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A History of Science, Volume 2, by Henry Smith Williams

Scanned by Charles Keller with OmniPage Professional OCR software

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, tonsellotomy,
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

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