metal would be found in the bottom
of his pot. This was the favorite method of mediocre performers, but
was, of course, easily detected.

An equally successful but more difficult way was to insert surreptitiously
a lump of metal into the mixture, using an ordinary crucible. This
required great dexterity, but was facilitated by the use of many mysterious
ceremonies on the part of the operator while performing, just as the
modern vaudeville performer diverts the attention of the audience
to his right hand while his left is engaged in the trick. Such ceremonies
were not questioned, for it was the common belief that the whole process
{}``lay in the spirit as much as in the substance,''\ many, as
we have seen, regarding the whole process as a divine manifestation.

Sometimes a hollow rod was used for stirring the mixture in the crucible,
this rod containing gold dust, and having the end plugged either with
wax or soft metal that was easily melted. Again, pieces of lead were
used which had been plugged with lumps of gold carefully covered over;
and a very simple and impressive demonstration was making use of a
nugget of gold that had been coated over with quicksilver and tarnished
so as to resemble lead or some base metal. When this was thrown into
acid the coating was removed by chemical action, leaving the shining
metal in the bottom of the vessel. In order to perform some of these
tricks, it is obvious that the alchemist must have been well supplied
with gold, as some of them, when performing before a royal audience,
gave the products to their visitors. But it was always a paying investment,
for once his reputation was established the gold-maker found an endless
variety of ways of turning his alleged knowledge to account, frequently
amassing great wealth.

Some of the cleverest of the charlatans often invited royal or other
distinguished guests to bring with them iron nails to be turned into
gold ones. They were transmuted in the alchemist's crucible before
the eyes of the visitors, the juggler adroitly extracting the iron
nail and inserting a gold one without detection. It mattered little
if the converted gold nail differed in size and shape from the original,
for this change in shape could be laid to the process of transmutation;
and even the very critical were hardly likely to find fault with the
exchange thus made. Furthermore, it was believed that gold possessed
the property of changing its bulk under certain conditions, some of
the more conservative alchemists maintaining that gold was only increased
in bulk, not necessarily created, by certain forms of the magic stone.
Thus a very proficient operator was thought to be able to increase
a grain of gold into a pound of pure metal, while one less expert
could only double, or possibly treble, its original weight.

The actual number of useful discoveries resulting from the efforts
of the alchemists is considerable, some of them of incalculable value.
Roger Bacon, who lived in the thirteenth century, while devoting much
of his time to alchemy, made such valuable discoveries as the theory,
at least, of the telescope, and probably gunpowder. Of this latter
we cannot be sure that the discovery was his own and that he had not
learned of it through the source of old manuscripts. But it is not
impossible nor improbable that he may have hit upon the mixture that
makes the explosives while searching for the philosopher's stone in
his laboratory. {}``Von Helmont, in the same pursuit, discoverd the
properties of gas,''\ says Mackay; {}``Geber made discoveries in
chemistry, which were equally important; and Paracelsus, amid his
perpetual visions of the transmutation of metals, found that mercury
was a remedy for one of the most odious and excruciating of all the
diseases that afflict humanity.''%
\footnote{ Mackay, \emph{op.\ cit.}, Vol.\ II., p.\ 289.%
} As we shall see a little farther on, alchemy finally evolved into
modern chemistry, but not until it had passed through several important
transitional stages.


\section*{\raggedright ASTROLOGY}

\addcontentsline{toc}{section}{ASTROLOGY}

In a general way modern astronomy may be considered as the outgrowth
of astrology, just as modern chemistry is the result of alchemy. It
is quite possible, however, that astronomy is the older of the two;
but astrology must have developed very shortly after. The primitive
astronomer, having acquired enough knowledge from his observations
of the heavenly bodies to make correct predictions, such as the time
of the coming of the new moon, would be led, naturally, to believe
that certain predictions other than purely astronomical ones could
be made by studying the heavens. Even if the astronomer himself did
not believe this, some of his superstitious admirers would; for to
the unscientific mind predictions of earthly events would surely seem
no more miraculous than correct predictions as to the future movements
of the sun, moon, and stars. When astronomy had reached a stage of
development so that such things as eclipses could be predicted with
anything like accuracy, the occult knowledge of the astronomer would
be unquestioned. Turning this apparently occult knowledge to account
in a mercenary way would then be the inevitable result, although it
cannot be doubted that many of the astrologers, in all ages, were
sincere in their beliefs.

Later, as the business of astrology became a profitable one, sincere
astronomers would find it expedient to practise astrology as a means
of gaining a livelihood. Such a philosopher as Kepler freely admitted
that he practised astrology {}``to keep from starving,''\ although
he confessed no faith in such predictions. {}``Ye otherwise philosophers,''\ he
said, {}``ye censure this daughter of astronomy beyond her deserts;
know ye not that she must support her mother by her charms.''

Once astrology had become an established practice, any considerable
knowledge of astronomy was unnecessary, for as it was at best but
a system of good guessing as to future events, clever impostors could
thrive equally well without troubling to study astronomy. The celebrated
astrologers, however, were usually astronomers as well, and undoubtedly
based many of their predictions on the position and movements of the
heavenly bodies. Thus, the casting of a horoscope---that is, the methods
by which the astrologers ascertained the relative position of the
heavenly bodies at the time of a birth---was a simple but fairly exact
procedure. Its basis was the zodiac, or the path traced by the sun
in his yearly course through certain constellations. At the moment
of the birth of a child, the first care of the astrologer was to note
the particular part of the zodiac that appeared on the horizon. The
zodiac was then divided into {}``houses''---that is, into twelve
spaces---on a chart. In these houses were inserted the places of the
planets, sun, and moon, with reference to the zodiac. When this chart
was completed it made a fairly correct diagram of the heavens and
the position of the heavenly bodies as they would appear to a person
standing at the place of birth at a certain time.

Up to this point the process was a simple one of astronomy. But the
next step---the really important one---that of interpreting this chart,
was the one which called forth the skill and imagination of the astrologer.
In this interpretation, not in his mere observations, lay the secret
of his success. Nor did his task cease with simply foretelling future
events that were to happen in the life of the newly born infant. He
must not only point out the dangers, but show the means whereby they
could be averted, and his prophylactic measures, like his predictions,
were alleged to be based on his reading of the stars.

But casting a horoscope at the time of births was, of course, only
a small part of the astrologer's duty. His offices were sought by
persons of all ages for predictions as to their futures, the movements
of an enemy, where to find stolen goods, and a host of everyday occurrences.
In such cases it is more than probable that the astrologers did very
little consulting of the stars in making their predictions. They became
expert physiognomists and excellent judges of human nature, and were
thus able to foretell futures with the same shrewdness and by the
same methods as the modern {}``mediums,''\ palmists, and fortune-tellers.
To strengthen belief in their powers, it became a common thing for
some supposedly lost document of the astrologer to be mysteriously
discovered after an important event, this document purporting to foretell
this very event. It was also a common practice with astrologers to
retain, or have access to, their original charts, cleverly altering
them from time to time to fit conditions.

The dangers attendant upon astrology were of such a nature that the
lot of the astrologer was likely to prove anything but an enviable
one. As in the case of the alchemist, the greater the reputation of
an astrologer the greater dangers he was likely to fall into. If he
became so famous that he was employed by kings or noblemen, his too
true or too false prophecies were likely to bring him into disrepute---even
to endanger his life.

Throughout the dark age the astrologers flourished, but the sixteenth
and seventeenth centuries were the golden age of these impostors.
A skilful astrologer was as much an essential to the government as
the highest official, and it would have been a bold monarch, indeed,
who would undertake any expedition of importance unless sanctioned
by the governing stars as interpreted by these officials.

It should not be understood, however, that belief in astrology died
with the advent of the Copernican doctrine. It did become separated
from astronomy very shortly after, to be sure, and undoubtedly among
the scientists it lost much of its prestige. But it cannot be considered
as entirely passed away, even to-day, and even if we leave out of
consideration street-corner {}``astrologers''\ and fortune-tellers,
whose signs may be seen in every large city, there still remains quite
a large class of relatively intelligent people who believe in what
they call {}``the science of astrology.'' Needless to say, such
people are not found among the scientific thinkers; but it is significant
that scarcely a year passes that some book or pamphlet is not published
by some ardent believer in astrology, attempting to prove by the illogical
dogmas characteristic of unscientific thinkers that astrology is a
science. The arguments contained in these pamphlets are very much
the same as those of the astrologers three hundred years ago, except
that they lack the quaint form of wording which is one of the features
that lends interest to the older documents. These pamphlets need not
be taken seriously, but they are interesting as exemplifying how difficult
it is, even in an age of science, to entirely stamp out firmly established
superstitions. Here are some of the arguments advanced in defence
of astrology, taken from a little brochure entitled {}``Astrology
Vindicated,''\ published in 1898: {}``It will be found that a person
born when the Sun is in twenty degrees Scorpio has the left ear as
his exceptional feature and the nose (Sagittarius)\ bent towards
the left ear. A person born when the Sun is in any of the latter degrees
of Taurus, say the twenty-fifth degree, will have a small, sharp,
weak chin, curved up towards Gemini, the two vertical lines on the
upper lip.''%
\footnote{ John B.\ Schmalz, \emph{Astrology Vindicated}, New York, 1898.%
} The time was when science went out of its way to prove that such
statements were untrue; but that time is past, and such writers are
usually classed among those energetic but misguided persons who are
unable to distinguish between logic and sophistry.

In England, from the time of Elizabeth to the reign of William and
Mary, judicial astrology was at its height. After the great London
fire, in 1666, a committee of the House of Commons publicly summoned
the famous astrologer, Lilly, to come before Parliament and report
to them on his alleged prediction of the calamity that had befallen
the city. Lilly, for some reason best known to himself, denied having
made such a prediction, being, as he explained, {}``more interested
in determining affairs of much more importance to the future welfare
of the country.'' Some of the explanations of his interpretations
will suffice to show their absurdities, which, however, were by no
means regarded as absurdities at that time, for Lilly was one of the
greatest astrologers of his day. He said that in 1588 a prophecy had
been printed in Greek characters which foretold exactly the troubles
of England between the years 1641 and 1660. {}``And after him shall
come a dreadful dead man,''\ ran the prophecy, {}``and with him
a royal G of the best blood in the world, and he shall have the crown
and shall set England on the right way and put out all \textit{\emph{heresies}}.''
His interpretation of this was that, {}``Monkery being extinguished
above eighty or ninety years, and the Lord General's name being Monk,
is the dead man. The royal G or C (it is gamma in the Greek, intending
C in the Latin, being the third letter in the alphabet)\ is Charles
\textit{\emph{II}}., who, for his extraction, may be said to be of
the best blood of the world.''%
\footnote{William Lilly, \emph{The Starry Messenger}, London, 1645, p.\ 63.%
}

This may be taken as a fair sample of Lilly's interpretations of astrological
prophesies, but many of his own writings, while somewhat more definite
and direct, are still left sufficiently vague to allow his skilful
interpretations to set right an apparent mistake. One of his famous
documents was {}``The Starry Messenger,''\ a little pamphlet purporting
to explain the phenomenon of a {}``strange apparition of three suns''\ that
were seen in London on November 19, 1644----the anniversary of the
birth of Charles I., then the reigning monarch. This phenomenon caused
a great stir among the English astrologers, coming, as it did, at
a time of great political disturbance. Prophecies were numerous, and
Lilly's brochure is only one of many that appeared at that time, most
of which, however, have been lost. Lilly, in his preface, says: {}``If
there be any of so prevaricate a judgment as to think that the apparition
of these three Suns doth intimate no Novelle thing to happen in our
own Climate, where they were manifestly visible, I shall lament their
indisposition, and conceive their brains to be shallow, and voyde
of understanding humanity, or notice of common History.''

Having thus forgiven his few doubting readers, who were by no means
in the majority in his day, he takes up in review the records of the
various appearances of three suns as they have occurred during the
Christian era, showing how such phenomena have governed certain human
events in a very definite manner. Some of these are worth recording.

{}``Anno 66. A comet was seen, and also three Suns: In which yeer,
Florus President of the Jews was by them slain. Paul writes to Timothy.
The Christians are warned by a divine Oracle, and depart out of Jerusalem.
Boadice a British Queen, killeth seventy thousand Romans. The \textit{\emph{Nazareni}},
a scurvie Sect, begun, that boasted much of Revelations and Visions.
About a year after Nero was proclaimed enemy to the State of Rome.''

Again, {}``Anno 1157, in September, there were seen three Suns together,
in as clear weather as could be: And a few days after, in the same
month, three Moons, and, in the Moon that stood in the middle, a white
Crosse. \textit{\emph{Sueno}}, King of Denmark, at a great Feast,
killeth \textit{\emph{Canutus}}\emph{:} \textit{\emph{Sueno}} is himself
slain, in pursuit of Waldemar. The Order of Eremites, according to
the rule of Saint Augustine, begun this year; and in the next, the
Pope submits to the Emperour: (was not this miraculous?)\ Lombardy
was also adjudged to the Emperour.''

Continuing this list of peculiar phenomena he comes down to within
a few years of his own time.

{}``Anno 1622, three Suns appeared at Heidelberg. The woful Calamities
that have ever since fallen upon the Palatinate, we are all sensible
of, and of the loss of it, for any thing I see, for ever, from the
right Heir. Osman the great Turk is strangled that year; and Spinola
besiegeth Bergen up Zoom, \textit{etc}.''

Fortified by the enumeration of these past events, he then proceeds
to make his deductions. {}``Only this I must tell thee,''\ he writes,
{}``that the interpretation I write is, I conceive, grounded upon
probable foundations; and who lives to see a few years over his head,
will easily perceive I have unfolded as much as was fit to discover,
and that my judgment was not a mile and a half from truth.''

There is a great significance in this {}``as much as was fit to discover''---a
mysterious something that Lilly thinks it expedient not to divulge.
But, nevertheless, one would imagine that he was about to make some
definite prediction about Charles I., since these three suns appeared
upon his birthday and surely must portend something concerning him.
But after rambling on through many pages of dissertations upon planets
and prophecies, he finally makes his own indefinite prediction.

{}``O all you Emperors, Kings, Princes, Rulers and Magistrates of
Europe, this unaccustomed Apparition is like the Handwriting in Daniel
to some of you; it premonisheth you, above all other people, to make
your peace with God in time. You shall every one of you smart, and
every one of you taste (none excepted)\ the heavie hand of God, who
will strengthen your subjects with invincible courage to suppress
your misgovernments and \textit{\emph{Oppressions}} in Church or Common-wealth;\ldots{}
Those words are general: a word for my own country of England\ldots{}.
Look to yourselves; here's some monstrous death towards you. But to
whom? wilt thou say. Herein we consider the Signe, Lord thereof, and
the House; The Sun signifies in that Royal Signe, great ones; the
House signifies captivity, poison, Treachery: From which is derived
thus much, That some very great man, what King, Prince, Duke, or the
like, I really affirm I perfectly know not, shall, I say, come to
some such untimely end.''%
\footnote{Lilly, \emph{op.\ cit}., p.\ 70.%
}

Here is shown a typical example of astrological prophecy, which seems
to tell something or nothing, according to the point of view of the
reader. According to a believer in astrology, after the execution
of Charles I., five years later, this could be made to seem a direct
and exact prophecy. For example, he says: {}``You Kings, Princes,
\textit{etc}.,\ \ldots{}\ it premonisheth you\ \ldots{}\ to make
your peace with God\ldots{}. Look to yourselves; here's some monstrous
death towards you\ldots{}. That some very great man, what King, Prince,
shall, I say, come to such untimely end.''

But by the doubter the complete prophecy could be shown to be absolutely
indefinite, and applicable as much to the king of France or Spain
as to Charles I., or to any king in the future, since no definite
time is stated. Furthermore, Lilly distinctly states, {}``What King,
Prince, Duke, or the like, I really affirm I perfectly know not''---which
last, at least, was a most truthful statement. The same ingenuity
that made {}``Gen.\ Monk''\ the {}``dreadful dead man,''\ could
easily make such a prediction apply to the execution of Charles I.\ Such
a definite statement that, on such and such a day a certain number
of years in the future, the monarch of England would be beheaded---such
an exact statement can scarcely be found in any of the works on astrology.
It should be borne in mind, also, that Lilly was of the Cromwell party
and opposed to the king.

After the death of Charles I., Lilly admitted that the monarch had
given him a thousand pounds to cast his horoscope. {}``I advised
him,''\ says Lilly, {}``to proceed eastwards; he went west, and
all the world knows the result.'' It is an unfortunate thing for
the cause of astrology that Lilly failed to mention this until after
the downfall of the monarch. In fact, the sudden death, or decline
in power, of any monarch, even to-day, brings out the perennial post-mortem
predictions of astrologers.

We see how Lilly, an opponent of the king, made his so-called prophecy
of the disaster of the king and his army. At the same time another
celebrated astrologer and rival of Lilly, George Wharton, also made
some predictions about the outcome of the eventful march from Oxford.
Wharton, unlike Lilly, was a follower of the king's party, but that,
of course, should have had no influence in his {}``scientific''\ reading
of the stars. Wharton's predictions are much less verbose than Lilly's,
much more explicit, and, incidentally, much more incorrect in this
particular instance. {}``The Moon Lady of the 12,''\ he wrote,
{}``and moving betwixt the 8 degree, 34 min., and 21 degree, 26 min.\ of
Aquarius, gives us to understand that His Majesty shall receive much
contentment by certain Messages brought him from foreign parts; and
that he shall receive some sudden and unexpected supply of\ \ldots{}\ by
the means of some that assimilate the condition of his Enemies: And
withal this comfort; that His Majesty shall be exceeding successful
in Besieging Towns, Castles, or Forts, and in persuing the enemy.

{}``Mars his Sextile to the Sun, Lord of the Ascendant (which happeneth
the 18 day of May)\ will encourage our Soldiers to advance with much
alacrity and cheerfulness of spirit; to show themselves gallant in
the most dangerous attempt\ldots{}. And now to sum up all: It is
most apparent to every impartial and ingenuous judgment; That although
His Majesty cannot expect to be secured from every trivial disaster
that may befall his army, either by the too much Presumption, Ignorance,
or Negligence of some particular Persons (which is frequently incident
and unavoidable in the best of Armies), yet the several positions
of the Heavens duly considered and compared among themselves, as well
in the prefixed Scheme as at the Quarterly Ingresses, do generally
render His Majesty and his whole Army unexpectedly victorious and
successful in all his designs; Believe it (London), thy Miseries approach,
they are like to be many, great, and grievous, and not to be diverted,
unless thou seasonably crave Pardon of God for being Nurse to this
present Rebellion, and speedily submit to thy Prince's Mercy; Which
shall be the daily Prayer of Geo. Wharton.''%
\footnote{George Wharton, \emph{An Astrological} \textit{jugement} \emph{upon
His Majesty's Present March begun from Oxford}, \emph{May 7, 1645},
\textit{\emph{pp}}.\ 7-10.%
}

In the light of after events, it is probable that Wharton's stock
as an astrologer was not greatly enhanced by this document, at least
among members of the Royal family. Lilly's book, on the other hand,
became a favorite with the Parliamentary army.

After the downfall and death of Napoleon there were unearthed many
alleged authentic astrological documents foretelling his ruin. And
on the death of George IV., in 1830, there appeared a document (unknown,
as usual, until that time)\ purporting to foretell the death of the
monarch to the day, and this without the astrologer knowing that his
horoscope was being cast for a monarch. A full account of this prophecy
is told, with full belief, by Roback, a nineteenth-century astrologer.
He says:\ 

\begin{quotation}
{}``In the year 1828, a stranger of noble mien, advanced in life,
but possessing the most bland manners, arrived at the abode of a celebrated
astrologer in London,''\ asking that the learned man foretell his
future. {}``The astrologer complied with the request of the mysterious
visitor, drew forth his tables, consulted his ephemeris, and cast
the horoscope or celestial map for the hour and the moment of the
inquiry, according to the established rules of his art.

{}``The elements of his calculation were adverse, and a feeling of
gloom cast a shade of serious thought, if not dejection, over his
countenance.

{}```You are of high rank,'\ said the astrologer, as he calculated
and looked on the stranger, `and of illustrious title.' The stranger
made a graceful inclination of the head in token of acknowledgment
of the complimentary remarks, and the astrologer proceeded with his
mission.

{}``The celestial signs were ominous of calamity to the stranger,
who, probably observing a sudden change in the countenance of the
astrologer, eagerly inquired what evil or good fortune had been assigned
him by the celestial orbs.

{}```To the first part of your inquiry,'\ said the astrologer, `I
can readily reply. You have been a favorite of fortune; her smiles
on you have been abundant, her frowns but few; you have had, perhaps
now possess, wealth and power; the impossibility of their accomplishment
is the only limit to the fulfilment of your desires.'''

{}```You have spoken truly of the past,'\ said the stranger. `I
have full faith in your revelations of the future: what say you of
my pilgrimage in this life---is it short or long?'

{}```I regret,'\ replied the astrologer, in answer to this inquiry,
`to be the herald of ill, though \textit{true}, fortune; your sojourn
on earth will be short.'

{}```How short?'\ eagerly inquired the excited and anxious stranger.

{}```Give me a momentary truce,'\ said the astrologer; `I will consult
the horoscope, and may possibly find some mitigating circumstances.'

{}``Having cast his eyes over the celestial map, and paused for some
moments, he surveyed the countenance of the stranger with great sympathy,
and said, `I am sorry that I can find no planetary influences that
oppose your destiny---your death will take place in two years.'

{}``The event justified the astrologic prediction: George IV.\ died
on May 18, 1830, exactly two years from the day on which he had visited
the astrologer.''%
\footnote{C.\ W.\ Roback, \emph{The Mysteries of Astrology}, Boston, 1854,
p.\ 29.%
}
\end{quotation}
{}

This makes a very pretty story, but it hardly seems like occult insight
that an astrologer should have been able to predict an early death
of a man nearly seventy years old, or to have guessed that his well-groomed
visitor {}``had, perhaps now possesses, wealth and power.'' Here
again, however, the point of view of each individual plays the governing
part in determining the importance of such a document. To the scientist
it proves nothing; to the believer in astrology, everything. The significant
thing is that it appeared shortly \textit{after} the death of the
monarch.

On the Continent astrologers were even more in favor than in England.
Charlemagne, and some of his immediate successors, to be sure, attempted
to exterminate them, but such rulers as Louis XI. and Catherine de'\ Medici
patronized and encouraged them, and it was many years after the time
of Copernicus before their influence was entirely stamped out even
in official life. There can be no question that what gave the color
of truth to many of the predictions was the fact that so many of the
prophecies of sudden deaths and great conflagrations were known to
have come true---in many instances were made to come true by the astrologer
himself. And so it happened that when the prediction of a great conflagration
at a certain time culminated in such a conflagration, many times a
second but less-important burning took place, in which the ambitious
astrologer, or his followers, took a central part about a stake, being
convicted of incendiarism, which they had committed in order that
their prophecies might be fulfilled.

But, on the other hand, these predictions were sometimes turned to
account by interested friends to warn certain persons of approaching
dangers.

For example, a certain astrologer foretold the death of Prince Alexander
de'\ Medici. He not only foretold the death, but described so minutely
the circumstances that would attend it, and gave such a correct description
of the assassin who should murder the prince, that he was at once
suspected of having a hand in the assassination. It developed later,
however, that such was probably not the case; but that some friend
of Prince Alexander, knowing of the plot to take his life, had induced
the astrologer to foretell the event in order that the prince might
have timely warning and so elude the conspirators.

The cause of the decline of astrology was the growing prevalence of
the new spirit of experimental science. Doubtless the most direct
blow was dealt by the Copernican theory. So soon as this was established,
the recognition of the earth's subordinate place in the universe must
have made it difficult for astronomers to be longer deceived by such
coincidences as had sufficed to convince the observers of a more credulous
generation. Tycho Brahe was, perhaps, the last astronomer of prominence
who was a conscientious practiser of the art of the astrologer.


\chapter*{\raggedright VII. FROM PARACELSUS TO HARVEY}

\addcontentsline{toc}{chapter}{VII. FROM PARACELSUS TO HARVEY}

\markboth{A HISTORY OF SCIENCE, VOLUME II}{VII. FROM PARACELSUS TO
HARVEY}


\section*{\raggedright PARACELSUS}

In the year 1526 there appeared a new lecturer on the platform at
the University at Basel---a small, beardless, effeminate-looking person---who
had already inflamed all Christendom with his peculiar philosophy,
his revolutionary methods of treating diseases, and his unparalleled
success in curing them. A man who was to be remembered in after-time
by some as the father of modern chemistry and the founder of modern
medicine; by others as madman, charlatan, impostor; and by still others
as a combination of all these. This soft-cheeked, effeminate, woman-hating
man, whose very sex has been questioned, was Theophrastus von Hohenheim,
better known as Paracelsus (1493-1541).

To appreciate his work, something must be known of the life of the
man. He was born near Maria-Einsiedeln, in Switzerland, the son of
a poor physician of the place. He began the study of medicine under
the instruction of his father, and later on came under the instruction
of several learned churchmen. At the age of sixteen he entered the
University of Basel, but, soon becoming disgusted with the philosophical
teachings of the time, he quitted the scholarly world of dogmas and
theories and went to live among the miners in the Tyrol, in order
that he might study nature and men at first hand. Ordinary methods
of study were thrown aside, and he devoted his time to personal observation---the
only true means of gaining useful knowledge, as he preached and practised
ever after. Here he became familiar with the art of mining, learned
the physical properties of minerals, ores, and metals, and acquired
some knowledge of mineral waters. More important still, he came in
contact with such diseases, wounds, and injuries as miners are subject
to, and he tried his hand at the practical treatment of these conditions,
untrammelled by the traditions of a profession in which his training
had been so scant.

Having acquired some empirical skill in treating diseases, Paracelsus
set out wandering from place to place all over Europe, gathering practical
information as he went, and learning more and more of the medicinal
virtues of plants and minerals. His wanderings covered a period of
about ten years, at the end of which time he returned to Basel, where
he was soon invited to give a course of lectures in the university.

These lectures were revolutionary in two respects---they were given
in German instead of time-honored Latin, and they were based upon
personal experience rather than upon the works of such writers as
Galen and Avicenna. Indeed, the iconoclastic teacher spoke with open
disparagement of these revered masters, and openly upbraided his fellow-practitioners
for following their tenets. Naturally such teaching raised a storm
of opposition among the older physicians, but for a time the unparalleled
success of Paracelsus in curing diseases more than offset his unpopularity.
Gradually, however, his bitter tongue and his coarse personality rendered
him so unpopular, even among his patients, that, finally, his liberty
and life being jeopardized, he was obliged to flee from Basel, and
became a wanderer. He lived for brief periods in Colmar, Nuremberg,
Appenzell, Zurich, \textit{\emph{Pfeffers}}\emph{,} \textit{\emph{Augsburg}}\emph{,}
and several other cities, until finally at Salzburg his eventful life
came to a close in 1541. His enemies said that he had died in a tavern
from the effects of a protracted debauch; his supporters maintained
that he had been murdered at the instigation of rival physicians and
apothecaries.

But the effects of his teachings had taken firm root, and continued
to spread after his death. He had shown the fallibility of many of
the teachings of the hitherto standard methods of treating diseases,
and had demonstrated the advantages of independent reasoning based
on observation. In his \textit{Magicum} he gives his reasons for breaking
with tradition. {}``I did,''\ he says, {}``embrace at the beginning
these doctrines, as my adversaries (followers of Galen)\ have done,
but since I saw that from their procedures nothing resulted but death,
murder, stranglings, anchylosed limbs, paralysis, and so forth, that
they held most diseases incurable\ \ldots{}\ therefore have I quitted
this wretched art, and sought for truth in any other direction. I
asked myself if there were no such thing as a teacher in medicine,
where could I learn this art best? Nowhere better than the open book
of nature, written with God's own finger.'' We shall see, however,
that this {}``book of nature''\ taught Paracelsus some very strange
lessons. Modesty was not one of these. {}``Now at this time,''\ he
declares, {}``I, Theophrastus Paracelsus, Bombast, Monarch of the
Arcana, was endowed by God with special gifts for this end, that every
searcher after this supreme philosopher's work may be forced to imitate
and to follow me, be he Italian, Pole, Gaul, German, or whatsoever
or whosoever he be. Come hither after me, all ye philosophers, astronomers,
and spagirists\ldots{}. I will show and open to you\ \ldots{}\ this
corporeal regeneration.''%
\footnote{A.\ E.\ Waite, \emph{The Hermetic and Alchemical Writings of Paracelsus},
2 \textit{\emph{vols}}., London, 1894. Vol.\ I., p.\ 21.%
}

Paracelsus based his medical teachings on four {}``pillars''---philosophy,
astronomy, alchemy, and virtue of the physician---a strange-enough
equipment surely, and yet, properly interpreted, not quite so anomalous
as it seems at first blush. Philosophy was the {}``gate of medicine,''\ whereby
the physician entered rightly upon the true course of learning; astronomy,
the study of the stars, was all-important because {}``they (the stars)\ caused
disease by their exhalations, as, for instance, the sun by excessive
heat''; alchemy, as he interpreted it, meant the improvement of natural
substances for man's benefit; while virtue in the physician was necessary
since {}``only the virtuous are permitted to penetrate into the innermost
nature of man and the universe.''

All his writings aim to promote progress in medicine, and to hold
before the physician a grand ideal of his profession. In this his
views are wide and far-reaching, based on the relationship which man
bears to nature as a whole; but in his sweeping condemnations he not
only rejected Galenic therapeutics and Galenic anatomy, but condemned
\textit{\emph{dissections}} of any kind. He laid the cause of all
diseases at the door of the three mystic elements---salt, sulphur,
and mercury. In health he supposed these to be mingled in the body
so as to be indistinguishable; a slight separation of them produced
disease; and death he supposed to be the result of their complete
separation. The spiritual agencies of diseases, he said, had nothing
to do with either angels or devils, but were the spirits of human
beings.

He believed that all food contained poisons, and that the function
of digestion was to separate the poisonous from the nutritious. In
the stomach was an \emph{arch\ae{}us}, or alchemist, whose duty was
to make this separation. In digestive disorders the \emph{arch\ae{}us}
failed to do this, and the poisons thus gaining access to the system
were {}``coagulated''\ and deposited in the joints and various
other parts of the body. Thus the deposits in the kidneys and tartar
on the teeth were formed; and the stony deposits of gout were particularly
familiar examples of this. All this is visionary enough, yet it shows
at least a groping after rational explanations of vital phenomena.

Like most others of his time, Paracelsus believed firmly in the doctrine
of {}``signatures''---a belief that every organ and part of the
body had a corresponding form in nature, whose function was to heal
diseases of the organ it resembled. The vagaries of this peculiar
doctrine are too numerous and complicated for lengthy discussion,
and varied greatly from generation to generation. In general, however,
the theory may be summed up in the words of Paracelsus: {}``As a
woman is known by her shape, so are the medicines.'' Hence the physicians
were constantly searching for some object of corresponding shape to
an organ of the body. The most natural application of this doctrine
would be the use of the organs of the lower animals for the treatment
of the corresponding diseased organs in man. Thus diseases of the
heart were to be treated with the hearts of animals, liver disorders
with livers, and so on. But this apparently simple form of treatment
had endless modifications and restrictions, for not all animals were
useful. For example, it was useless to give the stomach of an ox in
gastric diseases when the indication in such cases was really for
the stomach of a rat. Nor were the organs of animals the only {}``signatures''\ in
nature. Plants also played a very important role, and the herb-doctors
devoted endless labor to searching for such plants. Thus the blood-root,
with its red juice, was supposed to be useful in blood diseases, in
stopping hemorrhage, or in subduing the redness of an inflammation.

Paracelsus's system of signatures, however, was so complicated by
his theories of astronomy and alchemy that it is practically beyond
comprehension. It is possible that he himself may have understood
it, but it is improbable that any one else did---as shown by the endless
discussions that have taken place about it. But with all the vagaries
of his theories he was still rational in his applications, and he
attacked to good purpose the complicated {}``shot-gun''\ prescriptions
of his contemporaries, advocating more simple methods of treatment.

The ever-fascinating subject of electricity, or, more specifically,
{}``magnetism,''\ found great favor with him, and with properly
adjusted magnets he claimed to be able to cure many diseases. In epilepsy
and lockjaw, for example, one had but to fasten magnets to the four
extremities of the body, and then, {}``when the proper medicines
were given,''\ the cure would be effected. The easy loop-hole for
excusing failure on the ground of improper medicines is obvious, but
Paracelsus declares that this one prescription is of more value than
{}``all the humoralists have ever written or taught.''

Since Paracelsus condemned the study of anatomy as useless, he quite
naturally regarded surgery in the same light. In this he would have
done far better to have studied some of his predecessors, such as
Galen, Paul of Aegina, and Avicenna. But instead of {}``cutting men
to pieces,''\ he taught that surgeons would gain more by devoting
their time to searching for the universal panacea which would cure
all diseases, surgical as well as medical. In this we detect a taint
of the popular belief in the philosopher's stone and the magic elixir
of life, his belief in which have been stoutly denied by some of his
followers. He did admit, however, that one operation alone was perhaps
permissible---lithotomy, or the {}``cutting for stone.''

His influence upon medicine rests undoubtedly upon his revolutionary
attitude, rather than on any great or new discoveries made by him.
It is claimed by many that he brought prominently into use opium and
mercury, and if this were indisputably proven his services to medicine
could hardly be overestimated. Unfortunately, however, there are good
grounds for doubting that he was particularly influential in reintroducing
these medicines. His chief influence may perhaps be summed up in a
single phrase---he overthrew old traditions.

To Paracelsus's endeavors, however, if not to the actual products
of his work, is due the credit of setting in motion the chain of thought
that developed finally into scientific chemistry. Nor can the ultimate
aim of the modern chemist seek a higher object than that of this sixteenth-century
alchemist, who taught that {}``true alchemy has but one aim and object,
to extract the quintessence of things, and to prepare arcana, tinctures,
and \textit{\emph{elixirs}} which may restore to man the health and
soundness he has lost.''


\section*{\raggedright THE GREAT ANATOMISTS}

\addcontentsline{toc}{section}{THE GREAT ANATOMISTS}

About the beginning of the sixteenth century, while Paracelsus was
scoffing at the study of anatomy as useless, and using his influence
against it, there had already come upon the scene the first of the
great anatomists whose work was to make the century conspicuous in
that branch of medicine.

The young anatomist Charles Etienne (1503-1564)\ made one of the
first noteworthy discoveries, pointing out for the first time that
the spinal cord contains a canal, continuous throughout its length.
He also made other minor discoveries of some importance, but his researches
were completely overshadowed and obscured by the work of a young Fleming
who came upon the scene a few years later, and who shone with such
brilliancy in the medical world that he obscured completely the work
of his contemporary until many years later. This young physician,
who was destined to lead such an eventful career and meet such an
untimely end as a martyr to science, was Andrew Vesalius (1514-1564),
who is called the {}``greatest of anatomists.'' At the time he came
into the field medicine was struggling against the dominating Galenic
teachings and the theories of Paracelsus, but perhaps most of all
against the superstitions of the time. In \textit{\emph{France}} human
\textit{\emph{dissections}} were attended with such dangers that the
young Vesalius transferred his field of labors to Italy, where such
investigations were covertly permitted, if not openly countenanced.

From the very start the young Fleming looked askance at the accepted
teachings of the day, and began a series of independent investigations
based upon his own observations. The results of these investigations
he gave in a treatise on the subject which is regarded as the first
comprehensive and systematic work on human anatomy. This remarkable
work was published in the author's twenty-eighth or twenty-ninth year.
Soon after this Vesalius was invited as imperial physician to the
court of Emperor Charles V. He continued to act in the same capacity
at the court of Philip \textit{\emph{II}}., after the abdication of
his patron. But in spite of this royal favor there was at work a factor
more powerful than the influence of the monarch himself---an instrument
that did so much to retard scientific progress, and by which so many
lives were brought to a premature close.

Vesalius had received permission from the kinsmen of a certain grandee
to perform an autopsy. While making his observations the heart of
the outraged body was seen to palpitate---so at least it was reported.
This was brought immediately to the attention of the Inquisition,
and it was only by the intervention of the king himself that the anatomist
escaped the usual fate of those accused by that tribunal. As it was,
he was obliged to perform a pilgrimage to the Holy Land. While returning
from this he was shipwrecked, and perished from hunger and exposure
on the island of Zante.

At the very time when the anatomical writings of Vesalius were startling
the medical world, there was living and working contemporaneously
another great anatomist, Eustachius (died 1574), whose records of
his anatomical investigations were ready for publication only nine
years after the publication of the work of Vesalius. Owing to the
unfortunate circumstances of the anatomist, however, they were never
published during his lifetime---not, in fact, until 1714. When at
last they were given to the world as \emph{Anatomical Engravings},
they showed conclusively that Eustachius was equal, if not superior
to Vesalius in his knowledge of anatomy. It has been said of this
remarkable collection of engravings that if they had been published
when they were made in the sixteenth century, anatomy would have been
advanced by at least two centuries. But be this as it may, they certainly
show that their author was a most careful dissector and observer.

Eustachius described accurately for the first time certain structures
of the middle ear, and rediscovered the tube leading from the ear
to the throat that bears his name. He also made careful studies of
the teeth and the phenomena of first and second dentition. He was
not baffled by the minuteness of structures and where he was unable
to study them with the naked eye he used glasses for the purpose,
and resorted to macerations and injections for the study of certain
complicated structures. But while the fruit of his pen and pencil
were lost for more than a century after his death, the effects of
his teachings were not; and his two pupils, Fallopius and Columbus,
are almost as well known to-day as their illustrious teacher. Columbus
(1490-1559) did much in correcting the mistakes made in the anatomy
of the bones as described by Vesalius. He also added much to the science
by giving correct accounts of the shape and cavities of the heart,
and made many other discoveries of minor importance. Fallopius (1523-1562)\ added
considerably to the general knowledge of anatomy, made several discoveries
in the anatomy of the ear, and also several organs in the abdominal
cavity.

At this time a most vitally important controversy was in progress
as to whether or not the veins of the bodies were supplied with valves,
many anatomists being unable to find them.\ Etienne had first described
these structures, and Vesalius had confirmed his observations. It
would seem as if there could be no difficulty in settling the question
as to the fact of such valves being present in the vessels, for the
demonstration is so simple that it is now made daily by medical students
in all physiological laboratories and dissecting-rooms. But many of
the great anatomists of the sixteenth century were unable to make
this demonstration, even when it had been brought to their attention
by such an authority as Vesalius. Fallopius, writing to Vesalius on
the subject in 1562, declared that he was unable to find such valves.
Others, however, such as Eustachius and Fabricius (1537-1619), were
more successful, and found and described these structures. But the
purpose served by these valves was entirely misinterpreted. That they
act in preventing the backward flow of the blood in the veins on its
way to the heart, just as the valves of the heart itself prevent regurgitation,
has been known since the time of Harvey; but the best interpretation
that could be given at that time, even by such a man as Fabricius,
was that they acted in retarding the flow of the blood as it comes
from the heart, and thus prevent its too rapid distribution throughout
the body. The fact that the blood might have been going towards the
heart, instead of coming from it, seems never to have been considered
seriously until demonstrated so conclusively by Harvey.

Of this important and remarkable controversy over the valves in veins,
Withington has this to say: {}``This is truly a marvellous story.
A great Galenic anatomist is first to give a full and correct description
of the valves and their function, but fails to see that any modification
of the old view as to the motion of the blood is required. Two able
dissectors carefully test their action by experiment, and come to
a result the exact reverse of the truth. Urged by them, the two foremost
anatomists of the age make a special search for valves and fail to
find them. Finally, passing over lesser peculiarities, an aged and
honorable professor, who has lived through all this, calmly asserts
that no anatomist, ancient or modern, has ever mentioned valves in
veins till he discovered them in 1574!''%
\footnote{E.\ T.\ Withington, \emph{Medical History from the Earliest Times},
London, 1894, p.\ 278.%
}

Among the anatomists who probably discovered these valves was Michael
Servetus (1511-1553); but if this is somewhat in doubt, it is certain
that he discovered and described the pulmonary circulation, and had
a very clear idea of the process of respiration as carried on in the
lungs. The description was contained in a famous document sent to
Calvin in 1545---a document which the reformer carefully kept for
seven years in order that he might make use of some of the heretical
statements it contained to accomplish his desire of bringing its writer
to the stake. The awful fate of Servetus, the interesting character
of the man, and the fact that he came so near to anticipating the
discoveries of Harvey make him one of the most interesting figures
in medical history.

In this document which was sent to Calvin, Servetus rejected the doctrine
of natural, vital, and animal spirits, as contained in the veins,
arteries, and nerves respectively, and made the all-important statement
that the fluids contained in veins and arteries are the same. He showed
also that the blood is {}``purged from fume''\ and purified by
respiration in the lungs, and declared that there is a new vessel
in the lungs, {}``formed out of vein and artery.'' Even at the present
day there is little to add to or change in this description of Servetus's.

By keeping this document, pregnant with advanced scientific views,
from the world, and in the end only using it as a means of destroying
its author, the great reformer showed the same jealousy in retarding
scientific progress as had his arch-enemies of the Inquisition, at
whose dictates Vesalius became a martyr to science, and in whose dungeons
Etienne perished.


\section*{\raggedright THE COMING OF HARVEY}

\addcontentsline{toc}{section}{THE COMING OF HARVEY}

The time was ripe for the culminating discovery of the circulation
of the blood; but as yet no one had determined the all-important fact
that there are two currents of blood in the body, one going to the
heart, one coming from it. The valves in the veins would seem to show
conclusively that the venous current did not come from the heart,
and surgeons must have observed thousands of times the every-day phenomenon
of congested veins at the distal extremity of a limb around which
a ligature or constriction of any kind had been placed, and the simultaneous
depletion of the vessels at the proximal points above the ligature.
But it should be remembered that inductive science was in its infancy.
This was the sixteenth, not the nineteenth century, and few men had
learned to put implicit confidence in their observations and convictions
when opposed to existing doctrines. The time was at hand, however,
when such a man was to make his appearance, and, as in the case of
so many revolutionary doctrines in science, this man was an Englishman.
It remained for William Harvey (1578-1657)\ to solve the great mystery
which had puzzled the medical world since the beginning of history;
not only to solve it, but to prove his case so conclusively and so
simply that for all time his little booklet must he handed down as
one of the great masterpieces of lucid and almost faultless demonstration.

Harvey, the son of a prosperous Kentish yeoman, was born at Folkestone.
His education was begun at the grammar-school of Canterbury, and later
he became a pensioner of Caius College, Cambridge. Soon after taking
his degree of B.A., at the age of nineteen, he decided upon the profession
of medicine, and went to Padua as a pupil of Fabricius and Casserius.
Returning to England at the age of twenty-four, he soon after (1609)\ obtained
the reversion of the post of physician to St.\ Bartholomew's Hospital,
his application being supported by James I.\ himself. Even at this
time he was a popular physician, counting among his patients such
men as Francis Bacon. In 1618 he was appointed physician extraordinary
to the king, and, a little later, physician in ordinary. He was in
attendance upon Charles I.\ at the battle of Edgehill, in 1642, where,
with the young Prince of Wales and the Duke of York, after seeking
shelter under a hedge, he drew a book out of his pocket and, forgetful
of the battle, became absorbed in study, until finally the cannon-balls
from the enemy's artillery made him seek a more sheltered position.

On the fall of Charles I.\ he retired from practice, and lived in
retirement with his brother. He was then well along in years, but
still pursued his scientific researches with the same vigor as before,
directing his attention chiefly to the study of embryology. On June
3, 1657, he was attacked by paralysis and died, in his eightieth year.
He had lived to see his theory of the circulation accepted, several
years before, by all the eminent anatomists of the civilized world.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2S170}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small William Harvey}\end{center}
\end{figure}
A keenness in the observation of facts, characteristic of the mind
of the man, had led Harvey to doubt the truth of existing doctrines
as to the phenomena of the circulation. Galen had taught that {}``the
arteries are filled, like bellows, because they are expanded,''\ but
Harvey thought that the action of spurting blood from a severed vessel
disproved this. For the spurting was remittant, {}``now with greater,
now with less impetus,''\ and its greater force always corresponded
to the expansion (diastole), not the contraction (systole)\ of the
vessel. Furthermore, it was evident that contraction of the heart
and the arteries was not simultaneous, as was commonly taught, because
in that case there would be no marked propulsion of the blood in any
direction; and there was no gainsaying the fact that the blood was
forcibly propelled in a definite direction, and that direction away
from the heart.

Harvey's investigations led him to doubt also the accepted theory
that there was a porosity in the septum of tissue that divides the
two ventricles of the heart. It seemed unreasonable to suppose that
a thick fluid like the blood could find its way through pores so small
that they could not be demonstrated by any means devised by man. In
evidence that there could be no such openings he pointed out that,
since the two ventricles contract at the same time, this process would
impede rather than facilitate such an intra-ventricular passage of
blood. But what seemed the most conclusive proof of all was the fact
that in the f\oe{}tus there existed a demonstrable opening between
the two ventricles, and yet this is closed in the fully developed
heart. Why should Nature, if she intended that blood should pass between
the two cavities, choose to close this opening and substitute microscopic
openings in place of it? It would surely seem more reasonable to have
the small perforations in the thin, easily permeable membrane of the
f\oe{}tus, and the opening in the adult heart, rather than the reverse.
From all this Harvey drew his correct conclusions, declaring earnestly,
{}``By Hercules, there \textit{are} no such porosities, and they
cannot be demonstrated.''

Having convinced himself that no intra-ventricular opening existed,
he proceeded to study the action of the heart itself, untrammelled
by too much faith in established theories, and, as yet, with no theory
of his own. He soon discovered that the commonly accepted theory of
the heart striking against the chest-wall during the period of relaxation
was entirely wrong, and that its action was exactly the reverse of
this, the heart striking the chest-wall during contraction. Having
thus disproved the accepted theory concerning the heart's action,
he took up the subject of the action of arteries, and soon was able
to demonstrate by vivisection that the contraction of the arteries
was not simultaneous with contractions of the heart. His experiments
demonstrated that these vessels were simply elastic tubes whose pulsations
were {}``nothing else than the impulse of the blood within them.''
The reason that the arterial pulsation was not simultaneous with the
heart-beat he found to be because of the time required to carry the
impulse along the tube,

By a series of further careful examinations and experiments, which
are too extended to be given here, he was soon able further to demonstrate
the action and course of the blood during the contractions of the
heart. His explanations were practically the same as those given to-day---first
the contraction of the auricle, sending blood into the ventricle;
then ventricular contraction, making the pulse, and sending the blood
into the arteries. He had thus demonstrated what had not been generally
accepted before, that the heart was an organ for the propulsion of
blood. To make such a statement to-day seems not unlike the sober
announcement that the earth is round or that the sun does not revolve
about it. Before Harvey's time, however, it was considered as an organ
that was {}``in some mysterious way the source of vitality and warmth,
as an animated crucible for the concoction of blood and the generation
of vital spirits.''%
\footnote{John Dalton, \emph{Doctrines of the Circulation}, Philadelphia, 1884,
p.\ 179.%
}

In watching the rapid and ceaseless contractions of the heart, Harvey
was impressed with the fact that, even if a very small amount of blood
was sent out at each pulsation, an enormous quantity must pass through
the organ in a day, or even in an hour. Estimating the size of the
cavities of the heart, and noting that at least a drachm must be sent
out with each pulsation, it was evident that the two thousand beats
given by a very slow human heart in an hour must send out some forty
pounds of blood---more than twice the amount in the entire body. The
question was, what became of it all? For it should be remembered that
the return of the blood by the veins was unknown, and nothing like
a {}``circulation''\ more than vaguely conceived even by Harvey
himself. Once it could be shown that the veins were constantly returning
blood to the heart, the discovery that the blood in some way passes
from the arteries to the veins was only a short step. Harvey, by resorting
to \textit{\emph{vivisections}} of lower animals and reptiles, soon
demonstrated beyond question the fact that the veins do carry the
return blood. {}``But this, in particular, can be shown clearer than
daylight,''\ says Harvey. {}``The \textit{vena} \textit{cava} enters
the heart at an inferior portion, while the artery passes out above.
Now if the \textit{vena} \textit{cava} be taken up with forceps or
the thumb and finger, and the course of the blood intercepted for
some distance below the heart, you will at once see it almost emptied
between the fingers and the heart, the blood being exhausted by the
heart's pulsation, the heart at the same time becoming much paler
even in its dilatation, smaller in size, owing to the deficiency of
blood, and at length languid in pulsation, as if about to die. On
the other hand, when you release the vein the heart immediately regains
its color and dimensions. After that, if you leave the vein free and
tie and compress the arteries at some distance from the heart, you
will see, on the contrary, their included portion grow excessively
turgid, the heart becoming so beyond measure, assuming a dark-red
color, even to lividity, and at length so overloaded with blood as
to seem in danger of suffocation; but when the obstruction is removed
it returns to its normal condition, in size, color, and movement.''%
\footnote{William Harvey, \emph{De Motu} \textit{Cordis} \textit{et} \textit{Sanguinis},
London, 1803, chap.\ X.%
}

This conclusive demonstration that the veins return the blood to the
heart must have been most impressive to Harvey, who had been taught
to believe that the blood current in the veins pursued an opposite
course, and must have tended to shake his faith in all existing doctrines
of the day.

His next step was the natural one of demonstrating that the blood
passes from the arteries to the veins. He demonstrated conclusively
that this did occur, but for once his rejection of the ancient writers
and one modern one was a mistake. For Galen had taught, and had attempted
to demonstrate, that there are sets of minute vessels connecting the
arteries and the veins; and Servetus had shown that there must be
such vessels, at least in the lungs.

However, the little flaw in the otherwise complete demonstration of
Harvey detracts nothing from the main issue at stake. It was for others
who followed to show just how these small vessels acted in effecting
the transfer of the blood from artery to vein, and the grand general
statement that such a transfer does take place was, after all, the
all-important one, and the exact method of how it takes place a detail.
Harvey's experiments to demonstrate that the blood passes from the
arteries to the veins are so simply and concisely stated that they
may best be given in his own words.

\begin{quotation}
{}``I have here to cite certain experiments,''\ he wrote, {}``from
which it seems obvious that the blood enters a limb by the arteries,
and returns from it by the veins; that the arteries are the vessels
carrying the blood from the heart, and the veins the returning channels
of the blood to the heart; that in the limbs and extreme parts of
the body the blood passes either by anastomosis from the arteries
into the veins, or immediately by the pores of the flesh, or in both
ways, as has already been said in speaking of the passage of the blood
through the lungs; whence it appears manifest that in the circuit
the blood moves from thence hither, and hence thither; from the centre
to the extremities, to wit, and from the extreme parts back again
to the centre. Finally, upon grounds of circulation, with the same
elements as before, it will be obvious that the quantity can neither
be accounted for by the ingesta, nor yet be held necessary to nutrition.

{}``Now let any one make an experiment on the arm of a man, either
using such a fillet as is employed in blood-letting or grasping the
limb tightly with his hand, the best subject for it being one who
is lean, and who has large veins, and the best time after exercise,
when the body is warm, the pulse is full, and the blood carried in
large quantities to the extremities, for all then is more conspicuous;
under such circumstances let a ligature be thrown about the extremity
and drawn as tightly as can be borne: it will first be perceived that
beyond the ligature neither in the wrist nor anywhere else do the
arteries pulsate, that at the same time immediately above the ligature
the artery begins to rise higher at each diastole, to throb more violently,
and to swell in its vicinity with a kind of tide, as if it strove
to break through and overcome the obstacle to its current; the artery
here, in short, appears as if it were permanently full. The hand under
such circumstances retains its natural color and appearances; in the
course of time it begins to fall somewhat in temperature, indeed,
but nothing is \textit{drawn} into it.

{}``After the bandage has been kept on some short time in this way,
let it be slackened a little, brought to the state or term of middling
tightness which is used in bleeding, and it will be seen that the
whole hand and arm will instantly become deeply suffused and distended,
injected, gorged with blood, \textit{drawn}, as it is said, by this
middling ligature, without pain, or heat, or any horror of a vacuum,
or any other cause yet indicated.

{}``As we have noted, in connection with the tight ligature, that
the artery above the bandage was distended and pulsated, not below
it, so, in the case of the moderately tight bandage, on the contrary,
do we find that the veins below, never above, the fillet swell and
become dilated, while the arteries shrink; and such is the degree
of distention of the veins here that it is only very strong pressure
that will force the blood beyond the fillet and cause any of the veins
in the upper part of the arm to rise.

{}``From these facts it is easy for any careful observer to learn
that the blood enters an extremity by the arteries; for when they
are effectively compressed nothing is \textit{drawn} to the member;
the hand preserves its color; nothing flows into it, neither is it
distended; but when the pressure is diminished, as it is with the
bleeding fillet, it is manifest that the blood is instantly thrown
in with force, for then the hand begins to swell; which is as much
as to say that when the arteries pulsate the blood is flowing through
them, as it is when the moderately tight ligature is applied; but
when they do not pulsate, or when a tight ligature is used, they cease
from transmitting anything; they are only distended above the part
where the ligature is applied. The veins again being compressed, nothing
can flow through them; the certain indication of which is that below
the ligature they are much more tumid than above it, and than they
usually appear when there is no bandage upon the arm.

{}``It therefore plainly appears that the ligature prevents the return
of the blood through the veins to the parts above it, and maintains
those beneath it in a state of permanent distention. But the arteries,
in spite of the pressure, and under the force and impulse of the heart,
send on the blood from the internal parts of the body to the parts
beyond the bandage.''%
\footnote{\emph{The Works of William Harvey}, translated by Robert Willis, London,
1847, p.\ 56.%
}
\end{quotation}
{}

This use of ligatures is very significant, because, as shown, a very
tight ligature stops circulation in both arteries and veins, while
a loose one, while checking the circulation in the veins, which lie
nearer the surface and are not so directly influenced by the force
of the heart, does not stop the passage of blood in the arteries,
which are usually deeply imbedded in the tissues, and not so easily
influenced by pressure from without.

The last step of Harvey's demonstration was to prove that the blood
does flow along the veins to the heart, aided by the valves that had
been the cause of so much discussion and dispute between the great
sixteenth-century anatomists. Harvey not only demonstrated the presence
of these valves, but showed conclusively, by simple experiments, what
their function was, thus completing his demonstration of the phenomena
of the circulation.

The final ocular demonstration of the passage of the blood from the
arteries to the veins was not to be made until four years after Harvey's
death. This process, which can be observed easily in the web of a
frog's foot by the aid of a low-power lens, was first demonstrated
by Marcello Malpighi (1628-1694)\ in 1661. By the aid of a lens he
first saw the small {}``capillary''\ vessels connecting the veins
and arteries in a piece of dried lung. Taking his cue from this, he
examined the lung of a turtle, and was able to see in it the passage
of the corpuscles through these minute vessels, making their way along
these previously unknown channels from the arteries into the veins
on their journey back to the heart. Thus the work of Harvey, all but
complete, was made absolutely entire by the great Italian. And all
this in a single generation.


\section*{\raggedright LEEUWENHOEK DISCOVERS BACTERIA}

\addcontentsline{toc}{section}{LEEUWENHOEK DISCOVERS\\
BACTERIA}

The seventeenth century was not to close, however, without another
discovery in science, which, when applied to the causation of disease
almost two centuries later, revolutionized therapeutics more completely
than any one discovery. This was the discovery of microbes, by Antonius
von Leeuwenhoek (1632-1723), in 1683. Von Leeuwenhoek discovered that
{}``in the white matter between his teeth''\ there were millions
of microscopic {}``animals''---more, in fact, than {}``there were
human beings in the united Netherlands,''\ and all {}``moving in
the most delightful manner.'' There can be no question that he saw
them, for we can recognize in his descriptions of these various forms
of little {}``animals''\ the four principal forms of microbes---the
long and short rods of bacilli and bacteria, the spheres of micrococci,
and the corkscrew spirillum.

The presence of these microbes in his mouth greatly annoyed Antonius,
and he tried various methods of getting rid of them, such as using
vinegar and hot coffee. In doing this he little suspected that he
was anticipating modern antiseptic surgery by a century and three-quarters,
and to be attempting what antiseptic surgery is now able to accomplish.
For the fundamental principle of antisepsis is the use of medicines
for ridding wounds of similar microscopic organisms. Von Leenwenhoek
was only temporarily successful in his attempts, however, and took
occasion to communicate his discovery to the Royal Society of England,
hoping that they would be {}``interested in this novelty.'' Probably
they were, but not sufficiently so for any member to pursue any protracted
investigations or reach any satisfactory conclusions, and the whole
matter was practically forgotten until the middle of the nineteenth
century.


\chapter*{\raggedright VIII. MEDICINE IN THE SIXTEENTH AND SEVENTEENTH CENTURIES}

\addcontentsline{toc}{chapter}{VIII. MEDICINE IN THE SIXTEENTH\\
AND SEVENTEENTH CENTURIES}\markboth{A HISTORY OF SCIENCE, VOLUME II}{VIII.
16--17TH CENTURY MEDICINE}

Of the half-dozen surgeons who were prominent in the sixteenth century,
Ambroise Pare (1517-1590), called the father of French surgery, is
perhaps the most widely known. He rose from the position of a common
barber to that of surgeon to three French monarchs, Henry \textit{\emph{II}}.,
Francis \textit{\emph{II}}., and Charles IX. Some of his mottoes are
still first principles of the medical man. Among others are: {}``He
who becomes a surgeon for the sake of money, and not for the sake
of knowledge, will accomplish nothing''; and {}``A tried remedy
is better than a newly invented.'' On his statue is his modest estimate
of his work in caring for the wounded, {}``\textit{Je} \textit{le}
\emph{pansay}, \textit{Dieu} \textit{le} \emph{guarit}''---I dressed
him, God cured him.

It was in this dressing of wounds on the battlefield that he accidentally
discovered how useless and harmful was the terribly painful treatment
of applying boiling oil to gunshot wounds as advocated by John of
Vigo. It happened that after a certain battle, where there was an
unusually large number of casualties, Pare found, to his horror, that
no more boiling oil was available for the surgeons, and that he should
be obliged to dress the wounded by other simpler methods. To his amazement
the results proved entirely satisfactory, and from that day he discarded
the hot-oil treatment.

As Pare did not understand Latin he wrote his treatises in French,
thus inaugurating a custom in France that was begun by Paracelsus
in Germany half a century before. He reintroduced the use of the ligature
in controlling hemorrhage, introduced the {}``figure of eight''\ suture
in the operation for hare-lip, improved many of the medico-legal doctrines,
and advanced the practice of surgery generally. He is credited with
having successfully performed the operation for strangulated hernia,
but he probably borrowed it from Peter Franco (1505-1570), who published
an account of this operation in 1556. As this operation is considered
by some the most important operation in surgery, its discoverer is
entitled to more than passing notice, although he was despised and
ignored by the surgeons of his time.

Franco was an illiterate travelling lith\-ot\-om\-ist---a class
of itinerant physicians who were very generally frowned down by the
regular practitioners of medicine. But Franco possessed such skill
as an operator, and appears to have been so earnest in the pursuit
of what he considered a legitimate calling, that he finally overcame
the popular prejudice and became one of the salaried surgeons of the
republic of Bern. He was the first surgeon to perform the suprapubic
lithotomy operation---the removal of stone through the abdomen instead
of through the perineum. His works, while written in an illiterate
style, give the clearest descriptions of any of the early modern writers.

As the fame of Franco rests upon his operation for prolonging human
life, so the fame of his Italian contemporary, Gaspar Tagliacozzi
(1545-1599), rests upon his operation for increasing human comfort
and happiness by restoring amputated noses. At the time in which he
lived amputation of the nose was very common, partly from disease,
but also because a certain pope had fixed the amputation of that member
as the penalty for larceny. Tagliacozzi probably borrowed his operation
from the East; but he was the first Western surgeon to perform it
and describe it. So great was the fame of his operations that patients
flocked to him from all over Europe, and each {}``went away with
as many noses as he liked.'' Naturally, the man who directed his
efforts to restoring structures that had been removed by order of
the Church was regarded in the light of a heretic by many theologians;
and though he succeeded in cheating the stake or dungeon, and died
a natural death, his body was finally cast out of the church in which
it had been buried.

In the sixteenth century Germany produced a surgeon, Fabricius Hildanes
(1560-1639), whose work compares favorably with that of Pare, and
whose name would undoubtedly have been much better known had not the
circumstances of the time in which he lived tended to obscure his
merits. The blind followers of Paracelsus could see nothing outside
the pale of their master's teachings, and the disastrous Thirty Years'\ War
tended to obscure and retard all scientific advances in Germany. Unlike
many of his fellow-surgeons, Hildanes was well versed in Latin and
Greek; and, contrary to the teachings of Paracelsus, he laid particular
stress upon the necessity of the surgeon having a thorough knowledge
of anatomy. He had a helpmate in his wife, who was also something
of a surgeon, and she is credited with having first made use of the
magnet in removing particles of metal from the eye. Hildanes tells
of a certain man who had been injured by a small piece of steel in
the cornea, which resisted all his efforts to remove it. After observing
Hildanes'\ fruitless efforts for a time, it suddenly occurred to
his wife to attempt to make the extraction with a piece of loadstone.
While the physician held open the two lids, his wife attempted to
withdraw the steel with the magnet held close to the cornea, and after
several efforts she was successful---which Hildanes enumerates as
one of the advantages of being a married man.

Hildanes was particularly happy in his inventions of surgical instruments,
many of which were designed for locating and removing the various
missiles recently introduced in warfare.

The seventeenth century, which was such a flourishing one for anatomy
and physiology, was not as productive of great surgeons or advances
in surgery as the sixteenth had been or the eighteenth was to be.
There was a gradual improvement all along the line, however, and much
of the work begun by such surgeons as Pare and Hildanes was perfected
or improved. Perhaps the most progressive surgeon of the century was
an Englishman, Richard Wiseman (1625-1686), who, like Harvey, enjoyed
royal favor, being in the service of all the Stuart kings. He was
the first surgeon to advocate primary amputation, in gunshot wounds,
of the limbs, and also to introduce the treatment of aneurisms by
compression; but he is generally rated as a conservative operator,
who favored medication rather than radical operations, where possible.

In Italy, Marcus Aurelius Severinus (1580-1656)\ and Peter Marchettis
(1589-1675)\ were the leading surgeons of their nation. Like many
of his predecessors in Europe, Severinus ran amuck with the Holy Inquisition
and fled from Naples. But the waning of the powerful arm of the Church
is shown by the fact that he was brought back by the unanimous voice
of the grateful citizens, and lived in safety despite the frowns of
the theologians.

The sixteenth century cannot be said to have added much of importance
in the field of practical medicine, and, as in the preceding and succeeding
centuries, was at best only struggling along in the wake of anatomy,
physiology, and surgery. In the seventeenth century, however, at least
one discovery in therapeutics was made that has been an inestimable
boon to humanity ever since. This was the introduction of cinchona
bark (from which quinine is obtained)\ in 1640. But this century
was productive of many medical \textit{systems}, and could boast of
many great names among the medical profession, and, on the whole,
made considerably more progress than the preceding century.

Of the founders of medical systems, one of the most widely known is
Jan Baptista van Helmont (1578-1644), an eccentric genius who constructed
a system of medicine of his own and for a time exerted considerable
influence. But in the end his system was destined to pass out of existence,
not very long after the death of its author. Van Helmont was not only
a physician, but was master of all the other branches of learning
of the time, taking up the study of medicine and chemistry as an after-thought,
but devoting himself to them with the greatest enthusiasm once he
had begun his investigations. His attitude towards existing doctrines
was as revolutionary as that of Paracelsus, and he rejected the teachings
of Galen and all the ancient writers, although retaining some of the
views of Paracelsus. He modified the \emph{arch}\ae{}\emph{us} of
Paracelsus, and added many complications to it. He believed the whole
body to be controlled by an \emph{arch}\ae{}\emph{us influus}, the
soul by the \emph{arch}\ae{}\emph{i insiti}, and these in turn controlled
by the central \emph{arch}\ae{}\emph{us}. His system is too elaborate
and complicated for full explanation, but its chief service to medicine
was in introducing new chemical methods in the preparation of drugs.
In this way he was indirectly connected with the establishment of
the Iatrochemical school. It was he who first used the word {}``gas''---a
word coined by him, along with many others that soon fell into disuse.

The principles of the Iatrochemical school were the use of chemical
medicines, and a theory of pathology different from the prevailing
{}``humoral''\ pathology. The founder of this school was Sylvius
(Franz de \textit{\emph{le}} Boe, 1614-1672), professor of medicine
at Leyden. He attempted to establish a permanent system of medicine
based on the newly discovered theory of the circulation and the new
chemistry, but his name is remembered by medical men because of the
fissure in the brain (fissure of Sylvius)\ that bears it. He laid
great stress on the cause of fevers and other diseases as originating
in the disturbances of the process of fermentation in the stomach.
The doctrines of Sylvius spread widely over the continent, but were
not generally accepted in England until modified by Thomas Willis
(1622-1675), whose name, like that of Sylvius, is perpetuated by a
structure in the brain named after him, the circle of Willis. Willis's
descriptions of certain nervous diseases, and an account of diabetes,
are the first recorded, and added materially to scientific medicine.
These schools of medicine lasted until the end of the seventeenth
century, when they were finally overthrown by Sydenham.

The Iatrophysical school (also called iatromathematical, iatromechanical,
or physiatric)\ was founded on theories of physiology, probably by
Borelli, of Naples (1608-1679), although Sanctorius, a professor at
Padua, was a precursor, if not directly interested in establishing
it. Sanctorius discovered the fact that an {}``insensible perspiration''\ is
being given off by the body continually, and was amazed to find that
loss of weight in this way far exceeded the loss of weight by all
other excretions of the body combined. He made this discovery by means
of a peculiar weighing-machine to which a chair was attached, and
in which he spent most of his time. Very naturally he overestimated
the importance of this discovery, but it was, nevertheless, of great
value in pointing out the hygienic importance of the care of the skin.
He also introduced a thermometer which he advocated as valuable in
cases of fever, but the instrument was probably not his own invention,
but borrowed from his friend Galileo.

Harvey's discovery of the circulation of the blood laid the foundation
of the Iatrophysical school by showing that this vital process was
comparable to a hydraulic system. In his \emph{On the Motive of Animals},
Borelli first attempted to account for the phenomena of life and diseases
on these principles. The iatromechanics held that the great cause
of disease is due to different states of elasticity of the solids
of the body interfering with the movements of the fluids, which are
themselves subject to changes in density, one or both of these conditions
continuing to cause stagnation or congestion. The school thus founded
by Borelli was the outcome of the unbounded enthusiasm, with its accompanying
exaggeration of certain phenomena with the corresponding belittling
of others that naturally follows such a revolutionary discovery as
that of Harvey. Having such a founder as the brilliant Italian Borelli,
it was given a sufficient impetus by his writings to carry it some
distance before it finally collapsed. Some of the exaggerated mathematical
calculations of Borelli himself are worth noting. Each heart-beat,
as he calculated it, overcomes a resistance equal to one hundred and
eighty thousand pounds;---the modern physiologist estimates its force
at from five to nine ounces!


\section*{\raggedright THOMAS SYDENHAM}

\addcontentsline{toc}{section}{THOMAS SYDENHAM}

But while the Continent was struggling with these illusive {}``systems,''\ and
dabbling in mystic theories that were to scarcely outlive the men
who conceived them, there appeared in England---the {}``land of common-sense,''\ as
a German scientist has called it---{}``a cool, clear, and unprejudiced
spirit,''\ who in the golden age of systems declined {}``to be
like the man who builds the chambers of the upper story of his house
before he had laid securely the foundation walls.''%
\footnote{Hermann Baas, \emph{History of Medicine}, translated by H.\ E.\ Henderson,
New York, 1894, p.\ 504.%
} This man was Thomas Sydenham (1624-1689), who, while the great Harvey
was serving the king as surgeon, was fighting as a captain in the
parliamentary army. Sydenham took for his guide the teachings of Hippocrates,
modified to suit the advances that had been made in scientific knowledge
since the days of the great Greek, and established, as a standard,
observation and experience. He cared little for theory unless confirmed
by practice, but took the Hippocratic view that nature cured diseases,
assisted by the physician. He gave due credit, however, to the importance
of the part played by the assistant. As he saw it, medicine could
be advanced in three ways: (1)\ {}``By accurate descriptions or
natural histories of diseases; (2)\ by establishing a fixed principle
or method of treatment, founded upon experience; (3)\ by searching
for specific remedies, which he believes must exist in considerable
numbers, though he admits that the only one yet discovered is Peruvian
bark.''%
\footnote{E.\ T.\ Withington, \emph{Medical History from the Earliest Times},
London, 1894, p.\ 320.%
} As it happened, another equally specific remedy, mercury, when used
in certain diseases, was already known to him, but he evidently did
not recognize it as such.

The influence on future medicine of Sydenham's teachings was most
pronounced, due mostly to his teaching of careful observation. To
most physicians, however, he is now remembered chiefly for his introduction
of the use of laudanum, still considered one of the most valuable
remedies of modern pharmacop\oe{}ias. The German gives the honor
of introducing this preparation to Paracelsus, but the English-speaking
world will always believe that the credit should be given to Sydenham.


\chapter*{\raggedright IX. PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS OF
LEARNING}

\addcontentsline{toc}{chapter}{IX. PHILOSOPHER-SCIENTISTS AND\\
NEW INSTITUTIONS OF LEARNING}

\markboth{A HISTORY OF SCIENCE, VOLUME II}{IX. PHILOSOPHER-SCIENTISTS}

We saw that in the old Greek days there was no sharp line of demarcation
between the field of the philosopher and that of the scientist. In
the Hellenistic epoch, however, knowledge became more specialized,
and our recent chapters have shown us scientific investigators whose
efforts were far enough removed from the intangibilities of the philosopher.
It must not be overlooked, however, that even in the present epoch
there were men whose intellectual efforts were primarily directed
towards the subtleties of philosophy, yet who had also a penchant
for strictly scientific imaginings, if not indeed for practical scientific
experiments. At least three of these men were of sufficient importance
in the history of the development of science to demand more than passing
notice. These three are the Englishman Francis Bacon (1561-1626),
the Frenchman Rene Descartes (1596-1650); and the German Gottfried
Leibnitz (1646-1716). Bacon, as the earliest path-breaker, showed
the way, theoretically at least, in which the sciences should be studied;
Descartes, pursuing the methods pointed out by Bacon, carried the
same line of abstract reason into practice as well; while Leibnitz,
coming some years later, and having the advantage of the wisdom of
his two great predecessors, was naturally influenced by both in his
views of abstract scientific principles.

Bacon's career as a statesman and his faults and misfortunes as a
man do not concern us here. Our interest in him begins with his entrance
into Trinity College, Cambridge, where he took up the study of all
the sciences taught there at that time. During the three years he
became more and more convinced that science was not being studied
in a profitable manner, until at last, at the end of his college course,
he made ready to renounce the old Aristotelian methods of study and
advance his theory of inductive study. For although he was a great
admirer of Aristotle's work, he became convinced that his methods
of approaching study were entirely wrong.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2S192}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Francis Bacon}\end{center}
\end{figure}
{}``The opinion of Aristotle,''\ he says, in his \emph{De Argumentum
Scientiarum}, {}``seemeth to me a negligent opinion, that of those
things which exist by nature nothing can be changed by custom; using
for example, that if a stone be thrown ten thousand times up it will
not learn to ascend; and that by often seeing or hearing we do not
learn to see or hear better. For though this principle be true in
things wherein nature is peremptory (the reason whereof we cannot
now stand to discuss), yet it is otherwise in things wherein nature
admitteth a latitude. For he might see that a straight glove will
come more easily on with use; and that a wand will by use bend otherwise
than it grew; and that by use of the voice we speak louder and stronger;
and that by use of enduring heat or cold we endure it the better,
and the like; which latter sort have a nearer resemblance unto that
subject of manners he handleth than those instances which he allegeth.''%
\footnote{George L.\ Craik, \emph{Bacon and His Writings and Philosophy}, 2
\textit{\emph{vols}}., London, 1846. Vol.\ II., p.\ 121.%
}

These were his opinions, formed while a young man in college, repeated
at intervals through his maturer years, and reiterated and emphasized
in his old age. Masses of facts were to be obtained by observing nature
at first hand, and from such accumulations of facts deductions were
to be made. In short, reasoning was to be from the specific to the
general, and not vice versa.

It was by his teachings alone that Bacon thus contributed to the foundation
of modern science; and, while he was constantly thinking and writing
on scientific subjects, he contributed little in the way of actual
discoveries. {}``I only sound the clarion,''\ he said, {}``but
I enter not the battle.''

The case of Descartes, however, is different. He both sounded the
clarion and entered into the fight. He himself freely acknowledges
his debt to Bacon for his teachings of inductive methods of study,
but modern criticism places his work on the same plane as that of
the great Englishman. {}``If you lay hold of any characteristic product
of modern ways of thinking,''\ says Huxley, {}``either in the region
of philosophy or in that of science, you find the spirit of that thought,
if not its form, has been present in the mind of the great Frenchman.''%
\footnote{From Huxley's address {}``On Descartes's Discourse Touching the Method
of Using One's Reason Rightly and of Seeking Scientific Truth.''%
}

Descartes, the son of a noble family of France, was educated by Jesuit
teachers. Like Bacon, he very early conceived the idea that the methods
of teaching and studying science were wrong, but be pondered the matter
well into middle life before putting into writing his ideas of philosophy
and science. Then, in his \emph{Discourse Touching the Method of Using
One's Reason Rightly and of Seeking Scientific Truth}, he pointed
out the way of seeking after truth. His central idea in this was to
emphasize the importance of \textit{doubt}, and avoidance of accepting
as truth anything that does not admit of absolute and unqualified
proof. In reaching these conclusions he had before him the striking
examples of scientific deductions by Galileo, and more recently the
discovery of the circulation of the blood by Harvey. This last came
as a revelation to scientists, reducing this seemingly occult process,
as it did, to the field of mechanical phenomena. The same mechanical
laws that governed the heavenly bodies, as shown by Galileo, governed
the action of the human heart, and, for aught any one knew, every
part of the body, and even the mind itself.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2S194}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Ren\'{e} Descartes}\end{center}{\small \par}

\noindent \emph{\footnotesize (From the painting by Franz Hals, in
the gallery of the Louvre.) }
\end{figure}
Having once conceived this idea, Descartes began a series of \textit{\emph{dissections}}
and experiments upon the lower animals, to find, if possible, further
proof of this general law. To him the human body was simply a machine,
a complicated mechanism, whose functions were controlled just as any
other piece of machinery. He compared the human body to complicated
machinery run by water-falls and complicated pipes. {}``The nerves
of the machine which I am describing,''\ he says, {}``may very
well be compared to the pipes of these waterworks; its muscles and
its tendons to the other various engines and springs which seem to
move them; its animal spirits to the water which impels them, of which
the heart is the fountain; while the cavities of the brain are the
central office. Moreover, respiration and other such actions as are
natural and usual in the body, and which depend on the course of the
spirits, are like the movements of a clock, or a mill, which may be
kept up by the ordinary flow of water.''%
\footnote{\textit{\emph{Rene}} \emph{}\textit{\emph{Descartes}}, \textit{Traite}
\textit{de} \emph{l'Homme} (Cousins's edition.\ in 2 \textit{\emph{vols}}.),
Paris, 1824. Vol.\ VI., p.\ 347.%
}

In such passages as these Descartes anticipates the ideas of physiology
of the present time. He believed that the functions are performed
by the various organs of the bodies of animals and men as a mechanism,
to which in man was added the soul. This soul he located in the pineal
gland, a degenerate and presumably functionless little organ in the
brain. For years Descartes's idea of the function of this gland was
held by many physiologists, and it was only the introduction of modern
high-power microscopy that reduced this also to a mere mechanism,
and showed that it is apparently the remains of a Cyclopean eye once
common to man's remote ancestors.

Descartes was the originator of a theory of the movements of the universe
by a mechanical process---the Cartesian theory of vortices---which
for several decades after its promulgation reigned supreme in science.
It is the ingenuity of this theory, not the truth of its assertions,
that still excites admiration, for it has long since been supplanted.
It was certainly the best hitherto advanced---the best {}``that the
observations of the age admitted,''\ according to \textit{\emph{D'Alembert}}.

According to this theory the infinite universe is full of matter,
there being no such thing as a vacuum. Matter, as Descartes believed,
is uniform in character throughout the entire universe, and since
motion cannot take place in any part of a space completely filled,
without simultaneous movement in all other parts, there are constant
more or less circular movements, vortices, or whirlpools of particles,
varying, of course, in size and velocity. As a result of this circular
movement the particles of matter tend to become globular from contact
with one another. Two species of matter are thus formed, one larger
and globular, which continue their circular motion with a constant
tendency to fly from the centre of the axis of rotation, the other
composed of the clippings resulting from the grinding process. These
smaller {}``filings''\ from the main bodies, becoming smaller and
smaller, gradually lose their velocity and accumulate in the centre
of the vortex. This collection of the smaller matter in the centre
of the vortex constitutes the sun or star, while the spherical particles
propelled in straight lines from the centre towards the circumference
of the vortex produce the phenomenon of light radiating from the central
star. Thus this matter becomes the atmosphere revolving around the
accumulation at the centre. But the small particles being constantly
worn away from the revolving spherical particles in the vortex, become
entangled in their passage, and when they reach the edge of the inner
strata of solar dust they settle upon it and form what we call sun-spots.
These are constantly dissolved and reformed, until sometimes they
form a crust round the central nucleus.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2S196}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Gottfried Wilhelm von Leibnitz}\end{center}
\end{figure}
As the expansive force of the star diminishes in the course of time,
it is encroached upon by neighboring vortices. If the part of the
encroaching star be of a less velocity than the star which it has
swept up, it will presently lose its hold, and the smaller star pass
out of range, becoming a comet. But if the velocity of the vortex
into which the incrusted star settles be equivalent to that of the
surrounded vortex, it will hold it as a captive, still revolving and
{}``wrapt in its own firmament.'' Thus the several planets of our
solar system have been captured and held by the sun-vortex, as have
the moon and other satellites.

But although these new theories at first created great enthusiasm
among all classes of philosophers and scientists, they soon came under
the ban of the Church. While no actual harm came to Descartes himself,
his writings were condemned by the Catholic and Protestant churches
alike. The spirit of philosophical inquiry he had engendered, however,
lived on, and is largely responsible for modern philosophy.

In many ways the life and works of Leibnitz remind us of Bacon rather
than Descartes. His life was spent in filling high political positions,
and his philosophical and scientific writings were by-paths of his
fertile mind. He was a theoretical rather than a practical scientist,
his contributions to science being in the nature of philosophical
reasonings rather than practical demonstrations. Had he been able
to withdraw from public life and devote himself to science alone,
as Descartes did, he would undoubtedly have proved himself equally
great as a practical worker. But during the time of his greatest activity
in philosophical fields, between the years 1690 and 1716, he was all
the time performing extraordinary active duties in entirely foreign
fields. His work may be regarded, perhaps, as doing for Germany in
particular what Bacon's did for England and the rest of the world
in general.

Only a comparatively small part of his philosophical writings concern
us here. According to his theory of the ultimate elements of the universe,
the entire universe is composed of individual centres, or monads.
To these monads he ascribed numberless qualities by which every phase
of nature may be accounted. They were supposed by him to be percipient,
self-acting beings, not under arbitrary control of the deity, and
yet God himself was the original monad from which all the rest are
generated. With this conception as a basis, Leibnitz deduced his doctrine
of pre-established harmony, whereby the numerous independent substances
composing the world are made to form one universe. He believed that
by virtue of an inward energy monads develop themselves spontaneously,
each being independent of every other. In short, each monad is a kind
of deity in itself---a microcosm representing all the great features
of the macrocosm.

It would be impossible clearly to estimate the precise value of the
stimulative influence of these philosophers upon the scientific thought
of their time. There was one way, however, in which their influence
was made very tangible---namely, in the incentive they gave to the
foundation of scientific societies.


\section*{\raggedright SCIENTIFIC SOCIETIES}

\addcontentsline{toc}{section}{SCIENTIFIC SOCIETIES}

At the present time, when the elements of time and distance are practically
eliminated in the propagation of news, and when cheap printing has
minimized the difficulties of publishing scientific discoveries, it
is difficult to understand the isolated position of the scientific
investigation of the ages that preceded steam and electricity. Shut
off from the world and completely out of touch with fellow-laborers
perhaps only a few miles away, the investigators were naturally seriously
handicapped; and inventions and discoveries were not made with the
same rapidity that they would undoubtedly have been had the same men
been receiving daily, weekly, or monthly communications from fellow-laborers
all over the world, as they do to-day. Neither did they have the advantage
of public or semi-public laboratories, where they were brought into
contact with other men, from whom to gather fresh trains of thought
and receive the stimulus of their successes or failures. In the natural
course of events, however, neighbors who were interested in somewhat
similar pursuits, not of the character of the rivalry of trade or
commerce, would meet more or less frequently and discuss their progress.
The mutual advantages of such intercourse would be at once appreciated;
and it would be but a short step from the casual meeting of two neighborly
scientists to the establishment of {}``societies,''\ meeting at
fixed times, and composed of members living within reasonable travelling
distance. There would, perhaps, be the weekly or monthly meetings
of men in a limited area; and as the natural outgrowth of these little
local societies, with frequent meetings, would come the formation
of larger societies, meeting less often, where members travelled a
considerable distance to attend. And, finally, with increased facilities
for communication and travel, the great international societies of
to-day would be produced---the natural outcome of the neighborly meetings
of the primitive medi\ae{}val investigators.

In Italy, at about the time of Galileo, several small societies were
formed. One of the most important of these was the Lyncean Society,
founded about the year 1611, Galileo himself being a member. This
society was succeeded by the \textit{\emph{Accademia}} \emph{}\textit{\emph{del}}
\emph{}\textit{\emph{Cimento}}, at Florence, in 1657, which for a
time flourished, with such a famous scientist as Torricelli as one
of its members.

In England an impetus seems to have been given by Sir Francis Bacon's
writings in criticism and censure of the systern of teaching in colleges.
It is supposed that his suggestions as to what should be the aims
of a scientific society led eventually to the establishment of the
Royal Society. He pointed out how little had really been accomplished
by the existing institutions of learning in advancing science, and
asserted that little good could ever come from them while their methods
of teaching remained unchanged. He contended that the system which
made the lectures and exercises of such a nature that no deviation
from the established routine could be thought of was pernicious. But
he showed that if any teacher had the temerity to turn from the traditional
paths, the daring pioneer was likely to find insurmountable obstacles
placed in the way of his advancement. The studies were {}``imprisoned''\ within
the limits of a certain set of authors, and originality in thought
or teaching was to be neither contemplated nor tolerated.

The words of Bacon, given in strong and unsparing terms of censure
and condemnation, but nevertheless with perfect justification, soon
bore fruit. As early as the year 1645 a small company of scientists
had been in the habit of meeting at some place in London to discuss
philosophical and scientific subjects for mental advancement. In 1648,
owing to the political disturbances of the time, some of the members
of these meetings removed to Oxford, among them Boyle, Wallis, and
Wren, where the meetings were continued, as were also the meetings
of those left in London. In 1662, however, when the political situation
had become more settled, these two bodies of men were united under
a charter from Charles \textit{\emph{II}}., and Bacon's ideas were
practically expressed in that learned body, the Royal Society of London.
And it matters little that in some respects Bacon's views were not
followed in the practical workings of the society, or that the division
of labor in the early stages was somewhat different than at present.
The aim of the society has always been one for the advancement of
learning; and if Bacon himself could look over its records, he would
surely have little fault to find with the aid it has given in carrying
out his ideas for the promulgation of useful knowledge.

Ten years after the charter was granted to the Royal Society of London,
Lord Bacon's words took practical effect in Germany, with the result
that the \textit{\emph{Academia}} \emph{}\textit{\emph{Naturae}} Curiosorum
was founded, under the leadership of Professor J.\ C.\ Sturm. The
early labors of this society were devoted to a repetition of the most
notable experiments of the time, and the work of the embryo society
was published in two volumes, in 1672 and 1685 respectively, which
were practically text-books of the physics of the period. It was not
until 1700 that Frederick I.\ founded the Royal Academy of Sciences
at Berlin, after the elaborate plan of Leibnitz, who was himself the
first president.

Perhaps the nearest realization of Bacon's ideal, however, is in the
Royal Academy of Sciences at Paris, which was founded in 1666 under
the administration of Colbert, during the reign of Louis XIV. This
institution not only recognized independent members, but had besides
twenty \textit{pensionnaires} who received salaries from the government.
In this way a select body of scientists were enabled to pursue their
investigations without being obliged to {}``give thought to the morrow''\ for
their sustenance. In return they were to furnish the meetings with
scientific memoirs, and once a year give an account of the work they
were engaged upon. Thus a certain number of the brightest minds were
encouraged to devote their entire time to scientific research, {}``delivered
alike from the temptations of wealth or the embarrassments of poverty.''
That such a plan works well is amply attested by the results emanating
from the French academy. \textit{Pensionnaires} in various branches
of science, however, either paid by the state or by learned societies,
are no longer confined to France.

Among the other early scientific societies was the Imperial Academy
of Sciences at St.\ Petersburg, projected by Peter the Great, and
established by his widow, Catharine I., in 1725; and also the Royal
Swedish Academy, incorporated in 1781, and counting among its early
members such men as the celebrated Linn\ae{}us. But after the first
impulse had resulted in a few learned societies, their manifest advantage
was so evident that additional numbers increased rapidly, until at
present almost every branch of every science is represented by more
or less important bodies; and these are, individually and collectively,
adding to knowledge and stimulating interest in the many fields of
science, thus vindicating Lord Bacon's asseverations that knowledge
could be satisfactorily promulgated in this manner.


\chapter*{\raggedright X.\ THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE}

\addcontentsline{toc}{chapter}{X. THE SUCCESSORS OF GALILEO IN\\
PHYSICAL SCIENCE}

\markboth{A HISTORY OF SCIENCE, VOLUME II}{X. THE SUCCESSORS OF GALILEO}

We have now to witness the diversified efforts of a company of men
who, working for the most part independently, greatly added to the
data of the physical sciences---such men as Boyle, Huygens, Von Gericke,
and Hooke. It will be found that the studies of these men covered
the whole field of physical sciences as then understood---the field
of so-called natural philosophy. We shall best treat these successors
of Galileo and precursors of Newton somewhat biographically, pointing
out the correspondences and differences between their various accomplishments
as we proceed. It will be noted in due course that the work of some
of them was anticipatory of great achievements of a later century.


\section*{\raggedright ROBERT BOYLE (1627-1691)}

\addcontentsline{toc}{section}{ROBERT BOYLE (1627-1691)}

Some of Robert Boyle's views as to the possible structure of atmospheric
air will be considered a little farther on in this chapter, but for
the moment we will take up the consideration of some of his experiments
upon that as well as other gases. Boyle was always much interested
in alchemy, and carried on extensive experiments in attempting to
accomplish the transmutation of metals; but he did not confine himself
to these experiments, devoting himself to researches in all the fields
of natural philosophy. He was associated at Oxford with a company
of scientists, including Wallis and Wren, who held meetings and made
experiments together, these gatherings being the beginning, as mentioned
a moment ago, of what finally became the Royal Society. It was during
this residence at Oxford that many of his valuable researches upon
air were made, and during this time be invented his air-pump, now
exhibited in the Royal Society rooms at Burlington House.%
\footnote{See \emph{The Phlogiston Theory}, Vol.\ IV.%
}

His experiments to prove the atmospheric pressure are most interesting
and conclusive. {}``Having three small, round glass bubbles, blown
at the flame of a lamp, about the size of hazel-nuts,''\ he says,
{}``each of them with a short, slender stem, by means whereof they
were so exactly poised in water that a very small change of weight
would make them either emerge or sink; at a time when the atmosphere
was of convenient weight, I put them into a wide-mouthed glass of
common water, and leaving them in a quiet place, where they were frequently
in my eye, I observed that sometimes they would be at the top of the
water, and remain there for several days, or perhaps weeks, together,
and sometimes fall to the bottom, and after having continued there
for some time rise again. And sometimes they would rise or fall as
the air was hot or cold.''%
\footnote{Robert Boyle, \emph{Philosophical Works}, 3 \textit{\emph{vols}}.,
London, 1738. Vol.\ III., p.\ 41.%
}

It was in the course of these experiments that the observations made
by Boyle led to the invention of his {}``statical barometer,'' the
mercurial barometer having been invented, as we have seen, by Torricelli,
in 1643. In describing this invention he says: {}``Making choice
of a large, thin, and light glass bubble, blown at the flame of a
lamp, I counterpoised it with a metallic weight, in a pair of scales
that were suspended in a frame, that would turn with the thirtieth
part of a grain. Both the frame and the balance were then placed near
a good barometer, whence I might learn the present weight of the atmosphere;
when, though the scales were unable to show all the variations that
appeared in the mercurial barometer, yet they gave notice of those
that altered the height of the mercury half a quarter of an inch.''%
\footnote{\emph{Ibid}., Vol.\ III., p.\ 47.%
} A fairly sensitive barometer, after all. This statical barometer
suggested several useful applications to the fertile imagination of
its inventor, among others the measuring of mountain-peaks, as with
the mercurial barometer, the rarefication of the air at the top giving
a definite ratio to the more condensed air in the valley.

Another of his experiments was made to discover the atmospheric pressure
to the square inch. After considerable difficulty he determined that
the relative weight of a cubic inch of water and mercury was about
one to fourteen, and computing from other known weights he determined
that {}``when a column of quicksilver thirty inches high is sustained
in the barometer, as it frequently happens, a column of air that presses
upon an inch square near the surface of the earth must weigh about
fifteen avoirdupois pounds.''%
\footnote{\emph{Ibid}., Vol.\ II., p.\ 92.%
} As the pressure of air at the sea-level is now estimated at 14.7304
pounds to the square inch, it will be seen that Boyle's calculation
was not far wrong.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2S206}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small View in the Library of the
Royal Society}\end{center}{\small \par}

\noindent \emph{\footnotesize On the desk in the foreground is Boyle's
air-pump on the left. Priestly's electric machine on the right. }
\end{figure}
From his numerous experiments upon the air, Boyle was led to believe
that there were many {}``latent qualities''\ due to substances
contained in it that science had as yet been unable to fathom, believing
that there is {}``not a more heterogeneous body in the world.''
He believed that contagious diseases were carried by the air, and
suggested that eruptions of the earth, such as those made by earthquakes,
might send up {}``venomous exhalations''\ that produced diseases.
He suggested also that the air might play an important part in some
processes of calcination, which, as we shall see, was proved to be
true by Lavoisier late in the eighteenth century. Boyle's notions
of the exact chemical action in these phenomena were of course vague
and indefinite, but he had observed that some part was played by the
air, and he was right in supposing that the air {}``may have a great
share in varying the salts obtainable from calcined vitriol.''%
\footnote{\emph{Ibid}., Vol.\ II., p.\ 2.%
}

Although he was himself such a painstaking observer of facts, he had
the fault of his age of placing too much faith in hear-say evidence
of untrained observers. Thus, from the numerous stories he heard concerning
the growth of metals in previously exhausted mines, he believed that
the air was responsible for producing this growth---in which he undoubtedly
believed. The story of a tin-miner that, in his own time, after a
lapse of only twenty-five years, a heap of earth previously exhausted
of its ore became again even more richly impregnated than before by
lying exposed to the air, seems to have been believed by the philosopher.

As Boyle was an alchemist, and undoubtedly believed in the alchemic
theory that metals have {}``spirits''\ and various other qualities
that do not exist, it is not surprising that he was credulous in the
matter of beliefs concerning peculiar phenomena exhibited by them.
Furthermore, he undoubtedly fell into the error common to {}``specialists,''\ or
persons working for long periods of time on one subject---the error
of over-enthusiasm in his subject. He had discovered so many remarkable
qualities in the air that it is not surprising to find that he attributed
to it many more that he could not demonstrate.

Boyle's work upon colors, although probably of less importance than
his experiments and deductions upon air, show that he was in the van
as far as the science of his day was concerned. As he points out,
the schools of his time generally taught that {}``color is a penetrating
quality, reaching to the innermost part of the substance,''\ and,
as an example of this, sealing-wax was cited, which could be broken
into minute bits, each particle retaining the same color as its fellows
or the original mass. To refute this theory, and to show instances
to the contrary, Boyle, among other things, shows that various colors---blue,
red, yellow---may be produced upon tempered steel, and yet the metal
within {}``a hair's-breadth of its surface''\ have none of these
colors. Therefore, he was led to believe that color, in opaque bodies
at least, is superficial.

{}``But before we descend to a more particular consideration of our
subject,''\ he says, {}``'tis proper to observe that colors may
be regarded either as a quality residing in bodies to modify light
after a particular manner, or else as light itself so modified as
to strike upon the organs of sight, and cause the sensation we call
color; and that this latter is the more proper acceptation of the
word color will appear hereafter. And indeed it is the light itself,
which after a certain manner, either mixed with shades or other-wise,
strikes our eyes and immediately produces that motion in the organ
which gives us the color of an object.''%
\footnote{\emph{Ibid}., Vol.\ I., p.\ 8.%
}

In examining smooth and rough surfaces to determine the cause of their
color, he made use of the microscope, and pointed out the very obvious
example of the difference in color of a rough and a polished piece
of the same block of stone. He used some striking illustrations of
the effect of light and the position of the eye upon colors. {}``Thus
the color of plush or velvet will appear various if you stroke part
of it one way and part another, the posture of the particular threads
in regard to the light, or the eye, being thereby varied. And 'tis
observable that in a field of ripe corn, blown upon by the wind, there
will appear waves of a color different from that of the rest of the
corn, because the wind, by depressing some of the ears more than others,
causes one to reflect more light from the lateral and strawy parts
than another.''%
\footnote{\emph{Ibid}., \textit{\emph{vol}}.\ III., p.\ 508.%
} His work upon color, however, as upon light, was entirely overshadowed
by the work of his great fellow-countryman Newton.

Boyle's work on electricity was a continuation of Gilbert's, to which
he added several new facts. He added several substances to Gilbert's
list of {}``electrics,''\ experimented on smooth and rough surfaces
in exciting of electricity, and made the important discovery that
amber retained its attractive virtue after the friction that excited
it had ceased. {}``For the attrition having caused an intestine motion
in its parts,''\ he says, {}``the heat thereby excited ought not
to cease as soon as ever the rubbing is over, but to continue capable
of emitting effluvia for some time afterwards, longer or shorter according
to the goodness of the electric and the degree of the commotion made;
all which, joined together, may sometimes make the effect considerable;
and by this means, on a warm day, I, with a certain body not bigger
than a pea, but very vigorously attractive, moved a steel needle,
freely poised, about three minutes after I had left off rubbing it.''%
\footnote{\emph{Ibid}., Vol.\ III.\ p.\ 361.%
}


\section*{\raggedright MARIOTTE AND VON GUERICKE}

\addcontentsline{toc}{section}{MARIOTTE AND VON GUERICKE}

Working contemporaneously with Boyle, and a man whose name is usually
associated with his as the propounder of the law of density of gases,
was Edme Mariotte (died 1684), a native of Burgundy. Mariotte demonstrated
that but for the resistance of the atmosphere, all bodies, whether
light or heavy, dense or thin, would fall with equal rapidity, and
he proved this by the well-known {}``guinea-and-feather''\ experiment.
Having exhausted the air from a long glass tube in which a guinea
piece and a feather had been placed, he showed that in the vacuum
thus formed they fell with equal rapidity as often as the tube was
reversed. From his various experiments as to the pressure of the atmosphere
he deduced the law that the density and elasticity of the atmosphere
are precisely proportional to the compressing force (the law of Boyle
and Mariotte). He also ascertained that air existed in a state of
mechanical mixture with liquids, {}``existing between their particles
in a state of condensation.'' He made many other experiments, especially
on the collision of bodies, but his most important work was upon the
atmosphere.

But meanwhile another contemporary of Boyle and Mariotte was interesting
himself in the study of the atmosphere, and had made a wonderful invention
and a most striking demonstration. This was Otto von Guericke (1602-1686),
Burgomaster of Magdeburg, and councillor to his {}``most serene and
potent Highness''\ the elector of that place. When not engrossed
with the duties of public office, he devoted his time to the study
of the sciences, particularly pneumatics and electricity, both then
in their infancy. The discoveries of Galileo, Pascal, and Torricelli
incited him to solve the problem of the creation of a vacuum---a desideratum
since before the days of Aristotle. His first experiments were with
a wooden pump and a barrel of water, but he soon found that with such
porous material as wood a vacuum could not be created or maintained.
He therefore made use of a globe of copper, with pump and stop-cock;
and with this he was able to pump out air almost as easily as water.
Thus, in 1650, the air-pump was invented. Continuing his experiments
upon vacuums and atmospheric pressure with his newly discovered pump,
he made some startling discoveries as to the enormous pressure exerted
by the air.

It was not his intention, however, to demonstrate his newly acquired
knowledge by words or theories alone, nor by mere laboratory experiments;
but he chose instead an open field, to which were invited Emperor
Ferdinand \textit{\emph{III.}}, and all the princes of the Diet at
Ratisbon. When they were assembled he produced two hollow brass hemispheres
about two feet in diameter, and placing their exactly fitting surfaces
together, proceeded to pump out the air from their hollow interior,
thus causing them to stick together firmly in a most remarkable way,
apparently without anything holding them. This of itself was strange
enough; but now the worthy burgomaster produced teams of horses, and
harnessing them to either side of the hemispheres, attempted to pull
the adhering brasses apart. Five, ten, fifteen teams---thirty horses,
in all---were attached; but pull and tug as they would they could
not separate the firmly clasped hemispheres. The enormous pressure
of the atmosphere had been most strikingly demonstrated.

But it is one thing to demonstrate, another to convince; and many
of the good people of Magdeburg shook their heads over this {}``devil's
contrivance,''\ and predicted that Heaven would punish the Herr
Burgomaster, as indeed it had once by striking his house with lightning
and injuring some of his infernal contrivances. They predicted his
future punishment, but they did not molest him, for to his fellow-citizens,
who talked and laughed, drank and smoked with him, and knew him for
the honest citizen that he was, he did not seem bewitched at all.
And so he lived and worked and added other facts to science, and his
brass hemispheres were not destroyed by fanatical Inquisitors, but
are still preserved in the royal library at Berlin.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2S212}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Von Guericke's Air-Pump}\end{center}{\small \par}

\noindent \emph{\footnotesize (From Dannemann's} {\footnotesize Geschichte
der Naturwissenschaften}\emph{\footnotesize .) }
\end{figure}
In his experiments with his air-pump he discovered many things regarding
the action of gases, among others that animals cannot live in a vacuum.
He invented the anemoscope and the air-balance, and being thus enabled
to weigh the air and note the changes that preceded storms and calms,
he was able still further to dumfound his wondering fellow-Magdeburgers
by more or less accurate predictions about the weather.

Von Guericke did not accept Gilbert's theory that the earth was a
great magnet, but in his experiments along lines similar to those
pursued by Gilbert, he not only invented the first electrical machine,
but discovered electrical attraction and repulsion. The electrical
machine which he invented consisted of a sphere of sulphur mounted
on an iron axis to imitate the rotation of the earth, and which, when
rubbed, manifested electrical reactions. When this globe was revolved
and stroked with the dry hand it was found that it attached to it
{}``all sorts of little fragments, like leaves of gold, silver, paper,
\textit{etc}.'' {}``Thus this globe,''\ he says, {}``when brought
rather near drops of water causes them to swell and puff up. It likewise
attracts air, smoke, \textit{etc}.''%
\footnote{Otto von Guericke, in the P\emph{hilosophical Transactions of the
Royal Society of London}, No.\ 88, for 1672, p.\ 5103.%
} Before the time of Guericke's demonstrations, Cab\ae{}us had noted
that chaff leaped back from an {}``electric,''\ but he did not
interpret the phenomenon as electrical repulsion. Von Guericke, however,
recognized it as such, and refers to it as what he calls {}``expulsive
virtue.'' {}``Even expulsive virtue is seen in this globe,''\ he
says, {}``for it not only attracts, but also \textit{repels} again
from itself little bodies of this sort, nor does it receive them until
they have touched something else.'' It will be observed from this
that he was very close to discovering the discharge of the electrification
of attracted bodies by contact with some other object, after which
they are reattracted by the electric.

He performed a most interesting experiment with his sulphur globe
and a feather, and in doing so came near anticipating Benjamin Franklin
in his discovery of the effects of pointed conductors in drawing off
the discharge. Having revolved and stroked his globe until it repelled
a bit of down, he removed the globe from its rack and advancing it
towards the now repellent down, drove it before him about the room.
In this chase he observed that the down preferred to alight against
{}``the points of any object whatsoever.'' He noticed that should
the down chance to be driven within a few inches of a lighted candle,
its attitude towards the globe suddenly changed, and instead of running
away from it, it now {}``flew to it for protection''---the charge
on the down having been dissipated by the hot air. He also noted that
if one face of a feather had been first attracted and then repelled
by the sulphur ball, that the surface so affected was always turned
towards the globe; so that if the positions of the two were reversed,
the sides of the feather reversed also.

Still another important discovery, that of electrical conduction,
was made by Von Guericke. Until his discovery no one had observed
the transference of electricity from one body to another, although
Gilbert had some time before noted that a rod rendered magnetic at
one end became so at the other. Von Guericke's experiments were made
upon a linen thread with his sulphur globe, which, he says, {}``having
been previously excited by rubbing, can exercise likewise its virtue
through a linen thread an ell or more long, and there attract something.''
But this discovery, and his equally important one that the sulphur
ball becomes luminous when rubbed, were practically forgotten until
again brought to notice by the discoveries of Francis Hauksbee and
Stephen Gray early in the eighteenth century. From this we may gather
that Von Guericke himself did not realize the import of his discoveries,
for otherwise he would certainly have carried his investigations still
further. But as it was he turned his attention to other fields of
research.


\section*{\raggedright ROBERT HOOKE}

\addcontentsline{toc}{section}{ROBERT HOOKE}

A slender, crooked, shrivelled-limbed, cantankerous little man, with
dishevelled hair and haggard countenance, bad-tempered and irritable,
penurious and dishonest, at least in his claims for priority in discoveries---this
is the picture usually drawn, alike by friends and enemies, of Robert
Hooke (1635-1703), a man with an almost unparalleled genius for scientific
discoveries in almost all branches of science. History gives few examples
so striking of a man whose really great achievements in science would
alone have made his name immortal, and yet who had the pusillanimous
spirit of a charlatan---an almost insane mania, as it seems---for
claiming the credit of discoveries made by others. This attitude of
mind can hardly be explained except as a mania: it is certainly more
charitable so to regard it. For his own discoveries and inventions
were so numerous that a few more or less would hardly have added to
his fame, as his reputation as a philosopher was well established.
Admiration for his ability and his philosophical knowledge must always
be marred by the recollection of his arrogant claims to the discoveries
of other philosophers.

It seems pretty definitely determined that Hooke should be credited
with the invention of the balance-spring for regulating watches; but
for a long time a heated controversy was waged between Hooke and Huygens
as to who was the real inventor. It appears that Hooke conceived the
idea of the balance-spring, while to Huygens belongs the credit of
having adapted the \textit{coiled} spring in a working model. He thus
made practical Hooke's conception, which is without value except as
applied by the coiled spring; but, nevertheless, the inventor, as
well as the perfector, should receive credit. In this controversy,
unlike many others, the blame cannot be laid at Hooke's door.

Hooke was the first curator of the Royal Society, and when anything
was to be investigated, usually invented the mechanical devices for
doing so. Astronomical apparatus, instruments for measuring specific
weights, clocks and chronometers, methods of measuring the velocity
of falling bodies, freezing and boiling points, strength of gunpowder,
magnetic instruments---in short, all kinds of ingenious mechanical
devices in all branches of science and mechanics. It was he who made
the famous air-pump of Robert Boyle, based on Boyle's plans. Incidentally,
Hooke claimed to be the inventor of the first air-pump himself, although
this claim is now entirely discredited.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth,
  height=0.90\paperwidth,
  keepaspectratio]{2hsci10-Wil2S216}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Reproduction of a Plate in
Hooke's {}``Microscopical Observations''}\end{center}{\small \par}

\noindent \emph{\footnotesize Showing the points of a needle (Fig.}\ \emph{\footnotesize 1),
a printed dot (Fig.}\ \emph{\footnotesize 2), and the edge of a razor
(Fig.}\ \emph{\footnotesize 3), as magnified by Hooke's microscope. }
\end{figure}
Within a period of two years he devised no less than thirty different
methods of flying, all of which, of course, came to nothing, but go
to show the fertile imagination of the man, and his tireless energy.
He experimented with electricity and made some novel suggestions upon
the difference between the electric spark and the glow, although on
the whole his contributions in this field are unimportant. He also
first pointed out that the motions of the heavenly bodies must be
looked upon as a mechanical problem, and was almost within grasping
distance of the exact theory of gravitation, himself originating the
idea of making use of the pendulum in measuring gravity. Likewise,
he first proposed the wave theory of light; although it was Huygens
who established it on its present foundation.

Hooke published, among other things, a book of plates and descriptions
of his \emph{Microscopical Observations}, which gives an idea of the
advance that had already been made in microscopy in his time. Two
of these plates are given here, which, even in this age of microscopy,
are both interesting and instructive. These plates are made from prints
of Hooke's original copper plates, and show that excellent lenses
were made even at that time. They illustrate, also, how much might
have been accomplished in the field of medicine if more attention
had been given to microscopy by physicians. Even a century later,
had physicians made better use of their microscopes, they could hardly
have overlooked such an easily found parasite as the itch mite, which
is quite as easily detected as the cheese mite, pictured in Hooke's
book.

In justice to Hooke, and in extenuation of his otherwise inexcusable
peculiarities of mind, it should be remembered that for many years
he suffered from a painful and wasting disease. This may have affected
his mental equilibrium, without appreciably affecting his ingenuity.
In his own time this condition would hardly have been considered a
disease; but to-day, with our advanced ideas as to mental diseases,
we should be more inclined to ascribe his unfortunate attitude of
mind to a pathological condition, rather than to any manifestation
of normal mentality. From this point of view his mental deformity
seems not unlike that of Cavendish's, later, except that in the case
of Cavendish it manifested itself as an abnormal sensitiveness instead
of an abnormal irritability.


\section*{\raggedright CHRISTIAN HUYGENS}

\addcontentsline{toc}{section}{CHRISTIAN HUYGENS}

If for nothing else, the world is indebted to the man who invented
the pendulum clock, Christian Huygens (1629-1695), of the Hague, inventor,
mathematician, mechanician, astronomer, and physicist. Huygens was
the descendant of a noble and distinguished family, his father, Sir
Constantine Huygens, being a well-known poet and diplomatist. Early
in life young Huygens began his career in the legal profession, completing
his education in the juridical school at Breda; but his taste for
mathematics soon led him to neglect his legal studies, and his aptitude
for scientific researches was so marked that Descartes predicted great
things of him even while he was a mere tyro in the field of scientific
investigation.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2S218}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Robert Hooke's Microscope}\end{center}
\end{figure}
One of his first endeavors in science was to attempt an improvement
of the telescope. Reflecting upon the process of making lenses then
in vogue, young Huygens and his brother Constantine attempted a new
method of grinding and polishing, whereby they overcame a great deal
of the spherical and chromatic aberration. With this new telescope
a much clearer field of vision was obtained, so much so that Huygens
was able to detect, among other things, a hitherto unknown satellite
of Saturn. It was these astronomical researches that led him to apply
the pendulum to regulate the movements of clocks. The need for some
more exact method of measuring time in his observations of the stars
was keenly felt by the young astronomer, and after several experiments
along different lines, Huygens hit upon the use of a swinging weight;
and in 1656 made his invention of the pendulum clock. The year following,
his clock was presented to the states-general. Accuracy as to time
is absolutely essential in astronomy, but until the invention of Huygens's
clock there was no precise, nor even approximately precise, means
of measuring short intervals.

Huygens was one of the first to adapt the micrometer to the telescope---a
mechanical device on which all the nice determination of minute distances
depends. He also took up the controversy against Hooke as to the superiority
of telescopic over plain sights to quadrants, Hooke contending in
favor of the plain. In this controversy, the subject of which attracted
wide attention, Huygens was completely victorious; and Hooke, being
unable to refute Huygens's arguments, exhibited such irritability
that he increased his already general unpopularity. All of the arguments
for and against the telescope sight are too numerous to be given here.
In contending in its favor Huygens pointed out that the unaided eye
is unable to appreciate an angular space in the sky less than about
thirty seconds. Even in the best quadrant with a plain sight, therefore,
the altitude must be uncertain by that quantity. If in place of the
plain sight a telescope is substituted, even if it magnify only thirty
times, it will enable the observer to fix the position to one second,
with progressively increased accuracy as the magnifying power of the
telescope is increased. This was only one of the many telling arguments
advanced by Huygens.

In the field of optics, also, Huygens has added considerably to science,
and his work, \emph{Dioptrics}, is said to have been a favorite book
with Newton. During the later part of his life, however, Huygens again
devoted himself to inventing and constructing telescopes, grinding
the lenses, and devising, if not actually making, the frame for holding
them. These telescopes were of enormous lengths, three of his object-glasses,
now in possession of the Royal Society, being of 123, 180, and 210
feet focal length respectively. Such instruments, if constructed in
the ordinary form of the long tube, were very unmanageable, and to
obviate this Huygens adopted the plan of dispensing with the tube
altogether, mounting his lenses on long poles manipulated by machinery.
Even these were unwieldy enough, but the difficulties of manipulation
were fully compensated by the results obtained.

It had been discovered, among other things, that in oblique refraction
light is separated into colors. Therefore, any small portion of the
convex lens of the telescope, being a prism, the rays proceed to the
focus, separated into prismatic colors, which make the image thus
formed edged with a fringe of color and indistinct. But, fortunately
for the early telescope makers, the degree of this aberration is independent
of the focal length of the lens; so that, by increasing this focal
length and using the appropriate eye-piece, the image can be greatly
magnified, while the fringe of colors remains about the same as when
a less powerful lens is used. Hence the advantage of Huygens's long
telescope. He did not confine his efforts to simply lengthening the
focal length of his telescopes, however, but also added to their efficiency
by inventing an almost perfect achromatic eye-piece.

In 1663 he was elected a fellow of the Royal Society of London, and
in 1669 he gave to that body a concise statement of the laws governing
the collision of elastic bodies. Although the same views had been
given by Wallis and Wren a few weeks earlier, there is no doubt that
Huygens's views were reached independently; and it is probable that
he had arrived at his conclusions several years before. In the \emph{Philosophical
Transactions} for 1669 it is recorded that the society being interested
in the laws of the principles of motion, a request was made that M.\ Huygens,
Dr.\ Wallis, and Sir Christopher Wren submit their views on the subject.
Wallis submitted his paper first, November 15, 1668. A month later,
December 17th, Wren imparted to the society his laws as to the nature
of the collision of bodies. And a few days later, January 5, 1669,
Huygens sent in his {}``Rules Concerning the Motion of Bodies after
Mutual Impulse.'' Although Huygens's report was received last, he
was anticipated by such a brief space of time, and his views are so
clearly stated---on the whole rather more so than those of the other
two---that we give them in part here:\ 

{}``1. If a hard body should strike against a body equally hard at
rest, after contact the former will rest and the latter acquire a
velocity equal to that of the moving body.

{}``2. But if that other equal body be likewise in motion, and moving
in the same direction, after contact they will move with reciprocal
velocities.

{}``3. A body, however great, is moved by a body however small impelled
with any velocity whatsoever.

{}``5. The quantity of motion of two bodies may be either increased
or diminished by their shock; but the same quantity towards the same
part remains, after subtracting the quantity of the contrary motion.

{}``6. The sum of the products arising from multiplying the mass
of any hard body into the squares of its velocity is the same both
before and after the stroke.

{}``7. A hard body at rest will receive a greater quantity of motion
from another hard body, either greater or less than itself, by the
interposition of any third body of a mean quantity, than if it was
immediately struck by the body itself; and if the interposing body
be a mean proportional between the other two, its action upon the
quiescent body will be the greatest of all.''%
\footnote{Von Guericke, \emph{Phil}. \textit{Trans}.\ for 1669, Vol.\ I.,
\textit{\emph{pp}}. 173, 174.%
}

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth,
  height=0.90\paperwidth,
  keepaspectratio]{2hsci10-Wil2S222}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Huygens's Clock}\end{center}{\small \par}

\noindent \begin{center}\emph{\footnotesize (Side view, showing the
pendulum mechanism.) }\end{center}
\end{figure}
This was only one of several interesting and important communications
sent to the Royal Society during his lifetime. One of these was a
report on what he calls {}``Pneumatical Experiments.'' {}``Upon
including in a vacuum an insect resembling a beetle, but somewhat
larger,''\ he says, {}``when it seemed to be dead, the air was
readmitted, and soon after it revived; putting it again in the vacuum,
and leaving it for an hour, after which the air was readmitted, it
was observed that the insect required a longer time to recover; including
it the third time for two days, after which the air was admitted,
it was ten hours before it began to stir; but, putting it in a fourth
time, for eight days, it never afterwards recovered\ldots{}. Several
birds, rats, mice, rabbits, and cats were killed in a vacuum, but
if the air was admitted before the engine was quite exhausted some
of them would recover; yet none revived that had been in a perfect
vacuum\ldots{}. Upon putting the weight of eighteen grains of powder
with a gauge into a receiver that held several pounds of water, and
firing the powder, it raised the mercury an inch and a half; from
which it appears that there is one-fifth of air in gunpowder, upon
the supposition that air is about one thousand times lighter than
water; for in this experiment the mercury rose to the eighteenth part
of the height at which the air commonly sustains it, and consequently
the weight of eighteen grains of powder yielded air enough to fill
the eighteenth part of a receiver that contained seven pounds of water;
now this eighteenth part contains forty-nine drachms of water; wherefore
the air, that takes up an equal space, being a thousand times lighter,
weighs one-thousandth part of forty-nine drachms, which is more than
three grains and a half; it follows, therefore, that the weight of
eighteen grains of powder contains more than three and a half of air,
which is about one-fifth of eighteen grains\ldots{}.''

From 1665 to 1681, accepting the tempting offer made him through Colbert,
by Louis XIV., Huygens pursued his studies at the \textit{\emph{Bibliotheque}}
\emph{}\textit{\emph{du}} \emph{}\textit{\emph{Roi}} as a resident
of France. Here he published his \emph{Horologium Oscillatorium},
dedicated to the king, containing, among other things, his solution
of the problem of the {}``centre of oscillation.'' This in itself
was an important step in the history of mechanics. Assuming as true
that the centre of gravity of any number of interdependent bodies
cannot rise higher than the point from which it falls, he reached
correct conclusions as to the general principle of the conservation
of \emph{vis viva}, although he did not actually prove his conclusions.
This was the first attempt to deal with the dynamics of a system.
In this work, also, was the true determination of the relation between
the length of a pendulum and the time of its oscillation.

In 1681 he returned to Holland, influenced, it is believed, by the
attitude that was being taken in France against his religion. Here
he continued his investigations, built his immense telescopes, and,
among other things, discovered {}``polarization,'' which is recorded
in \textit{Traite} \textit{de} \textit{la} \textit{Lumiere}, published
at Leyden in 1690. Five years later he died, bequeathing his manuscripts
to the University of Leyden. It is interesting to note that he never
accepted Newton's theory of gravitation as a universal property of
matter.


\chapter*{\raggedright XI. NEWTON AND THE COMPOSITION OF LIGHT}

\addcontentsline{toc}{chapter}{XI. NEWTON AND THE COMPOSITION\\
OF LIGHT}

\markboth{A HISTORY OF SCIENCE, VOLUME II}{XI. THE COMPOSITION OF
LIGHT}

Galileo, that giant in physical science of the early seventeenth century,
died in 1642. On Christmas day of the same year there was born in
England another intellectual giant who was destined to carry forward
the work of Copernicus, Kepler, and Galileo to a marvellous consummation
through the discovery of the great unifying law in accordance with
which the planetary motions are performed. We refer, of course, to
the greatest of English physical scientists, Isaac Newton, the Shakespeare
of the scientific world. Born thus before the middle of the seventeenth
century, Newton lived beyond the first quarter of the eighteenth (1727).
For the last forty years of that period his was the dominating scientific
personality of the world. With full propriety that time has been spoken
of as the {}``Age of Newton.''

Yet the man who was to achieve such distinction gave no early premonition
of future greatness. He was a sickly child from birth, and a boy of
little seeming promise. He was an indifferent student, yet, on the
other hand, he cared little for the common amusements of boyhood.
He early exhibited, however, a taste for mechanical contrivances,
and spent much time in devising windmills, water-clocks, sun-dials,
and kites. While other boys were interested only in having kites that
would fly, Newton---at least so the stories of a later time would
have us understand---cared more for the investigation of the seeming
principles involved, or for testing the best methods of attaching
the strings, or the best materials to be used in construction.

Meanwhile the future philosopher was acquiring a taste for reading
and study, delving into old volumes whenever he found an opportunity.
These habits convinced his relatives that it was useless to attempt
to make a farmer of the youth, as had been their intention. He was
therefore sent back to school, and in the summer of 1661 he matriculated
at Trinity College, Cambridge. Even at college Newton seems to have
shown no unusual mental capacity, and in 1664, when examined for a
scholarship by Dr.\ Barrow, that gentleman is said to have formed
a poor opinion of the applicant. It is said that the knowledge of
the estimate placed upon his abilities by his instructor piqued Newton,
and led him to take up in earnest the mathematical studies in which
he afterwards attained such distinction. The study of Euclid and Descartes's
{}``Geometry''\ roused in him a latent interest in mathematics,
and from that time forward his investigations were carried on with
enthusiasm. In 1667 he was elected Fellow of Trinity College, taking
the degree of M.A.\ the following spring.

It will thus appear that Newton's boyhood and early manhood were passed
during that troublous time in British political annals which saw the
overthrow of Charles I., the autocracy of Cromwell, and the eventual
restoration of the Stuarts. His maturer years witnessed the overthrow
of the last Stuart and the reign of the Dutchman, William of Orange.
In his old age he saw the first of the Hanoverians mount the throne
of England. Within a decade of his death such scientific path-finders
as Cavendish, Black, and Priestley were born---men who lived on to
the close of the eighteenth century. In a full sense, then, the age
of Newton bridges the gap from that early time of scientific awakening
under Kepler and Galileo to the time which we of the twentieth century
think of as essentially modern.


\section*{\raggedright THE COMPOSITION OF WHITE LIGHT}

\addcontentsline{toc}{section}{THE COMPOSITION OF WHITE LIGHT}

In December, 1672, Newton was elected a Fellow of the Royal Society,
and at this meeting a paper describing his invention of the reflecting
telescope was read. A few days later he wrote to the secretary, making
some inquiries as to the weekly meetings of the society, and intimating
that he had an account of an interesting discovery that he wished
to lay before the society. When this communication was made public,
it proved to be an explanation of the discovery of the composition
of white light. We have seen that the question as to the nature of
color had commanded the attention of such investigators as Huygens,
but that no very satisfactory solution of the question had been attained.
Newton proved by demonstrative experiments that white light is composed
of the blending of the rays of diverse colors, and that the color
that we ascribe to any object is merely due to the fact that the object
in question reflects rays of that color, absorbing the rest. That
white light is really made up of many colors blended would seem incredible
had not the experiments by which this composition is demonstrated
become familiar to every one. The experiments were absolutely novel
when Newton brought them forward, and his demonstration of the composition
of light was one of the most striking expositions ever brought to
the attention of the Royal Society. It is hardly necessary to add
that, notwithstanding the conclusive character of Newton's work, his
explanations did not for a long time meet with general acceptance.

Newton was led to his discovery by some experiments made with an ordinary
glass prism applied to a hole in the shutter of a darkened room, the
refracted rays of the sunlight being received upon the opposite wall
and forming there the familiar spectrum. 

\begin{quotation}
{}``It was a very pleasing diversion,''\ he wrote, {}``to view
the vivid and intense colors produced thereby; and after a time, applying
myself to consider them very circumspectly, I became surprised to
see them in varying form, which, according to the received laws of
refraction, I expected should have been circular. They were terminated
at the sides with straight lines, but at the ends the decay of light
was so gradual that it was difficult to determine justly what was
their figure, yet they seemed semicircular.

{}``Comparing the length of this colored spectrum with its breadth,
I found it almost five times greater; a disproportion so extravagant
that it excited me to a more than ordinary curiosity of examining
from whence it might proceed. I could scarce think that the various
thicknesses of the glass, or the termination with shadow or darkness,
could have any influence on light to produce such an effect; yet I
thought it not amiss, first, to examine those circumstances, and so
tried what would happen by transmitting light through parts of the
glass of divers thickness, or through holes in the window of divers
bigness, or by setting the prism without so that the light might pass
through it and be refracted before it was transmitted through the
hole; but I found none of those circumstances material. The fashion
of the colors was in all these cases the same.

{}``Then I suspected whether by any unevenness of the glass or other
contingent irregularity these colors might be thus dilated. And to
try this I took another prism like the former, and so placed it that
the light, passing through them both, might be refracted contrary
ways, and so by the latter returned into that course from which the
former diverted it. For, by this means, I thought, the regular effects
of the first prism would be destroyed by the second prism, but the
irregular ones more augmented by the multiplicity of \textit{\emph{refractions}}.
The event was that the light, which by the first prism was diffused
into an oblong form, was by the second reduced into an orbicular one
with as much regularity as when it did not all pass through them.
So that, whatever was the cause of that length, 'twas not any contingent
irregularity.

{}``I then proceeded to examine more critically what might be effected
by the difference of the incidence of rays coming from divers parts
of the sun; and to that end measured the several lines and angles
belonging to the image. Its distance from the hole or prism was 22
feet; its utmost length 13$\frac{1}{4}$ inches; its breadth 2$\frac{5}{8}$;
the diameter of the hole $\frac{1}{4}$ of an inch; the angle which
the rays, tending towards the middle of the image, made with those
lines, in which they would have proceeded without refraction, was
44$^\circ$ 56'; and the vertical angle of the prism, 63$^\circ$
12'. Also the \textit{\emph{refractions}} on both sides of the prism---that
is, of the incident and emergent rays---were, as near as I could make
them, equal, and consequently about 54$^\circ$ 4'; and the rays fell
perpendicularly upon the wall. Now, subducting the diameter of the
hole from the length and breadth of the image, there remains 13 inches
the length, and 2$\frac{3}{8}$ the breadth, comprehended by those
rays, which, passing through the centre of the said hole, which that
breadth subtended, was about 31', answerable to the sun's diameter;
but the angle which its length subtended was more than five such diameters,
namely 2$^\circ$ 49'.

{}``Having made these observations, I first computed from them the
refractive power of the glass, and found it measured by the ratio
of the sines 20 to 31. And then, by that ratio, I computed the \textit{\emph{refractions}}
of two rays flowing from opposite parts of the sun's discus, so as
to differ 31'\ in their obliquity of incidence, and found that the
emergent rays should have comprehended an angle of 31', as they did,
before they were incident.

{}``But because this computation was founded on the hypothesis of
the proportionality of the sines of incidence and refraction, which
though by my own experience I could not imagine to be so erroneous
as to make that angle but 31', which in reality was 2$^\circ$ 49',
yet my curiosity caused me again to make my prism. And having placed
it at my window, as before, I observed that by turning it a little
about its axis to and fro, so as to vary its obliquity to the light
more than an angle of 4$^\circ$ or 5$^\circ$, the colors were not
thereby sensibly translated from their place on the wall, and consequently
by that variation of incidence the quantity of refraction was not
sensibly varied. By this experiment, therefore, as well as by the
former computation, it was evident that the difference of the incidence
of rays flowing from divers parts of the sun could not make them after
decussation diverge at a sensibly greater angle than that at which
they before converged; which being, at most, but about 31' or 32',
there still remained some other cause to be found out, from whence
it could be 2$^\circ$ 49'.''
\end{quotation}
{}

All this caused Newton to suspect that the rays, after their trajection
through the prism, moved in curved rather than in straight lines,
thus tending to be cast upon the wall at different places according
to the amount of this curve. His suspicions were increased, also,
by happening to recall that a tennis-ball sometimes describes such
a curve when {}``cut''\ by a tennis-racket striking the ball obliquely.

\begin{quotation}
{}``For a circular as well as a progressive motion being communicated
to it by the stroke,''\ he says, {}``its parts on that side where
the motions conspire must press and beat the contiguous air more violently
than on the other, and there excite a reluctancy and reaction of the
air proportionately greater. And for the same reason, if the rays
of light should possibly be globular bodies, and by their oblique
passage out of one medium into another acquire a circulating motion,
they ought to feel the greater resistance from the ambient ether on
that side where the motions conspire, and thence be continually bowed
to the other. But notwithstanding this plausible ground of suspicion,
when I came to examine it I could observe no such curvity in them.
And, besides (which was enough for my purpose), I observed that the
difference 'twixt the length of the image and diameter of the hole
through which the light was transmitted was proportionable to their
distance.

{}``The gradual removal of these suspicions at length led me to the
\textit{experimentum} \textit{crucis}, which was this: I took two
boards, and, placing one of them close behind the prism at the window,
so that the light must pass through a small hole, made in it for the
purpose, and fall on the other board, which I placed at about twelve
feet distance, having first made a small hole in it also, for some
of the incident light to pass through. Then I placed another prism
behind this second board, so that the light trajected through both
the boards might pass through that also, and be again refracted before
it arrived at the wall. This done, I took the first prism in my hands
and turned it to and fro slowly about its axis, so much as to make
the several parts of the image, cast on the second board, successively
pass through the hole in it, that I might observe to what places on
the wall the second prism would refract them. And I saw by the variation
of these places that the light, tending to that end of the image towards
which the refraction of the first prism was made, did in the second
prism suffer a refraction considerably greater than the light tending
to the other end. And so the true cause of the length of that image
was detected to be no other than that \textit{light} consists of \textit{rays}
\textit{differently} \textit{refrangible}, which, without any respect
to a difference in their incidence, were, according to their degrees
of refrangibility, transmitted towards divers parts of the wall.''%
\footnote{\emph{Phil}. \textit{Trans}.\ of Royal Soc.\ of London, No.\ 80,
1672, \textit{\emph{pp}}.\ 3076-3079.\ %
}
\end{quotation}

\section*{\raggedright THE NATURE OF COLOR}

\addcontentsline{toc}{section}{THE NATURE OF COLOR}

Having thus proved the composition of light, Newton took up an exhaustive
discussion as to colors, which cannot be entered into at length here.
Some of his remarks on the subject of compound colors, however, may
be stated in part. Newton's views are of particular interest in this
connection, since, as we have already pointed out, the question as
to what constituted color could not be agreed upon by the philosophers.
Some held that color was an integral part of the substance; others
maintained that it was simply a reflection from the surface; and no
scientific explanation had been generally accepted. Newton concludes
his paper as follows:\ 

\begin{quote}
{}``I might add more instances of this nature, but I shall conclude
with the general one that the colors of all natural bodies have no
other origin than this, that they are variously qualified to reflect
one sort of light in greater plenty than another. And this I have
experimented in a dark room by illuminating those bodies with uncompounded
light of divers colors. For by that means any body may be made to
appear of any color. They have there no appropriate color, but ever
appear of the color of the light cast upon them, but yet with this
difference, that they are most brisk and vivid in the light of their
own daylight color. Minium appeareth there of any color indifferently
with which 'tis illustrated, but yet most luminous in red; and so
Bise appeareth indifferently of any color with which 'tis illustrated,
but yet most luminous in blue. And therefore Minium reflecteth rays
of any color, but most copiously those indued with red; and consequently,
when illustrated with daylight---that is, with all sorts of rays promiscuously
blended---those qualified with red shall abound most in the reflected
light, and by their prevalence cause it to appear of that color. And
for the same reason, Bise, reflecting blue most copiously, shall appear
blue by the excess of those rays in its reflected light; and the like
of other bodies. And that this is the entire and adequate cause of
their colors is manifest, because they have no power to change or
alter the colors of any sort of rays incident apart, but put on all
colors indifferently with which they are enlightened.''%
\footnote{\emph{Ibid}., \textit{\emph{pp}}.\ 3084, 3085.%
}
\end{quote}
{}

This epoch-making paper aroused a storm of opposition. Some of Newton's
opponents criticised his methods, others even doubted the truth of
his experiments. There was one slight mistake in Newton's belief that
all prisms would give a spectrum of exactly the same length, and it
was some time before he corrected this error. Meanwhile he patiently
met and answered the arguments of his opponents until he began to
feel that patience was no longer a virtue. At one time he even went
so far as to declare that, once he was {}``free of this business,''\ he
would renounce scientific research forever, at least in a public way.
Fortunately for the world, however, he did not adhere to this determination,
but went on to even greater discoveries---which, it may be added,
involved still greater controversies.

In commenting on Newton's discovery of the composition of light, Voltaire
said: {}``Sir Isaac Newton has demonstrated to the eye, by the bare
assistance of a prism, that light is a composition of colored rays,
which, being united, form white color. A single ray is by him divided
into seven, which all fall upon a piece of linen or a sheet of white
paper, in their order one above the other, and at equal distances.
The first is red, the second orange, the third yellow, the fourth
green, the fifth blue, the sixth indigo, the seventh a violet purple.
Each of these rays transmitted afterwards by a hundred other prisms
will never change the color it bears; in like manner as gold, when
completely purged from its dross, will never change afterwards in
the crucible.''%
\footnote{Voltaire, \emph{Letters Concerning the English Nation}, London, 1811.%
}


\chapter*{\raggedright XII. NEWTON AND THE LAW OF GRAVITATION}

\addcontentsline{toc}{chapter}{XII. NEWTON AND THE LAW OF\\
GRAVITATION}

\markboth{A HISTORY OF SCIENCE, VOLUME II}{XII. THE LAW OF GRAVITATION}

We come now to the story of what is by common consent the greatest
of scientific achievements. The law of universal gravitation is the
most far-reaching principle as yet discovered. It has application
equally to the minutest particle of matter and to the most distant
suns in the universe, yet it is amazing in its very simplicity. As
usually phrased, the law is this: That every particle of matter in
the universe attracts every other particle with a force that varies
directly with the mass of the particles and inversely as the squares
of their mutual distance. Newton did not vault at once to the full
expression of this law, though he had formulated it fully before he
gave the results of his investigations to the world. We have now to
follow the steps by which he reached this culminating achievement.

At the very beginning we must understand that the idea of universal
gravitation was not absolutely original with Newton. Away back in
the old Greek days, as we have seen, Anaxagoras conceived and clearly
expressed the idea that the force which holds the heavenly bodies
in their orbits may be the same that operates upon substances at the
surface of the earth. With Anaxagoras this was scarcely more than
a guess. After his day the idea seems not to have been expressed by
any one until the seventeenth century's awakening of science. Then
the consideration of Kepler's Third Law of planetary motion suggested
to many minds perhaps independently the probability that the force
hitherto mentioned merely as centripetal, through the operation of
which the planets are held in their orbits is a force varying inversely
as the square of the distance from the sun. This idea had come to
Robert Hooke, to Wren, and perhaps to Halley, as well as to Newton;
but as yet no one had conceived a method by which the validity of
the suggestion might be tested. It was claimed later on by Hooke that
he had discovered a method demonstrating the truth of the theory of
inverse squares, and after the full announcement of Newton's discovery
a heated controversy was precipitated in which Hooke put forward his
claims with accustomed acrimony. Hooke, however, never produced his
demonstration, and it may well be doubted whether he had found a method
which did more than vaguely suggest the law which the observations
of Kepler had partially revealed. Newton's great merit lay not so
much in conceiving the law of inverse squares as in the demonstration
of the law. He was led to this demonstration through considering the
orbital motion of the moon. According to the familiar story, which
has become one of the classic myths of science, Newton was led to
take up the problem through observing the fall of an apple. Voltaire
is responsible for the story, which serves as well as another; its
truth or falsity need not in the least concern us. Suffice it that
through pondering on the familiar fact of terrestrial gravitation,
Newton was led to question whether this force which operates so tangibly
here at the earth's surface may not extend its influence out into
the depths of space, so as to include, for example, the moon. Obviously
some force pulls the moon constantly towards the earth; otherwise
that body would fly off at a tangent and never return. May not this
so-called centripetal force be identical with terrestrial gravitation?
Such was Newton's query. Probably many another man since Anaxagoras
had asked the same question, but assuredly Newton was the first man
to find an answer.

The thought that suggested itself to Newton's mind was this: If we
make a diagram illustrating the orbital course of the moon for any
given period, say one minute, we shall find that the course of the
moon departs from a straight line during that period by a measurable
distance---that: is to say, the moon has been virtually pulled towards
the earth by an amount that is represented by the difference between
its actual position at the end of the minute under observation and
the position it would occupy had its course been tangential, as, according
to the first law of motion, it must have been had not some force deflected
it towards the earth. Measuring the deflection in question---which
is equivalent to the so-called versed sine of the arc traversed---we
have a basis for determining the strength of the deflecting force.
Newton constructed such a diagram, and, measuring the amount of the
moon's departure from a tangential rectilinear course in one minute,
determined this to be, by his calculation, thirteen feet. Obviously,
then, the force acting upon the moon is one that would cause that
body to fall towards the earth to the distance of thirteen feet in
the first minute of its fall. Would such be the force of gravitation
acting at the distance of the moon if the power of gravitation varies
inversely as the square of the distance? That was the tangible form
in which the problem presented itself to Newton. The mathematical
solution of the problem was simple enough. It is based on a comparison
of the moon's distance with the length of the earth's radius. On making
this calculation, Newton found that the pull of gravitation---if that
were really the force that controls the moon---gives that body a fall
of slightly over fifteen feet in the first minute, instead of thirteen
feet. Here was surely a suggestive approximation, yet, on the other
band, the discrepancy seemed to be too great to warrant him in the
supposition that he had found the true solution. He therefore dismissed
the matter from his mind for the time being, nor did he return to
it definitely for some years.

%
\begin{figure}
\noindent \begin{center}\includegraphics[  height=1.4in]{2hsci10-inverse}\end{center}

\noindent \begin{center}\textit{\emph{\noun{\small Newton's}}} \emph{\noun{\small }}\textit{\emph{\noun{\small Law}}}
\emph{\noun{\small }}\textit{\emph{\noun{\small of}}} \emph{\noun{\small }}\textit{\emph{\noun{\small Gravitation}}} \emph{\noun{\small }}\end{center}{\small \par}

\noindent \emph{\footnotesize $E$ represents the earth and $A$ the
moon. Were the earth's pull on the moon to cease, the moon's inertia
would cause it to take the tangential course, $AB$. On the other
hand, were the moon's motion to be stopped for an instant, the moon
would fall directly towards the earth, along the line $AD$. The moon's
actual orbit, resulting from these component forces, is $AC$. Let
$AC$ represent the actual flight of the moon in one minute. Then
$BC$, which is obviously equal to $AD$, represents the distance
which the moon virtually falls towards the earth in one minute. Actual
computation, based on measurements of the moon's orbit, showed this
distance to be about fifteen feet. Another computation showed that
this is the distance that the moon would fall towards the earth under
the influence of gravity, on the supposition that the force of gravity
decreases inversely with the square of the distance; the basis of
comparison being furnished by falling bodies at the surface of the
earth. Theory and observations thus coinciding, Newton was justified
in declaring that the force that pulls the moon towards the earth
and keeps it in its orbit, is the familiar force of gravity, and that
this varies inversely as the square of the distance.}
\end{figure}


It was to appear in due time that Newton's hypothesis was perfectly
valid and that his method of attempted demonstration was equally so.
The difficulty was that the earth's proper dimensions were not at
that time known. A wrong estimate of the earth's size vitiated all
the other calculations involved, since the measurement of the moon's
distance depends upon the observation of the parallax, which cannot
lead to a correct computation unless the length of the earth's radius
is accurately known. Newton's first calculation was made as early
as 1666, and it was not until 1682 that his attention was called to
a new and apparently accurate measurement of a degree of the earth's
meridian made by the French astronomer Picard. The new measurement
made a degree of the earth's surface 69.10 miles, instead of sixty
miles.

Learning of this materially altered calculation as to the earth's
size, Newton was led to take up again his problem of the falling moon.
As he proceeded with his computation, it became more and more certain
that this time the result was to harmonize with the observed facts.
As the story goes, he was so completely overwhelmed with emotion that
he was forced to ask a friend to complete the simple calculation.
That story may well be true, for, simple though the computation was,
its result was perhaps the most wonderful demonstration hitherto achieved
in the entire field of science. Now at last it was known that the
force of gravitation operates at the distance of the moon, and holds
that body in its elliptical orbit, and it required but a slight effort
of the imagination to assume that the force which operates through
such a reach of space extends its influence yet more widely. That
such is really the case was demonstrated presently through calculations
as to the moons of Jupiter and by similar computations regarding the
orbital motions of the various planets. All results harmonizing, Newton
was justified in reaching the conclusion that gravitation is a universal
property of matter. It remained, as we shall see, for nineteenth-century
scientists to prove that the same force actually operates upon the
stars, though it should be added that this demonstration merely fortified
a belief that had already found full acceptance.

Having thus epitomized Newton's discovery, we must now take up the
steps of his progress somewhat in detail, and state his theories and
their demonstration in his own words. Proposition IV., theorem 4,
of his \emph{Principia} is as follows:\ 

\begin{quotation}
{}``That the moon gravitates towards the earth and by the force of
gravity is continually drawn off from a rectilinear motion and retained
in its orbit.

{}``The mean distance of the moon from the earth, in the \textit{\emph{syzygies}}
in semi-diameters of the earth, is, according to Ptolemy and most
astronomers, 59; according to Vendelin and Huygens, 60; to Copernicus,
60$\frac{1}{3}$; to Street, 60$\frac{2}{3}$; and to Tycho, 56$\frac{1}{2}$.
But Tycho, and all that follow his tables of \textit{\emph{refractions}},
making the \textit{\emph{refractions}} of the sun and moon (altogether
against the nature of light)\ to exceed the \textit{\emph{refractions}}
of the fixed stars, and that by four or five minutes \textit{near}
\textit{the} \textit{horizon}, did thereby increase the moon's \textit{horizontal}
parallax by a like number of minutes, that is, by a twelfth or fifteenth
part of the whole parallax. Correct this error and the distance will
become about 60$\frac{1}{2}$ semi-diameters of the earth, near to
what others have assigned. Let us assume the mean distance of 60 diameters
in the \textit{\emph{syzygies}}; and suppose one revolution of the
moon, in respect to the fixed stars, to be completed in 27d.\ 7h.\ 43',
as astronomers have determined; and the circumference of the earth
to amount to 123,249,600 Paris feet, as the French have found by mensuration.
And now, if we imagine the moon, deprived of all motion, to be let
go, so as to descend towards the earth with the impulse of all that
force by which (by \textit{\emph{Cor}}. Prop.\ iii.)\ it is retained
in its orb, it will in the space of one minute of time describe in
its fall 15$\frac{1}{12}$ Paris feet. For the versed sine of that
arc which the moon, in the space of one minute of time, would by its
mean motion describe at the distance of sixty semi-diameters of the
earth, is nearly 15$\frac{1}{12}$ Paris feet, or more accurately
15 feet, 1 inch, 1 line $\frac{4}{9}$. Wherefore, since that force,
in approaching the earth, increases in the reciprocal-duplicate proportion
of the distance, and upon that account, at the surface of the earth,
is 60$\times $60 times greater than at the moon, a body in our regions,
falling with that force, ought in the space of one minute of time
to describe 60$\times $60$\times $15$\frac{1}{12}$ Paris feet;
and in the space of one second of time, to describe 15$\frac{1}{12}$
of those feet, or more accurately, 15 feet, 1 inch, 1 line $\frac{4}{9}$.
And with this very force we actually find that bodies here upon earth
do really descend; for a pendulum oscillating seconds in the latitude
of Paris will be 3 Paris feet, and 8 lines $\frac{1}{2}$ in length,
as Mr.\ Huygens has observed. And the space which a heavy body describes
by falling in one second of time is to half the length of the pendulum
in the duplicate ratio of the circumference of a circle to its diameter
(as Mr.\ Huygens has also shown), and is therefore 15 Paris feet,
1 inch, 1 line $\frac{4}{9}$. And therefore the force by which the
moon is retained in its orbit is that very same force which we commonly
call gravity; for, were gravity another force different from that,
then bodies descending to the earth with the joint impulse of both
forces would fall with a double velocity, and in the space of one
second of time would describe 30$\frac{1}{6}$ Paris feet; altogether
against experience.''%
\footnote{Sir Isaac Newton, \emph{Principia}, translated by Andrew \textit{\emph{Motte}}\emph{,}
\textit{\emph{New}} York, 1848, \textit{\emph{pp}}.\ 391, 392.%
}
\end{quotation}
{}

All this is beautifully clear, and its validity has never in recent
generations been called in question; yet it should be explained that
the argument does not amount to an actually indisputable demonstration.
It is at least possible that the coincidence between the observed
and computed motion of the moon may be a mere coincidence and nothing
more. This probability, however, is so remote that Newton is fully
justified in disregarding it, and, as has been said, all subsequent
generations have accepted the computation as demonstrative.

Let us produce now Newton's further computations as to the other planetary
bodies, passing on to his final conclusion that gravity is a universal
force.

\begin{quotation}
\noindent \noun{\hspace{\stretch{1}}}{}``\textit{\emph{\noun{Proposition}}}
\emph{\noun{V.,}} \textit{\emph{\noun{Theorem}}} \emph{\noun{V.}}\noun{\hspace{\stretch{1}}}

{}``That the circumjovial planets gravitate towards Jupiter; the
circumsaturnal towards Saturn; the circumsolar towards the sun; and
by the forces of their gravity are drawn off from rectilinear motions,
and retained in curvilinear orbits.

{}``For the revolutions of the circumjovial planets about Jupiter,
of the circumsaturnal about Saturn, and of Mercury and Venus and the
other circumsolar planets about the sun, are appearances of the same
sort with the revolution of the moon about the earth; and therefore,
by Rule II., must be owing to the same sort of causes; especially
since it has been demonstrated that the forces upon which those revolutions
depend tend to the centres of Jupiter, of Saturn, and of the sun;
and that those forces, in receding from Jupiter, from Saturn, and
from the sun, decrease in the same proportion, and according to the
same law, as the force of gravity does in receding from the earth.

{}``\textit{\emph{Cor}}.\ 1.---There is, therefore, a power of gravity
tending to all the planets; for doubtless Venus, Mercury, and the
rest are bodies of the same sort with Jupiter and Saturn. And since
all attraction (by Law III.)\ is mutual, Jupiter will therefore gravitate
towards all his own satellites, Saturn towards his, the earth towards
the moon, and the sun towards all the primary planets.

{}``\textit{\emph{Cor}}.\ 2.---The force of gravity which tends
to any one planet is reciprocally as the square of the distance of
places from the planet's centre.

{}``\textit{\emph{Cor}}.\ 3.---All the planets do mutually gravitate
towards one another, by \textit{\emph{Cor}}.\ 1 and 2, and hence
it is that Jupiter and Saturn, when near their conjunction, by their
mutual attractions sensibly disturb each other's motions. So the sun
disturbs the motions of the moon; and both sun and moon disturb our
sea, as we shall hereafter explain.

\noindent \noun{\hspace{\stretch{1}}{}``}\textit{\noun{Scholium}}\noun{\hspace{\stretch{1}}}

{}``The force which retains the celestial bodies in their orbits
has been hitherto called centripetal force; but it being now made
plain that it can be no other than a gravitating force, we shall hereafter
call it gravity. For the cause of the centripetal force which retains
the moon in its orbit will extend itself to all the planets by Rules
I., II., and III.

\noindent \noun{\hspace{\stretch{1}}{}``}\textit{\noun{Proposition}}
\noun{VI.,} \textit{\noun{Theorem}} \noun{VI.\hspace{\stretch{1}}}

{}``That all bodies gravitate towards every planet; and that the
weights of the bodies towards any the same planet, at equal distances
from the centre of the planet, are proportional to the quantities
of matter which they severally contain.

{}``It has been now a long time observed by others that all sorts
of heavy bodies (allowance being made for the inability of retardation
which they suffer from a small power of resistance in the air)\ descend
to the earth \textit{from} \textit{equal} \textit{heights} in equal
times; and that equality of times we may distinguish to a great accuracy
by help of pendulums. I tried the thing in gold, silver, lead, glass,
sand, common salt, wood, water, and wheat. I provided two wooden boxes,
round and equal: I filled the one with wood, and suspended an equal
weight of gold (as exactly as I could)\ in the centre of oscillation
of the other. The boxes hanging by eleven feet, made a couple of pendulums
exactly equal in weight and figure, and equally receiving the resistance
of the air. And, placing the one by the other, I observed them to
play together forward and backward, for a long time, with equal vibrations.
And therefore the quantity of matter in gold was to the quantity of
matter in the wood as the action of the motive force (or \emph{vis
motrix})\ upon all the gold to the action of the same upon all the
wood---that is, as the weight of the one to the weight of the other:
and the like happened in the other bodies. By these experiments, in
bodies of the same weight, I could manifestly have discovered a difference
of matter less than the thousandth part of the whole, had any such
been. But, without all doubt, the nature of gravity towards the planets
is the same as towards the earth. For, should we imagine our terrestrial
bodies removed to the orb of the moon, and there, together with the
moon, deprived of all motion, to be let go, so as to fall together
towards the earth, it is certain, from what we have demonstrated before,
that, in equal times, they would describe equal spaces with the moon,
and of consequence are to the moon, in quantity and matter, as their
weights to its weight.

{}``Moreover, since the satellites of Jupiter perform their revolutions
in times which observe the sesquiplicate proportion of their distances
from Jupiter's centre, their accelerative gravities towards Jupiter
will be reciprocally as the square of their distances from Jupiter's
centre---that is, equal, at equal distances. And, therefore, these
satellites, if supposed to fall \textit{towards} \textit{Jupiter}
from equal heights, would describe equal spaces in equal times, in
like manner as heavy bodies do on our earth. And, by the same argument,
if the circumsolar planets were supposed to be let fall at equal distances
from the sun, they would, in their descent towards the sun, describe
equal spaces in equal times. But forces which equally accelerate unequal
bodies must be as those bodies---that is to say, the weights of the
planets (\textit{towards} \textit{the} \textit{sun}) must be as their
quantities of matter. Further, that the weights of Jupiter and his
satellites towards the sun are proportional to the several quantities
of their matter, appears from the exceedingly regular motions of the
satellites. For if some of these bodies were more strongly attracted
to the sun in proportion to their quantity of matter than others,
the motions of the satellites would be disturbed by that inequality
of attraction. If at equal distances from the sun any satellite, in
proportion to the quantity of its matter, did gravitate towards the
sun with a force greater than Jupiter in proportion to his, according
to any given proportion, suppose $d$ to $e$; then the distance between
the centres of the sun and of the satellite's orbit would be always
greater than the distance between the centres of the sun and of Jupiter
nearly in the subduplicate of that proportion: as by some computations
I have found. And if the satellite did gravitate towards the sun with
a force, lesser in the proportion of $e$ to $d$, the distance of
the centre of the satellite's orb from the sun would be less than
the distance of the centre of Jupiter from the sun in the subduplicate
of the same proportion. Therefore, if at equal distances from the
sun, the accelerative gravity of any satellite towards the sun were
greater or less than the accelerative gravity of Jupiter towards the
sun by one-one-thousandth part of the whole gravity, the distance
of the centre of the satellite's orbit from the sun would be greater
or less than the distance of Jupiter from the sun by one one-two-thousandth
part of the whole distance---that is, by a fifth part of the distance
of the utmost satellite from the centre of Jupiter; an eccentricity
of the orbit which would be very sensible. But the orbits of the satellites
are concentric to Jupiter, and therefore the accelerative gravities
of Jupiter and of all its satellites towards the sun, at equal distances
from the sun, are as their several quantities of matter; and the weights
of the moon and of the earth towards the sun are either none, or accurately
proportional to the masses of matter which they contain.

{}``\textit{\emph{Cor}}.\ 5.---The power of gravity is of a different
nature from the power of magnetism; for the magnetic attraction is
not as the matter attracted. Some bodies are attracted more by the
magnet; others less; most bodies not at all. The power of magnetism
in one and the same body may be increased and diminished; and is sometimes
far stronger, for the quantity of matter, than the power of gravity;
and in receding from the magnet decreases not in the duplicate, but
almost in the triplicate proportion of the distance, as nearly as
I could judge from some rude observations.

\noindent \noun{\hspace{\stretch{1}}{}``}\textit{\noun{Prop.}}
\noun{VII.,} \textit{\noun{Theorem}} \noun{VII.\hspace{\stretch{1}}}

{}``That there is a power of gravity tending to all bodies, proportional
to the several quantities of matter which they contain. That all the
planets mutually gravitate one towards another we have proved before;
as well as that the force of gravity towards every one of them considered
apart, is reciprocally as the square of the distance of places from
the centre of the planet. And thence it follows, that the gravity
tending towards all the planets is proportional to the matter which
they contain.

{}``Moreover, since all the parts of any planet $A$ gravitates towards
any other planet $B$; and the gravity of every part is to the gravity
of the whole as the matter of the part is to the matter of the whole;
and to every action corresponds a reaction; therefore the planet $B$
will, on the other hand, gravitate towards all the parts of planet
$A$, and its gravity towards any one part will be to the gravity
towards the whole as the matter of the part to the matter of the whole.
Q.E.D.

{}``\textit{Hence} \textit{it} \textit{would} \textit{appear} \textit{that}
the force of the whole must arise from the force of the component
parts.''
\end{quotation}
{}

Newton closes this remarkable Book III.\ with the following words:\ 

\begin{quote}
{}``Hitherto we have explained the phenomena of the heavens and of
our sea by the power of gravity, but have not yet assigned the cause
of this power. This is certain, that it must proceed from a cause
that penetrates to the very centre of the sun and planets, without
suffering the least diminution of its force; that operates not according
to the quantity of the surfaces of the particles upon which it acts
(as mechanical causes used to do), but according to the quantity of
solid matter which they contain, and propagates its virtue on all
sides to immense distances, decreasing always in the duplicate proportions
of the distances. Gravitation towards the sun is made up out of the
gravitations towards the several particles of which the body of the
sun is composed; and in receding from the sun decreases accurately
in the duplicate proportion of the distances as far as the orb of
Saturn, as evidently appears from the quiescence of the aphelions
of the planets; nay, and even to the remotest aphelions of the comets,
if those aphelions are also quiescent. But hitherto I have not been
able to discover the cause of those properties of gravity from phenomena,
and I frame no hypothesis; for whatever is not deduced from the phenomena
is to be called an hypothesis; and hypotheses, whether metaphysical
or physical, whether of occult qualities or mechanical, have no place
in experimental philosophy\ldots{}. And to us it is enough that gravity
does really exist, and act according to the laws which we have explained,
and abundantly serves to account for all the motions of the celestial
bodies and of our sea.''%
\footnote{Newton \emph{op.\ cit.}, \textit{\emph{pp}}.\ 506, 507.%
}
\end{quote}
{}

The very magnitude of the importance of the theory of universal gravitation
made its general acceptance a matter of considerable time after the
actual discovery. This opposition had of course been foreseen by Newton,
and, much as be dreaded controversy, he was prepared to face it and
combat it to the bitter end. He knew that his theory was right; it
remained for him to convince the world of its truth. He knew that
some of his contemporary philosophers would accept it at once; others
would at first doubt, question, and dispute, but finally accept; while
still others would doubt and dispute until the end of their days.
This had been the history of other great discoveries; and this will
probably be the history of most great discoveries for all time. But
in this case the discoverer lived to see his theory accepted by practically
all the great minds of his time.

Delambre is authority for the following estimate of Newton by Lagrange.
{}``The celebrated Lagrange,''\ he says, {}``who frequently asserted
that Newton was the greatest genius that ever existed, used to add---`and
the most fortunate, for we cannot find \textit{more} \textit{than}
\textit{once} a system of the world to establish.''' With pardonable
exaggeration the admiring followers of the great generalizer pronounced
this epitaph:\ 

\begin{verse}\footnotesize\ \\

\mbox{``Nature and Nature's laws lay hid in night;}\\*

\mbox{God said `Let Newton be!'and all was light.''}

\end{verse}


\chapter*{\raggedright XIII. INSTRUMENTS OF PRECISION IN THE AGE OF NEWTON}

\addcontentsline{toc}{chapter}{XIII. INSTRUMENTS OF PRECISION IN\\
THE AGE OF NEWTON}

\markboth{A HISTORY OF SCIENCE, VOLUME II}{XIII. INSTRUMENTS OF PRECISION}

During the Newtonian epoch there were numerous important inventions
of scientific instruments, as well as many improvements made upon
the older ones. Some of these discoveries have been referred to briefly
in other places, but their importance in promoting scientific investigation
warrants a fuller treatment of some of the more significant.

Many of the errors that had arisen in various scientific calculations
before the seventeenth century may be ascribed to the crudeness and
inaccuracy in the construction of most scientific instruments. Scientists
had not as yet learned that an approach to absolute accuracy was necessary
in every investigation in the field of science, and that such accuracy
must be extended to the construction of the instruments used in these
investigations and observations. In astronomy it is obvious that instruments
of delicate exactness are most essential; yet Tycho Brahe, who lived
in the sixteenth century, is credited with being the first astronomer
whose instruments show extreme care in construction.

It seems practically settled that the first telescope was invented
in Holland in 1608; but three men, Hans Lippershey, James Metius,
and Zacharias Jansen, have been given the credit of the invention
at different times. It would seem from certain papers, now in the
library of the University of Leyden, and included in Huygens's papers,
that Lippershey was probably the first to invent a telescope and to
describe his invention. The story is told that Lippershey, who was
a spectacle-maker, stumbled by accident upon the discovery that when
two lenses are held at a certain distance apart, objects at a distance
appear nearer and larger. Having made this discovery, be fitted two
lenses with a tube so as to maintain them at the proper distance,
and thus constructed the first telescope.

It was Galileo, however, as referred to in a preceding chapter, who
first constructed a telescope based on his knowledge of the laws of
refraction. In 1609, having heard that an instrument had been invented,
consisting of two lenses fixed in a tube, whereby objects were made
to appear larger and nearer, he set about constructing such an instrument
that should follow out the known effects of refraction. His first
telescope, made of two lenses fixed in a lead pipe, was soon followed
by others of improved types, Galileo devoting much time and labor
to perfecting lenses and correcting errors. In fact, his work in developing
the instrument was so important that the telescope came gradually
to be known as the {}``Galilean telescope.''

In the construction of his telescope Galileo made use of a convex
and a concave lens; but shortly after this Kepler invented an instrument
in which both the lenses used were convex. This telescope gave a much
larger field of view than the Galilean telescope, but did not give
as clear an image, and in consequence did not come into general use
until the middle of the seventeenth century. The first powerful telescope
of this type was made by Huygens and his brother. It was of twelve
feet focal length, and enabled Huygens to discover a new satellite
of Saturn, and to determine also the true explanation of Saturn's
ring.

It was Huygens, together with Malvasia and Auzout, who first applied
the micrometer to the telescope, although the inventor of the first
micrometer was William Gascoigne, of Yorkshire, about 1636. The micrometer
as used in telescopes enables the observer to measure accurately small
angular distances. Before the invention of the telescope such measurements
were limited to the angle that could be distinguished by the naked
eye, and were, of course, only approximately accurate. Even very careful
observers, such as Tycho Brahe, were able to obtain only fairly accurate
results. But by applying Gascoigne's invention to the telescope almost
absolute accuracy became at once possible. The principle of Gascoigne's
micrometer was that of two pointers lying parallel, and in this position
pointing to zero. These were arranged so that the turning of a single
screw separated or approximated them at will, and the angle thus formed
could be determined with absolute accuracy.

Huygens's micrometer was a slip of metal of variable breadth inserted
at the focus of the telescope. By observing at what point this exactly
covered an object under examination, and knowing the focal length
of the telescope and the width of the metal, he could then deduce
the apparent angular breadth of the object. Huygens discovered also
that an object placed in the common focus of the two lenses of a Kepler
telescope appears distinct and clearly defined. The micrometers of
Malvasia, and later of Auzout and Picard, are the development of this
discovery. Malvasia's micrometer, which he described in 1662, consisted
of fine silver wires placed at right-angles at the focus of his telescope.

As telescopes increased in power, however, it was found that even
the finest wire, or silk filaments, were much too thick for astronomical
observations, as they obliterated the image, and so, finally, the
spider-web came into use and is still used in micrometers and other
similar instruments. Before that time, however, the fine crossed wires
had revolutionized astronomical observations. {}``We may judge how
great was the improvement which these contrivances introduced into
the art of observing,''\ says Whewell, {}``by finding that Hevelius
refused to adopt them because they would make all the old observations
of no value. He had spent a laborious and active life in the exercise
of the old methods, and could not bear to think that all the treasures
which he had accumulated had lost their worth by the discovery of
a new mine of richer ones.'' Until the time of Newton, all the telescopes
in use were either of the Galilean or Keplerian type, that is, \textit{\emph{refractors}}.
But about the year 1670 Newton constructed his first reflecting telescope,
which was greatly superior to, although much smaller than, the telescopes
then in use. He was led to this invention by his experiments with
light and colors. In 1671 he presented to the Royal Society a second
and somewhat larger telescope, which he had made; and this type of
instrument was little improved upon until the introduction of the
achromatic telescope, invented by Chester Moor Hall in 1733.

As is generally known, the element of accurate measurements of time
plays an important part in the measurements of the movements of the
heavenly bodies. In fact, one was scarcely possible without the other,
and as it happened it was the same man, Huygens, who perfected Kepler's
telescope and invented the pendulum clock. The general idea had been
suggested by Galileo; or, better perhaps, the equal time occupied
by the successive oscillations of the pendulum had been noted by him.
He had not been able, however, to put this discovery to practical
account. But in 1656 Huygens invented the necessary machinery for
maintaining the motion of the pendulum and perfected several accurate
clocks. These clocks were of invaluable assistance to the astronomers,
affording as they did a means of keeping time {}``more accurate than
the sun itself.'' When Picard had corrected the variation caused
by heat and cold acting upon the pendulum rod by combining metals
of different degrees of expansibility, a high degree of accuracy was
possible.

But while the pendulum clock was an unequalled stationary time-piece,
it was useless in such unstable situations as, for example, on shipboard.
But here again Huygens played a prominent part by first applying the
coiled balance-spring for regulating watches and marine clocks. The
idea of applying a spring to the balance-wheel was not original with
Huygens, however, as it had been first conceived by Robert Hooke;
but Huygens's application made practical Hooke's idea. In England
the importance of securing accurate watches or marine clocks was so
fully appreciated that a reward of \pounds{}20,000 sterling was offered
by Parliament as a stimulus to the inventor of such a time-piece.
The immediate incentive for this offer was the obvious fact that with
such an instrument the determination of the longitude of places would
be much simplified. Encouraged by these offers, a certain carpenter
named Harrison turned his attention to the subject of watch-making,
and, after many years of labor, in 1758 produced a spring time-keeper
which, during a sea-voyage occupying one hundred and sixty-one days,
varied only one minute and five seconds. This gained for Harrison
a reward of \pounds{}5000 sterling at once, and a little later \pounds{}10,000
more, from Parliament.

While inventors were busy with the problem of accurate chronometers,
however, another instrument for taking longitude at sea had been invented.
This was the reflecting quadrant, or sextant, as the improved instrument
is now called, invented by John Hadley in 1731, and independently
by Thomas Godfrey, a poor glazier of Philadelphia, in 1730. Godfrey's
invention, which was constructed on the same principle as that of
the Hadley instrument, was not generally recognized until two years
after Hadley's discovery, although the instrument was finished and
actually in use on a sea-voyage some months before Hadley reported
his invention. The principle of the sextant, however, seems to have
been known to Newton, who constructed an instrument not very unlike
that of Hadley; but this invention was lost sight of until several
years after the philosopher's death and some time after Hadley's invention.

The introduction of the sextant greatly simplified taking reckonings
at sea as well as facilitating taking the correct longitude of distant
places. Before that time the mariner was obliged to depend upon his
compass, a cross-staff, or an astrolabe, a table of the sun's declination
and a correction for the altitude of the polestar, and very inadequate
and incorrect charts. Such were the instruments used by Columbus and
\textit{\emph{Vasco}} \emph{}\textit{\emph{da}} Gama and their immediate
successors.

During the Newtonian period the microscopes generally in use were
those constructed of simple lenses, for although compound microscopes
were known, the difficulties of correcting aberration had not been
surmounted, and a much clearer field was given by the simple instrument.
The results obtained by the use of such instruments, however, were
very satisfactory in many ways. By referring to certain plates in
this volume, which reproduce illustrations from Robert Hooke's work
on the microscope, it will be seen that quite a high degree of effectiveness
had been attained. And it should be recalled that Antony von Leeuwenhoek,
whose death took place shortly before Newton's, had discovered such
micro-organisms as bacteria, had seen the blood corpuscles in circulation,
and examined and described other microscopic structures of the body.


\chapter*{\raggedright XIV. PROGRESS IN ELECTRICITY FROM GILBERT AND VON GUERICKE
TO FRANKLIN}

\addcontentsline{toc}{chapter}{XIV. PROGRESS IN ELECTRICITY FROM\\
GILBERT AND VON GUERICKE TO\\
FRANKLIN}

\markboth{A HISTORY OF SCIENCE, VOLUME II}{XIV. PROGRESS IN ELECTRICITY}

We have seen how Gilbert, by his experiments with magnets, gave an
impetus to the study of magnetism and electricity. Gilbert himself
demonstrated some facts and advanced some theories, but the system
of general laws was to come later. To this end the discovery of electrical
repulsion, as well as attraction, by Von Guericke, with his sulphur
ball, was a step forward; but something like a century passed after
Gilbert's beginning before anything of much importance was done in
the field of electricity.

In 1705, however, Francis Hauksbee began a series of experiments that
resulted in some startling demonstrations. For many years it had been
observed that a peculiar light was seen sometimes in the mercurial
barometer, but Hauksbee and the other scientific investigators supposed
the radiance to be due to the mercury in a vacuum, brought about,
perhaps, by some agitation. That this light might have any connection
with electricity did not, at first, occur to Hauksbee any more than
it had to his predecessors. The problem that interested him was whether
the vacuum in the tube of the barometer was essential to the light;
and in experimenting to determine this, he invented his {}``mercurial
fountain.'' Having exhausted the air in a receiver containing some
mercury, he found that by allowing air to rush through the mercury
the metal became a jet thrown in all directions against the sides
of the vessel, making a great, flaming shower, {}``like flashes of
lightning,''\ as he said. But it seemed to him that there was a
difference between this light and the glow noted in the barometer.
This was a bright light, whereas the barometer light was only a glow.
Pondering over this, Hauksbee tried various experiments, revolving
pieces of amber, flint, steel, and other substances in his exhausted
air-pump receiver, with negative, or unsatisfactory, results. Finally,
it occurred to him to revolve an exhausted glass tube itself. Mounting
such a globe of glass on an axis so that it could be revolved rapidly
by a belt running on a large wheel, he found that by holding his fingers
against the whirling globe a purplish glow appeared, giving sufficient
light so that coarse print could be read, and the walls of a dark
room sensibly lightened several feet away. As air was admitted to
the globe the light gradually diminished, and it seemed to him that
this diminished glow was very similar in appearance to the pale light
seen in the mercurial barometer. Could it be that it was the glass,
and not the mercury, that caused it? Going to a barometer he proceeded
to rub the glass above the column of mercury over the vacuum, without
disturbing the mercury, when, to his astonishment, the same faint
light, to all appearances identical with the glow seen in the whirling
globe, was produced.

Turning these demonstrations over in his mind, he recalled the well-known
fact that rubbed glass attracted bits of paper, leaf-brass, and other
light substances, and that this phenomenon was supposed to be electrical.
This led him finally to determine the hitherto unsuspected fact, that
the glow in the barometer was electrical as was also the glow seen
in his whirling globe. Continuing his investigations, he soon discovered
that solid glass rods when rubbed produced the same effects as the
tube. By mere chance, happening to hold a rubbed tube to his cheek,
he felt the effect of electricity upon the skin like {}``a number
of fine, limber hairs,''\ and this suggested to him that, since
the mysterious manifestation was so plain, it could be made to show
its effects upon various substances. Suspending some woollen threads
over the whirling glass cylinder, he found that as soon as he touched
the glass with his hands the threads, which were waved about by the
wind of the revolution, suddenly straightened themselves in a peculiar
manner, and stood in a radical position, pointing to the axis of the
cylinder.

Encouraged by these successes, he continued his experiments with breathless
expectancy, and soon made another important discovery, that of {}``induction,''\ although
the real significance of this discovery was not appreciated by him
or, for that matter, by any one else for several generations following.
This discovery was made by placing two revolving cylinders within
an inch of each other, one with the air exhausted and the other unexhausted.
Placing his hand on the unexhausted tube caused the light to appear
not only upon it, but on the other tube as well. A little later he
discovered that it is not necessary to whirl the exhausted tube to
produce this effect, but simply to place it in close proximity to
the other whirling cylinder.

These demonstrations of Hauksbee attracted wide attention and gave
an impetus to investigators in the field of electricity; but still
no great advance was made for something like a quarter of a century.
Possibly the energies of the scientists were exhausted for the moment
in exploring the new fields thrown open to investigation by the colossal
work of Newton.


\section*{\raggedright THE EXPERIMENTS OF STEPHEN GRAY}

\addcontentsline{toc}{section}{THE EXPERIMENTS OF STEPHEN\\
GRAY}

In 1729 Stephen Gray (died in 1736), an eccentric and irascible old
pensioner of the Charter House in London, undertook some investigations
along lines similar to those of Hauksbee. While experimenting with
a glass tube for producing electricity, as Hauksbee had done, he noticed
that the corks with which he had stopped the ends of the tube to exclude
the dust, seemed to attract bits of paper and leaf-brass as well as
the glass itself. He surmised at once that this mysterious electricity,
or {}``virtue,''\ as it was called, might be transmitted through
other substances as it seemed to be through glass.

\begin{quote}
{}``Having by me an ivory ball of about one and three-tenths of an
inch in diameter,''\ he writes, {}``with a hole through it, this
I fixed upon a fir-stick about four inches long, thrusting the other
end into the cork, and upon rubbing the tube found that the ball attracted
and repelled the feather with more vigor than the cork had done, repeating
its attractions and repulsions for many times together. I then fixed
the ball on longer sticks, first upon one of eight inches, and afterwards
upon one of twenty-four inches long, and found the effect the same.
Then I made use of iron, and then brass wire, to fix the ball on,
inserting the other end of the wire in the cork, as before, and found
that the attraction was the same as when the fir-sticks were made
use of, and that when the feather was held over against any part of
the wire it was attracted by it; but though it was then nearer the
tube, yet its attraction was not so strong as that of the ball. When
the wire of two or three feet long was used, its vibrations, caused
by the rubbing of the tube, made it somewhat troublesome to be managed.
This put me to thinking whether, if the ball was hung by a pack-thread
and suspended by a loop on the tube, the electricity would not be
carried down the line to the ball; I found it to succeed accordingly;
for upon suspending the ball on the tube by a pack-thread about three
feet long, when the tube had been excited by rubbing, the ivory ball
attracted and repelled the leaf-brass over which it was held as freely
as it had done when it was suspended on sticks or wire, as did also
a ball of cork, and another of lead that weighed one pound and a quarter.''
\end{quote}
{}

Gray next attempted to determine what other bodies would attract the
bits of paper, and for this purpose he tried coins, pieces of metal,
and even a tea-kettle, {}``both empty and filled with hot or cold
water''; but he found that the attractive power appeared to be the
same regardless of the substance used.

\begin{quote}
{}``I next proceeded,''\ he continues, {}``to try at what greater
distances the electric virtues might be carried, and having by me
a hollow walking-cane, which I suppose was part of a fishing-rod,
two feet seven inches long, I cut the great end of it to fit into
the bore of the tube, into which it went about five inches; then when
the cane was put into the end of the tube, and this excited, the cane
drew the leaf-brass to the height of more than two inches, as did
also the ivory ball, when by a cork and stick it had been fixed to
the end of the cane\ldots{}. With several pieces of Spanish cane
and fir-sticks I afterwards made a rod, which, together with the tube,
was somewhat more than eighteen feet long, which was the greatest
length I could conveniently use in my chamber, and found the attraction
very nearly, if not altogether, as strong as when the ball was placed
on the shorter rods.''
\end{quote}
{}

This experiment exhausted the capacity of his small room, but on going
to the country a little later he was able to continue his experiments. 

\begin{quote}
{}``To a pole of eighteen feet there was tied a line of thirty-four
feet in length, so that the pole and line together were fifty-two
feet. With the pole and tube I stood in the balcony, the assistant
below in the court, where he held the board with the leaf-brass on
it. Then the tube being excited, as usual, the electric virtue passed
from the tube up the pole and down the line to the ivory ball, which
attracted the leaf-brass, and as the ball passed over it in its vibrations
the leaf-brass would follow it till it was carried off the board.''
\end{quote}
{}

Gray next attempted to send the electricity over a line suspended
horizontally. To do this he suspended the pack-thread by pieces of
string looped over nails driven into beams for that purpose. But when
thus suspended he found that the ivory ball no longer excited the
leaf-brass, and he guessed correctly that the explanation of this
lay in the fact that {}``when the electric virtue came to the loop
that was suspended on the beam it went up the same to the beam,''\ none
of it reaching the ball. As we shall see from what follows, however,
Gray had not as yet determined that certain substances will conduct
electricity while others will not. But by a lucky accident he made
the discovery that silk, for example, was a poor conductor, and could
be turned to account in insulating the conducting-cord.

A certain Mr.\ Wheler had become much interested in the old pensioner
and his work, and, as a guest at the Wheler house, Gray had been repeating
some of his former experiments with the fishing-rod, line, and ivory
ball. He had finally exhausted the heights from which these experiments
could be made by climbing to the clock-tower and exciting bits of
leaf-brass on the ground below.

\begin{quotation}
{}``As we had no greater heights here,''\ he says, {}``Mr.\ Wheler
was desirous to try whether we could not carry the electric virtue
horizontally. I then told him of the attempt I had made with that
design, but without success, telling him the method and materials
made use of, as mentioned above. He then proposed a silk line to support
the line by which the electric virtue was to pass. I told him it might
do better upon account of its smallness; so that there would be less
virtue carried from the line of communication.

{}``The first experiment was made in the matted gallery, July 2,
1729, about ten in the morning. About four feet from the end of the
gallery there was a cross line that was fixed by its ends to each
side of the gallery by two nails; the middle part of the line was
silk, the rest at each end pack-thread; then the line to which the
ivory ball was hung and by which the electric virtue was to be conveyed
to it from the tube, being eighty and one-half feet in length, was
laid on the cross silk line, so that the ball hung about nine feet
below it. Then the other end of the line was by a loop suspended on
the glass cane, and the leaf-brass held under the ball on a piece
of white paper; when, the tube being rubbed, the ball attracted the
leaf-brass, and kept it suspended on it for some time.''
\end{quotation}
{}

This experiment succeeded so well that the string was lengthened until
it was some two hundred and ninety-three feet long; and still the
attractive force continued, apparently as strong as ever. On lengthening
the string still more, however, the extra weight proved too much for
the strength of the silk suspending-thread. 

\begin{quote}
{}``Upon this,''\ says Gray, {}``having brought with me both brass
and iron wire, instead of the silk we put up small iron wire; but
this was too weak to bear the weight of the line. We then took brass
wire of a somewhat larger size than that of iron. This supported our
line of communication; but though the tube was well rubbed, yet there
was not the least motion or attraction given by the ball, neither
with the great tube, which we made use of when we found the small
solid cane to be ineffectual; by which we were now convinced that
the success we had before depended upon the lines that supported the
line of communication being silk, and not upon their being small,
as before trial I had imagined it might be; the same effect happening
here as it did when the line that is to convey the electric virtue
is supported by pack-thread.''
\end{quote}
{}

Soon after this Gray and his host suspended a pack-thread six hundred
and sixty-six feet long on poles across a field, these poles being
slightly inclined so that the thread could be suspended from the top
by small silk cords, thus securing the necessary insulation. This
pack-thread line, suspended upon poles along which Gray was able to
transmit the electricity, is very suggestive of the modern telegraph,
but the idea of signalling or making use of it for communicating in
any way seems not to have occurred to any one at that time. Even the
successors of Gray who constructed lines some thousands of feet long
made no attempt to use them for anything but experimental purposes---simply
to test the distances that the current could be sent. Nevertheless,
Gray should probably be credited with the discovery of two of the
most important properties of electricity---that it can be conducted
and insulated, although, as we have seen, Gilbert and Von Guericke
had an inkling of both these properties.


\section*{\raggedright EXPERIMENTS OF CISTERNAY DUFAY}

\addcontentsline{toc}{section}{EXPERIMENTS OF CISTERNAY DUFAY}

So far England had produced the two foremost workers in electricity.
It was now France's turn to take a hand, and, through the efforts
of Charles Francois de Cisternay Dufay, to advance the science of
electricity very materially. Dufay was a highly educated savant, who
had been soldier and diplomat betimes, but whose versatility and ability
as a scientist is shown by the fact that he was the only man who had
ever contributed to the annals of the academy investigations in every
one of the six subjects admitted by that institution as worthy of
recognition. Dufay upheld his reputation in this new field of science,
making many discoveries and correcting many mistakes of former observers.
In this work also he proved himself a great diplomat by remaining
on terms of intimate friendship with Dr. Gray---a thing that few people
were able to do.

Almost his first step was to overthrow the belief that certain bodies
are {}``electrics''\ and others {}``non-electrics''---that is,
that some substances when rubbed show certain peculiarities in attracting
pieces of paper and foil which others do not. Dufay proved that all
bodies possess this quality in a certain degree.

\begin{quotation}
{}``I have found that all bodies (metallic, soft, or fluid ones excepted),''\ he
says, {}``may be made electric by first heating them more or less
and then rubbing them on any sort of cloth. So that all kinds of stones,
as well precious as common, all kinds of wood, and, in general, everything
that I have made trial of, became electric by beating and rubbing,
except such bodies as grow soft by beat, as the gums, which dissolve
in water, glue, and such like substances. 'Tis also to be remarked
that the hardest stones or marbles require more chafing or heating
than others, and that the same rule obtains with regard to the woods;
so that box, \emph{lignum vitae}, and such others must be chafed almost
to the degree of browning, whereas fir, lime-tree, and cork require
but a moderate heat.

{}``Having read in one of Mr.\ Gray's letters that water may be
made electrical by holding the excited glass tube near it (a dish
of water being fixed to a stand and that set on a plate of glass,
or on the brim of a drinking-glass, previously chafed, or otherwise
warmed), I have found, upon trial, that the same thing happened to
all bodies without exception, whether solid or fluid, and that for
that purpose 'twas sufficient to set them on a glass stand slightly
warmed, or only dried, and then by bringing the tube near them they
immediately became electrical. I made this experiment with ice, with
a lighted wood-coal, and with everything that came into my mind; and
I constantly remarked that such bodies of themselves as were least
electrical had the greatest degree of electricity communicated to
them at the approval of the glass tube.''
\end{quotation}
{}

His next important discovery was that colors had nothing to do with
the conduction of electricity. 

\begin{quote}
{}``Mr.\ Gray says, towards the end of one of his letters,''\ he
writes, {}``that bodies attract more or less according to their colors.
This led me to make several very singular experiments. I took nine
silk ribbons of equal size, one white, one black, and the other seven
of the seven primitive colors, and having hung them all in order in
the same line, and then bringing the tube near them, the black one
was first attracted, the white one next, and others in order successively
to the red one, which was attracted least, and the last of them all.
I afterwards cut out nine square pieces of gauze of the same colors
with the ribbons, and having put them one after another on a hoop
of wood, with leaf-gold under them, the leaf-gold was attracted through
all the colored pieces of gauze, but not through the white or black.
This inclined me first to think that colors contribute much to electricity,
but three experiments convinced me to the contrary. The first, that
by warming the pieces of gauze neither the black nor white pieces
obstructed the action of the electrical tube more than those of the
other colors. In like manner, the ribbons being warmed, the black
and white are not more strongly attracted than the rest. The second
is, the gauzes and ribbons being wetted, the ribbons are all attracted
equally, and all the pieces of gauze equally intercept the action
of electric bodies. The third is, that the colors of a prism being
thrown on a white gauze, there appear no differences of attraction.
Whence it proceeds that this difference proceeds, not from the color,
as a color, but from the substances that are employed in the dyeing.
For when I colored ribbons by rubbing them with charcoal, carmine,
and such other substances, the differences no longer proved the same.''
\end{quote}
{}

In connection with his experiments with his thread suspended on glass
poles, Dufay noted that a certain amount of the current is lost, being
given off to the surrounding air. He recommended, therefore, that
the cords experimented with be wrapped with some non-conductor---that
it should be {}``insulated'' (\textit{{}``isolee}''), as he said,
first making use of this term.


\section*{\raggedright DUFAY DISCOVERS VITREOUS AND RESINOUS ELECTRICITY}

\addcontentsline{toc}{section}{DUFAY DISCOVERS VITREOUS AND\\
RESINOUS ELECTRICITY}

It has been shown in an earlier chapter how Von Guericke discovered
that light substances like feathers, after being attracted to the
sulphur-ball electric-machine, were repelled by it until they touched
some object. Von Guericke noted this, but failed to explain it satisfactorily.
Dufay, repeating Von Guericke's experiments, found that if, while
the excited tube or sulphur ball is driving the repelled feather before
it, the ball be touched or rubbed anew, the feather comes to it again,
and is repelled alternately, as, the hand touches the ball, or is
withdrawn. From this he concluded that electrified bodies first attract
bodies not electrified, {}``charge''\ them with electricity, and
then repel them, the body so charged not being attracted again until
it has discharged its electricity by touching something.

\begin{quotation}
{}``On making the experiment related by Otto von Guericke,''\ he
says, {}``which consists in making a ball of sulphur rendered electrical
to repel a down feather, I perceived that the same effects were produced
not only by the tube, but by all electric bodies whatsoever, and I
discovered that which accounts for a great part of the irregularities
and, if I may use the term, of the \textit{\emph{caprices}} that seem
to accompany most of the experiments on electricity. This principle
is that electric bodies attract all that are not so, and repel them
as soon as they are become electric by the vicinity or contact of
the electric body. Thus gold-leaf is first attracted by the tube,
and acquires an electricity by approaching it, and of consequence
is immediately repelled by it. Nor is it reattracted while it retains
its electric quality. But if while it is thus sustained in the air
it chance to light on some other body, it straightway loses its electricity,
and in consequence is reattracted by the tube, which, after having
given it a new electricity, repels it a second time, which continues
as long as the tube keeps its electricity. Upon applying this principle
to the various experiments of electricity, one will be surprised at
the number of obscure and puzzling facts that it clears up. For Mr.\ Hauksbee's
famous experiment of the glass globe, in which silk threads are put,
is a necessary consequence of it. When these threads are arranged
in the form of rays by the electricity of the sides of the globe,
if the finger be put near the outside of the globe the silk threads
within fly from it, as is well known, which happens only because the
finger or any other body applied near the glass globe is thereby rendered
electrical, and consequently repels the silk threads which are endowed
with the same quality. With a little reflection we may in the same
manner account for most of the other phenomena, and which seem inexplicable
without attending to this principle.

{}``Chance has thrown in my way another principle, more universal
and remarkable than the preceding one, and which throws a new light
on the subject of electricity. This principle is that there are two
distinct electricities, very different from each other, one of which
I call vitreous electricity and the other resinous electricity. The
first is that of glass, rock-crystal, precious stones, hair of animals,
wool, and many other bodies. The second is that of amber, copal, gumsack,
silk thread, paper, and a number of other substances. The characteristic
of these two electricities is that a body of the vitreous electricity,
for example, repels all such as are of the same electricity, and on
the contrary attracts all those of the resinous electricity; so that
the tube, made electrical, will repel glass, crystal, hair of animals,
\textit{etc}., when rendered electric, and will attract silk thread,
paper, \textit{etc}., though rendered electrical likewise. Amber,
on the contrary, will attract electric glass and other substances
of the same class, and will repel gum-sack, copal, silk thread, \textit{etc}.
Two silk ribbons rendered electrical will repel each other; two woollen
threads will do the like; but a woollen thread and a silken thread
will mutually attract each other. This principle very naturally explains
why the ends of threads of silk or wool recede from each other, in
the form of pencil or broom, when they have acquired an electric quality.
From this principle one may with the same ease deduce the explanation
of a great number of other phenomena; and it is probable that this
truth will lead us to the further discovery of many other things.

{}``In order to know immediately to which of the two classes of electrics
belongs any body whatsoever, one need only render electric a silk
thread, which is known to be of the resinuous electricity, and see
whether that body, rendered electrical, attracts or repels it. If
it attracts it, it is certainly of the kind of electricity which I
call \textit{vitreous}; if, on the contrary, it repels it, it is of
the same kind of electricity with the silk---that is, of the \textit{resinous}.
I have likewise observed that communicated electricity retains the
same properties; for if a ball of ivory or wood be set on a glass
stand, and this ball be rendered electric by the tube, it will repel
such substances as the tube repels; but if it be rendered electric
by applying a cylinder of gum-sack near it, it will produce quite
contrary effects---namely, precisely the same as gum-sack would produce.
In order to succeed in these experiments, it is requisite that the
two bodies which are put near each other, to find out the nature of
their electricity, be rendered as electrical as possible, for if one
of them was not at all or but weakly electrical, it would be attracted
by the other, though it be of that sort that should naturally be repelled
by it. But the experiment will always succeed perfectly well if both
bodies are sufficiently electrical.''%
\footnote{A letter from M.\ Dufay, F.R.S.\ and of the Royal Academy of Sciences
at Paris, \textit{etc}., in the \emph{Phil}. \textit{Trans}.\ of
the Royal Soc., \textit{\emph{vol}}.\ XXXVIII., \textit{\emph{pp}}.\ 258-265.%
}
\end{quotation}
{}

As we now know, Dufay was wrong in supposing that there were two different
kinds of electricity, vitreous and resinous. A little later the matter
was explained by calling one {}``positive'' electricity and the
other {}``negative,''\ and it was believed that certain substances
produced only the one kind peculiar to that particular substance.
We shall see presently, however, that some twenty years later an English
scientist dispelled this illusion by producing both positive (or vitreous)\ and
negative (or resinous)\ electricity on the same tube of glass at
the same time.

After the death of Dufay his work was continued by his fellow-countryman
Dr.\ Joseph Desaguliers, who was the first experimenter to electrify
running water, and who was probably the first to suggest that clouds
might be electrified bodies. But about this time---that is, just before
the middle of the eighteenth century---the field of greatest experimental
activity was transferred to Germany, although both England and France
were still active. The two German philosophers who accomplished most
at this time were Christian August Hansen and George Matthias Bose,
both professors in Leipsic. Both seem to have conceived the idea,
simultaneously and independently, of generating electricity by revolving
globes run by belt and wheel in much the same manner as the apparatus
of Hauksbee.

With such machines it was possible to generate a much greater amount
of electricity than Dufay had been able to do with the rubbed tube,
and so equipped, the two German professors were able to generate electric
sparks and jets of fire in a most startling manner. Bose in particular
had a love for the spectacular, which he turned to account with his
new electrical machine upon many occasions. On one of these occasions
he prepared an elaborate dinner, to which a large number of distinguished
guests were invited. Before the arrival of the company, however, Bose
insulated the great banquet-table on cakes of pitch, and then connected
it with a huge electrical machine concealed in another room. All being
ready, and the guests in their places about to be seated, Bose gave
a secret signal for starting this machine, when, to the astonishment
of the party, flames of fire shot from flowers, dishes, and viands,
giving a most startling but beautiful display.

To add still further to the astonishment of his guests, Bose then
presented a beautiful young lady, to whom each of the young men of
the party was introduced. In some mysterious manner she was insulated
and connected with the concealed electrical machine, so that as each
gallant touched her fingertips he received an electric shock that
{}``made him reel.'' Not content with this, the host invited the
young men to kiss the beautiful maid. But those who were bold enough
to attempt it received an electric shock that nearly {}``knocked
their teeth out,''\ as the professor tells it.


\section*{\raggedright LUDOLFF'S EXPERIMENT WITH THE ELECTRIC SPARK}

\addcontentsline{toc}{section}{LUDOLFF'S EXPERIMENT WITH THE\\
ELECTRIC SPARK}

But Bose was only one of several German scientists who were making
elaborate experiments. While Bose was constructing and experimenting
with his huge machine, another German, Christian Friedrich Ludolff,
demonstrated that electric sparks are actual fire---a fact long suspected
but hitherto unproved. Ludolff's discovery, as it chanced, was made
in the lecture-hall of the reorganized Academy of Sciences at Berlin,
before an audience of scientists and great personages, at the opening
lecture in 1744.

In the course of this lecture on electricity, during which some of
the well-known manifestations of electricity were being shown, it
occurred to Ludolff to attempt to ignite some inflammable fluid by
projecting an electric spark upon its surface with a glass rod. This
idea was suggested to him while performing the familiar experiment
of producing a spark on the surface of a bowl of water by touching
it with a charged glass rod. He announced to his audience the experiment
he was about to attempt, and having warmed a spoonful of sulphuric
ether, he touched its surface with the glass rod, causing it to burst
into flame. This experiment left no room for doubt that the electric
spark was actual fire.

As soon as this experiment of Ludolff's was made known to Bose, he
immediately claimed that he had previously made similar demonstrations
on various inflammable substances, both liquid and solid; and it seems
highly probable that he had done so, as he was constantly experimenting
with the sparks, and must almost certainly have set certain substances
ablaze by accident, if not by intent. At all events, he carried on
a series of experiments along this line to good purpose, finally succeeding
in exploding gun-powder, and so making the first forerunner of the
electric fuses now so universally used in blasting, firing cannon,
and other similar purposes. It was Bose also who, observing some of
the peculiar manifestations in electrified tubes, and noticing their
resemblance to {}``northern lights,''\ was one of the first, if
not the first, to suggest that the \textit{aurora} \textit{borealis}
is of electric origin.

These spectacular demonstrations had the effect of calling public
attention to the fact that electricity is a most wonderful and mysterious
thing, to say the least, and kept both scientists and laymen agog
with expectancy. Bose himself was aflame with excitement, and so determined
in his efforts to produce still stronger electric currents, that he
sacrificed the tube of his twenty-foot telescope for the construction
of a mammoth electrical machine. With this great machine a discharge
of electricity was generated powerful enough to wound the skin when
it happened to strike it.

Until this time electricity had been little more than a plaything
of the scientists---or, at least, no practical use had been made of
it. As it was a practising physician, Gilbert, who first laid the
foundation for experimenting with the new substance, so again it was
a medical man who first attempted to put it to practical use, and
that in the field of his profession. Gottlieb Kruger, a professor
of medicine at Halle in 1743, suggested that electricity might be
of use in some branches of medicine; and the year following Christian
Gottlieb Kratzenstein made a first experiment to determine the effects
of electricity upon the body. He found that {}``the action of the
heart was accelerated, the circulation increased, and that muscles
were made to contract by the discharge'': and he began at once administering
electricity in the treatment of certain diseases. He found that it
acted beneficially in rheumatic affections, and that it was particularly
useful in certain nervous diseases, such as palsies. This was over
a century ago, and to-day about the most important use made of the
particular kind of electricity with which he experimented (the static,
or frictional)\ is for the treatment of diseases affecting the nervous
system.

By the middle of the century a perfect mania for making electrical
machines had spread over Europe, and the whirling, hand-rubbed globes
were gradually replaced by great cylinders rubbed by woollen cloths
or pads, and generating an {}``enormous power of electricity.''
These cylinders were run by belts and foot-treadles, and gave a more
powerful, constant, and satisfactory current than known heretofore.
While making experiments with one of these machines, Johann Heinrichs
Winkler attempted to measure the speed at which electricity travels.
To do this he extended a cord suspended on silk threads, with the
end attached to the machine and the end which was to attract the bits
of gold-leaf near enough together so that the operator could watch
and measure the interval of time that elapsed between the starting
of the current along the cord and its attracting the gold-leaf. The
length of the cord used in this experiment was only a little over
a hundred feet, and this was, of course, entirely inadequate, the
current travelling that space apparently instantaneously.

The improved method of generating electricity that had come into general
use made several of the scientists again turn their attention more
particularly to attempt putting it to some practical account. They
were stimulated to these efforts by the constant reproaches that were
beginning to be heard on all sides that electricity was merely a {}``philosopher's
plaything.'' One of the first to succeed in inventing something that
approached a practical mechanical contrivance was Andrew Gordon, a
Scotch Benedictine monk. He invented an electric bell which would
ring automatically, and a little {}``motor,''\ if it may be so
called. And while neither of these inventions were of any practical
importance in themselves, they were attempts in the right direction,
and were the first ancestors of modern electric bells and motors,
although the principle upon which they worked was entirely different
from modern electrical machines. The motor was simply a wheel with
several protruding metal points around its rim. These points were
arranged to receive an electrical discharge from a frictional machine,
the discharge causing the wheel to rotate. There was very little force
given to this rotation, however, not enough, in fact, to make it possible
to more than barely turn the wheel itself. Two more great discoveries,
galvanism and electro-magnetic induction, were necessary before the
practical motor became possible.

The sober Gordon had a taste for the spectacular almost equal to that
of Bose. It was he who ignited a bowl of alcohol by turning a stream
of electrified water upon it, thus presenting the seeming paradox
of fire produced by a stream of water. Gordon also demonstrated the
power of the electrical discharge by killing small birds and animals
at a distance of two hundred ells, the electricity being conveyed
that distance through small wires.


\section*{\raggedright THE LEYDEN JAR DISCOVERED}

\addcontentsline{toc}{section}{THE LEYDEN JAR DISCOVERED}

As yet no one had discovered that electricity could be stored, or
generated in any way other than by some friction device. But very
soon two experimenters, Dean von Kleist, of Camin, Pomerania, and
\textit{\emph{Pieter}} \emph{}\textit{\emph{van}} Musschenbroek, the
famous teacher of Leyden, apparently independently, made the discovery
of what has been known ever since as the Leyden jar. And although
Musschenbroek is sometimes credited with being the discoverer, there
can be no doubt that Von Kleist's discovery antedated his by a few
months at least.

Von Kleist found that by a device made of a narrow-necked bottle containing
alcohol or mercury, into which an iron nail was inserted, be was able
to retain the charge of electricity, after electrifying this apparatus
with the frictional machine. He made also a similar device, more closely
resembling the modern Leyden jar, from a thermometer tube partly filled
with water and a wire tipped with a ball of lead. With these devices
he found that he could retain the charge of electricity for several
hours, and could produce the usual electrical manifestations, even
to igniting spirits, quite as well as with the frictional machine.
These experiments were first made in October, 1745, and after a month
of further experimenting, Von Kleist sent the following account of
them to several of the leading scientists, among others, Dr.\ Lieberkuhn,
in Berlin, and Dr.\ Kruger, of Halle.

\begin{quotation}
{}``When a nail, or a piece of thick brass wire, is put into a small
apothecary's phial and electrified, remarkable effects follow; but
the phial must be very dry, or warm. I commonly rub it over beforehand
with a finger on which I put some pounded chalk. If a little mercury
or a few drops of spirit of wine be put into it, the experiment succeeds
better. As soon as this phial and nail are removed from the electrifying-glass,
or the prime conductor, to which it has been exposed, is taken away,
it throws out a pencil of flame so long that, with this burning machine
in my hand, I have taken above sixty steps in walking about my room.
When it is electrified strongly, I can take it into another room and
there fire spirits of wine with it. If while it is electrifying I
put my finger, or a piece of gold which I hold in my hand, to the
nail, I receive a shock which stuns my arms and shoulders.

{}``A tin tube, or a man, placed upon electrics, is electrified much
stronger by this means than in the common way. When I present this
phial and nail to a tin tube, which I have, fifteen feet long, nothing
but experience can make a person believe how strongly it is electrified.
I am persuaded,''\ he adds, {}``that in this manner Mr.\ Bose
would not have taken a second electrical kiss. Two thin glasses have
been broken by the shock of it. It appears to me very extraordinary,
that when this phial and nail are in contact with either conducting
or non-conducting matter, the strong shock does not follow. I have
cemented it to wood, metal, glass, sealing-wax, \textit{etc}., when
I have electrified without any great effect. The human body, therefore,
must contribute something to it. This opinion is confirmed by my observing
that unless I hold the phial in my hand I cannot fire spirits of wine
with it.''%
\footnote{Dean von Kleist, in the Danzick Memoirs, Vol.\ I., p.\ 407. From
Joseph Priestley's \emph{History of Electricity}, London, 1775, \textit{\emph{pp}}.\ 83,
84.%
}
\end{quotation}
{}

But it seems that none of the men who saw this account were able to
repeat the experiment and produce the effects claimed by Von Kleist,
and probably for this reason the discovery of the obscure Pomeranian
was for a time lost sight of.

Musschenbroek's discovery was made within a short time after Von Kleist's---in
fact, only a matter of about two months later. But the difference
in the reputations of the two discoverers insured a very different
reception for their discoveries. Musschenbroek was one of the foremost
teachers of Europe, and so widely known that the great universities
vied with each other, and kings were bidding, for his services. Naturally,
any discovery made by such a famous person would soon be heralded
from one end of Europe to the other. And so when this professor of
Leyden made his discovery, the apparatus came to be called the {}``Leyden
jar,''\ for want of a better name. There can be little doubt that
Musschenbroek made his discovery entirely independently of any knowledge
of Von Kleist's, or, for that matter, without ever having heard of
the Pomeranian, and his actions in the matter are entirely honorable.

His discovery was the result of an accident. While experimenting to
determine the strength of electricity he suspended a gun-barrel, which
he charged with electricity from a revolving glass globe. From the
end of the gun-barrel opposite the globe was a brass wire, which extended
into a glass jar partly filled with water. Musschenbroek held in one
hand this jar, while with the other he attempted to draw sparks from
the barrel. Suddenly he received a shock in the hand holding the jar,
that {}``shook him like a stroke of lightning,''\ and for a moment
made him believe that {}``he was done for.'' Continuing his experiments,
nevertheless, he found that if the jar were placed on a piece of metal
on the table, a shock would be received by touching this piece of
metal with one hand and touching the wire with the other---that is,
a path was made for the electrical discharge through the body. This
was practically the same experiment as made by Von Kleist with his
bottle and nail, but carried one step farther, as it showed that the
{}``jar''\ need not necessarily be held in the hand, as believed
by Von Kleist. Further experiments, continued by many philosophers
at the time, revealed what Von Kleist had already pointed out, that
the electrified jar remained charged for some time.

Soon after this Daniel Gralath, wishing to obtain stronger discharges
than could be had from a single Leyden jar, conceived the idea of
combining several jars, thus for the first time grouping the generators
in a {}``battery''\ which produced a discharge strong enough to
kill birds and small animals. He also attempted to measure the strength
of the discharges, but soon gave it up in despair, and the solution
of this problem was left for late nineteenth-century scientists.

The advent of the Leyden jar, which made it possible to produce strong
electrical discharges from a small and comparatively simple device,
was followed by more spectacular demonstrations of various kinds all
over Europe. These exhibitions aroused the interest of the kings and
noblemen, so that electricity no longer remained a {}``plaything
of the philosophers''\ alone, but of kings as well. A favorite demonstration
was that of sending the electrical discharge through long lines of
soldiers linked together by pieces of wire, the discharge causing
them to {}``spring into the air simultaneously''\ in a most astonishing
manner. A certain monk in Paris prepared a most elaborate series of
demonstrations for the amusement of the king, among other things linking
together an entire regiment of nine hundred men, causing them to perform
simultaneous springs and contortions in a manner most amusing to the
royal guests. But not all the experiments being made were of a purely
spectacular character, although most of them accomplished little except
in a negative way. The famous Abbe Nollet, for example, combined useful
experiments with spectacular demonstrations, thus keeping up popular
interest while aiding the cause of scientific electricity.


\section*{\raggedright WILLIAM WATSON}

\addcontentsline{toc}{section}{WILLIAM WATSON}

Naturally, the new discoveries made necessary a new nomenclature,
new words and electrical terms being constantly employed by the various
writers of that day. Among these writers was the English scientist
William Watson, who was not only a most prolific writer but a tireless
investigator. Many of the words coined by him are now obsolete, but
one at least, {}``circuit,''\ still remains in use.

In 1746, a French scientist, \textit{\emph{Louis}} \emph{}\textit{\emph{Guillaume}}
\emph{}\textit{\emph{le}} Monnier, had made a circuit including metal
and water by laying a chain half-way around the edge of a pond, a
man at either end holding it. One of these men dipped his free hand
in the water, the other presenting a Leyden jar to a rod suspended
on a cork float on the water, both men receiving a shock simultaneously.
Watson, a year later, attempted the same experiment on a larger scale.
He laid a wire about twelve hundred feet long across Westminster Bridge
over the Thames, bringing the ends to the water's edge on the opposite
banks, a man at one end holding the wire and touching the water. A
second man on the opposite side held the wire and a Leyden jar; and
a third touched the jar with one hand, while with the other he grasped
a wire that extended into the river. In this way they not only received
the shock, but fired alcohol as readily across the stream as could
be done in the laboratory. In this experiment Watson discovered the
superiority of wire over chain as a conductor, rightly ascribing this
superiority to the continuity of the metal.

Watson continued making similar experiments over longer watercourses,
some of them as long as eight thousand feet, and while engaged in
making one of these he made the discovery so essential to later inventions,
that the earth could be used as part of the circuit in the same manner
as bodies of water. Lengthening his wires he continued his experiments
until a circuit of four miles was made, and still the electricity
seemed to traverse the course instantaneously, and with apparently
undiminished force, if the insulation was perfect.


\section*{\raggedright BENJAMIN FRANKLIN}

\addcontentsline{toc}{section}{BENJAMIN FRANKLIN}

Watson's writings now carried the field of active discovery across
the Atlantic, and for the first time an American scientist appeared---a
scientist who not only rivalled, but excelled, his European contemporaries.
Benjamin Franklin, of Philadelphia, coming into possession of some
of Watson's books, became so interested in the experiments described
in them that he began at once experimenting with electricity. In Watson's
book were given directions for making various experiments, and these
assisted Franklin in repeating the old experiments, and eventually
adding new ones. Associated with Franklin, and equally interested
and enthusiastic, if not equally successful in making discoveries,
were three other men, Thomas Hopkinson, Philip Sing, and Ebenezer
Kinnersley. These men worked together constantly, although it appears
to have been Franklin who made independently the important discoveries,
and formulated the famous Franklinian theory.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2S286}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Benjamin Franklin}\end{center}
\end{figure}
Working steadily, and keeping constantly in touch with the progress
of the European investigators, Franklin soon made some experiments
which he thought demonstrated some hitherto unknown phases of electrical
manifestation. This was the effect of pointed bodies {}``in \textit{drawing}
\textit{off} and \textit{throwing} \textit{off} the electrical fire.''
In his description of this phenomenon, Franklin writes:\ 

\begin{quotation}
{}``Place an iron shot of three or four inches diameter on the mouth
of a clean, dry, glass bottle. By a fine silken thread from the ceiling
right over the mouth of the bottle, suspend a small cork ball, about
the bigness of a marble; the thread of such a length that the cork
ball may rest against the side of the shot. Electrify the shot, and
the ball will be repelled to the distance of four or five inches,
more or less, according to the quantity of electricity. When in this
state, if you present to the shot the point of a long, slender shaft-bodkin,
at six or eight inches distance, the repellency is instantly destroyed,
and the cork flies to the shot. A blunt body must be brought within
an inch, and draw a spark, to produce the same effect.

{}``To prove that the electrical fire is \textit{drawn} \textit{off}
by the point, if you take the blade of the bodkin out of the wooden
handle and fix it in a stick of sealing-wax, and then present it at
the distance aforesaid, or if you bring it very near, no such effect
follows; but sliding one finger along the wax till you touch the blade,
and the ball flies to the shot immediately. If you present the point
in the dark you will see, sometimes at a foot distance, and more,
a light gather upon it like that of a fire-fly or glow-worm; the less
sharp the point, the nearer you must bring it to observe the light;
and at whatever distance you see the light, you may draw off the electrical
fire and destroy the repellency. If a cork ball so suspended be repelled
by the tube, and a point be presented quick to it, though at a considerable
distance, 'tis surprising to see how suddenly it flies back to the
tube. Points of wood will do as well as those of iron, provided the
wood is not dry; for perfectly dry wood will no more conduct electricity
than sealing-wax.

{}``To show that points will \textit{throw} \textit{off} as well
as \textit{draw} \textit{off} the electrical fire, lay a long, sharp
needle upon the shot, and you cannot electrify the shot so as to make
it repel the cork ball. Or fix a needle to the end of a suspended
gun-barrel or iron rod, so as to point beyond it like a little bayonet,
and while it remains there, the gun-barrel or rod cannot, by applying
the tube to the other end, be electrified so as to give a spark, the
fire continually running out silently at the point. In the dark you
may see it make the same appearance as it does in the case before
mentioned.''%
\footnote{Benjamin Franklin, \emph{New Experiments and Observations on Electricity},
London, 1760, \textit{\emph{pp}}.\ 107, 108.%
}
\end{quotation}
{}

Von Guericke, Hauksbee, and Gray had noticed that pointed bodies attracted
electricity in a peculiar manner, but this demonstration of the {}``drawing
off''\ of {}``electrical fire''\ was original with Franklin.
Original also was the theory that he now suggested, which had at least
the merit of being thinkable even by non-philosophical minds. It assumes
that electricity is like a fluid, that will flow along conductors
and accumulate in proper receptacles, very much as ordinary fluids
do. This conception is probably entirely incorrect, but nevertheless
it is likely to remain a popular one, at least outside of scientific
circles, or until something equally tangible is substituted.


\section*{\raggedright FRANKLIN'S THEORY OF ELECTRICITY}

\addcontentsline{toc}{section}{FRANKLIN'S THEORY OF\\
ELECTRICITY}

According to Franklin's theory, electricity exists in all bodies as
a {}``common stock,''\ and tends to seek and remain in a state
of equilibrium, just as fluids naturally tend to seek a level. But
it may, nevertheless, be raised or lowered, and this equilibrium be
thus disturbed. If a body has more electricity than its normal amount
it is said to be \textit{positively} electrified; but if it has less,
it is \textit{negatively} electrified. An over-electrified or {}``plus''
body tends to give its surplus stock to a body containing the normal
amount; while the {}``minus''\ or under-electrified body will draw
electricity from one containing the normal amount.

Working along lines suggested by this theory, Franklin attempted to
show that electricity is not created by friction, but simply collected
from its diversified state, the rubbed glass globe attracting a certain
quantity of {}``electrical fire,''\ but ever ready to give it up
to any body that has less. He explained the charged Leyden jar by
showing that the inner coating of tin-foil received more than the
ordinary quantity of electricity, and in consequence is \textit{positively}
electrified, while the outer coating, having the ordinary quantity
of electricity diminished, is electrified \textit{negatively}.

These studies of the Leyden jar, and the studies of pieces of glass
coated with sheet metal, led Franklin to invent his battery, constructed
of eleven large glass plates coated with sheets of lead. With this
machine, after overcoming some defects, he was able to produce electrical
manifestations of great force---a force that {}``knew no bounds,''\ as
he declared ({}``except in the matter of expense and of labor''),
and which could be made to exceed {}``the greatest known effects
of common lightning.''

This reference to lightning would seem to show Franklin's belief,
even at that time, that lightning is electricity. Many eminent observers,
such as Hauksbee, Wall, Gray, and Nollet, had noticed the resemblance
between electric sparks and lightning, but none of these had more
than surmised that the two might be identical. In 1746, the surgeon,
John Freke, also asserted his belief in this identity. Winkler, shortly
after this time, expressed the same belief, and, assuming that they
were the same, declared that {}``there is no proof that they are
of different natures''; and still he did not prove that they were
the same nature.


\section*{\raggedright FRANKLIN INVENTS THE LIGHTNING-ROD}

\addcontentsline{toc}{section}{FRANKLIN INVENTS THE\\
LIGHTNING-ROD}

Even before Franklin proved conclusively the nature of lightning,
his experiments in drawing off the electric charge with points led
to some practical suggestions which resulted in the invention of the
lightning-rod. In the letter of July, 1750, which he wrote on the
subject, he gave careful instructions as to the way in which these
rods might be constructed. In part Franklin wrote: 

\begin{quotation}
{}``May not the knowledge of this power of points be of use to mankind
in preserving houses, churches, ships, \textit{etc}., from the stroke
of lightning by directing us to fix on the highest parts of the edifices
upright rods of iron made sharp as a needle, and gilt to prevent rusting,
and from the foot of these rods a wire down the outside of the building
into the grounds, or down round one of the shrouds of a ship and down
her side till it reaches the water? Would not these pointed rods probably
draw the electrical fire silently out of a cloud before it came nigh
enough to strike, and thereby secure us from that most sudden and
terrible mischief?

{}``To determine this question, whether the clouds that contain the
lightning are electrified or not, I propose an experiment to be tried
where it may be done conveniently. On the top of some high tower or
steeple, place a kind of sentry-box, big enough to contain a man and
an electrical stand. From the middle of the stand let an iron rod
rise and pass, bending out of the door, and then upright twenty or
thirty feet, pointed very sharp at the end. If the electrical stand
be kept clean and dry, a man standing on it when such clouds are passing
low might be electrified and afford sparks, the rod drawing fire to
him from a cloud. If any danger to the man be apprehended (though
I think there would be none), let him stand on the floor of his box
and now and then bring near to the rod the loop of a wire that has
one end fastened to the leads, he holding it by a wax handle; so the
sparks, if the rod is electrified, will strike from the rod to the
wire and not effect him.''%
\footnote{Franklin, \emph{op.\ cit.,} \textit{\emph{pp}}\emph{.}\ 62, 63.%
}
\end{quotation}
{}

Not satisfied with all the evidence that he had collected pointing
to the identity of lightning and electricity, he adds one more striking
and very suggestive piece of evidence. Lightning was known sometimes
to strike persons blind without killing them. In experimenting on
pigeons and pullets with his electrical machine, Franklin found that
a fowl, when not killed outright, was sometimes rendered blind. The
report of these experiments were incorporated in this famous letter
of the Philadelphia philosopher.

The attitude of the Royal Society towards this clearly stated letter,
with its useful suggestions, must always remain as a blot on the record
of this usually very receptive and liberal-minded body. Far from publishing
it or receiving it at all, they derided the whole matter as too visionary
for discussion by the society. How was it possible that any great
scientific discovery could be made by a self-educated colonial newspaper
editor, who knew nothing of European science except by hearsay, when
all the great scientific minds of Europe had failed to make the discovery?
How indeed! And yet it would seem that if any of the influential members
of the learned society had taken the trouble to read over Franklin's
clearly stated letter, they could hardly have failed to see that his
suggestions were worthy of consideration. But at all events, whether
they did or did not matters little. The fact remains that they refused
to consider the paper seriously at the time; and later on, when its
true value became known, were obliged to acknowledge their error by
a tardy report on the already well-known document.

But if English scientists were cold in their reception of Franklin's
theory and suggestions, the French scientists were not. Buffon, perceiving
at once the importance of some of Franklin's experiments, took steps
to have the famous letter translated into French, and soon not only
the savants, but members of the court and the king himself were intensely
interested. Two scientists, De Lor and D'Alibard, undertook to test
the truth of Franklin's suggestions as to pointed rods {}``drawing
off lightning.'' In a garden near Paris, the latter erected a pointed
iron rod fifty feet high and an inch in diameter. As no thunder-clouds
appeared for several days, a guard was stationed, armed with an insulated
brass wire, who was directed to test the iron rods with it in case
a storm came on during D'Alibard's absence. The storm did come on,
and the guard, not waiting for his employer's arrival, seized the
wire and touched the rod. Instantly there was a report. Sparks flew
and the guard received such a shock that he thought his time had come.
Believing from his outcry that he was mortally hurt, his friends rushed
for a spiritual adviser, who came running through rain and hail to
administer the last rites; but when he found the guard still alive
and uninjured, he turned his visit to account by testing the rod himself
several times, and later writing a report of his experiments to M.\ d'Alibard.
This scientist at once reported the affair to the French Academy,
remarking that {}``Franklin's idea was no longer a conjecture, but
a reality.''


\section*{\raggedright FRANKLIN PROVES THAT LIGHTNING IS ELECTRICITY}

\addcontentsline{toc}{section}{FRANKLIN PROVES THAT\\
LIGHTNING IS ELECTRICITY}

Europe, hitherto somewhat sceptical of Franklin's views, was by this
time convinced of the identity of lightning and electricity. It was
now Franklin's turn to be sceptical. To him the fact that a rod, one
hundred feet high, became electrified during a storm did not necessarily
prove that the storm-clouds were electrified. A rod of that length
was not really projected into the cloud, for even a very low thunder-cloud
was more than a hundred feet above the ground. Irrefutable proof could
only be had, as he saw it, by {}``extracting''\ the lightning with
something actually sent up into the storm-cloud; and to accomplish
this Franklin made his silk kite, with which he finally demonstrated
to his own and the world's satisfaction that his theory was correct.

Taking his kite out into an open common on the approach of a thunder-storm,
he flew it well up into the threatening clouds, and then, touching,
the suspended key with his knuckle, received the electric spark; and
a little later he charged a Leyden jar from the electricity drawn
from the clouds with his kite.

In a brief but direct letter, he sent an account of his kite and his
experiment to England:\ 

\begin{quote}
{}``Make a small cross of two light strips of cedar,''\ he wrote,
{}``the arms so long as to reach to the four corners of a large,
thin, silk handkerchief when extended; tie the corners of the handkerchief
to the extremities of the cross so you have the body of a kite; which
being properly accommodated with a tail, loop, and string, will rise
in the air like those made of paper; but this being of silk is fitter
to bear the wind and wet of a thunder-gust without tearing. To the
top of the upright stick of the cross is to be fixed a very sharp-pointed
wire, rising a foot or more above the wood. To the end of the twine,
next the hand, is to be tied a silk ribbon; where the silk and twine
join a key may be fastened. This kite is to be raised when a thunder-gust
appears to be coming on, and the person who holds the string must
stand within a door or window or under some cover, so that the silk
ribbon may not be wet; and care must be taken that the twine does
not touch the frame of the door or window. As soon as any of the thunder-clouds
come over the kite, the pointed wire will draw the electric fire from
them, and the kite, with all the twine, will be electrified and the
loose filaments will stand out everywhere and be attracted by the
approaching finger, and when the rain has wet the kite and twine so
that it can conduct the electric fire freely, you will find it stream
out plentifully from the key on the approach of your knuckle, and
with this key the phial may be charged; and from electric fire thus
obtained spirits may be kindled and all other electric experiments
performed which are usually done by the help of a rubbed glass globe
or tube, and thereby the sameness of the electric matter with that
of lightning completely demonstrated.''%
\footnote{Franklin, \emph{op.\ cit.,} \textit{\emph{pp}}.\ 107, 108.%
}
\end{quote}
{}

In experimenting with lightning and Franklin's pointed rods in Europe,
several scientists received severe shocks, in one case with a fatal
result. Professor Richman, of St.\ Petersburg, while experimenting
during a thunder-storm, with an iron rod which he had erected on his
house, received a shock that killed him instantly.

About 1733, as we have seen, Dufay had demonstrated that there were
two apparently different kinds of electricity; one called \textit{vitreous}
because produced by rubbing glass, and the other \textit{resinous}
because produced by rubbed resinous bodies. Dufay supposed that these
two apparently different electricities could only be produced by their
respective substances; but twenty years later, John Canton (1715-1772),
an Englishman, demonstrated that under certain conditions both might
be produced by rubbing the same substance. Canton's experiment, made
upon a glass tube with a roughened surface, proved that if the surface
of the tube were rubbed with oiled silk, vitreous or positive electricity
was produced, but if rubbed with flannel, resinous electricity was
produced. He discovered still further that both kinds could be excited
on the same tube simultaneously with a single rubber. To demonstrate
this he used a tube, one-half of which had a roughened the other a
glazed surface. With a single stroke of the rubber he was able to
excite both kinds of electricity on this tube. He found also that
certain substances, such as glass and amber, were electrified positively
when taken out of mercury, and this led to his important discovery
that an amalgam of mercury and tin, when used on the surface of the
rubber, was very effective in exciting glass.


\chapter*{\raggedright XV. NATURAL HISTORY TO THE TIME OF LINN\AE{}US}

\addcontentsline{toc}{chapter}{XV. NATURAL HISTORY TO THE TIME\\
OF LINN\AE{}US}

\markboth{A HISTORY OF SCIENCE, VOLUME II}{XV. NATURAL HISTORY}

Modern systematic botany and zoology are usually held to have their
beginnings with Linn\ae{}us. But there were certain precursors of
the famous Swedish naturalist, some of them antedating him by more
than a century, whose work must not be altogether ignored---such men
as Konrad Gesner (1516-1565), Andreas C\ae{}salpinus (1579-1603),
Francisco Redi (1618-1676), Giovanni Alfonso Borelli (1608-1679),
John Ray (1628-1705), Robert Hooke (1635-1703), John Swammerdam (1637-1680),
Marcello Malpighi (1628-1694), Nehemiah Grew (1628-1711), Joseph Tournefort
(1656-1708), Rudolf Jacob \textit{\emph{Camerarius}} (1665-1721),
and Stephen Hales (1677-1761). The last named of these was, to be
sure, a contemporary of Linn\ae{}us himself, but Gesner and C\ae{}salpinus
belong, it will be observed, to so remote an epoch as that of Copernicus.

Reference has been made in an earlier chapter to the microscopic investigations
of Marcello Malpighi, who, as there related, was the first observer
who actually saw blood corpuscles pass through the capillaries. Another
feat of this earliest of great microscopists was to dissect muscular
tissue, and thus become the father of microscopic anatomy. But Malpighi
did not confine his observations to animal tissues. He dissected plants
as well, and he is almost as fully entitled to be called the father
of vegetable anatomy, though here his honors are shared by the Englishman
Grew. In 1681, while Malpighi's work, \textit{Anatomia} \emph{Plantarum},
was on its way to the Royal Society for publication, Grew's \emph{Anatomy
of Vegetables} was in the hands of the publishers, making its appearance
a few months earlier than the work of the great Italian. Grew's book
was epoch-marking in pointing out the sex-differences in plants.

Robert Hooke developed the microscope, and took the first steps towards
studying vegetable anatomy, publishing in 1667, among other results,
the discovery of the cellular structure of cork. Hooke applied the
name {}``cell''\ for the first time in this connection. These discoveries
of Hooke, Malpighi, and Grew, and the discovery of the circulation
of the blood by William Harvey shortly before, had called attention
to the similarity of animal and vegetable structures. Hales made a
series of investigations upon animals to determine the force of the
blood pressure; and similarly he made numerous statical experiments
to determine the pressure of the flow of sap in vegetables. His \emph{Vegetable
Statics}, published in 1727, was the first important work on the subject
of vegetable physiology, and for this reason Hales has been called
the father of this branch of science.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth,
  height=0.90\paperwidth,
  keepaspectratio]{2hsci10-Wil2S298}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Stephen Hales's Experiment
to Determine the Pressure of the Flow of Sap}\end{center}{\small \par}

\noindent \emph{\footnotesize (A branch, $b$, has been cut off and
an open glass tube fitted over the end, the pressure being indicated
by the rise of sap in the tube) }
\end{figure}
In botany, as well as in zoology, the classifications of Linn\ae{}us
of course supplanted all preceding classifications, for the obvious
reason that they were much more satisfactory; but his work was a culmination
of many similar and more or less satisfactory attempts of his predecessors.
About the year 1670 Dr.\ Robert Morison (1620-1683), of Aberdeen,
published a classification of plants, his system taking into account
the woody or herbaceous structure, as well as the flowers and fruit.
This classification was supplanted twelve years later by the classification
of Ray, who arranged all known vegetables into thirty-three classes,
the basis of this classification being the fruit. A few years later
Rivinus, a professor of botany in the University of Leipzig, made
still another classification, determining the distinguishing character
chiefly from the flower, and \textit{\emph{Camerarius}} and Tournefort
also made elaborate classifications. On the Continent Tournefort's
classification was the most popular until the time of Linn\ae{}us,
his systematic arrangement including about eight thousand species
of plants, arranged chiefly according to the form of the corolla.

Most of these early workers gave attention to both vegetable and animal
kingdoms. They were called naturalists, and the field of their investigations
was spoken of as {}``natural history.'' The specialization of knowledge
had not reached that later stage in which botanist, zoologist, and
physiologist felt their labors to be sharply divided. Such a division
was becoming more and more necessary as the field of knowledge extended;
but it did not become imperative until long after the time of Linn\ae{}us.
That naturalist himself, as we shall see, was equally distinguished
as botanist and as zoologist. His great task of organizing knowledge
was applied to the entire range of living things.

Carolus Linn\ae{}us was born in the town of Rashult, in Sweden, on
May 13, 1707. As a child he showed great aptitude in learning botanical
names, and remembering facts about various plants as told him by his
father. His eagerness for knowledge did not extend to the ordinary
primary studies, however, and, aside from the single exception of
the study of physiology, he proved himself an indifferent pupil. His
backwardness was a sore trial to his father, who was desirous that
his son should enter the ministry; but as the young Linn\ae{}us showed
no liking for that calling, and as he had acquitted himself well in
his study of physiology, his father at last decided to allow him to
take up the study of medicine. Here at last was a field more to the
liking of the boy, who soon vied with the best of his fellow-students
for first honors. Meanwhile he kept steadily at work in his study
of natural history, acquiring considerable knowledge of ornithology,
entomology, and botany, and adding continually to his collection of
botanical specimens. In 1729 his botanical knowledge was brought to
the attention of Olaf Rudbeck, professor of botany in the University
of Upsala, by a short paper on the sexes of plants which Linn\ae{}us
had prepared. Rudbeck was so impressed by some of the ideas expressed
in this paper that he appointed the author as his assistant the following
year.

This was the beginning of Linn\ae{}us's career as a botanist. The
academic gardens were thus thrown open to him, and he found time at
his disposal for pursuing his studies between lecture hours and in
the evenings. It was at this time that he began the preparation of
his work the \emph{Systema} \textit{Naturae}, the first of his great
works, containing a comprehensive sketch of the whole field of natural
history. When this work was published, the clearness of the views
expressed and the systematic arrangement of the various classifications
excited great astonishment and admiration, and placed Linn\ae{}us
at once in the foremost rank of naturalists. This work was followed
shortly by other publications, mostly on botanical subjects, in which,
among other things, he worked out in detail his famous {}``system.''

This system is founded on the sexes of plants, and is usually referred
to as an {}``artificial method''\ of classification because it
takes into account only a few marked characters of plants, without
uniting them by more general natural affinities. At the present time
it is considered only as a stepping-stone to the {}``natural''\ system;
but at the time of its promulgation it was epoch-marking in its directness
and simplicity, and therefore superiority, over any existing systems.

One of the great reforms effected by Linn\ae{}us was in the matter
of scientific terminology. Technical terms are absolutely necessary
to scientific progress, and particularly so in botany, where obscurity,
ambiguity, or prolixity in descriptions are fatally misleading. Linn\ae{}us's
work contains something like a thousand terms, whose meanings and
uses are carefully explained. Such an array seems at first glance
arbitrary and unnecessary, but the fact that it has remained in use
for something like two centuries is indisputable evidence of its practicality.
The descriptive language of botany, as employed by Linn\ae{}us, still
stands as a model for all other subjects.

%
\begin{figure}
\noindent \begin{center}\noun{\small \includegraphics[  width=1.0\columnwidth]{2hsci10-Wil2S302}}\end{center}{\small \par}

\noindent \begin{center}\noun{\small Carolus Linn\ae{}us}\end{center}
\end{figure}
Closely allied to botanical terminology is the subject of botanical
nomenclature. The old method of using a number of Latin words to describe
each different plant is obviously too cumbersome, and several attempts
had been made prior to the time of Linn\ae{}us to substitute simpler
methods. Linn\ae{}us himself made several unsatisfactory attempts
before he finally hit upon his system of {}``trivial names,''\ which
was developed in his \emph{Species Plantarum}, and which, with some,
minor alterations, remains in use to this day. The essence of the
system is the introduction of binomial nomenclature---that is to say,
the use of two names and no more to designate any single species of
animal or plant. The principle is quite the same as that according
to which in modern society a man has two names, let us say, John Doe,
the one designating his family, the other being individual. Similarly
each species of animal or plant, according to the Linn\ae{}ean system,
received a specific or {}``trivial''\ name; while various species,
associated according to their seeming natural affinities into groups
called genera, were given the same generic name. Thus the generic
name given all members of the cat tribe being \textit{Felis}, the
name \textit{Felis} \textit{leo} designates the lion; \textit{Felis}
\textit{pardus}, the leopard; \textit{Felis} \textit{domestica}, the
house cat, and so on. This seems perfectly simple and natural now,
but to understand how great a reform the binomial nomenclature introduced
we have but to consult the work of Linn\ae{}us's predecessors. A
single illustration will suffice. There is, for example, a kind of
grass, in referring to which the naturalist anterior to Linn\ae{}us,
if he would be absolutely unambiguous, was obliged to use the following
descriptive formula: \textit{Gramen} \emph{Xerampelino}, \emph{Miliacea,
pr}\ae{}\emph{tenuis ramosaque sparsa} \textit{panicula}, \textit{sive}
\emph{Xerampelino congener, arvense,} \ae{}\textit{stivum}; \textit{gramen}
\textit{minutissimo} \emph{semine}. Linn\ae{}us gave to this plant
the name \emph{Poa} \textit{bulbosa}---a name that sufficed, according
to the new system, to distinguish this from every other species of
vegetable. It does not require any special knowledge to appreciate
the advantage of such a simplification.

While visiting Paris in 1738 Linn\ae{}us met and botanized with the
two botanists whose {}``natural method''\ of classification was
later to supplant his own {}``artificial system.'' These were Bernard
and Antoine Laurent de Jussieu. The efforts of these two scientists
were directed towards obtaining a system which should aim at clearness,
simplicity, and precision, and at the same time be governed by the
natural affinities of plants. The natural system, as finally propounded
by them, is based on the number of cotyledons, the structure of the
seed, and the insertion of the stamens. Succeeding writers on botany
have made various modifications of this system, but nevertheless it
stands as the foundation-stone of modern botanical classification.
\end{document}
