_Galileo at Pisa—Aristotle—Leonardo da Vinci—Galileo becomes a
Copernican—Urstisius—Bruno—Experiments on falling
bodies—Galileo at Padua—Thermometer._
NO sooner was Galileo settled in his new office than he renewed his
inquiries into the phenomena of nature with increased diligence. He
instituted a course of experiments for the purpose of putting to the
test the mechanical doctrines of Aristotle, most of which he found
unsupported even by the pretence of experience. It is to be regretted
that we do not more frequently find detailed his method of
experimenting, than occasionally in the course of his dialogues, and it
is chiefly upon the references which he makes to the results with which
the experiments furnished him, and upon the avowed and notorious
character of his philosophy, that the truth of these accounts must be
made to depend. Venturi has found several unpublished papers by Galileo
on the subject of motion, in the Grand Duke's private library at
Florence, bearing the date of 1590, in which are many of the theorems
which he afterwards developed in his Dialogues on Motion. These were not
published till fifty years afterwards, and we shall reserve an account
of their contents till we reach that period of his life.
Galileo was by no means the first who had ventured to call in question
the authority of Aristotle in matters of science, although he was
undoubtedly the first whose opinions and writings produced a very marked
and general effect. Nizzoli, a celebrated scholar who lived in the early
part of the 16th century, had condemned Aristotle's philosophy,
especially his Physics, in very unequivocal and forcible terms,
declaring that, although there were many excellent truths in his
writings, the number was scarcely less of false, useless, and ridiculous
propositions.[9] About the time of Galileo's birth, Benedetti had
written expressly in confutation of several propositions contained in
Aristotle's mechanics, and had expounded in a clear manner some of the
doctrines of statical equilibrium.[10] Within the last forty years it
has been established that the celebrated painter Leonardo da Vinci, who
died in 1519, amused his leisure hours in scientific pursuits; and many
ideas appear to have occurred to him which are to be found in the
writings of Galileo at a later date. It is not impossible (though there
are probably no means of directly ascertaining the fact) that Galileo
may have been acquainted with Leonardo's investigations, although they
remained, till very lately, almost unknown to the mathematical world.
This supposition is rendered more probable from the fact, that Mazenta,
the preserver of Leonardo's manuscripts, was, at the very time of their
discovery, a contemporary student with Galileo at Pisa. Kopernik, or, as
he is usually called, Copernicus, a native of Thorn in Prussia, had
published his great work, De Revolutionibus, in 1543, restoring the
knowledge of the true theory of the solar system, and his opinions were
gradually and silently gaining ground.
It is not satisfactorily ascertained at what period Galileo embraced
the new astronomical theory. Gerard Voss attributes his conversion
to a public lecture of Mæstlin, the instructor of Kepler; and later
writers (among whom is Laplace) repeat the same story, but without
referring to any additional sources of information, and in most
instances merely transcribing Voss's words, so as to shew indisputably
whence they derived their account. Voss himself gives no authority,
and his general inaccuracy makes his mere word not of much weight. The
assertion appears, on many accounts, destitute of much probability.
If the story were correct, it seems likely that some degree of
acquaintance, if not of friendly intercourse, would have subsisted
between Mæstlin, and his supposed pupil, such as in fact we find
subsisting between Mæstlin and his acknowledged pupil Kepler, the
devoted friend of Galileo; but, on the contrary, we find Mæstlin
writing to Kepler himself of Galileo as an entire stranger, and in
the most disparaging terms. If Mæstlin could lay claim to the honour
of so celebrated a disciple, it is not likely that he could fail so
entirely to comprehend the distinction it must confer upon himself as
to attempt diminishing it by underrating his pupil's reputation. There
is a passage in Galileo's works which more directly controverts the
claim advanced for Mæstlin, although Salusbury, in his life of Galileo,
having apparently an imperfect recollection of its tenor, refers to
this very passage in confirmation of Voss's statement. In the second
part of the dialogue on the Copernican system, Galileo makes Sagredo,
one of the speakers in it, give the following account:—"Being very
young, and having scarcely finished my course of philosophy, which I
left off as being set upon other employments, there chanced to come
into these parts a certain foreigner of Rostoch, _whose name, as I
remember, was Christianus Urstisius_, a follower of Copernicus, who,
in an academy, gave two or three lectures upon this point, to whom
many flocked as auditors; but I, thinking they went more for the
novelty of the subject than otherwise, did not go to hear him; for I
had concluded with myself that that opinion could be no other than a
solemn madness; and questioning some of those who had been there, I
perceived they all made a jest thereof, except one, who told me that
the business was not altogether to be laughed at: and because the man
was reputed by me to be very intelligent and wary, I repented that I
was not there, and began from that time forward, as oft as I met with
any one of the Copernican persuasion, to demand of them if they had
been always of the same judgment. Of as many as I examined I found not
so much as one who told me not that he had been a long time of the
contrary opinion, but to have changed it for this, as convinced by the
strength of the reasons proving the same; and afterwards questioning
them one by one, to see whether they were well possessed of the reasons
of the other side, I found them all to be very ready and perfect in
them, so that I could not truly say that they took this opinion out
of ignorance, vanity, or to show the acuteness of their wits. On the
contrary, of as many of the Peripatetics and Ptolemeans as I have
asked, (and out of curiosity I have talked with many,) what pains they
had taken in the book of Copernicus, I found very few that had so much
as superficially perused it, but of those who I thought had understood
the same, not one: and, moreover, I have inquired amongst the followers
of the Peripatetic doctrine, if ever any of them had held the contrary
opinion, and likewise found none that had. Whereupon, considering that
there was no man who followed the opinion of Copernicus that had not
been first on the contrary side, and that was not very well acquainted
with the reasons of Aristotle and Ptolemy, and, on the contrary, that
there was not one of the followers of Ptolemy that had ever been of
the judgment of Copernicus, and had left that to embrace this of
Aristotle;—considering, I say, these things, I began to think that
one who leaveth an opinion imbued with his milk and followed by very
many, to take up another, owned by very few, and denied by all the
schools, and that really seems a great paradox, must needs have been
moved, not to say forced, by more powerful reasons. For this cause I
am become very curious to dive, as they say, into the bottom of this
business." It seems improbable that Galileo should think it worth while
to give so detailed an account of the birth and growth of opinion in
any one besides himself; and although Sagredo is not the personage who
generally in the dialogue represents Galileo, yet as the real Sagredo
was a young nobleman, a pupil of Galileo himself, the account cannot
refer to him. The circumstance mentioned of the intermission of his
philosophical studies, though in itself trivial, agrees very well with
Galileo's original medical destination. Urstisius is not a fictitious
name, as possibly Salusbury may have thought, when alluding to this
passage; he was mathematical professor at Bâle, about 1567, and several
treatises by him are still extant. According to Kästner, his German name
was Wursteisen. In 1568 Voss informs us that he published some new
questions on Purbach's Theory of the Planets. He died at Bâle in 1586,
when Galileo was about twenty-two years old.
It is not unlikely that Galileo also, in part, owed his emancipation
from popular prejudices to the writings of Giordano Bruno, an
unfortunate man, whose unsparing boldness in exposing fallacies and
absurdities was rewarded by a judicial murder, and by the character of
heretic and infidel, with which his executioners endeavoured to
stigmatize him for the purpose of covering over their own atrocious
crime. Bruno was burnt at Rome in 1600, but not, as Montucla supposes,
on account of his "Spaccio della Bestia trionfante." The title of this
book has led him to suppose that it was directed against the church of
Rome, to which it does not in the slightest degree relate. Bruno
attacked the fashionable philosophy alternately with reason and
ridicule, and numerous passages in his writings, tedious and obscure as
they generally are, show that he had completely outstripped the age in
which he lived. Among his astronomical opinions, he believed that the
universe consisted of innumerable systems of suns with assemblages of
planets revolving round each of them, like our own earth, the smallness
of which, alone, prevented their being observed by us. He remarked
further, "that it is by no means improbable that there are yet other
planets revolving round our own sun, which we have not yet noticed,
either on account of their minute size or too remote distance from us."
He declined asserting that all the apparently fixed stars are really so,
considering this as not sufficiently proved, "because at such enormous
distances the motions become difficult to estimate, and it is only by
long observation that we can determine if any of these move round each
other, or what other motions they may have." He ridiculed the
Aristotelians in no very measured terms—"They harden themselves, and
heat themselves, and embroil themselves for Aristotle; they call
themselves his champions, they hate all but Aristotle's friends, they
are ready to live and die for Aristotle, and yet they do not understand
so much as the titles of Aristotle's chapters." And in another place he
introduces an Aristotelian inquiring, "Do you take Plato for an
ignoramus—Aristotle for an ass?" to whom he answers, "My son, I neither
call them asses, nor you mules,—them baboons, nor you apes,—as you
would have me: I told you that I esteem them the heroes of the world,
but I will not credit them without sufficient reason; and if you were
not both blind and deaf, you would understand that I must disbelieve
their absurd and contradictory assertions."[11] Bruno's works, though in
general considered those of a visionary and madman, were in very
extensive circulation, probably not the less eagerly sought after from
being included among the books prohibited by the Romish church; and
although it has been reserved for later observations to furnish complete
verification of his most daring speculations, yet there was enough,
abstractedly taken, in the wild freedom of his remarks, to attract a
mind like Galileo's; and it is with more satisfaction that we refer the
formation of his opinions to a man of undoubted though eccentric genius,
like Bruno, than to such as Maestlin, who, though a diligent and careful
observer, seems seldom to have taken any very enlarged views of the
science on which he was engaged.
With a few exceptions similar to those above mentioned, the rest of
Galileo's contemporaries well deserved the contemptuous epithet which he
fixed on them of Paper Philosophers, for, to use his own words, in a
letter to Kepler on this subject, "this sort of men fancied philosophy
was to be studied like the Æneid or Odyssey, and that the true reading
of nature was to be detected by the collation of texts." Galileo's own
method of philosophizing was widely different; seldom omitting to bring
with every new assertion the test of experiment, either directly in
confirmation of it, or tending to show its probability and consistency.
We have already seen that he engaged in a series of experiments to
investigate the truth of some of Aristotle's positions. As fast as he
succeeded in demonstrating the falsehood of any of them, he denounced
them from his professorial chair with an energy and success which
irritated more and more against him the other members of the academic
body.
There seems something in the stubborn opposition which he encountered in
establishing the truth of his mechanical theorems, still more stupidly
absurd than in the ill will to which, at a later period of his life, his
astronomical opinions exposed him: it is intelligible that the vulgar
should withhold their assent from one who pretended to discoveries in
the remote heavens, which few possessed instruments to verify, or
talents to appreciate; but it is difficult to find terms for
stigmatizing the obdurate folly of those who preferred the evidence of
their books to that of their senses, in judging of phenomena so obvious
as those, for instance, presented by the fall of bodies to the ground.
Aristotle had asserted, that if two different weights of the same
material were let fall from the same height, the heavier one would reach
the ground sooner than the other, in the proportion of their weights.
The experiment is certainly not a very difficult one, but nobody thought
of that method of argument, and consequently this assertion had been
long received, upon his word, among the axioms of the science of motion.
Galileo ventured to appeal from the authority of Aristotle to that of
his own senses, and maintained that, with the exception of an
inconsiderable difference, which he attributed to the disproportionate
resistance of the air, they would fall in the same time. The
Aristotelians ridiculed and refused to listen to such an idea. Galileo
repeated his experiments in their presence from the famous leaning tower
at Pisa: and with the sound of the simultaneously falling weights still
ringing in their ears, they could persist in gravely maintaining that a
weight of ten pounds would reach the ground in a tenth part of the time
taken by one of a single pound, because they were able to quote chapter
and verse in which Aristotle assures them that such is the fact. A
temper of mind like this could not fail to produce ill will towards him
who felt no scruples in exposing their wilful folly; and the watchful
malice of these men soon found the means of making Galileo desirous of
quitting his situation at Pisa. Don Giovanni de' Medici, a natural son
of Cosmo, who possessed a slight knowledge of mechanics on which he
prided himself, had proposed a contrivance for cleansing the port of
Leghorn, on the efficiency of which Galileo was consulted. His opinion
was unfavourable, and the violence of the inventor's disappointment,
(for Galileo's judgment was verified by the result,) took the somewhat
unreasonable direction of hatred towards the man whose penetration had
foreseen the failure. Galileo's situation was rendered so unpleasant by
the machinations of this person, that he decided on accepting overtures
elsewhere, which had already been made to him; accordingly, under the
negotiation of his staunch friend Guido Ubaldi, and with the consent of
Ferdinand, he procured from the republic of Venice a nomination for six
years to the professorship of mathematics in the university of Padua,
whither he removed in September 1592.
Galileo's predecessor in the mathematical chair at Padua was Moleti, who
died in 1588, and the situation had remained unfilled during the
intervening four years. This seems to show that the directors attributed
but little importance to the knowledge which it was the professor's duty
to impart. This inference is strengthened by the fact, that the amount
of the annual salary attached to it did not exceed 180 florins, whilst
the professors of philosophy and civil law, in the same university, were
rated at the annual stipends of 1400 and 1680 florins.[12] Galileo
joined the university about a year after its triumph over the Jesuits,
who had established a school in Padua about the year 1542, and,
increasing yearly in influence, had shown symptoms of a design to get
the whole management of the public education into the hands of their own
body.[13] After several violent disputes it was at length decreed by the
Venetian senate, in 1591, that no Jesuit should be allowed to give
instruction at Padua in any of the sciences professed in the university.
It does not appear that after this decree they were again troublesome to
the university, but this first decree against them was followed, in
1606, by a second more peremptory, which banished them entirely from the
Venetian territory. Galileo would of course find his fellow-professors
much embittered against that society, and would naturally feel inclined
to make common cause with them, so that it is not unlikely that the
hatred which the Jesuits afterwards bore to Galileo on personal
considerations, might be enforced by their recollection of the
university to which he had belonged.
Galileo's writings now began to follow each other with great rapidity,
but he was at this time apparently so careless of his reputation, that
many of his works and inventions, after a long circulation in manuscript
among his pupils and friends, found their way into the hands of those
who were not ashamed to publish them as their own, and to denounce
Galileo's claim to the authorship as the pretence of an impudent
plagiarist. He was, however, so much beloved and esteemed by his
friends, that they vied with each other in resenting affronts of this
nature offered to him, and in more than one instance he was relieved, by
their full and triumphant answers, from the trouble of vindicating his
own character.
To this epoch of Galileo's life may be referred his re-invention of the
thermometer. The original idea of this useful instrument belongs to the
Greek mathematician Hero; and Santorio himself, who has been named as
the inventor by Italian writers, and at one time claimed it himself,
refers it to him. In 1638, Castelli wrote to Cesarini that "he
remembered an experiment shown to him more than thirty-five years back
by Galileo, who took a small glass bottle, about the size of a hen's
egg, the neck of which was twenty-two inches long, and as narrow as a
straw. Having well heated the bulb in his hands, and then introducing
its mouth into a vessel in which was a little water, and withdrawing the
heat of his hand from the bulb, the water rose in the neck of the bottle
more than eleven inches above the level in the vessel, and Galileo
employed this principle in the construction of an instrument for
measuring heat and cold."[14] In 1613, a Venetian nobleman named
Sagredo, who has been already mentioned as Galileo's friend and pupil,
writes to him in the following words: "I have brought the instrument
which you invented for measuring heat into several convenient and
perfect forms, so that the difference of temperature between two rooms
is seen as far as 100 degrees."[15] This date is anterior to the claims
both of Santorio and Drebbel, a Dutch physician, who was the first to
introduce it into Holland.
Galileo's thermometer, as we have just seen, consisted merely of a glass
tube ending in a bulb, the air in which, being partly expelled by heat,
was replaced by water from a glass into which the open end of the tube
was plunged, and the different degrees of temperature were indicated by
the expansion of the air which yet remained in the bulb, so that the
scale would be the reverse of that of the thermometer now in use, for
the water would stand at the highest level in the coldest weather. It
was, in truth, a barometer also, in consequence of the communication
between the tube and external air, although Galileo did not intend it
for this purpose, and when he attempted to determine the relative weight
of the air, employed a contrivance still more imperfect than this rude
barometer would have been. A passage among his posthumous fragments
intimates that he subsequently used spirit of wine instead of water.
Viviani attributes an improvement of this imperfect instrument, but
without specifying its nature, to Ferdinand II., a pupil and subsequent
patron of Galileo, and, after the death of his father Cosmo, reigning
duke of Florence. It was still further improved by Ferdinand's younger
brother, Leopold de' Medici, who invented the modern process of
expelling all the air from the tube by boiling the spirit of wine in it,
and of hermetically sealing the end of the tube, whilst the contained
liquid is in this expanded state, which deprived it of its barometrical
character, and first made it an accurate thermometer. The final
improvement was the employment of mercury instead of spirit of wine,
which is recommended by Lana so early as 1670, on account of its equable
expansion.[16] For further details on the history and use of this
instrument, the reader may consult the Treatises on the THERMOMETER and
PYROMETER.
FOOTNOTES:
[9] Antibarbarus Philosophicus. Francofurti, 1674.
[10] Speculationum liber. Venetiis, 1585.
[11] De l'Infinito Universo. Dial. 3. La Cena de le Cenere, 1584.
[12] Riccoboni, Commentarii de Gymnasio Patavino, 1598.
[13] Nelli.
[14] Nelli.
[15] Venturi. Memorie e Lettere di Gal. Galilei. Modena, 1821.
[16] Prodromo all' Arte Maestra. Brescia, 1670.