Title: A History of Science — Volume 2
Author: Williams, Henry Smith, 1863-1943, Williams, Edward Huntington, 1868-1944
Language: English
As this book started as an ASCII text book there are no pictures available.


*** Start of this LibraryBlog Digital Book "A History of Science — Volume 2" ***


A HISTORY OF SCIENCE

BY HENRY SMITH WILLIAMS, M.D., LL.D.

ASSISTED BY EDWARD H. WILLIAMS, M.D.

IN FIVE VOLUMES

VOLUME II.



CONTENTS

   BOOK II

   CHAPTER I. SCIENCE IN THE DARK AGE

   CHAPTER II. MEDIAEVAL SCIENCE AMONG THE ARABIANS

   CHAPTER III. MEDIAEVAL SCIENCE IN THE WEST

   CHAPTER IV. THE NEW COSMOLOGY--COPERNICUS TO KEPLER AND GALILEO

   CHAPTER V. GALILEO AND THE NEW PHYSICS

   CHAPTER VI. TWO PSEUDO-SCIENCES--ALCHEMY AND ASTROLOGY

   CHAPTER VII. FROM PARACELSUS TO HARVEY

   CHAPTER VIII. MEDICINE IN THE SIXTEENTH AND SEVENTEENTH CENTURIES

   CHAPTER IX. PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS OF
   LEARNING

   CHAPTER X. THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE

   CHAPTER XI. NEWTON AND THE COMPOSITION OF LIGHT

   CHAPTER XII. NEWTON AND THE LAW OF GRAVITATION

   CHAPTER XIII. INSTRUMENTS OF PRECISION IN THE AGE OF NEWTON

   CHAPTER XIV. PROGRESS IN ELECTRICITY FROM GILBERT AND VON
   GUERICKE TO FRANKLIN

   CHAPTER XV. NATURAL HISTORY TO THE TIME OF LINNAEUS

   APPENDIX



A HISTORY OF SCIENCE



BOOK II. THE BEGINNINGS OF MODERN SCIENCE

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 Linnaean
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.



I. SCIENCE IN THE DARK AGE

An obvious distinction between the classical and mediaeval 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, bad 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(1) 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 mediaeval 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 mediaeval thought.
Instead of investigating natural laws, they paid heed (as, for example,
Thomas Aquinas does in his Summa 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,(2) 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 archaeological 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 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 Greek Anthology and the famous
anthologies of Stobaeus and Athanasius and Eusebius give us glimpses
of a host of writers--more than seven hundred are quoted by Stobaeus--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 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 mediaeval
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 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 bad 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.



II. MEDIAEVAL SCIENCE AMONG THE ARABIANS

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 al-Mamun, the son of the famous Harun-al-Rashid. Both father
and son were famous for their interest in science. Harun-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 ben Jabir
Albategnius, or El-batani, who was born at 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
degrees, but Albategnius found it in longitude 82 degrees, 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
II. of Sicily--the "Wonder of the World," as he was called by his
contemporaries. The 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 mediaeval 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.

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, tinder 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.


ARABIAN MEDICINE

The influence of Arabian physicians rested chiefly upon their use
of drugs rather than upon anatomical knowledge. Like the mediaeval
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 pharmacopoeia,
issued from the hospital at Gondisapor, and elaborated from time to
time, formed the basis for Western pharmacopoeias. 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 mediaeval 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 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 Harets ben Kaladah, who
received his education in the Nestonian school at Gondisapor, about the
beginning of the seventh century. Notwithstanding the fact that 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 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 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 encyclopaedia of medicine, called 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 materia 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 mediaeval 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.


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 pharmacopoeia, 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 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.



III. MEDIAEVAL SCIENCE IN THE WEST

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 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 polypi in the air-passages, and gives the
method of their removal. Such operations as tracheotomy, tonsillotomy,
bronchotomy, staphylotomy, 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.


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 mediaeval 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
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 anaesthetic 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 anaesthetic,
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 anaesthetic. 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 anaesthetized and to have recovered, after a painless
amputation had been performed by the surgeons.

Peter of 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 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 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 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 Ages 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
dissections were occasionally sanctioned by the ruling monarch. Thus
Emperor Frederick H. (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 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 be 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.


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 Celsus, the 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 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 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 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 Practica
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.


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 mediaeval 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.


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 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 virtus, species, imago,
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.


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 Regio 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 Leonardo da
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,(1) 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, "Il sole non si mouve"--the sun does
not move.(2)

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 Institut de France,
Da 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.

It is believed that Leonardo is the true discoverer of the
camera-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 Da 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 Da 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 bad 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.



IV. THE NEW COSMOLOGY--COPERNICUS TO KEPLER AND GALILEO

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,
Nikolaus of Cusa, who lived in the first half of the fifteenth century,
and was distinguished as a philosophical writer and mathematician. His
De Docta 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.

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 De Orbium Coelestium 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.

"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."


In chapter X. of book I., "On the Order of the Spheres," occurs a more
detailed presentation of the system, as follows:

"That which Martianus Capella, 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."(1)


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
Leonardo da Vinci anticipated Maestlin in this regard.(2)

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 mediaeval 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.

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.


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 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 Caesar, 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 Caesar, 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.

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 Mysterium
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."(3)

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.

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.


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 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.

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 camera-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.

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:

"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, 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(4) 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, 'Frustra fit per plura, quod potest fieri per p auciora' (It is
vain to expend many means where a few are sufficient)."(2)


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, "E pur si 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 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.



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 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 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 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 Principia 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.(1) 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 bad 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."(2) 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.


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.


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.

"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."(3)

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.


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, De 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."(4)

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."(5)

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 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."(6)

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 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 degrees at London; eight years later Hudson found the
dip at 75 degrees 22' north latitude to be 89 degrees 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 degrees 5' north
latitude, and 96 degrees 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, lac 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."


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 degrees 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 valies 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 Accademia del 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.


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.

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 Gilles 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.



VI. TWO PSEUDO-SCIENCES--ALCHEMY AND ASTROLOGY

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 mediaeval 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.(1) 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
mediaeval 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.

"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!'"(2)

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, lie
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
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, 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
mediaeval 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 II., and Frederick 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 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
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 mediaeval 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, discovered 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."' 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.


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."(4) 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 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 II., who, for his extraction, may be said to be
of the best blood of the world."(5)

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 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.
Sueno, King of Denmark, at a great Feast, killeth Canutus: 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, 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
Oppressions in Church or Common-wealth;... Those words are general: a
word for my own country of England.... 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."(6)

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, etc.,... it
premonisheth you... to make your peace with God.... Look to yourselves;
here's some monstrous death towards you.... 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... 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.... 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."(7)

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:

"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 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."(8)

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 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.



VII. FROM PARACELSUS TO HARVEY

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, Pfeffers, Augsburg, 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 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.... 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.... I will show and open to you... this corporeal
regeneration."(1)

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
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 archaeus, or alchemist, whose duty was to make this
separation. In digestive disorders the archaeus 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 elixirs which may restore to man the health and
soundness he has lost."


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 France human 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 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 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!"(2)

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.


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.

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 foetus
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 foetus, and the opening in
the adult heart, rather than the reverse. From all this Harvey drew his
correct conclusions, declaring earnestly, "By Hercules, there 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."(3)

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 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 vena cava enters
the heart at an inferior portion, while the artery passes out above. Now
if the vena 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."(4)

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.

"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 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, 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 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."(5)


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.


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.



VIII. MEDICINE IN THE SIXTEENTH AND SEVENTEENTH CENTURIES

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 II., Francis
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, "Je
le pansay, Dieu le 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 lithotomist--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 bad 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 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 archaeus of
Paracelsus, and added many complications to it. He believed the whole
body to be controlled by an archaeus influus, the soul by the archaei
insiti, and these in turn controlled by the central archeus. 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
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;
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 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!


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."(1) 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."(2) 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 pharmacopoeias. 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.



IX. PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS OF LEARNING

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.

"The opinion of Aristotle," he says, in his 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."(1)

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."(2)

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 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 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.

Having once conceived this idea, Descartes began a series of 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."(3)

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 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.

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.


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 mediaeval 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 Accademia del 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 system 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 bad become
more settled, these two bodies of men were united under a charter
from Charles 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 Academia 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 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. 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 Linnaeus. 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.



X. THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE

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.


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.(1)

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."(2)

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."(3) 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."(4) 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.

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."(5)

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."(6)

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."(7) 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 bad 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."(8)


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 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.

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 weight the air and note the changes that preceded storms and calms,
he was able still further to dumfound his wondering fellow-Magde-burgers
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, 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, etc."(9)
Before the time of Guericke's demonstrations, Cabaeus 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 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.


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 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.

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 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.


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.

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, 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 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."(10)


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.... 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.... 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...."

From 1665 to 1681, accepting the tempting offer made him through
Colbert, by Louis XIV., Huygens pursued his studies at the Bibliotheque
du Roi as a resident of France. Here he published his 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
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 Traite
de la 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.



XI. NEWTON AND 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.


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 refracting
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. "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 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 1/4 inches; its breadth 2 5/8; the diameter of the hole 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 degrees 56'; and the vertical angle of the prism, 63
degrees 12'. Also the 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 degrees 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 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 degrees 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 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 degrees 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
degrees or 5 degrees, 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 degrees 49'."

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.

"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
experimentum 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 LIGHT
consists of RAYS DIFFERENTLY 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."(1)


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:

"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."(2)

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."(3)



XII. NEWTON AND 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.

{illustration caption = DIAGRAM TO ILLUSTRATE NEWTON'S LAW OF
GRAVITATION (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.)}

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
Principia is as follows:

"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 syzygies
in semi-diameters of the earth, is, according to Ptolemy and most
astronomers, 59; according to Vendelin and Huygens, 60; to Copernicus,
60 1/3; to Street, 60 2/3; and to Tycho, 56 1/2. But Tycho, and all that
follow his tables of refractions, making the refractions of the sun and
moon (altogether against the nature of light) to exceed the refractions
of the fixed stars, and that by four or five minutes NEAR THE HORIZON,
did thereby increase the moon's 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 1/2
semi-diameters of the earth, near to what others have assigned. Let us
assume the mean distance of 60 diameters in the 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 Cor. Prop. iii.) it is
retained in its orb, it will in the space of one minute of time describe
in its fall 15 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 1/12 Paris feet, or more accurately 15 feet, 1 inch, 1 line 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 x 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 x 60 x 15 1/12 Paris feet; and in the
space of one second of time, to describe 15 1/12 of those feet, or more
accurately, 15 feet, 1 inch, 1 line 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 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 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 1/6 Paris feet;
altogether against experience."(1)

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.

          "PROPOSITION V., THEOREM V.

"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.

"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.

"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.

"COR. 3.--All the planets do mutually gravitate towards one another, by
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.

          "SCHOLIUM

"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.

          "PROPOSITION VI., THEOREM VI.

"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
FROM EQUAL 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 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 TOWARDS 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 (TOWARDS THE
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.

"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.

          "PROPOSITION VII., THEOREM VII.

"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.


"HENCE IT WOULD APPEAR THAT the force of the whole must arise from the
force of the component parts."


Newton closes this remarkable Book iii. with the following words:

"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.... 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."(2)


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 he 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 MORE THAN ONCE a system of the world to
establish.'" With pardonable exaggeration the admiring followers of the
great generalizer pronounced this epitaph:

 "Nature and Nature's laws lay hid in night;
  God said 'Let Newton be!' and all was light."



XIII. INSTRUMENTS OF PRECISION IN THE AGE OF NEWTON

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, he 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."(1)

Until the time of Newton, all the telescopes in use were either of the
Galilean or Keplerian type, that is, 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 L20,000 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 L5000 sterling at
once, and a little later L10,000 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 Vasco 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.



XIV. PROGRESS IN ELECTRICITY FROM GILBERT AND VON GUERICKE TO FRANKLIN

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.


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.

"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."

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.

"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.... 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."

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.
"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."

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.

"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."

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. "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."

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.


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.

"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,
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."

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

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" ("isolee"), as he said, first making use of this
term.


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.

"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 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,
etc., when rendered electric, and will attract silk thread, paper,
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, 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
VITREOUS; if, on the contrary, it repels it, it is of the same kind of
electricity with the silk--that is, of the 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."(1)

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.


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 aurora 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.


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 Pieter 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, he
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.

"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, 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."(2)

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.


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, Louis Guillaume le Monnier, bad 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.


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.

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 DRAWING OFF
and THROWING OFF the electrical fire." In his description of this
phenomenon, Franklin writes:

"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 DRAWN 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 THROW OFF as well as DRAW 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."(3)

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.


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 POSITIVELY
electrified; but if it has less, it is 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 POSITIVELY electrified, while the
outer coating, having the ordinary quantity of electricity diminished,
is electrified 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 know 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.


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: "May not the knowledge
of this power of points be of use to mankind in preserving houses,
churches, ships, 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."(4)

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."


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:

"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."(5)

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 VITREOUS because
produced by rubbing glass, and the other 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.



XV. NATURAL HISTORY TO THE TIME OF LINNAEUS

Modern systematic botany and zoology are usually held to have their
beginnings with Linnaeus. 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 Caesalpinus (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 Camerarius (1665-1721), and Stephen Hales (1677-1761). The
last named of these was, to be sure, a contemporary of Linnaeus himself,
but Gesner and Caesalpinus 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, Anatomia
plantarum, was on its way to the Royal Society for publication, Grew's
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 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.

In botany, as well as in zoology, the classifications of Linnaeus 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 Camerarius and Tournefort also made elaborate
classifications. On the Continent Tournefort's classification was the
most popular until the time of Linnaeus, 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 Linnaeus. 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 Linnaeus 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 Linnaeus 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 Linnaeus 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 Linnaes'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 Systema
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 Linaeus 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 Linnaeus 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.
Linnaeus'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
Linnaeus, still stands as a model for all other subjects.

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 Linnaeus to substitute
simpler methods. Linnaeus himself made several unsatisfactory attempts
before he finally hit upon his system of "trivial names," which
was developed in his 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 Linnaeean 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 Felis, the name Felis leo designates the
lion; Felis pardus, the leopard; Felis 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 Linnaeus's predecessors. A single illustration will
suffice. There is, for example, a kind of grass, in referring to
which the naturalist anterior to Linnaeus, if he would be absolutely
unambiguous, was obliged to use the following descriptive formula:
Gramen Xerampelino, Miliacea, praetenuis ramosaque sparsa panicula,
sive Xerampelino congener, arvense, aestivum; gramen minutissimo semine.
Linnaeus gave to this plant the name Poa 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 Linnaeus 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.



APPENDIX

REFERENCE LIST

CHAPTER I

SCIENCE IN THE DARK AGE

(1) (p. 4). James Harvey Robinson, An Introduction to the History of
Western Europe, New York, 1898, p. 330.

(2) (p. 6). Henry Smith Williams, A Prefatory Characterization of The
History of Italy, in vol. IX. of The Historians' History of the World,
25 vols., London and New York, 1904.


CHAPTER III

MEDIAEVAL SCIENCE IN THE WEST

(1) (p. 47). Etigene Muntz, Leonardo do Vinci, Artist, Thinker, and Man
of Science, 2 vols., New York, 1892. Vol. II., p. 73.


CHAPTER IV

THE NEW COSMOLOGY--COPERNICUS TO KEPLER AND GALILEO

(1) (p. 62). Copernicus, uber die Kreisbewegungen der Welfkorper, trans.
from Dannemann's Geschichle du Naturwissenschaften, 2 vols., Leipzig,
1896.

(2) (p. 90). Galileo, Dialogo dei due Massimi Systemi del Mondo, trans.
from Dannemann, op. cit.

CHAPTER V

GALILEO AND THE NEW PHYSICS (1) (p. 101). Rothmann, History of Astronomy
(in the Library of Useful Knowledge), London, 1834.

(2) (p. 102). William Whewell, History of the Inductive Sciences, 3
Vols, London, 1847-Vol. II., p. 48.

(3) (p. 111). The Lives of Eminent Persons, by Biot, Jardine, Bethune,
etc., London, 1833.

(4) (p. 113). William Gilbert, De Magnete, translated by P. Fleury
Motteley, London, 1893. In the biographical memoir, p. xvi.

(5) (p. 114). Gilbert, op. cit., p. x1vii.

(6) (p. 114). Gilbert, op. cit., p. 24.


CHAPTER VI

TWO PSEUDO-SCIENCES--ALCHEMY AND ASTROLOGY

(1) (p. 125). Exodus xxxii, 20.

(2) (p. 126). Charles Mackay, Popular Delusions, 3 vols., London, 1850.
Vol. II., p. 280.

(3) (p. 140). Mackay, op. cit., Vol. 11., p. 289.

(4) (P. 145). John B. Schmalz, Astrology Vindicated, New York, 1898.

(5) (p. 146). William Lilly, The Starry Messenger, London, 1645, p. 63.

(6) (p. 149). Lilly, op. cit., p. 70.

(7) (p. 152). George Wharton, An Astrological judgement upon His
Majesty's Present March begun from Oxford, May 7, 1645, pp. 7-10.

(8) (p. 154). C. W. Roback, The Mysteries of Astrology, Boston, 1854, p.
29.


CHAPTER VII

FROM PARACELSUS TO HARVEY

(1) (p. 159). A. E. Waite, The Hermetic and Alchemical Writings of
Paracelsus, 2 vols., London, 1894. Vol. I., p. 21.

(2) (p. 167). E. T. Withington, Medical History from the Earliest Times,
London, 1894, p. 278.

(3) (p. 173). John Dalton, Doctrines of the Circulation, Philadelphia,
1884, p. 179.

(4) (p. 174). William Harvey, De Motu Cordis et Sanguinis, London, 1803,
chap. X.

(5) (p. 178). The Works of William Harvey, translated by Robert Willis,
London, 1847, p. 56.


CHAPTER VIII

MEDICINE IN THE SIXTEENTH AND SEVENTEENTH CENTURIES

(1) (p. 189). Hermann Baas, History of Medicine, translated by H. E.
Henderson, New York, 1894, p. 504.

(2) (p. 189). E. T. Withington, Medical History from the Earliest Times,
London, 1894, p. 320.


CHAPTER IX

PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS OF LEARNING

(1) (p. 193). George L. Craik, Bacon and His Writings and Philosophy, 2
vols., London, 1846. Vol. II., p. 121.

(2) (p. 193). From Huxley's address On Descartes's Discourse Touching
the Method of Using One's Reason Rightly and of Seeking Scientific
Truth.

(3) (p. 195). Rene Descartes, Traite de l'Homme (Cousins's edition. in
ii vols.), Paris, 1824. Vol, VI., p. 347.


CHAPTER X

THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE

(1) (p. 205). See The Phlogiston Theory, Vol, IV.

(2) (p. 205). Robert Boyle, Philosophical Works, 3 vols., London, 1738.
Vol. III., p. 41.

(3) (p. 206). Ibid., Vol. III., p. 47.

(4) (p. 206). Ibid., Vol. II., p. 92.

(5) (p. 207). Ibid., Vol. II., p. 2.

(6) (p. 209). Ibid., Vol. I., p. 8.

(7) (p. 209). Ibid., vol. III., p. 508.

(8) (p. 210). Ibid., Vol. III., p. 361.

(9) (p. 213). Otto von Guericke, in the Philosophical Transactions of
the Royal Society of London, No. 88, for 1672, p. 5103.

(10) (p. 222). Von Guericke, Phil. Trans. for 1669, Vol I., pp. 173,
174.

CHAPTER XI

NEWTON AND THE COMPOSITION OF LIGHT

(1) (p. 233). Phil. Trans. of Royal Soc. of London, No. 80, 1672, pp.
3076-3079. (2) (p 234). Ibid., pp. 3084, 3085.

(3) (p. 235). Voltaire, Letters Concerning the English Nation, London,
1811.

CHAPTER XII

NEWTON AND THE LAW OF GRAVITATION

(1) (p. 242). Sir Isaac Newton, Principia, translated by Andrew Motte,
New York, 1848, pp. 391, 392.

(2) (p. 250). Newton op. cit., pp. 506, 507.

CHAPTER XIV

PROGRESS IN ELECTRICITY FROM GILBERT AND VON GUERICKE TO FRANKLIN

(1) (p. 274). A letter from M. Dufay, F.R.S. and of the Royal Academy
of Sciences at Paris, etc., in the Phil. Trans. of the Royal Soc., vol.
XXXVIII., pp. 258-265.

(2) (p. 282). Dean von Kleist, in the Danzick Memoirs, Vol. I., p. 407.
From Joseph Priestley's History of Electricity, London, 1775, pp. 83,
84.

(3) (p. 288). Benjamin Franklin, New Experiments and Observations on
Electricity, London, 1760, pp. 107, 108.

(4) (p. 291). Franklin, op. cit., pp. 62, 63.

(5) (p. 295). Franklin, op. cit., pp. 107, 108.

(For notes and bibliography to vol. II. see vol. V.)





*** End of this LibraryBlog Digital Book "A History of Science — Volume 2" ***

Copyright 2023 LibraryBlog. All rights reserved.