APPENDIX
A HISTORY OF SCIENCE
BOOK II. THE BEGINNINGS OF MODERN SCIENCE
The studies of the present book cover the progress of science from the
close of the Roman period in the fifth century A.D. to about the middle
of the eighteenth century. In tracing the course of events through so
long a period, a difficulty becomes prominent which everywhere besets
the historian in less degree--a difficulty due to the conflict between
the strictly chronological and the topical method of treatment. We must
hold as closely as possible to the actual sequence of events, since,
as already pointed out, one discovery leads on to another. But, on the
other hand, progressive steps are taken contemporaneously in the various
fields of science, and if we were to attempt to introduce these
in strict chronological order we should lose all sense of topical
continuity.
Our method has been to adopt a compromise, following the course of a
single science in each great epoch to a convenient stopping-point, and
then turning back to bring forward the story of another science. Thus,
for example, we tell the story of Copernicus and Galileo, bringing the
record of cosmical and mechanical progress down to about the middle
of the seventeenth century, before turning back to take up the
physiological progress of the fifteenth and sixteenth centuries. Once
the latter stream is entered, however, we follow it without interruption
to the time of Harvey and his contemporaries in the middle of the
seventeenth century, where we leave it to return to the field of
mechanics as exploited by the successors of Galileo, who were also the
predecessors and contemporaries of Newton.
In general, it will aid the reader to recall that, so far as
possible, we hold always to the same sequences of topical treatment of
contemporary events; as a rule we treat first the cosmical, then the
physical, then the biological sciences. The same order of treatment will
be held to in succeeding volumes.
Several of the very greatest of scientific generalizations are developed
in the period covered by the present book: for example, the Copernican
theory of the solar system, the true doctrine of planetary motions,
the laws of motion, the theory of the circulation of the blood, and the
Newtonian theory of gravitation. The labors of the investigators of the
early decades of the eighteenth century, terminating with Franklin's
discovery of the nature of lightning and with the Linnaean
classification of plants and animals, bring us to the close of our
second great epoch; or, to put it otherwise, to the threshold of the
modern period.
I. SCIENCE IN THE DARK AGE
An obvious distinction between the classical and mediaeval epochs may be
found in the fact that the former produced, whereas the latter failed
to produce, a few great thinkers in each generation who were imbued with
that scepticism which is the foundation of the investigating spirit; who
thought for themselves and supplied more or less rational explanations
of observed phenomena. Could we eliminate the work of some score or so
of classical observers and thinkers, the classical epoch would seem as
much a dark age as does the epoch that succeeded it.
But immediately we are met with the question: Why do no great original
investigators appear during all these later centuries? We have already
offered a part explanation in the fact that the borders of civilization,
where racial mingling naturally took place, were peopled with
semi-barbarians. But we must not forget that in the centres of
civilization all along there were many men of powerful intellect.
Indeed, it would violate the principle of historical continuity to
suppose that there was any sudden change in the level of mentality of
the Roman world at the close of the classical period. We must assume,
then, that the direction in which the great minds turned was for
some reason changed. Newton is said to have alleged that he made his
discoveries by "intending" his mind in a certain direction continuously.
It is probable that the same explanation may be given of almost every
great scientific discovery. Anaxagoras could not have thought out the
theory of the moon's phases; Aristarchus could not have found out
the true mechanism of the solar system; Eratosthenes could not have
developed his plan for measuring the earth, had not each of these
investigators "intended" his mind persistently towards the problems in
question.
Nor can we doubt that men lived in every generation of the dark age
who were capable of creative thought in the field of science, bad they
chosen similarly to "intend" their minds in the right direction. The
difficulty was that they did not so choose. Their minds had a quite
different bent. They were under the spell of different ideals; all
their mental efforts were directed into different channels. What these
different channels were cannot be in doubt--they were the channels of
oriental ecclesiasticism. One all-significant fact speaks volumes here.
It is the fact that, as Professor Robinson(1) points out, from the time
of Boethius (died 524 or 525 A.D.) to that of Dante (1265-1321 A.D.)
there was not a single writer of renown in western Europe who was not a
professional churchman. All the learning of the time, then, centred in
the priesthood. We know that the same condition of things pertained in
Egypt, when science became static there. But, contrariwise, we have
seen that in Greece and early Rome the scientific workers were largely
physicians or professional teachers; there was scarcely a professional
theologian among them.
Similarly, as we shall see in the Arabic world, where alone there was
progress in the mediaeval epoch, the learned men were, for the most
part, physicians. Now the meaning of this must be self-evident. The
physician naturally "intends" his mind towards the practicalities. His
professional studies tend to make him an investigator of the operations
of nature. He is usually a sceptic, with a spontaneous interest in
practical science. But the theologian "intends" his mind away from
practicalities and towards mysticism. He is a professional believer in
the supernatural; he discounts the value of merely "natural" phenomena.
His whole attitude of mind is unscientific; the fundamental tenets
of his faith are based on alleged occurrences which inductive science
cannot admit--namely, miracles. And so the minds "intended" towards
the supernatural achieved only the hazy mysticism of mediaeval thought.
Instead of investigating natural laws, they paid heed (as, for example,
Thomas Aquinas does in his Summa Theologia) to the "acts of angels,"
the "speaking of angels," the "subordination of angels," the "deeds of
guardian angels," and the like. They disputed such important questions
as, How many angels can stand upon the point of a needle? They argued
pro and con as to whether Christ were coeval with God, or whether he had
been merely created "in the beginning," perhaps ages before the creation
of the world. How could it be expected that science should flourish when
the greatest minds of the age could concern themselves with problems
such as these?
Despite our preconceptions or prejudices, there can be but one answer to
that question. Oriental superstition cast its blight upon the fair field
of science, whatever compensation it may or may not have brought in
other fields. But we must be on our guard lest we overestimate or
incorrectly estimate this influence. Posterity, in glancing backward,
is always prone to stamp any given age of the past with one idea, and to
desire to characterize it with a single phrase; whereas in reality all
ages are diversified, and any generalization regarding an epoch is sure
to do that epoch something less or something more than justice. We
may be sure, then, that the ideal of ecclesiasticism is not solely
responsible for the scientific stasis of the dark age. Indeed, there was
another influence of a totally different character that is too patent
to be overlooked--the influence, namely, of the economic condition of
western Europe during this period. As I have elsewhere pointed
out,(2) Italy, the centre of western civilization, was at this time
impoverished, and hence could not provide the monetary stimulus so
essential to artistic and scientific no less than to material progress.
There were no patrons of science and literature such as the Ptolemies of
that elder Alexandrian day. There were no great libraries; no colleges
to supply opportunities and afford stimuli to the rising generation.
Worst of all, it became increasingly difficult to secure books.
This phase of the subject is often overlooked. Yet a moment's
consideration will show its importance. How should we fare to-day if no
new scientific books were being produced, and if the records of former
generations were destroyed? That is what actually happened in
Europe during the Middle Ages. At an earlier day books were made and
distributed much more abundantly than is sometimes supposed. Bookmaking
had, indeed, been an important profession in Rome, the actual makers of
books being slaves who worked under the direction of a publisher. It was
through the efforts of these workers that the classical works in Greek
and Latin were multiplied and disseminated. Unfortunately the climate of
Europe does not conduce to the indefinite preservation of a book;
hence very few remnants of classical works have come down to us in the
original from a remote period. The rare exceptions are certain papyrus
fragments, found in Egypt, some of which are Greek manuscripts dating
from the third century B.C. Even from these sources the output is
meagre; and the only other repository of classical books is a single
room in the buried city of Herculaneum, which contained several hundred
manuscripts, mostly in a charred condition, a considerable number of
which, however, have been unrolled and found more or less legible. This
library in the buried city was chiefly made up of philosophical works,
some of which were quite unknown to the modern world until discovered
there.
But this find, interesting as it was from an archaeological stand-point,
had no very important bearing on our knowledge of the literature of
antiquity. Our chief dependence for our knowledge of that literature
must still be placed in such copies of books as were made in the
successive generations. Comparatively few of the extant manuscripts are
older than the tenth century of our era. It requires but a momentary
consideration of the conditions under which ancient books were produced
to realize how slow and difficult the process was before the invention
of printing. The taste of the book-buying public demanded a clearly
written text, and in the Middle Ages it became customary to produce a
richly ornamented text as well. The script employed being the prototype
of the modern printed text, it will be obvious that a scribe could
produce but a few pages at best in a day. A large work would therefore
require the labor of a scribe for many months or even for several years.
We may assume, then, that it would be a very flourishing publisher who
could produce a hundred volumes all told per annum; and probably there
were not many publishers at any given time, even in the period of Rome's
greatest glory, who had anything like this output.
As there was a large number of authors in every generation of the
classical period, it follows that most of these authors must have been
obliged to content themselves with editions numbering very few copies;
and it goes without saying that the greater number of books were never
reproduced in what might be called a second edition. Even books that
retained their popularity for several generations would presently fail
to arouse sufficient interest to be copied; and in due course such works
would pass out of existence altogether. Doubtless many hundreds of books
were thus lost before the close of the classical period, the names of
their authors being quite forgotten, or preserved only through a chance
reference; and of course the work of elimination went on much more
rapidly during the Middle Ages, when the interest in classical
literature sank to so low an ebb in the West. Such collections of
references and quotations as the Greek Anthology and the famous
anthologies of Stobaeus and Athanasius and Eusebius give us glimpses
of a host of writers--more than seven hundred are quoted by Stobaeus--a
very large proportion of whom are quite unknown except through these
brief excerpts from their lost works.
Quite naturally the scientific works suffered at least as largely as
any others in an age given over to ecclesiastical dreamings. Yet in some
regards there is matter for surprise as to the works preserved. Thus, as
we have seen, the very extensive works of Aristotle on natural history,
and the equally extensive natural history of Pliny, which were preserved
throughout this period, and are still extant, make up relatively bulky
volumes. These works seem to have interested the monks of the Middle
Ages, while many much more important scientific books were allowed to
perish. A considerable bulk of scientific literature was also preserved
through the curious channels of Arabic and Armenian translations.
Reference has already been made to the Almagest of Ptolemy, which, as
we have seen, was translated into Arabic, and which was at a later
day brought by the Arabs into western Europe and (at the instance of
Frederick II of Sicily) translated out of their language into mediaeval
Latin.
It remains to inquire, however, through what channels the Greek works
reached the Arabs themselves. To gain an answer to this question we must
follow the stream of history from its Roman course eastward to the new
seat of the Roman empire in Byzantium. Here civilization centred from
about the fifth century A.D., and here the European came in contact
with the civilization of the Syrians, the Persians, the Armenians, and
finally of the Arabs. The Byzantines themselves, unlike the inhabitants
of western Europe, did not ignore the literature of old Greece; the
Greek language became the regular speech of the Byzantine people, and
their writers made a strenuous effort to perpetuate the idiom and style
of the classical period. Naturally they also made transcriptions of the
classical authors, and thus a great mass of literature was preserved,
while the corresponding works were quite forgotten in western Europe.
Meantime many of these works were translated into Syriac, Armenian, and
Persian, and when later on the Byzantine civilization degenerated, many
works that were no longer to be had in the Greek originals continued to
be widely circulated in Syriac, Persian, Armenian, and, ultimately,
in Arabic translations. When the Arabs started out in their conquests,
which carried them through Egypt and along the southern coast of the
Mediterranean, until they finally invaded Europe from the west by way
of Gibraltar, they carried with them their translations of many a Greek
classical author, who was introduced anew to the western world through
this strange channel.
We are told, for example, that Averrhoes, the famous commentator of
Aristotle, who lived in Spain in the twelfth century, did not know
a word of Greek and was obliged to gain his knowledge of the master
through a Syriac translation; or, as others alleged (denying that he
knew even Syriac), through an Arabic version translated from the Syriac.
We know, too, that the famous chronology of Eusebius was preserved
through an Armenian translation; and reference has more than once been
made to the Arabic translation of Ptolemy's great work, to which we
still apply its Arabic title of Almagest.
The familiar story that when the Arabs invaded Egypt they burned the
Alexandrian library is now regarded as an invention of later times. It
seems much more probable that the library bad been largely scattered
before the coming of the Moslems. Indeed, it has even been suggested
that the Christians of an earlier day removed the records of pagan
thought. Be that as it may, the famous Alexandrian library had
disappeared long before the revival of interest in classical learning.
Meanwhile, as we have said, the Arabs, far from destroying the western
literature, were its chief preservers. Partly at least because of their
regard for the records of the creative work of earlier generations of
alien peoples, the Arabs were enabled to outstrip their contemporaries.
For it cannot be in doubt that, during that long stretch of time when
the western world was ignoring science altogether or at most contenting
itself with the casual reading of Aristotle and Pliny, the Arabs had the
unique distinction of attempting original investigations in science.
To them were due all important progressive steps which were made in any
scientific field whatever for about a thousand years after the time of
Ptolemy and Galen. The progress made even by the Arabs during this long
period seems meagre enough, yet it has some significant features. These
will now demand our attention.
II. MEDIAEVAL SCIENCE AMONG THE ARABIANS
The successors of Mohammed showed themselves curiously receptive of the
ideas of the western people whom they conquered. They came in contact
with the Greeks in western Asia and in Egypt, and, as has been said,
became their virtual successors in carrying forward the torch of
learning. It must not be inferred, however, that the Arabian scholars,
as a class, were comparable to their predecessors in creative genius.
On the contrary, they retained much of the conservative oriental spirit.
They were under the spell of tradition, and, in the main, what they
accepted from the Greeks they regarded as almost final in its teaching.
There were, however, a few notable exceptions among their men of
science, and to these must be ascribed several discoveries of some
importance.
The chief subjects that excited the interest and exercised the ingenuity
of the Arabian scholars were astronomy, mathematics, and medicine. The
practical phases of all these subjects were given particular attention.
Thus it is well known that our so-called Arabian numerals date from
this period. The revolutionary effect of these characters, as applied to
practical mathematics, can hardly be overestimated; but it is generally
considered, and in fact was admitted by the Arabs themselves, that these
numerals were really borrowed from the Hindoos, with whom the Arabs came
in contact on the east. Certain of the Hindoo alphabets, notably that of
the Battaks of Sumatra, give us clews to the originals of the numerals.
It does not seem certain, however, that the Hindoos employed these
characters according to the decimal system, which is the prime element
of their importance. Knowledge is not forthcoming as to just when or by
whom such application was made. If this was an Arabic innovation, it was
perhaps the most important one with which that nation is to be credited.
Another mathematical improvement was the introduction into trigonometry
of the sine--the half-chord of the double arc--instead of the chord
of the arc itself which the Greek astronomers had employed. This
improvement was due to the famous Albategnius, whose work in other
fields we shall examine in a moment.
Another evidence of practicality was shown in the Arabian method of
attempting to advance upon Eratosthenes' measurement of the earth.
Instead of trusting to the measurement of angles, the Arabs decided to
measure directly a degree of the earth's surface--or rather two degrees.
Selecting a level plain in Mesopotamia for the experiment, one party
of the surveyors progressed northward, another party southward, from
a given point to the distance of one degree of arc, as determined by
astronomical observations. The result found was fifty-six miles for the
northern degree, and fifty-six and two-third miles for the southern.
Unfortunately, we do not know the precise length of the mile in
question, and therefore cannot be assured as to the accuracy of the
measurement. It is interesting to note, however, that the two degrees
were found of unequal lengths, suggesting that the earth is not a
perfect sphere--a suggestion the validity of which was not to be put
to the test of conclusive measurements until about the close of the
eighteenth century. The Arab measurement was made in the time of Caliph
Abdallah al-Mamun, the son of the famous Harun-al-Rashid. Both father
and son were famous for their interest in science. Harun-al-Rashid was,
it will be recalled, the friend of Charlemagne. It is said that he sent
that ruler, as a token of friendship, a marvellous clock which let fall
a metal ball to mark the hours. This mechanism, which is alleged to
have excited great wonder in the West, furnishes yet another instance of
Arabian practicality.
Perhaps the greatest of the Arabian astronomers was Mohammed ben Jabir
Albategnius, or El-batani, who was born at Batan, in Mesopotamia, about
the year 850 A.D., and died in 929. Albategnius was a student of the
Ptolemaic astronomy, but he was also a practical observer. He made the
important discovery of the motion of the solar apogee. That is to say,
he found that the position of the sun among the stars, at the time of
its greatest distance from the earth, was not what it had been in the
time of Ptolemy. The Greek astronomer placed the sun in longitude 65
degrees, but Albategnius found it in longitude 82 degrees, a distance
too great to be accounted for by inaccuracy of measurement. The modern
inference from this observation is that the solar system is moving
through space; but of course this inference could not well be drawn
while the earth was regarded as the fixed centre of the universe.
In the eleventh century another Arabian discoverer, Arzachel, observing
the sun to be less advanced than Albategnius had found it, inferred
incorrectly that the sun had receded in the mean time. The modern
explanation of this observation is that the measurement of Albategnius
was somewhat in error, since we know that the sun's motion is steadily
progressive. Arzachel, however, accepting the measurement of his
predecessor, drew the false inference of an oscillatory motion of the
stars, the idea of the motion of the solar system not being permissible.
This assumed phenomenon, which really has no existence in point of fact,
was named the "trepidation of the fixed stars," and was for centuries
accepted as an actual phenomenon. Arzachel explained this supposed
phenomenon by assuming that the equinoctial points, or the points of
intersection of the equator and the ecliptic, revolve in circles of
eight degrees' radius. The first points of Aries and Libra were supposed
to describe the circumference of these circles in about eight hundred
years. All of which illustrates how a difficult and false explanation
may take the place of a simple and correct one. The observations of
later generations have shown conclusively that the sun's shift of
position is regularly progressive, hence that there is no "trepidation"
of the stars and no revolution of the equinoctial points.
If the Arabs were wrong as regards this supposed motion of the fixed
stars, they made at least one correct observation as to the inequality
of motion of the moon. Two inequalities of the motion of this body were
already known. A third, called the moon's variation, was discovered by
an Arabian astronomer who lived at Cairo and observed at Bagdad in 975,
and who bore the formidable name of Mohammed Aboul Wefaal-Bouzdjani.
The inequality of motion in question, in virtue of which the moon moves
quickest when she is at new or full, and slowest at the first and third
quarter, was rediscovered by Tycho Brahe six centuries later; a fact
which in itself evidences the neglect of the Arabian astronomer's
discovery by his immediate successors.
In the ninth and tenth centuries the Arabian city of Cordova, in Spain,
was another important centre of scientific influence. There was a
library of several hundred thousand volumes here, and a college where
mathematics and astronomy were taught. Granada, Toledo, and Salamanca
were also important centres, to which students flocked from western
Europe. It was the proximity of these Arabian centres that stimulated
the scientific interests of Alfonso X. of Castile, at whose instance the
celebrated Alfonsine tables were constructed. A familiar story records
that Alfonso, pondering the complications of the Ptolemaic cycles and
epicycles, was led to remark that, had he been consulted at the time of
creation, he could have suggested a much better and simpler plan for the
universe. Some centuries were to elapse before Copernicus was to show
that it was not the plan of the universe, but man's interpretation of
it, that was at fault.
Another royal personage who came under Arabian influence was Frederick
II. of Sicily--the "Wonder of the World," as he was called by his
contemporaries. The Almagest of Ptolemy was translated into Latin at
his instance, being introduced to the Western world through this curious
channel. At this time it became quite usual for the Italian and Spanish
scholars to understand Arabic although they were totally ignorant of
Greek.
In the field of physical science one of the most important of the
Arabian scientists was Alhazen. His work, published about the year 1100
A.D., had great celebrity throughout the mediaeval period. The original
investigations of Alhazen had to do largely with optics. He made
particular studies of the eye itself, and the names given by him to
various parts of the eye, as the vitreous humor, the cornea, and the
retina, are still retained by anatomists. It is known that Ptolemy
had studied the refraction of light, and that he, in common with his
immediate predecessors, was aware that atmospheric refraction affects
the apparent position of stars near the horizon. Alhazen carried forward
these studies, and was led through them to make the first recorded
scientific estimate of the phenomena of twilight and of the height of
the atmosphere. The persistence of a glow in the atmosphere after the
sun has disappeared beneath the horizon is so familiar a phenomenon that
the ancient philosophers seem not to have thought of it as requiring an
explanation. Yet a moment's consideration makes it clear that, if
light travels in straight lines and the rays of the sun were in no wise
deflected, the complete darkness of night should instantly succeed to
day when the sun passes below the horizon. That this sudden change does
not occur, Alhazen explained as due to the reflection of light by the
earth's atmosphere.
Alhazen appears to have conceived the atmosphere as a sharply defined
layer, and, assuming that twilight continues only so long as rays of
the sun reflected from the outer surface of this layer can reach the
spectator at any given point, he hit upon a means of measurement that
seemed to solve the hitherto inscrutable problem as to the atmospheric
depth. Like the measurements of Aristarchus and Eratosthenes, this
calculation of Alhazen is simple enough in theory. Its defect consists
largely in the difficulty of fixing its terms with precision, combined
with the further fact that the rays of the sun, in taking the slanting
course through the earth's atmosphere, are really deflected from a
straight line in virtue of the constantly increasing density of the air
near the earth's surface. Alhazen must have been aware of this latter
fact, since it was known to the later Alexandrian astronomers, but he
takes no account of it in the present measurement. The diagram will make
the method of Alhazen clear.
His important premises are two: first, the well-recognized fact that,
when light is reflected from any surface, the angle of incidence is
equal to the angle of reflection; and, second, the much more doubtful
observation that twilight continues until such time as the sun,
according to a simple calculation, is nineteen degrees below the
horizon. Referring to the diagram, let the inner circle represent the
earth's surface, the outer circle the limits of the atmosphere, C being
the earth's centre, and RR radii of the earth. Then the observer at the
point A will continue to receive the reflected rays of the sun until
that body reaches the point S, which is, according to the hypothesis,
nineteen degrees below the horizon line of the observer at A. This
horizon line, being represented by AH, and the sun's ray by SM, the
angle HMS is an angle of nineteen degrees. The complementary angle SMA
is, obviously, an angle of (180-19) one hundred and sixty-one degrees.
But since M is the reflecting surface and the angle of incidence equals
the angle of reflection, the angle AMC is an angle of one-half of one
hundred and sixty-one degrees, or eighty degrees and thirty minutes.
Now this angle AMC, being known, the right-angled triangle MAC is easily
resolved, since the side AC of that triangle, being the radius of the
earth, is a known dimension. Resolution of this triangle gives us the
length of the hypotenuse MC, and the difference between this and the
radius (AC), or CD, is obviously the height of the atmosphere (h), which
was the measurement desired. According to the calculation of Alhazen,
this h, or the height of the atmosphere, represents from twenty to
thirty miles. The modern computation extends this to about fifty miles.
But, considering the various ambiguities that necessarily attended
the experiment, the result was a remarkably close approximation to the
truth.
Turning from physics to chemistry, we find as perhaps the greatest
Arabian name that of Geber, who taught in the College of Seville in the
first half of the eighth century. The most important researches of this
really remarkable experimenter had to do with the acids. The ancient
world had had no knowledge of any acid more powerful than acetic. Geber,
however, vastly increased the possibilities of chemical experiment by
the discovery of sulphuric, nitric, and nitromuriatic acids. He made
use also of the processes of sublimation and filtration, and his works
describe the water bath and the chemical oven. Among the important
chemicals which he first differentiated is oxide of mercury, and his
studies of sulphur in its various compounds have peculiar interest.
In particular is this true of his observation that, tinder certain
conditions of oxidation, the weight of a metal was lessened.
From the record of these studies in the fields of astronomy, physics,
and chemistry, we turn to a somewhat extended survey of the Arabian
advances in the field of medicine.
ARABIAN MEDICINE
The influence of Arabian physicians rested chiefly upon their use
of drugs rather than upon anatomical knowledge. Like the mediaeval
Christians, they looked with horror on dissection of the human body;
yet there were always among them investigators who turned constantly
to nature herself for hidden truths, and were ready to uphold the
superiority of actual observation to mere reading. Thus the physician
Abd el-Letif, while in Egypt, made careful studies of a mound of bones
containing more than twenty thousand skeletons. While examining these
bones he discovered that the lower jaw consists of a single bone, not
of two, as had been taught by Galen. He also discovered several other
important mistakes in Galenic anatomy, and was so impressed with his
discoveries that he contemplated writing a work on anatomy which should
correct the great classical authority's mistakes.
It was the Arabs who invented the apothecary, and their pharmacopoeia,
issued from the hospital at Gondisapor, and elaborated from time to
time, formed the basis for Western pharmacopoeias. Just how many drugs
originated with them, and how many were borrowed from the Hindoos, Jews,
Syrians, and Persians, cannot be determined. It is certain, however,
that through them various new and useful drugs, such as senna, aconite,
rhubarb, camphor, and mercury, were handed down through the Middle Ages,
and that they are responsible for the introduction of alcohol in the
field of therapeutics.
In mediaeval Europe, Arabian science came to be regarded with
superstitious awe, and the works of certain Arabian physicians were
exalted to a position above all the ancient writers. In modern times,
however, there has been a reaction and a tendency to depreciation of
their work. By some they are held to be mere copyists or translators
of Greek books, and in no sense original investigators in medicine. Yet
there can be little doubt that while the Arabians did copy and
translate freely, they also originated and added considerably to medical
knowledge. It is certain that in the time when Christian monarchs in
western Europe were paying little attention to science or education,
the caliphs and vizirs were encouraging physicians and philosophers,
building schools, and erecting libraries and hospitals. They made at
least a creditable effort to uphold and advance upon the scientific
standards of an earlier age.
The first distinguished Arabian physician was Harets ben Kaladah, who
received his education in the Nestonian school at Gondisapor, about the
beginning of the seventh century. Notwithstanding the fact that Harets
was a Christian, he was chosen by Mohammed as his chief medical adviser,
and recommended as such to his successor, the Caliph Abu Bekr. Thus,
at the very outset, the science of medicine was divorced from religion
among the Arabians; for if the prophet himself could employ the services
of an unbeliever, surely others might follow his example. And that this
example was followed is shown in the fact that many Christian physicians
were raised to honorable positions by succeeding generations of
Arabian monarchs. This broad-minded view of medicine taken by the Arabs
undoubtedly assisted as much as any one single factor in upbuilding
the science, just as the narrow and superstitious view taken by Western
nations helped to destroy it.
The education of the Arabians made it natural for them to associate
medicine with the natural sciences, rather than with religion. An
Arabian savant was supposed to be equally well educated in philosophy,
jurisprudence, theology, mathematics, and medicine, and to practise law,
theology, and medicine with equal skill upon occasion. It is easy to
understand, therefore, why these religious fanatics were willing to
employ unbelieving physicians, and their physicians themselves to
turn to the scientific works of Hippocrates and Galen for medical
instruction, rather than to religious works. Even Mohammed himself
professed some knowledge of medicine, and often relied upon this
knowledge in treating ailments rather than upon prayers or incantations.
He is said, for example, to have recommended and applied the cautery
in the case of a friend who, when suffering from angina, had sought his
aid.
The list of eminent Arabian physicians is too long to be given here,
but some of them are of such importance in their influence upon later
medicine that they cannot be entirely ignored. One of the first of these
was Honain ben Isaac (809-873 A.D.), a Christian Arab of Bagdad. He made
translations of the works of Hippocrates, and practised the art
along the lines indicated by his teachings and those of Galen. He is
considered the greatest translator of the ninth century and one of the
greatest philosophers of that period.
Another great Arabian physician, whose work was just beginning as
Honain's was drawing to a close, was Rhazes (850-923 A.D.), who during
his life was no less noted as a philosopher and musician than as a
physician. He continued the work of Honain, and advanced therapeutics by
introducing more extensive use of chemical remedies, such as mercurial
ointments, sulphuric acid, and aqua vitae. He is also credited with
being the first physician to describe small-pox and measles accurately.
While Rhazes was still alive another Arabian, Haly Abbas (died about
994), was writing his famous encyclopaedia of medicine, called The Royal
Book. But the names of all these great physicians have been considerably
obscured by the reputation of Avicenna (980-1037), the Arabian "Prince
of Physicians," the greatest name in Arabic medicine, and one of the
most remarkable men in history. Leclerc says that "he was perhaps
never surpassed by any man in brilliancy of intellect and indefatigable
activity." His career was a most varied one. He was at all times a
boisterous reveller, but whether flaunting gayly among the guests of
an emir or biding in some obscure apothecary cellar, his work of
philosophical writing was carried on steadily. When a friendly emir was
in power, he taught and wrote and caroused at court; but between times,
when some unfriendly ruler was supreme, he was hiding away obscurely,
still pouring out his great mass of manuscripts. In this way his entire
life was spent.
By his extensive writings he revived and kept alive the best of the
teachings of the Greek physicians, adding to them such observations
as he had made in anatomy, physiology, and materia medica. Among his
discoveries is that of the contagiousness of pulmonary tuberculosis. His
works for several centuries continued to be looked upon as the highest
standard by physicians, and he should undoubtedly be credited with
having at least retarded the decline of mediaeval medicine.
But it was not the Eastern Arabs alone who were active in the field of
medicine. Cordova, the capital of the western caliphate, became also a
great centre of learning and produced several great physicians. One of
these, Albucasis (died in 1013 A.D.), is credited with having published
the first illustrated work on surgery, this book being remarkable in
still another way, in that it was also the first book, since classical
times, written from the practical experience of the physician, and not a
mere compilation of ancient authors. A century after Albucasis came the
great physician Avenzoar (1113-1196), with whom he divides about
equally the medical honors of the western caliphate. Among Avenzoar's
discoveries was that of the cause of "itch"--a little parasite, "so
small that he is hardly visible." The discovery of the cause of this
common disease seems of minor importance now, but it is of interest
in medical history because, had Avenzoar's discovery been remembered a
hundred years ago, "itch struck in" could hardly have been considered
the cause of three-fourths of all diseases, as it was by the famous
Hahnemann.
The illustrious pupil of Avenzoar, Averrhoes, who died in 1198 A.D., was
the last of the great Arabian physicians who, by rational conception
of medicine, attempted to stem the flood of superstition that was
overwhelming medicine. For a time he succeeded; but at last the Moslem
theologians prevailed, and he was degraded and banished to a town
inhabited only by the despised Jews.
ARABIAN HOSPITALS
To early Christians belong the credit of having established the first
charitable institutions for caring for the sick; but their efforts were
soon eclipsed by both Eastern and Western Mohammedans. As early as
the eighth century the Arabs had begun building hospitals, but the
flourishing time of hospital building seems to have begun early in the
tenth century. Lady Seidel, in 918 A.D., opened a hospital at Bagdad,
endowed with an amount corresponding to about three hundred pounds
sterling a month. Other similar hospitals were erected in the years
immediately following, and in 977 the Emir Adad-adaula established an
enormous institution with a staff of twenty-four medical officers. The
great physician Rhazes is said to have selected the site for one of
these hospitals by hanging pieces of meat in various places about
the city, selecting the site near the place at which putrefaction was
slowest in making its appearance. By the middle of the twelfth century
there were something like sixty medical institutions in Bagdad alone,
and these institutions were free to all patients and supported by
official charity.
The Emir Nureddin, about the year 1160, founded a great hospital at
Damascus, as a thank-offering for his victories over the Crusaders.
This great institution completely overshadowed all the earlier Moslem
hospitals in size and in the completeness of its equipment. It was
furnished with facilities for teaching, and was conducted for several
centuries in a lavish manner, regardless of expense. But little over a
century after its foundation the fame of its methods of treatment led to
the establishment of a larger and still more luxurious institution--the
Mansuri hospital at Cairo. It seems that a certain sultan, having been
cured by medicines from the Damascene hospital, determined to build
one of his own at Cairo which should eclipse even the great Damascene
institution.
In a single year (1283-1284) this hospital was begun and completed. No
efforts were spared in hurrying on the good work, and no one was exempt
from performing labor on the building if he chanced to pass one of
the adjoining streets. It was the order of the sultan that any person
passing near could be impressed into the work, and this order was
carried out to the letter, noblemen and beggars alike being forced to
lend a hand. Very naturally, the adjacent thoroughfares became unpopular
and practically deserted, but still the holy work progressed rapidly and
was shortly completed.
This immense structure is said to have contained four courts, each
having a fountain in the centre; lecture-halls, wards for isolating
certain diseases, and a department that corresponded to the modern
hospital's "out-patient" department. The yearly endowment amounted to
something like the equivalent of one hundred and twenty-five thousand
dollars. A novel feature was a hall where musicians played day and
night, and another where story-tellers were employed, so that persons
troubled with insomnia were amused and melancholiacs cheered. Those of a
religious turn of mind could listen to readings of the Koran, conducted
continuously by a staff of some fifty chaplains. Each patient on leaving
the hospital received some gold pieces, that he need not be obliged to
attempt hard labor at once.
In considering the astonishing tales of these sumptuous Arabian
institutions, it should be borne in mind that our accounts of them are,
for the most part, from Mohammedan sources. Nevertheless, there can be
little question that they were enormous institutions, far surpassing any
similar institutions in western Europe. The so-called hospitals in the
West were, at this time, branches of monasteries under supervision of
the monks, and did not compare favorably with the Arabian hospitals.
But while the medical science of the Mohammedans greatly overshadowed
that of the Christians during this period, it did not completely
obliterate it. About the year 1000 A.D. came into prominence the
Christian medical school at Salerno, situated on the Italian coast, some
thirty miles southeast of Naples. Just how long this school had been
in existence, or by whom it was founded, cannot be determined, but its
period of greatest influence was the eleventh, twelfth, and thirteenth
centuries. The members of this school gradually adopted Arabic medicine,
making use of many drugs from the Arabic pharmacopoeia, and this formed
one of the stepping-stones to the introduction of Arabian medicine all
through western Europe.
It was not the adoption of Arabian medicines, however, that has made the
school at Salerno famous both in rhyme and prose, but rather the fact
that women there practised the healing art. Greatest among them was
Trotula, who lived in the eleventh century, and whose learning is
reputed to have equalled that of the greatest physicians of the day. She
is accredited with a work on Diseases of Women, still extant, and many
of her writings on general medical subjects were quoted through two
succeeding centuries. If we may judge from these writings, she seemed
to have had many excellent ideas as to the proper methods of treating
diseases, but it is difficult to determine just which of the writings
credited to her are in reality hers. Indeed, the uncertainty is even
greater than this implies, for, according to some writers, "Trotula"
is merely the title of a book. Such an authority as Malgaigne, however,
believed that such a woman existed, and that the works accredited to
her are authentic. The truth of the matter may perhaps never be fully
established, but this at least is certain--the tradition in regard
to Trotula could never have arisen had not women held a far different
position among the Arabians of this period from that accorded them in
contemporary Christendom.
III. MEDIAEVAL SCIENCE IN THE WEST
We have previously referred to the influence of the Byzantine
civilization in transmitting the learning of antiquity across the abysm
of the dark age. It must be admitted, however, that the importance of
that civilization did not extend much beyond the task of the common
carrier. There were no great creative scientists in the later Roman
empire of the East any more than in the corresponding empire of
the West. There was, however, one field in which the Byzantine made
respectable progress and regarding which their efforts require a few
words of special comment. This was the field of medicine.
The Byzantines of this time could boast of two great medical men, Aetius
of Amida (about 502-575 A.D.) and Paul of Aegina (about 620-690).
The works of Aetius were of value largely because they recorded the
teachings of many of his eminent predecessors, but he was not entirely
lacking in originality, and was perhaps the first physician to mention
diphtheria, with an allusion to some observations of the paralysis of
the palate which sometimes follows this disease.
Paul of Aegina, who came from the Alexandrian school about a century
later, was one of those remarkable men whose ideas are centuries ahead
of their time. This was particularly true of Paul in regard to surgery,
and his attitude towards the supernatural in the causation and treatment
of diseases. He was essentially a surgeon, being particularly familiar
with military surgery, and some of his descriptions of complicated
and difficult operations have been little improved upon even in modern
times. In his books he describes such operations as the removal of
foreign bodies from the nose, ear, and esophagus; and he recognizes
foreign growths such as polypi in the air-passages, and gives the
method of their removal. Such operations as tracheotomy, tonsillotomy,
bronchotomy, staphylotomy, etc., were performed by him, and he even
advocated and described puncture of the abdominal cavity, giving careful
directions as to the location in which such punctures should be made. He
advocated amputation of the breast for the cure of cancer, and described
extirpation of the uterus. Just how successful this last operation may
have been as performed by him does not appear; but he would hardly have
recommended it if it had not been sometimes, at least, successful.
That he mentions it at all, however, is significant, as this difficult
operation is considered one of the great triumphs of modern surgery.
But Paul of Aegina is a striking exception to the rule among Byzantine
surgeons, and as he was their greatest, so he was also their last
important surgeon. The energies of all Byzantium were so expended in
religious controversies that medicine, like the other sciences, was soon
relegated to a place among the other superstitions, and the influence
of the Byzantine school was presently replaced by that of the conquering
Arabians.
THIRTEENTH-CENTURY MEDICINE
The thirteenth century marks the beginning of a gradual change in
medicine, and a tendency to leave the time-worn rut of superstitious
dogmas that so long retarded the progress of science. It is thought that
the great epidemics which raged during the Middle Ages acted powerfully
in diverting the medical thought of the times into new and entirely
different channels. It will be remembered that the teachings of Galen
were handed through mediaeval times as the highest and best authority
on the subject of all diseases. When, however, the great epidemics made
their appearance, the medical men appealed to the works of Galen in vain
for enlightenment, as these works, having been written several centuries
before the time of the plagues, naturally contained no information
concerning them. It was evident, therefore, that on this subject, at
least, Galen was not infallible; and it would naturally follow that,
one fallible point having been revealed, others would be sought for. In
other words, scepticism in regard to accepted methods would be aroused,
and would lead naturally, as such scepticism usually does, to
progress. The devastating effects of these plagues, despite prayers and
incantations, would arouse doubt in the minds of many as to the efficacy
of superstitious rites and ceremonies in curing diseases. They had seen
thousands and tens of thousands of their fellow-beings swept away by
these awful scourges. They had seen the ravages of these epidemics
continue for months or even years, notwithstanding the fact that
multitudes of God-fearing people prayed hourly that such ravages might
be checked. And they must have observed also that when even very simple
rules of cleanliness and hygiene were followed there was a diminution
in the ravages of the plague, even without the aid of incantations. Such
observations as these would have a tendency to awaken a suspicion in the
minds of many of the physicians that disease was not a manifestation
of the supernatural, but a natural phenomenon, to be treated by natural
methods.
But, be the causes what they may, it is a fact that the thirteenth
century marks a turning-point, or the beginning of an attitude of mind
which resulted in bringing medicine to a much more rational position.
Among the thirteenth-century physicians, two men are deserving of
special mention. These are Arnald of Villanova (1235-1312) and Peter of
Abano (1250-1315). Both these men suffered persecution for expressing
their belief in natural, as against the supernatural, causes of disease,
and at one time Arnald was obliged to flee from Barcelona for declaring
that the "bulls" of popes were human works, and that "acts of charity
were dearer to God than hecatombs." He was also accused of alchemy.
Fleeing from persecution, he finally perished by shipwreck.
Arnald was the first great representative of the school of Montpellier.
He devoted much time to the study of chemicals, and was active in
attempting to re-establish the teachings of Hippocrates and Galen.
He was one of the first of a long line of alchemists who, for several
succeeding centuries, expended so much time and energy in attempting to
find the "elixir of life." The Arab discovery of alcohol first deluded
him into the belief that the "elixir" had at last been found; but later
he discarded it and made extensive experiments with brandy, employing
it in the treatment of certain diseases--the first record of the
administration of this liquor as a medicine. Arnald also revived the
search for some anaesthetic that would produce insensibility to pain in
surgical operations. This idea was not original with him, for since very
early times physicians had attempted to discover such an anaesthetic,
and even so early a writer as Herodotus tells how the Scythians,
by inhalation of the vapors of some kind of hemp, produced complete
insensibility. It may have been these writings that stimulated Arnald
to search for such an anaesthetic. In a book usually credited to him,
medicines are named and methods of administration described which will
make the patient insensible to pain, so that "he may be cut and feel
nothing, as though he were dead." For this purpose a mixture of opium,
mandragora, and henbane is to be used. This mixture was held at the
patient's nostrils much as ether and chloroform are administered by the
modern surgeon. The method was modified by Hugo of Lucca (died in 1252
or 1268), who added certain other narcotics, such as hemlock, to the
mixture, and boiled a new sponge in this decoction. After boiling for a
certain time, this sponge was dried, and when wanted for use was dipped
in hot water and applied to the nostrils.
Just how frequently patients recovered from the administration of such
a combination of powerful poisons does not appear, but the percentage
of deaths must have been very high, as the practice was generally
condemned. Insensibility could have been produced only by swallowing
large quantities of the liquid, which dripped into the nose and mouth
when the sponge was applied, and a lethal quantity might thus be
swallowed. The method was revived, with various modifications, from time
to time, but as often fell into disuse. As late as 1782 it was sometimes
attempted, and in that year the King of Poland is said to have been
completely anaesthetized and to have recovered, after a painless
amputation had been performed by the surgeons.
Peter of Abano was one of the first great men produced by the University
of Padua. His fate would have been even more tragic than that of the
shipwrecked Arnald had he not cheated the purifying fagots of the church
by dying opportunely on the eve of his execution for heresy. But if his
spirit had cheated the fanatics, his body could not, and his bones were
burned for his heresy. He had dared to deny the existence of a devil,
and had suggested that the case of a patient who lay in a trance for
three days might help to explain some miracles, like the raising of
Lazarus.
His great work was Conciliator Differentiarum, an attempt to reconcile
physicians and philosophers. But his researches were not confined to
medicine, for he seems to have had an inkling of the hitherto unknown
fact that air possesses weight, and his calculation of the length of the
year at three hundred and sixty-five days, six hours, and four minutes,
is exceptionally accurate for the age in which he lived. He was probably
the first of the Western writers to teach that the brain is the source
of the nerves, and the heart the source of the vessels. From this it
is seen that he was groping in the direction of an explanation of the
circulation of the blood, as demonstrated by Harvey three centuries
later.
The work of Arnald and Peter of Abano in "reviving" medicine was
continued actively by Mondino (1276-1326) of Bologna, the "restorer of
anatomy," and by Guy of Chauliac: (born about 1300), the "restorer of
surgery." All through the early Middle Ages dissections of human bodies
had been forbidden, and even dissection of the lower animals gradually
fell into disrepute because physicians detected in such practices
were sometimes accused of sorcery. Before the close of the thirteenth
century, however, a reaction had begun, physicians were protected, and
dissections were occasionally sanctioned by the ruling monarch. Thus
Emperor Frederick H. (1194-1250 A.D.)--whose services to science we have
already had occasion to mention--ordered that at least one human body
should be dissected by physicians in his kingdom every five years. By
the time of Mondino dissections were becoming more frequent, and he
himself is known to have dissected and demonstrated several bodies. His
writings on anatomy have been called merely plagiarisms of Galen, but
in all probability be made many discoveries independently, and on
the whole, his work may be taken as more advanced than Galen's. His
description of the heart is particularly accurate, and he seems to have
come nearer to determining the course of the blood in its circulation
than any of his predecessors. In this quest he was greatly handicapped
by the prevailing belief in the idea that blood-vessels must contain air
as well as blood, and this led him to assume that one of the cavities of
the heart contained "spirits," or air. It is probable, however, that his
accurate observations, so far as they went, were helpful stepping-stones
to Harvey in his discovery of the circulation.
Guy of Chauliac, whose innovations in surgery reestablished that science
on a firm basis, was not only one of the most cultured, but also the
most practical surgeon of his time. He had great reverence for the works
of Galen, Albucasis, and others of his noted predecessors; but this
reverence did not blind him to their mistakes nor prevent him from using
rational methods of treatment far in advance of theirs. His practicality
is shown in some of his simple but useful inventions for the sick-room,
such as the device of a rope, suspended from the ceiling over the bed,
by which a patient may move himself about more easily; and in some of
his improvements in surgical dressings, such as stiffening bandages by
dipping them in the white of an egg so that they are held firmly.
He treated broken limbs in the suspended cradle still in use, and
introduced the method of making "traction" on a broken limb by means
of a weight and pulley, to prevent deformity through shortening of the
member. He was one of the first physicians to recognize the utility of
spectacles, and recommended them in cases not amenable to treatment
with lotions and eye-waters. In some of his surgical operations, such
as trephining for fracture of the skull, his technique has been little
improved upon even in modern times. In one of these operations he
successfully removed a portion of a man's brain.
Surgery was undoubtedly stimulated greatly at this period by the
constant wars. Lay physicians, as a class, had been looked down
upon during the Dark Ages; but with the beginning of the return to
rationalism, the services of surgeons on the battle-field, to remove
missiles from wounds, and to care for wounds and apply dressings, came
to be more fully appreciated. In return for his labors the surgeon was
thus afforded better opportunities for observing wounds and diseases,
which led naturally to a gradual improvement in surgical methods.
FIFTEENTH-CENTURY MEDICINE
The thirteenth and fourteenth centuries had seen some slight advancement
in the science of medicine; at least, certain surgeons and physicians,
if not the generality, had made advances; but it was not until the
fifteenth century that the general revival of medical learning became
assured. In this movement, naturally, the printing-press played an
all-important part. Medical books, hitherto practically inaccessible
to the great mass of physicians, now became common, and this output of
reprints of Greek and Arabic treatises revealed the fact that many of
the supposed true copies were spurious. These discoveries very naturally
aroused all manner of doubt and criticism, which in turn helped in the
development of independent thought.
A certain manuscript of the great Cornelius Celsus, the De Medicine,
which had been lost for many centuries, was found in the church of St.
Ambrose, at Milan, in 1443, and was at once put into print. The effect
of the publication of this book, which had lain in hiding for so many
centuries, was a revelation, showing the medical profession how far
most of their supposed true copies of Celsus had drifted away from the
original. The indisputable authenticity of this manuscript, discovered
and vouched for by the man who shortly after became Pope Nicholas V.,
made its publication the more impressive. The output in book form of
other authorities followed rapidly, and the manifest discrepancies
between such teachers as Celsus, Hippocrates, Galen, and Pliny
heightened still more the growing spirit of criticism.
These doubts resulted in great controversies as to the proper treatment
of certain diseases, some physicians following Hippocrates, others Galen
or Celsus, still others the Arabian masters. One of the most bitter
of these contests was over the question of "revulsion," and
"derivation"--that is, whether in cases of pleurisy treated by bleeding,
the venesection should be made at a point distant from the seat of the
disease, as held by the "revulsionists," or at a point nearer and on the
same side of the body, as practised by the "derivationists." That any
great point for discussion could be raised in the fifteenth or sixteenth
centuries on so simple a matter as it seems to-day shows how necessary
to the progress of medicine was the discovery of the circulation of the
blood made by Harvey two centuries later. After Harvey's discovery no
such discussion could have been possible, because this discovery made
it evident that as far as the general effect upon the circulation is
concerned, it made little difference whether the bleeding was done near
a diseased part or remote from it. But in the sixteenth century this
question was the all-absorbing one among the doctors. At one time the
faculty of Paris condemned "derivation"; but the supporters of this
method carried the war still higher, and Emperor Charles V. himself was
appealed to. He reversed the decision of the Paris faculty, and decided
in favor of "derivation." His decision was further supported by Pope
Clement VII., although the discussion dragged on until cut short by
Harvey's discovery.
But a new form of injury now claimed the attention of the surgeons,
something that could be decided by neither Greek nor Arabian authors, as
the treatment of gun-shot wounds was, for obvious reasons, not given in
their writings. About this time, also, came the great epidemics, "the
sweating sickness" and scurvy; and upon these subjects, also, the
Greeks and Arabians were silent. John of Vigo, in his book, the Practica
Copiosa, published in 1514, and repeated in many editions, became the
standard authority on all these subjects, and thus supplanted the works
of the ancient writers.
According to Vigo, gun-shot wounds differed from the wounds made by
ordinary weapons--that is, spear, arrow, sword, or axe--in that the
bullet, being round, bruised rather than cut its way through the
tissues; it burned the flesh; and, worst of all, it poisoned it. Vigo
laid especial stress upon treating this last condition, recommending the
use of the cautery or the oil of elder, boiling hot. It is little wonder
that gun-shot wounds were so likely to prove fatal. Yet, after all, here
was the germ of the idea of antisepsis.
NEW BEGINNINGS IN GENERAL SCIENCE
We have dwelt thus at length on the subject of medical science, because
it was chiefly in this field that progress was made in the Western world
during the mediaeval period, and because these studies furnished the
point of departure for the revival all along the line. It will be
understood, however, from what was stated in the preceding chapter,
that the Arabian influences in particular were to some extent making
themselves felt along other lines. The opportunity afforded a portion
of the Western world--notably Spain and Sicily--to gain access to the
scientific ideas of antiquity through Arabic translations could not fail
of influence. Of like character, and perhaps even more pronounced in
degree, was the influence wrought by the Byzantine refugees, who, when
Constantinople began to be threatened by the Turks, migrated to the
West in considerable numbers, bringing with them a knowledge of Greek
literature and a large number of precious works which for centuries
had been quite forgotten or absolutely ignored in Italy. Now Western
scholars began to take an interest in the Greek language, which had been
utterly neglected since the beginning of the Middle Ages. Interesting
stories are told of the efforts made by such men as Cosmo de' Medici to
gain possession of classical manuscripts. The revival of learning
thus brought about had its first permanent influence in the fields of
literature and art, but its effect on science could not be long delayed.
Quite independently of the Byzantine influence, however, the striving
for better intellectual things had manifested itself in many ways before
the close of the thirteenth century. An illustration of this is found
in the almost simultaneous development of centres of teaching, which
developed into the universities of Italy, France, England, and, a little
later, of Germany.
The regular list of studies that came to be adopted everywhere
comprised seven nominal branches, divided into two groups--the so-called
quadrivium, comprising music, arithmetic, geometry, and astronomy; and
the trivium comprising grammar, rhetoric, and logic. The vagueness of
implication of some of these branches gave opportunity to the teacher
for the promulgation of almost any knowledge of which he might be
possessed, but there can be no doubt that, in general, science had
but meagre share in the curriculum. In so far as it was given
representation, its chief field must have been Ptolemaic astronomy. The
utter lack of scientific thought and scientific method is illustrated
most vividly in the works of the greatest men of that period--such men
as Albertus Magnus, Thomas Aquinas, Bonaventura, and the hosts of other
scholastics of lesser rank. Yet the mental awakening implied in their
efforts was sure to extend to other fields, and in point of fact there
was at least one contemporary of these great scholastics whose mind
was intended towards scientific subjects, and who produced writings
strangely at variance in tone and in content with the others. This
anachronistic thinker was the English monk, Roger Bacon.
ROGER BACON
Bacon was born in 1214 and died in 1292. By some it is held that he was
not appreciated in his own time because he was really a modern scientist
living in an age two centuries before modern science or methods of
modern scientific thinking were known. Such an estimate, however, is a
manifest exaggeration of the facts, although there is probably a grain
of truth in it withal. His learning certainly brought him into contact
with the great thinkers of the time, and his writings caused him to
be imprisoned by his fellow-churchmen at different times, from which
circumstances we may gather that he was advanced thinker, even if not a
modern scientist.
Although Bacon was at various times in durance, or under surveillance,
and forbidden to write, he was nevertheless a marvellously prolific
writer, as is shown by the numerous books and unpublished manuscripts of
his still extant. His master-production was the Opus Majus. In Part IV.
of this work he attempts to show that all sciences rest ultimately on
mathematics; but Part V., which treats of perspective, is of particular
interest to modern scientists, because in this he discusses reflection
and refraction, and the properties of mirrors and lenses. In this part,
also, it is evident that he is making use of such Arabian writers as
Alkindi and Alhazen, and this is of especial interest, since it has been
used by his detractors, who accuse him of lack of originality, to prove
that his seeming inventions and discoveries were in reality adaptations
of the Arab scientists. It is difficult to determine just how fully such
criticisms are justified. It is certain, however, that in this part
he describes the anatomy of the eye with great accuracy, and discusses
mirrors and lenses.
The magnifying power of the segment of a glass sphere had been noted by
Alhazen, who had observed also that the magnification was increased by
increasing the size of the segment used. Bacon took up the discussion of
the comparative advantages of segments, and in this discussion seems to
show that he understood how to trace the progress of the rays of light
through a spherical transparent body, and how to determine the place of
the image. He also described a method of constructing a telescope, but
it is by no means clear that he had ever actually constructed such an
instrument. It is also a mooted question as to whether his instructions
as to the construction of such an instrument would have enabled any one
to construct one. The vagaries of the names of terms as he uses them
allow such latitude in interpretation that modern scientists are not
agreed as to the practicability of Bacon's suggestions. For example, he
constantly refers to force under such names as virtus, species, imago,
agentis, and a score of other names, and this naturally gives rise
to the great differences in the interpretations of his writings, with
corresponding differences in estimates of them.
The claim that Bacon originated the use of lenses, in the form of
spectacles, cannot be proven. Smith has determined that as early as the
opening years of the fourteenth century such lenses were in use, but
this proves nothing as regards Bacon's connection with their invention.
The knowledge of lenses seems to be very ancient, if we may judge from
the convex lens of rock crystal found by Layard in his excavations
at Nimrud. There is nothing to show, however, that the ancients ever
thought of using them to correct defects of vision. Neither, apparently,
is it feasible to determine whether the idea of such an application
originated with Bacon.
Another mechanical discovery about which there has been a great deal of
discussion is Bacon's supposed invention of gunpowder. It appears that
in a certain passage of his work he describes the process of making a
substance that is, in effect, ordinary gunpowder; but it is more than
doubtful whether he understood the properties of the substance he
describes. It is fairly well established, however, that in Bacon's time
gunpowder was known to the Arabs, so that it should not be surprising
to find references made to it in Bacon's work, since there is reason to
believe that he constantly consulted Arabian writings.
The great merit of Bacon's work, however, depends on the principles
taught as regards experiment and the observation of nature, rather than
on any single invention. He had the all-important idea of breaking with
tradition. He championed unfettered inquiry in every field of thought.
He had the instinct of a scientific worker--a rare instinct indeed in
that age. Nor need we doubt that to the best of his opportunities he was
himself an original investigator.
LEONARDO DA VINCI
The relative infertility of Bacon's thought is shown by the fact that he
founded no school and left no trace of discipleship. The entire century
after his death shows no single European name that need claim the
attention of the historian of science. In the latter part of the
fifteenth century, however, there is evidence of a renaissance of
science no less than of art. The German Muller became famous under
the latinized named of Regio Montanus (1437-1472), although his actual
scientific attainments would appear to have been important only in
comparison with the utter ignorance of his contemporaries. The most
distinguished worker of the new era was the famous Italian Leonardo da
Vinci--a man who has been called by Hamerton the most universal genius
that ever lived. Leonardo's position in the history of art is known to
every one. With that, of course, we have no present concern; but it is
worth our while to inquire at some length as to the famous painter's
accomplishments as a scientist.
From a passage in the works of Leonardo, first brought to light by
Venturi,(1) it would seem that the great painter anticipated Copernicus
in determining the movement of the earth. He made mathematical
calculations to prove this, and appears to have reached the definite
conclusion that the earth does move--or what amounts to the same thing,
that the sun does not move. Muntz is authority for the statement that
in one of his writings he declares, "Il sole non si mouve"--the sun does
not move.(2)
Among his inventions is a dynamometer for determining the traction power
of machines and animals, and his experiments with steam have led some
of his enthusiastic partisans to claim for him priority to Watt in the
invention of the steam-engine. In these experiments, however, Leonardo
seems to have advanced little beyond Hero of Alexandria and his steam
toy. Hero's steam-engine did nothing but rotate itself by virtue of
escaping jets of steam forced from the bent tubes, while Leonardo's
"steam-engine" "drove a ball weighing one talent over a distance of six
stadia." In a manuscript now in the library of the Institut de France,
Da Vinci describes this engine minutely. The action of this machine was
due to the sudden conversion of small quantities of water into steam
("smoke," as he called it) by coming suddenly in contact with a heated
surface in a proper receptacle, the rapidly formed steam acting as
a propulsive force after the manner of an explosive. It is really a
steam-gun, rather than a steam-engine, and it is not unlikely that the
study of the action of gunpowder may have suggested it to Leonardo.
It is believed that Leonardo is the true discoverer of the
camera-obscura, although the Neapolitan philosopher, Giambattista Porta,
who was not born until some twenty years after the death of Leonardo,
is usually credited with first describing this device. There is
little doubt, however, that Da Vinci understood the principle of this
mechanism, for he describes how such a camera can be made by cutting a
small, round hole through the shutter of a darkened room, the reversed
image of objects outside being shown on the opposite wall.
Like other philosophers in all ages, he had observed a great number of
facts which he was unable to explain correctly. But such accumulations
of scientific observations are always interesting, as showing how many
centuries of observation frequently precede correct explanation. He
observed many facts about sounds, among others that blows struck upon
a bell produced sympathetic sounds in a bell of the same kind; and
that striking the string of a lute produced vibration in corresponding
strings of lutes strung to the same pitch. He knew, also, that sounds
could be heard at a distance at sea by listening at one end of a tube,
the other end of which was placed in the water; and that the same
expedient worked successfully on land, the end of the tube being placed
against the ground.
The knowledge of this great number of unexplained facts is often
interpreted by the admirers of Da Vinci, as showing an almost occult
insight into science many centuries in advance of his time. Such
interpretations, however, are illusive. The observation, for example,
that a tube placed against the ground enables one to hear movements on
the earth at a distance, is not in itself evidence of anything more than
acute scientific observation, as a similar method is in use among almost
every race of savages, notably the American Indians. On the other hand,
one is inclined to give credence to almost any story of the breadth of
knowledge of the man who came so near anticipating Hutton, Lyell, and
Darwin in his interpretation of the geological records as he found them
written on the rocks.
It is in this field of geology that Leonardo is entitled to the greatest
admiration by modern scientists. He had observed the deposit of fossil
shells in various strata of rocks, even on the tops of mountains, and he
rejected once for all the theory that they had been deposited there by
the Deluge. He rightly interpreted their presence as evidence that
they had once been deposited at the bottom of the sea. This process
he assumed bad taken hundreds and thousands of centuries, thus tacitly
rejecting the biblical tradition as to the date of the creation.
Notwithstanding the obvious interest that attaches to the investigations
of Leonardo, it must be admitted that his work in science remained
almost as infertile as that of his great precursor, Bacon. The really
stimulative work of this generation was done by a man of affairs, who
knew little of theoretical science except in one line, but who pursued
that one practical line until he achieved a wonderful result. This man
was Christopher Columbus. It is not necessary here to tell the trite
story of his accomplishment. Suffice it that his practical demonstration
of the rotundity of the earth is regarded by most modern writers as
marking an epoch in history. With the year of his voyage the epoch of
the Middle Ages is usually regarded as coming to an end. It must not be
supposed that any very sudden change came over the aspect of scholarship
of the time, but the preliminaries of great things had been achieved,
and when Columbus made his famous voyage in 1492, the man was already
alive who was to bring forward the first great vitalizing thought in
the field of pure science that the Western world had originated for more
than a thousand years. This man bore the name of Kopernik, or in its
familiar Anglicized form, Copernicus. His life work and that of his
disciples will claim our attention in the succeeding chapter.
IV. THE NEW COSMOLOGY--COPERNICUS TO KEPLER AND GALILEO
We have seen that the Ptolemaic astronomy, which was the accepted
doctrine throughout the Middle Ages, taught that the earth is round.
Doubtless there was a popular opinion current which regarded the earth
as flat, but it must be understood that this opinion had no champions
among men of science during the Middle Ages. When, in the year 1492,
Columbus sailed out to the west on his memorable voyage, his expectation
of reaching India had full scientific warrant, however much it may have
been scouted by certain ecclesiastics and by the average man of the
period. Nevertheless, we may well suppose that the successful voyage of
Columbus, and the still more demonstrative one made about thirty years
later by Magellan, gave the theory of the earth's rotundity a certainty
it could never previously have had. Alexandrian geographers had measured
the size of the earth, and had not hesitated to assert that by sailing
westward one might reach India. But there is a wide gap between theory
and practice, and it required the voyages of Columbus and his successors
to bridge that gap.
After the companions of Magellan completed the circumnavigation of the
globe, the general shape of our earth would, obviously, never again be
called in question. But demonstration of the sphericity of the earth
had, of course, no direct bearing upon the question of the earth's
position in the universe. Therefore the voyage of Magellan served to
fortify, rather than to dispute, the Ptolemaic theory. According to that
theory, as we have seen, the earth was supposed to lie immovable at the
centre of the universe; the various heavenly bodies, including the sun,
revolving about it in eccentric circles. We have seen that several
of the ancient Greeks, notably Aristarchus, disputed this conception,
declaring for the central position of the sun in the universe, and
the motion of the earth and other planets about that body. But this
revolutionary theory seemed so opposed to the ordinary observation that,
having been discountenanced by Hipparchus and Ptolemy, it did not find a
single important champion for more than a thousand years after the time
of the last great Alexandrian astronomer.
The first man, seemingly, to hark back to the Aristarchian conception
in the new scientific era that was now dawning was the noted cardinal,
Nikolaus of Cusa, who lived in the first half of the fifteenth century,
and was distinguished as a philosophical writer and mathematician. His
De Docta Ignorantia expressly propounds the doctrine of the earth's
motion. No one, however, paid the slightest attention to his suggestion,
which, therefore, merely serves to furnish us with another interesting
illustration of the futility of propounding even a correct hypothesis
before the time is ripe to receive it--particularly if the hypothesis is
not fully fortified by reasoning based on experiment or observation.
The man who was destined to put forward the theory of the earth's motion
in a way to command attention was born in 1473, at the village of Thorn,
in eastern Prussia. His name was Nicholas Copernicus. There is no more
famous name in the entire annals of science than this, yet posterity has
never been able fully to establish the lineage of the famous expositor
of the true doctrine of the solar system. The city of Thorn lies in
a province of that border territory which was then under control of
Poland, but which subsequently became a part of Prussia. It is claimed
that the aspects of the city were essentially German, and it is admitted
that the mother of Copernicus belonged to that race. The nationality of
the father is more in doubt, but it is urged that Copernicus used German
as his mother-tongue. His great work was, of course, written in Latin,
according to the custom of the time; but it is said that, when not
employing that language, he always wrote in German. The disputed
nationality of Copernicus strongly suggests that he came of a mixed
racial lineage, and we are reminded again of the influences of those
ethnical minglings to which we have previously more than once referred.
The acknowledged centres of civilization towards the close of the
fifteenth century were Italy and Spain. Therefore, the birthplace of
Copernicus lay almost at the confines of civilization, reminding us of
that earlier period when Greece was the centre of culture, but when the
great Greek thinkers were born in Asia Minor and in Italy.
As a young man, Copernicus made his way to Vienna to study medicine,
and subsequently he journeyed into Italy and remained there many years,
About the year 1500 he held the chair of mathematics in a college
at Rome. Subsequently he returned to his native land and passed his
remaining years there, dying at Domkerr, in Frauenburg, East Prussia, in
the year 1543.
It would appear that Copernicus conceived the idea of the heliocentric
system of the universe while he was a comparatively young man, since
in the introduction to his great work, which he addressed to Pope Paul
III., he states that he has pondered his system not merely nine years,
in accordance with the maxim of Horace, but well into the fourth period
of nine years. Throughout a considerable portion of this period the
great work of Copernicus was in manuscript, but it was not published
until the year of his death. The reasons for the delay are not very
fully established. Copernicus undoubtedly taught his system throughout
the later decades of his life. He himself tells us that he had even
questioned whether it were not better for him to confine himself to such
verbal teaching, following thus the example of Pythagoras. Just as his
life was drawing to a close, he decided to pursue the opposite course,
and the first copy of his work is said to have been placed in his hands
as he lay on his deathbed.
The violent opposition which the new system met from ecclesiastical
sources led subsequent commentators to suppose that Copernicus had
delayed publication of his work through fear of the church authorities.
There seems, however, to be no direct evidence for this opinion. It has
been thought significant that Copernicus addressed his work to the pope.
It is, of course, quite conceivable that the aged astronomer might wish
by this means to demonstrate that he wrote in no spirit of hostility
to the church. His address to the pope might have been considered as a
desirable shield precisely because the author recognized that his
work must needs meet with ecclesiastical criticism. Be that as it
may, Copernicus was removed by death from the danger of attack, and it
remained for his disciples of a later generation to run the gauntlet of
criticism and suffer the charges of heresy.
The work of Copernicus, published thus in the year 1543 at Nuremberg,
bears the title De Orbium Coelestium Revolutionibus.
It is not necessary to go into details as to the cosmological system
which Copernicus advocated, since it is familiar to every one. In a
word, he supposed the sun to be the centre of all the planetary motions,
the earth taking its place among the other planets, the list of which,
as known at that time, comprised Mercury, Venus, the Earth, Mars,
Jupiter, and Saturn. The fixed stars were alleged to be stationary, and
it was necessary to suppose that they are almost infinitely distant,
inasmuch as they showed to the observers of that time no parallax; that
is to say, they preserved the same apparent position when viewed from
the opposite points of the earth's orbit.
But let us allow Copernicus to speak for himself regarding his system,
His exposition is full of interest. We quote first the introduction just
referred to, in which appeal is made directly to the pope.
"I can well believe, most holy father, that certain people, when they
hear of my attributing motion to the earth in these books of mine, will
at once declare that such an opinion ought to be rejected. Now, my own
theories do not please me so much as not to consider what others may
judge of them. Accordingly, when I began to reflect upon what those
persons who accept the stability of the earth, as confirmed by the
opinion of many centuries, would say when I claimed that the earth
moves, I hesitated for a long time as to whether I should publish that
which I have written to demonstrate its motion, or whether it would not
be better to follow the example of the Pythagoreans, who used to hand
down the secrets of philosophy to their relatives and friends only in
oral form. As I well considered all this, I was almost impelled to
put the finished work wholly aside, through the scorn I had reason to
anticipate on account of the newness and apparent contrariness to reason
of my theory.
"My friends, however, dissuaded me from such a course and admonished
me that I ought to publish my book, which had lain concealed in my
possession not only nine years, but already into four times the ninth
year. Not a few other distinguished and very learned men asked me to do
the same thing, and told me that I ought not, on account of my anxiety,
to delay any longer in consecrating my work to the general service of
mathematicians.
"But your holiness will perhaps not so much wonder that I have dared to
bring the results of my night labors to the light of day, after having
taken so much care in elaborating them, but is waiting instead to hear
how it entered my mind to imagine that the earth moved, contrary to the
accepted opinion of mathematicians--nay, almost contrary to ordinary
human understanding. Therefore I will not conceal from your holiness
that what moved me to consider another way of reckoning the motions
of the heavenly bodies was nothing else than the fact that the
mathematicians do not agree with one another in their investigations. In
the first place, they are so uncertain about the motions of the sun and
moon that they cannot find out the length of a full year. In the
second place, they apply neither the same laws of cause and effect, in
determining the motions of the sun and moon and of the five planets,
nor the same proofs. Some employ only concentric circles, others use
eccentric and epicyclic ones, with which, however, they do not fully
attain the desired end. They could not even discover nor compute the
main thing--namely, the form of the universe and the symmetry of its
parts. It was with them as if some should, from different places, take
hands, feet, head, and other parts of the body, which, although very
beautiful, were not drawn in their proper relations, and, without making
them in any way correspond, should construct a monster instead of a
human being.
"Accordingly, when I had long reflected on this uncertainty of
mathematical tradition, I took the trouble to read again the books of
all the philosophers I could get hold of, to see if some one of them had
not once believed that there were other motions of the heavenly bodies.
First I found in Cicero that Niceties had believed in the motion of the
earth. Afterwards I found in Plutarch, likewise, that some others had
held the same opinion. This induced me also to begin to consider the
movability of the earth, and, although the theory appeared contrary to
reason, I did so because I knew that others before me had been allowed
to assume rotary movements at will, in order to explain the phenomena
of these celestial bodies. I was of the opinion that I, too, might be
permitted to see whether, by presupposing motion in the earth, more
reliable conclusions than hitherto reached could not be discovered for
the rotary motions of the spheres. And thus, acting on the hypothesis of
the motion which, in the following book, I ascribe to the earth, and by
long and continued observations, I have finally discovered that if the
motion of the other planets be carried over to the relation of the earth
and this is made the basis for the rotation of every star, not only will
the phenomena of the planets be explained thereby, but also the laws and
the size of the stars; all their spheres and the heavens themselves will
appear so harmoniously connected that nothing could be changed in any
part of them without confusion in the remaining parts and in the whole
universe. I do not doubt that clever and learned men will agree with me
if they are willing fully to comprehend and to consider the proofs
which I advance in the book before us. In order, however, that both
the learned and the unlearned may see that I fear no man's judgment, I
wanted to dedicate these, my night labors, to your holiness, rather than
to any one else, because you, even in this remote corner of the earth
where I live, are held to be the greatest in dignity of station and in
love for all sciences and for mathematics, so that you, through your
position and judgment, can easily suppress the bites of slanderers,
although the proverb says that there is no remedy against the bite of
calumny."
In chapter X. of book I., "On the Order of the Spheres," occurs a more
detailed presentation of the system, as follows:
"That which Martianus Capella, and a few other Latins, very well knew,
appears to me extremely noteworthy. He believed that Venus and Mercury
revolve about the sun as their centre and that they cannot go farther
away from it than the circles of their orbits permit, since they do
not revolve about the earth like the other planets. According to this
theory, then, Mercury's orbit would be included within that of Venus,
which is more than twice as great, and would find room enough within it
for its revolution.
"If, acting upon this supposition, we connect Saturn, Jupiter, and
Mars with the same centre, keeping in mind the greater extent of their
orbits, which include the earth's sphere besides those of Mercury and
Venus, we cannot fail to see the explanation of the regular order of
their motions. He is certain that Saturn, Jupiter, and Mars are always
nearest the earth when they rise in the evening--that is, when they
appear over against the sun, or the earth stands between them and the
sun--but that they are farthest from the earth when they set in the
evening--that is, when we have the sun between them and the earth. This
proves sufficiently that their centre belongs to the sun and is the same
about which the orbits of Venus and Mercury circle. Since, however, all
have one centre, it is necessary for the space intervening between the
orbits of Venus and Mars to include the earth with her accompanying
moon and all that is beneath the moon; for the moon, which stands
unquestionably nearest the earth, can in no way be separated from her,
especially as there is sufficient room for the moon in the aforesaid
space. Hence we do not hesitate to claim that the whole system, which
includes the moon with the earth for its centre, makes the round of that
great circle between the planets, in yearly motion about the sun,
and revolves about the centre of the universe, in which the sun rests
motionless, and that all which looks like motion in the sun is explained
by the motion of the earth. The extent of the universe, however, is
so great that, whereas the distance of the earth from the sun is
considerable in comparison with the size of the other planetary orbits,
it disappears when compared with the sphere of the fixed stars. I hold
this to be more easily comprehensible than when the mind is confused by
an almost endless number of circles, which is necessarily the case with
those who keep the earth in the middle of the universe. Although this
may appear incomprehensible and contrary to the opinion of many, I
shall, if God wills, make it clearer than the sun, at least to those who
are not ignorant of mathematics.
"The order of the spheres is as follows: The first and lightest of all
the spheres is that of the fixed stars, which includes itself and all
others, and hence is motionless as the place in the universe to which
the motion and position of all other stars is referred.
"Then follows the outermost planet, Saturn, which completes its
revolution around the sun in thirty years; next comes Jupiter with a
twelve years' revolution; then Mars, which completes its course in two
years. The fourth one in order is the yearly revolution which includes
the earth with the moon's orbit as an epicycle. In the fifth place is
Venus with a revolution of nine months. The sixth place is taken by
Mercury, which completes its course in eighty days. In the middle of
all stands the sun, and who could wish to place the lamp of this most
beautiful temple in another or better place. Thus, in fact, the sun,
seated upon the royal throne, controls the family of the stars which
circle around him. We find in their order a harmonious connection which
cannot be found elsewhere. Here the attentive observer can see why the
waxing and waning of Jupiter seems greater than with Saturn and smaller
than with Mars, and again greater with Venus than with Mercury. Also,
why Saturn, Jupiter, and Mars are nearer to the earth when they rise
in the evening than when they disappear in the rays of the sun. More
prominently, however, is it seen in the case of Mars, which when it
appears in the heavens at night, seems to equal Jupiter in size, but
soon afterwards is found among the stars of second magnitude. All of
this results from the same cause--namely, from the earth's motion. The
fact that nothing of this is to be seen in the case of the fixed stars
is a proof of their immeasurable distance, which makes even the orbit of
yearly motion or its counterpart invisible to us."(1)
The fact that the stars show no parallax had been regarded as an
important argument against the motion of the earth, and it was still so
considered by the opponents of the system of Copernicus. It had, indeed,
been necessary for Aristarchus to explain the fact as due to the extreme
distance of the stars; a perfectly correct explanation, but one that
implies distances that are altogether inconceivable. It remained for
nineteenth-century astronomers to show, with the aid of instruments of
greater precision, that certain of the stars have a parallax. But
long before this demonstration had been brought forward, the system of
Copernicus had been accepted as a part of common knowledge.
While Copernicus postulated a cosmical scheme that was correct as to its
main features, he did not altogether break away from certain defects of
the Ptolemaic hypothesis. Indeed, he seems to have retained as much of
this as practicable, in deference to the prejudice of his time. Thus
he records the planetary orbits as circular, and explains their
eccentricities by resorting to the theory of epicycles, quite after
the Ptolemaic method. But now, of course, a much more simple mechanism
sufficed to explain the planetary motions, since the orbits were
correctly referred to the central sun and not to the earth.
Needless to say, the revolutionary conception of Copernicus did not meet
with immediate acceptance. A number of prominent astronomers, however,
took it up almost at once, among these being Rhaeticus, who wrote
a commentary on the evolutions; Erasmus Reinhold, the author of the
Prutenic tables; Rothmann, astronomer to the Landgrave of Hesse, and
Maestlin, the instructor of Kepler. The Prutenic tables, just referred
to, so called because of their Prussian origin, were considered an
improvement on the tables of Copernicus, and were highly esteemed by
the astronomers of the time. The commentary of Rhaeticus gives us the
interesting information that it was the observation of the orbit of
Mars and of the very great difference between his apparent diameters at
different times which first led Copernicus to conceive the heliocentric
idea. Of Reinhold it is recorded that he considered the orbit of Mercury
elliptical, and that he advocated a theory of the moon, according to
which her epicycle revolved on an elliptical orbit, thus in a measure
anticipating one of the great discoveries of Kepler to which we shall
refer presently. The Landgrave of Hesse was a practical astronomer, who
produced a catalogue of fixed stars which has been compared with that
of Tycho Brahe. He was assisted by Rothmann and by Justus Byrgius.
Maestlin, the preceptor of Kepler, is reputed to have been the first
modern observer to give a correct explanation of the light seen on
portions of the moon not directly illumined by the sun. He explained
this as not due to any proper light of the moon itself, but as light
reflected from the earth. Certain of the Greek philosophers, however,
are said to have given the same explanation, and it is alleged also that
Leonardo da Vinci anticipated Maestlin in this regard.(2)
While, various astronomers of some eminence thus gave support to the
Copernican system, almost from the beginning, it unfortunately chanced
that by far the most famous of the immediate successors of Copernicus
declined to accept the theory of the earth's motion. This was Tycho
Brahe, one of the greatest observing astronomers of any age. Tycho
Brahe was a Dane, born at Knudstrup in the year 1546. He died in 1601 at
Prague, in Bohemia. During a considerable portion of his life he found
a patron in Frederick, King of Denmark, who assisted him to build a
splendid observatory on the Island of Huene. On the death of his patron
Tycho moved to Germany, where, as good luck would have it, he came in
contact with the youthful Kepler, and thus, no doubt, was instrumental
in stimulating the ambitions of one who in later years was to be known
as a far greater theorist than himself. As has been said, Tycho rejected
the Copernican theory of the earth's motion. It should be added,
however, that he accepted that part of the Copernican theory which
makes the sun the centre of all the planetary motions, the earth being
excepted. He thus developed a system of his own, which was in some sort
a compromise between the Ptolemaic and the Copernican systems. As Tycho
conceived it, the sun revolves about the earth, carrying with it the
planets-Mercury, Venus, Mars, Jupiter, and Saturn, which planets have
the sun and not the earth as the centre of their orbits. This cosmical
scheme, it should be added, may be made to explain the observed motions
of the heavenly bodies, but it involves a much more complex mechanism
than is postulated by the Copernican theory.
Various explanations have been offered of the conservatism which held
the great Danish astronomer back from full acceptance of the relatively
simple and, as we now know, correct Copernican doctrine. From our
latter-day point of view, it seems so much more natural to accept
than to reject the Copernican system, that we find it difficult to put
ourselves in the place of a sixteenth-century observer. Yet if we recall
that the traditional view, having warrant of acceptance by nearly all
thinkers of every age, recorded the earth as a fixed, immovable body, we
shall see that our surprise should be excited rather by the thinker who
can break away from this view than by the one who still tends to cling
to it.
Moreover, it is useless to attempt to disguise the fact that something
more than a mere vague tradition was supposed to support the idea of
the earth's overshadowing importance in the cosmical scheme.
The sixteenth-century mind was overmastered by the tenets of
ecclesiasticism, and it was a dangerous heresy to doubt that the Hebrew
writings, upon which ecclesiasticism based its claim, contained the last
word regarding matters of science. But the writers of the Hebrew text
had been under the influence of that Babylonian conception of the
universe which accepted the earth as unqualifiedly central--which,
indeed, had never so much as conceived a contradictory hypothesis;
and so the Western world, which had come to accept these writings as
actually supernatural in origin, lay under the spell of Oriental ideas
of a pre-scientific era. In our own day, no one speaking with authority
thinks of these Hebrew writings as having any scientific weight
whatever. Their interest in this regard is purely antiquarian; hence
from our changed point of view it seems scarcely credible that Tycho
Brahe can have been in earnest when he quotes the Hebrew traditions as
proof that the sun revolves about the earth. Yet we shall see that for
almost three centuries after the time of Tycho, these same dreamings
continued to be cited in opposition to those scientific advances which
new observations made necessary; and this notwithstanding the fact that
the Oriental phrasing is, for the most part, poetically ambiguous and
susceptible of shifting interpretations, as the criticism of successive
generations has amply testified.
As we have said, Tycho Brahe, great observer as he was, could not shake
himself free from the Oriental incubus. He began his objections, then,
to the Copernican system by quoting the adverse testimony of a Hebrew
prophet who lived more than a thousand years B.C. All of this shows
sufficiently that Tycho Brahe was not a great theorist. He was
essentially an observer, but in this regard he won a secure place in the
very first rank. Indeed, he was easily the greatest observing astronomer
since Hipparchus, between whom and himself there were many points of
resemblance. Hipparchus, it will be recalled, rejected the Aristarchian
conception of the universe just as Tycho rejected the conception of
Copernicus.
But if Tycho propounded no great generalizations, the list of specific
advances due to him is a long one, and some of these were to prove
important aids in the hands of later workers to the secure demonstration
of the Copernican idea. One of his most important series of studies had
to do with comets. Regarding these bodies there had been the greatest
uncertainty in the minds of astronomers. The greatest variety of
opinions regarding them prevailed; they were thought on the one hand to
be divine messengers, and on the other to be merely igneous phenomena
of the earth's atmosphere. Tycho Brahe declared that a comet which he
observed in the year 1577 had no parallax, proving its extreme distance.
The observed course of the comet intersected the planetary orbits,
which fact gave a quietus to the long-mooted question as to whether the
Ptolemaic spheres were transparent solids or merely imaginary; since the
comet was seen to intersect these alleged spheres, it was obvious that
they could not be the solid substance that they were commonly imagined
to be, and this fact in itself went far towards discrediting the
Ptolemaic system. It should be recalled, however, that this supposition
of tangible spheres for the various planetary and stellar orbits was
a mediaeval interpretation of Ptolemy's theory rather than an
interpretation of Ptolemy himself, there being nothing to show that the
Alexandrian astronomer regarded his cycles and epicycles as other than
theoretical.
An interesting practical discovery made by Tycho was his method of
determining the latitude of a place by means of two observations made at
an interval of twelve hours. Hitherto it had been necessary to observe
the sun's angle on the equinoctial days, a period of six months being
therefore required. Tycho measured the angle of elevation of some star
situated near the pole, when on the meridian, and then, twelve hours
later, measured the angle of elevation of the same star when it again
came to the meridian at the opposite point of its apparent circle about
the polestar. Half the sum of these angles gives the latitude of the
place of observation.
As illustrating the accuracy of Tycho's observations, it may be noted
that he rediscovered a third inequality of the moon's motion at its
variation, he, in common with other European astronomers, being then
quite unaware that this inequality had been observed by an Arabian
astronomer. Tycho proved also that the angle of inclination of the
moon's orbit to the ecliptic is subject to slight variation.
The very brilliant new star which shone forth suddenly in the
constellation of Cassiopeia in the year 1572, was made the object of
special studies by Tycho, who proved that the star had no sensible
parallax and consequently was far beyond the planetary regions. The
appearance of a new star was a phenomenon not unknown to the ancients,
since Pliny records that Hipparchus was led by such an appearance
to make his catalogue of the fixed stars. But the phenomenon is
sufficiently uncommon to attract unusual attention. A similar phenomenon
occurred in the year 1604, when the new star--in this case appearing in
the constellation of Serpentarius--was explained by Kepler as probably
proceeding from a vast combustion. This explanation--in which Kepler is
said to have followed. Tycho--is fully in accord with the most recent
theories on the subject, as we shall see in due course. It is surprising
to hear Tycho credited with so startling a theory, but, on the other
hand, such an explanation is precisely what should be expected from
the other astronomer named. For Johann Kepler, or, as he was originally
named, Johann von Kappel, was one of the most speculative astronomers of
any age. He was forever theorizing, but such was the peculiar quality of
his mind that his theories never satisfied him for long unless he could
put them to the test of observation. Thanks to this happy combination
of qualities, Kepler became the discoverer of three famous laws of
planetary motion which lie at the very foundation of modern astronomy,
and which were to be largely instrumental in guiding Newton to his
still greater generalization. These laws of planetary motion were vastly
important as corroborating the Copernican theory of the universe,
though their position in this regard was not immediately recognized
by contemporary thinkers. Let us examine with some detail into their
discovery, meantime catching a glimpse of the life history of the
remarkable man whose name they bear.
JOHANN KEPLER AND THE LAWS OF PLANETARY MOTION
Johann Kepler was born the 27th of December, 1571, in the little town of
Weil, in Wurtemburg. He was a weak, sickly child, further enfeebled by a
severe attack of small-pox. It would seem paradoxical to assert that the
parents of such a genius were mismated, but their home was not a happy
one, the mother being of a nervous temperament, which perhaps in some
measure accounted for the genius of the child. The father led the life
of a soldier, and finally perished in the campaign against the Turks.
Young Kepler's studies were directed with an eye to the ministry. After
a preliminary training he attended the university at Tubingen, where
he came under the influence of the celebrated Maestlin and became his
life-long friend.
Curiously enough, it is recorded that at first Kepler had no taste
for astronomy or for mathematics. But the doors of the ministry being
presently barred to him, he turned with enthusiasm to the study of
astronomy, being from the first an ardent advocate of the Copernican
system. His teacher, Maestlin, accepted the same doctrine, though he was
obliged, for theological reasons, to teach the Ptolemaic system, as also
to oppose the Gregorian reform of the calendar.
The Gregorian calendar, it should be explained, is so called because it
was instituted by Pope Gregory XIII., who put it into effect in the year
1582, up to which time the so-called Julian calendar, as introduced by
Julius Caesar, had been everywhere accepted in Christendom. This Julian
calendar, as we have seen, was a great improvement on preceding ones,
but still lacked something of perfection inasmuch as its theoretical
day differed appreciably from the actual day. In the course of fifteen
hundred years, since the time of Caesar, this defect amounted to a
discrepancy of about eleven days. Pope Gregory proposed to correct this
by omitting ten days from the calendar, which was done in September,
1582. To prevent similar inaccuracies in the future, the Gregorian
calendar provided that once in four centuries the additional day to make
a leap-year should be omitted, the date selected for such omission being
the last year of every fourth century. Thus the years 1500, 1900, and
2300, A.D., would not be leap-years. By this arrangement an approximate
rectification of the calendar was effected, though even this does not
make it absolutely exact.
Such a rectification as this was obviously desirable, but there was
really no necessity for the omission of the ten days from the calendar.
The equinoctial day had shifted so that in the year 1582 it fell on the
10th of March and September. There was no reason why it should not have
remained there. It would greatly have simplified the task of future
historians had Gregory contented himself with providing for the future
stability of the calendar without making the needless shift in question.
We are so accustomed to think of the 21st of March and 21st of September
as the natural periods of the equinox, that we are likely to forget
that these are purely arbitrary dates for which the 10th might have been
substituted without any inconvenience or inconsistency.
But the opposition to the new calendar, to which reference has been
made, was not based on any such considerations as these. It was due,
largely at any rate, to the fact that Germany at this time was under
sway of the Lutheran revolt against the papacy. So effective was the
opposition that the Gregorian calendar did not come into vogue in
Germany until the year 1699. It may be added that England, under stress
of the same manner of prejudice, held out against the new reckoning
until the year 1751, while Russia does not accept it even now.
As the Protestant leaders thus opposed the papal attitude in a matter
of so practical a character as the calendar, it might perhaps have
been expected that the Lutherans would have had a leaning towards the
Copernican theory of the universe, since this theory was opposed by the
papacy. Such, however, was not the case. Luther himself pointed out with
great strenuousness, as a final and demonstrative argument, the fact
that Joshua commanded the sun and not the earth to stand still; and
his followers were quite as intolerant towards the new teaching as were
their ultramontane opponents. Kepler himself was, at various times, to
feel the restraint of ecclesiastical opposition, though he was never
subjected to direct persecution, as was his friend and contemporary,
Galileo. At the very outset of Kepler's career there was, indeed,
question as to the publication of a work he had written, because that
work took for granted the truth of the Copernican doctrine. This
work appeared, however, in the year 1596. It bore the title Mysterium
Cosmographium, and it attempted to explain the positions of the various
planetary bodies. Copernicus had devoted much time to observation of the
planets with reference to measuring their distance, and his efforts had
been attended with considerable success. He did not, indeed, know the
actual distance of the sun, and, therefore, was quite unable to fix
the distance of any planet; but, on the other hand, he determined the
relative distance of all the planets then known, as measured in terms of
the sun's distance, with remarkable accuracy.
With these measurements as a guide, Kepler was led to a very fanciful
theory, according to which the orbits of the five principal planets
sustain a peculiar relation to the five regular solids of geometry.
His theory was this: "Around the orbit of the earth describe a
dodecahedron--the circle comprising it will be that of Mars; around
Mars describe a tetrahedron--the circle comprising it will be that of
Jupiter; around Jupiter describe a cube--the circle comprising it
will be that of Saturn; now within the earth's orbit inscribe an
icosahedron--the inscribed circle will be that of Venus; in the orbit
of Venus inscribe an octahedron--the circle inscribed will be that of
Mercury."(3)
Though this arrangement was a fanciful one, which no one would
now recall had not the theorizer obtained subsequent fame on more
substantial grounds, yet it evidenced a philosophical spirit on the
part of the astronomer which, misdirected as it was in this instance,
promised well for the future. Tycho Brahe, to whom a copy of the
work was sent, had the acumen to recognize it as a work of genius. He
summoned the young astronomer to be his assistant at Prague, and no
doubt the association thus begun was instrumental in determining the
character of Kepler's future work. It was precisely the training
in minute observation that could avail most for a mind which, like
Kepler's, tended instinctively to the formulation of theories. When
Tycho Brahe died, in 1601, Kepler became his successor. In due time
he secured access to all the unpublished observations of his great
predecessor, and these were of inestimable value to him in the progress
of his own studies.
Kepler was not only an ardent worker and an enthusiastic theorizer, but
he was an indefatigable writer, and it pleased him to take the public
fully into his confidence, not merely as to his successes, but as to
his failures. Thus his works elaborate false theories as well as correct
ones, and detail the observations through which the incorrect guesses
were refuted by their originator. Some of these accounts are highly
interesting, but they must not detain us here. For our present purpose
it must suffice to point out the three important theories, which, as
culled from among a score or so of incorrect ones, Kepler was able to
demonstrate to his own satisfaction and to that of subsequent observers.
Stated in a few words, these theories, which have come to bear the name
of Kepler's Laws, are the following:
1. That the planetary orbits are not circular, but elliptical, the sun
occupying one focus of the ellipses.
2. That the speed of planetary motion varies in different parts of the
orbit in such a way that an imaginary line drawn from the sun to the
planet--that is to say, the radius vector of the planet's orbit--always
sweeps the same area in a given time.
These two laws Kepler published as early as 1609. Many years more of
patient investigation were required before he found out the secret of
the relation between planetary distances and times of revolution which
his third law expresses. In 1618, however, he was able to formulate this
relation also, as follows:
3. The squares of the distance of the various planets from the sun are
proportional to the cubes of their periods of revolution about the sun.
All these laws, it will be observed, take for granted the fact that the
sun is the centre of the planetary orbits. It must be understood, too,
that the earth is constantly regarded, in accordance with the Copernican
system, as being itself a member of the planetary system, subject to
precisely the same laws as the other planets. Long familiarity has made
these wonderful laws of Kepler seem such a matter of course that it is
difficult now to appreciate them at their full value. Yet, as has been
already pointed out, it was the knowledge of these marvellously simple
relations between the planetary orbits that laid the foundation for the
Newtonian law of universal gravitation. Contemporary judgment could not,
of course, anticipate this culmination of a later generation. What it
could understand was that the first law of Kepler attacked one of the
most time-honored of metaphysical conceptions--namely, the Aristotelian
idea that the circle is the perfect figure, and hence that the planetary
orbits must be circular. Not even Copernicus had doubted the validity of
this assumption. That Kepler dared dispute so firmly fixed a belief,
and one that seemingly had so sound a philosophical basis, evidenced the
iconoclastic nature of his genius. That he did not rest content until he
had demonstrated the validity of his revolutionary assumption shows how
truly this great theorizer made his hypotheses subservient to the most
rigid inductions.
GALILEO GALILEI
While Kepler was solving these riddles of planetary motion, there was
an even more famous man in Italy whose championship of the Copernican
doctrine was destined to give the greatest possible publicity to the
new ideas. This was Galileo Galilei, one of the most extraordinary
scientific observers of any age. Galileo was born at Pisa, on the 18th
of February (old style), 1564. The day of his birth is doubly memorable,
since on the same day the greatest Italian of the preceding epoch,
Michael Angelo, breathed his last. Persons fond of symbolism have found
in the coincidence a forecast of the transit from the artistic to
the scientific epoch of the later Renaissance. Galileo came of an
impoverished noble family. He was educated for the profession of
medicine, but did not progress far before his natural proclivities
directed him towards the physical sciences. Meeting with opposition in
Pisa, he early accepted a call to the chair of natural philosophy in the
University of Padua, and later in life he made his home at Florence. The
mechanical and physical discoveries of Galileo will claim our attention
in another chapter. Our present concern is with his contribution to the
Copernican theory.
Galileo himself records in a letter to Kepler that he became a convert
to this theory at an early day. He was not enabled, however, to make any
marked contribution to the subject, beyond the influence of his general
teachings, until about the year 1610. The brilliant contributions which
he made were due largely to a single discovery--namely, that of the
telescope. Hitherto the astronomical observations had been made with the
unaided eye. Glass lenses had been known since the thirteenth century,
but, until now, no one had thought of their possible use as aids to
distant vision. The question of priority of discovery has never been
settled. It is admitted, however, that the chief honors belong to the
opticians of the Netherlands.
As early as the year 1590 the Dutch optician Zacharias Jensen placed
a concave and a convex lens respectively at the ends of a tube about
eighteen inches long, and used this instrument for the purpose of
magnifying small objects--producing, in short, a crude microscope. Some
years later, Johannes Lippershey, of whom not much is known except that
he died in 1619, experimented with a somewhat similar combination of
lenses, and made the startling observation that the weather-vane on
a distant church-steeple seemed to be brought much nearer when viewed
through the lens. The combination of lenses he employed is that still
used in the construction of opera-glasses; the Germans still call such a
combination a Dutch telescope.
Doubtless a large number of experimenters took the matter up and the
fame of the new instrument spread rapidly abroad. Galileo, down in
Italy, heard rumors of this remarkable contrivance, through the use of
which it was said "distant objects might be seen as clearly as those
near at hand." He at once set to work to construct for himself a similar
instrument, and his efforts were so far successful that at first he "saw
objects three times as near and nine times enlarged." Continuing his
efforts, he presently so improved his glass that objects were enlarged
almost a thousand times and made to appear thirty times nearer than
when seen with the naked eye. Naturally enough, Galileo turned this
fascinating instrument towards the skies, and he was almost immediately
rewarded by several startling discoveries. At the very outset, his
magnifying-glass brought to view a vast number of stars that are
invisible to the naked eye, and enabled the observer to reach the
conclusion that the hazy light of the Milky Way is merely due to the
aggregation of a vast number of tiny stars.
Turning his telescope towards the moon, Galileo found that body rough
and earth-like in contour, its surface covered with mountains, whose
height could be approximately measured through study of their shadows.
This was disquieting, because the current Aristotelian doctrine supposed
the moon, in common with the planets, to be a perfectly spherical,
smooth body. The metaphysical idea of a perfect universe was sure to
be disturbed by this seemingly rough workmanship of the moon. Thus
far, however, there was nothing in the observations of Galileo to bear
directly upon the Copernican theory; but when an inspection was made of
the planets the case was quite different. With the aid of his telescope,
Galileo saw that Venus, for example, passes through phases precisely
similar to those of the moon, due, of course, to the same cause. Here,
then, was demonstrative evidence that the planets are dark bodies
reflecting the light of the sun, and an explanation was given of the
fact, hitherto urged in opposition to the Copernican theory, that the
inferior planets do not seem many times brighter when nearer the earth
than when in the most distant parts of their orbits; the explanation
being, of course, that when the planets are between the earth and the
sun only a small portion of their illumined surfaces is visible from the
earth.