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The Life of Galileo Galilei, with Illustrations of the Advancement of Experimental Philosophy

by John Elliot Drinkwater Bethune · English · Gutenberg #43877 · 770,470 chars · public domain (US)

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Title: The Life of Galileo Galilei, with Illustrations of the Advancement of Experimental Philosophy

Author: John Elliot Drinkwater Bethune


        
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*** START OF THE PROJECT GUTENBERG EBOOK THE LIFE OF GALILEO GALILEI, WITH ILLUSTRATIONS OF THE ADVANCEMENT OF EXPERIMENTAL PHILOSOPHY ***

Transcriber's Note.

Variable spelling and hyphenation have been retained. Minor punctuation
inconsistencies have been silently repaired. The author's corrections,
additions and comments have been applied in the text. Changes made by
the transcriber can be found at the end of the book. The original text
is printed in a two-column layout. Formatting and special characters are
indicated as follows:

    _italic_




[Illustration: Galileo Galilei]




                                  THE
                                  LIFE
                                   OF
                            GALILEO GALILEI,
                                  WITH
                    ILLUSTRATIONS OF THE ADVANCEMENT
                                   OF
                        EXPERIMENTAL PHILOSOPHY.

                               MDCCCXXX.

                                LONDON.




LIFE OF GALILEO:

WITH ILLUSTRATIONS OF THE ADVANCEMENT OF EXPERIMENTAL PHILOSOPHY.




CHAPTER I.

    _Introduction._


THE knowledge which we at present possess of the phenomena of nature and
of their connection has not by any means been regularly progressive, as
we might have expected, from the time when they first drew the attention
of mankind. Without entering into the question touching the scientific
acquirements of eastern nations at a remote period, it is certain that
some among the early Greeks were in possession of several truths,
however acquired, connected with the economy of the universe, which were
afterwards suffered to fall into neglect and oblivion. But the
philosophers of the old school appear in general to have confined
themselves at the best to observations; very few traces remain of their
having instituted _experiments_, properly so called. This putting of
nature to the torture, as Bacon calls it, has occasioned the principal
part of modern philosophical discoveries. The experimentalist may so
order his examination of nature as to vary at pleasure the circumstances
in which it is made, often to discard accidents which complicate the
general appearances, and at once to bring any theory which he may form
to a decisive test. The province of the mere observer is necessarily
limited: the power of selection among the phenomena to be presented is
in great measure denied to him, and he may consider himself fortunate if
they are such as to lead him readily to a knowledge of the laws which
they follow.

Perhaps to this imperfection of method it may be attributed that natural
philosophy continued to be stationary, or even to decline, during a long
series of ages, until little more than two centuries ago. Within this
comparatively short period it has rapidly reached a degree of perfection
so different from its former degraded state, that we can hardly
institute any comparison between the two. Before that epoch, a few
insulated facts, such as might first happen to be noticed, often
inaccurately observed and always too hastily generalized, were found
sufficient to excite the naturalist's lively imagination; and having
once pleased his fancy with the supposed fitness of his artificial
scheme, his perverted ingenuity was thenceforward employed in forcing
the observed phenomena into an imaginary agreement with the result of
his theory; instead of taking the more rational, and it should seem, the
more obvious, method of correcting the theory by the result of his
observations, and considering the one merely as the general and
abbreviated expression of the other. But natural phenomena were not then
valued on their own account, and for the proofs which they afford of a
vast and beneficent design in the structure of the universe, so much as
for the fertile topics which the favourite mode of viewing the subject
supplied to the spirit of scholastic disputation: and it is a
humiliating reflection that mankind never reasoned so ill as when they
most professed to cultivate the art of reasoning. However specious the
objects, and alluring the announcements of this art, the then prevailing
manner of studying it curbed and corrupted all that is free and noble in
the human mind. Innumerable fallacies lurked every where among the most
generally received opinions, and crowds of dogmatic and self-sufficient
pedants fully justified the lively definition, that "logic is the art of
talking unintelligibly on things of which we are ignorant."[1]

The error which lay at the root of the philosophy of the middle ages was
this:—from the belief that general laws and universal principles might
be discovered, of which the natural phenomena were _effects_, it was
thought that the proper order of study was, first to detect the general
_cause_, and then to pursue it into its consequences; it was considered
absurd to begin with the effect instead of the cause; whereas the real
choice lay between proceeding from particular facts to general facts,
or from general facts to particular facts; and it was under this
misrepresentation of the real question that all the sophistry lurked. As
soon as it is well understood that the general _cause_ is no other than
a single fact, common to a great number of phenomena, it is necessarily
perceived that an accurate scrutiny of these latter must precede any
safe reasoning with respect to the former. But at the time of which we
are speaking, those who adopted this order of reasoning, and who began
their inquiries by a minute and sedulous investigation of facts, were
treated with disdain, as men who degraded the lofty name of philosophy
by bestowing it upon mere mechanical operations. Among the earliest and
noblest of these was Galileo.

It is common, especially in this country, to name Bacon as the founder
of the present school of experimental philosophy; we speak of the
Baconian or inductive method of reasoning as synonimous and convertible
terms, and we are apt to overlook what Galileo had already done before
Bacon's writings appeared. Certainly the Italian did not range over the
circle of the sciences with the supreme and searching glance of the
English philosopher, but we find in every part of his writings
philosophical maxims which do not lose by comparison with those of
Bacon; and Galileo deserves the additional praise, that he himself gave
to the world a splendid practical illustration of the value of the
principles which he constantly recommended. In support of this view of
the comparative deserts of these two celebrated men, we are able to
adduce the authority of Hume, who will be readily admitted as a
competent judge of philosophical merit, where his prejudices cannot bias
his decision. Discussing the character of Bacon, he says, "If we
consider the variety of talents displayed by this man, as a public
speaker, a man of business, a wit, a courtier, a companion, an author, a
philosopher, he is justly the object of great admiration. If we consider
him merely as an author and philosopher, the light in which we view him
at present, though very estimable, he was yet inferior to his
contemporary Galileo, perhaps even to Kepler. Bacon pointed out at a
distance the road to true philosophy: Galileo both pointed it out to
others, and made himself considerable advances in it. The Englishman was
ignorant of geometry: the Florentine revived that science, excelled in
it, and was the first that applied it, together with experiment, to
natural philosophy. The former rejected with the most positive disdain
the system of Copernicus: the latter fortified it with new proofs
derived both from reason and the senses."[2]

If we compare them from another point of view, not so much in respect of
their intrinsic merit, as of the influence which each exercised on the
philosophy of his age, Galileo's superior talent or better fortune, in
arresting the attention of his contemporaries, seems indisputable. The
fate of the two writers is directly opposed the one to the other;
Bacon's works seem to be most studied and appreciated when his readers
have come to their perusal, imbued with knowledge and a philosophical
spirit, which, however, they have attained independently of his
assistance. The proud appeal to posterity which he uttered in his will,
"For my name and memory, I leave it to men's charitable speeches, and to
foreign nations, and the next ages," of itself indicates a consciousness
of the fact that his contemporary countrymen were but slightly affected
by his philosophical precepts. But Galileo's personal exertions changed
the general character of philosophy in Italy: at the time of his death,
his immediate pupils had obtained possession of the most celebrated
universities, and were busily engaged in practising and enforcing the
lessons which he had taught them; nor was it then easy to find there a
single student of natural philosophy who did not readily ascribe the
formation of his principles to the direct or remote influence of
Galileo's example. Unlike Bacon's, his reputation, and the value of his
writings, were higher among his contemporaries than they have since
become. This judgment perhaps awards the highest intellectual prize to
him whose disregarded services rise in estimation with the advance of
knowledge; but the praise due to superior usefulness belongs to him who
succeeded in training round him a school of imitators, and thereby
enabled his imitators to surpass himself.

The biography of men who have devoted themselves to philosophical
pursuits seldom affords so various and striking a succession of
incidents as that of a soldier or statesman. The life of a man who is
shut up during the greater part of his time in his study or laboratory
supplies but scanty materials for personal details; and the lapse of
time rapidly removes from us the opportunities of preserving such
peculiarities as might have been worth recording. An account of it will
therefore consist chiefly in a review of his works and opinions, and of
the influence which he and they have exercised over his own and
succeeding ages. Viewed in this light, few lives can be considered more
interesting than that of Galileo; and if we compare the state in which
he found, with that in which he left, the study of nature, we shall feel
how justly an enthusiastic panegyric pronounced upon the age immediately
following him may be transferred to this earlier period. "This is the
age wherein all men's minds are in a kind of fermentation, and the
spirit of wisdom and learning begins to mount and free itself from those
drossie and terrene impediments wherewith it has been so long clogged,
and from the insipid phlegm and _caput mortuum_ of useless notions in
which it hath endured so violent and long a fixation. This is the age
wherein, methinks, philosophy comes in with a spring tide, and the
peripatetics may as well hope to stop the current of the tide, or, with
Xerxes, to fetter the ocean, as hinder the overflowing of free
philosophy. Methinks I see how all the old rubbish must be thrown away,
and the rotten buildings be overthrown and carried away, with so
powerful an inundation. These are the days that must lay a new
foundation of a more magnificent philosophy, never to be overthrown,
that will empirically and sensibly canvass the phenomena of nature,
deducing the causes of things from such originals in nature as we
observe are producible by art, and the infallible demonstration of
mechanics: and certainly this is the way, and no other, to build a true
and permanent philosophy."[3]


FOOTNOTES:

[1] Ménage.

[2] Hume's England, James I.

[3] Power's Experimental Philosophy, 1663.




CHAPTER II.

    _Galileo's Birth—Family—Education—Observation of the
      Pendulum—Pulsilogies—Hydrostatical Balance—Lecturer at Pisa._


GALILEO GALILEI was born at Pisa, on the 15th day of February, 1564, of
a noble and ancient Florentine family, which, in the middle of the
fourteenth century, adopted this surname instead of Bonajuti, under
which several of their ancestors filled distinguished offices in the
Florentine state. Some misapprehension has occasionally existed, in
consequence of the identity of his proper name with that of his family;
his most correct appellation would perhaps be Galileo de' Galilei, but
the surname usually occurs as we have written it. He is most commonly
spoken of by his Christian name, agreeably to the Italian custom; just
as Sanzio, Buonarotti, Sarpi, Reni, Vecelli, are universally known by
their Christian names of Raphael, Michel Angelo, Fra Paolo, Guido, and
Titian.

Several authors have followed Rossi in styling Galileo illegitimate, but
without having any probable grounds even when they wrote, and the
assertion has since been completely disproved by an inspection of the
registers at Pisa and Florence, in which are preserved the dates of his
birth, and of his mother's marriage, eighteen months previous to it.[4]

His father, Vincenzo Galilei, was a man of considerable talent and
learning, with a competent knowledge of mathematics, and particularly
devoted to the theory and practice of music, on which he published
several esteemed treatises. The only one which it is at present easy to
procure—his Dialogue on ancient and modern music—exhibits proofs, not
only of a thorough acquaintance with his subject, but of a sound and
vigorous understanding applied to other topics incidentally discussed.
There is a passage in the introductory part, which becomes interesting
when considered as affording some traces of the precepts by which
Galileo was in all probability trained to reach his preeminent station
in the intellectual world. "It appears to me," says one of the speakers
in the dialogue, "that they who in proof of any assertion rely simply on
the weight of authority, without adducing any argument in support of it,
act very absurdly: I, on the contrary, wish to be allowed freely to
question and freely to answer you without any sort of adulation, as well
becomes those who are truly in search of truth." Sentiments like these
were of rare occurrence at the close of the sixteenth century, and it is
to be regretted that Vincenzo hardly lived long enough to witness his
idea of a true philosopher splendidly realized in the person of his son.
Vincenzo died at an advanced age, in 1591. His family consisted of three
sons, Galileo, Michel Angelo, and Benedetto, and the same number of
daughters, Giulia, Virginia, and Livia. After Vincenzo's death the chief
support of the family devolved upon Galileo, who seems to have assisted
them to his utmost power. In a letter to his mother, dated 1600,
relative to the intended marriage of his sister Livia with a certain
Pompeo Baldi, he agrees to the match, but recommends its temporary
postponement, as he was at that time exerting himself to furnish money
to his brother Michel Angelo, who had received the offer of an
advantageous settlement in Poland. As the sum advanced to his brother,
which prevented him from promoting his sister's marriage, did not exceed
200 crowns, it may be inferred that the family were in a somewhat
straitened condition. However he promises, as soon as his brother should
repay him, "to take measures for the young lady, since she too is bent
upon _coming out_ to prove the miseries of this world."—As Livia was at
the date of this letter in a convent, the last expression seems to
denote that she had been destined to take the veil. This proposed
marriage never took place, but Livia was afterwards married to Taddeo
Galletti: her sister Virginia married Benedetto Landucci. Galileo
mentions one of his sisters, (without naming her) as living with him in
1619 at Bellosguardo. Michel Angelo is probably the same brother of
Galileo who is mentioned by Liceti as having communicated from Germany
some observations on natural history.[5] He finally settled in the
service of the Elector of Bavaria; in what situation is not known, but
upon his death the Elector granted a pension to his family, who then
took up their abode at Munich. On the taking of that city in 1636, in
the course of the bloody thirty years' war, which was then raging
between the Austrians and Swedes, his widow and four of his children
were killed, and every thing which they possessed was either burnt or
carried away. Galileo sent for his two nephews, Alberto and a younger
brother, to Arcetri near Florence, where he was then living. These two
were then the only survivors of Michel Angelo's family; and many of
Galileo's letters about that date contain allusions to the assistance he
had been affording them. The last trace of Alberto is on his return into
Germany to the Elector, in whose service his father had died. These
details include almost every thing which is known of the rest of
Vincenzo's family.

Galileo exhibited early symptoms of an active and intelligent mind, and
distinguished himself in his childhood by his skill in the construction
of ingenious toys and models of machinery, supplying the deficiencies of
his information from the resources of his own invention; and he
conciliated the universal good-will of his companions by the ready good
nature with which he employed himself in their service and for their
amusement. It is worthy of observation, that the boyhood of his great
follower Newton, whose genius in many respects so closely resembled his
own, was marked by a similar talent. Galileo's father was not opulent,
as has been already stated: he was burdened with a large family, and was
unable to provide expensive instructors for his son; but Galileo's own
energetic industry rapidly supplied the want of better opportunities;
and he acquired, under considerable disadvantages, the ordinary
rudiments of a classical education, and a competent knowledge of the
other branches of literature which were then usually studied. His
leisure hours were applied to music and drawing; for the former
accomplishment he inherited his father's talent, being an excellent
performer on several instruments, especially on the lute; this continued
to be a favourite recreation during the whole of his life. He was also
passionately fond of painting, and at one time he wished to make it his
profession: and his skill and judgment of pictures were highly esteemed
by the most eminent contemporary artists, who did not scruple to own
publicly their deference to young Galileo's criticism.

When he had reached his nineteenth year, his father, becoming daily more
sensible of his superior genius, determined, although at a great
personal sacrifice, to give him the advantages of an university
education. Accordingly, in 1581, he commenced his academical studies in
the university of his native town, Pisa, his father at this time
intending that he should adopt the profession of medicine. In the
matriculation lists at Pisa, he is styled Galileo, the son of Vincenzo
Galilei, a Florentine, Scholar in Arts. His instructor was the
celebrated botanist, Andreas Cæsalpinus, who was professor of medicine
at Pisa from 1567 to 1592. Hist. Acad. Pisan.; Pisis, 1791. It is dated
5th November, 1581. Viviani, his pupil, friend, and panegyrist, declares
that, almost from the first day of his being enrolled on the lists of
the academy, he was noticed for the reluctance with which he listened to
the dogmas of the Aristotelian philosophy, then universally taught; and
he soon became obnoxious to the professors from the boldness with which
he promulgated what they styled his philosophical paradoxes. His early
habits of free inquiry were irreconcileable with the mental quietude of
his instructors, whose philosophic doubts, when they ventured to
entertain any, were speedily lulled by a quotation from Aristotle.
Galileo thought himself capable of giving the world an example of a
sounder and more original mode of thinking; he felt himself destined to
be the founder of a new school of rational and experimental philosophy.
Of this we are now securely enjoying the benefits; and it is difficult
at this time fully to appreciate the obstacles which then presented
themselves to free inquiry: but we shall see, in the course of this
narrative, how arduous their struggle was who happily effected this
important revolution. The vindictive rancour with which the partisans of
the old philosophy never ceased to assail Galileo is of itself a
sufficient proof of the prominent station which he occupied in the
contest.

Galileo's earliest mechanical discovery, to the superficial observer
apparently an unimportant one, occurred during the period of his studies
at Pisa. His attention was one day arrested by the vibrations of a lamp
swinging from the roof of the cathedral, which, whether great or small,
seemed to recur at equal intervals. The instruments then employed for
measuring time were very imperfect: Galileo attempted to bring his
observation to the test before quitting the church, by comparing the
vibrations with the beatings of his own pulse, and his mind being then
principally employed upon his intended profession, it occurred to him,
when he had further satisfied himself of their regularity by repeated
and varied experiments, that the process he at first adopted might be
reversed, and that an instrument on this principle might be usefully
employed in ascertaining the rate of the pulse, and its variation from
day to day. He immediately carried the idea into execution, and it was
for this sole and limited purpose that the first pendulum was
constructed. Viviani tells us, that the value of the invention was
rapidly appreciated by the physicians of the day, and was in common use
in 1654, when he wrote.

[Illustration: Instrument No. 1, No. 2, No. 3]

Santorio, who was professor of medicine at Padua, has given
representations of four different forms of these instruments, which he
calls pulsilogies, (_pulsilogias_,) and strongly recommends to medical
practitioners.[6] These instruments seem to have been used in the
following manner: No. 1 consists merely of a weight fastened to a string
and a graduated scale. The string being gathered up into the hand till
the vibrations of the weight coincided with the beatings of the
patient's pulse, the length was ascertained from the scale, which, of
course, if great, indicated a languid, if shorter, a more lively action.
In No. 2 the improvement is introduced of connecting the scale and
string, the length of the latter is regulated by the turns of a peg at
_a_, and a bead upon the string at _b_ showed the measure. No. 3 is
still more compact, the string being shortened by winding upon an axle
at the back of the dial-plate. The construction of No. 4, which Santorio
claims as his own improvement, is not given, but it is probable that the
principal index, by its motion, shifted a weight to different distances
from the point of suspension, and that the period of vibration was
still more accurately adjusted by a smaller weight connected with the
second index. Venturi seems to have mistaken the third figure for that
of a pendulum clock, as he mentions this as one of the earliest
adaptations of Galileo's principle to that purpose;[7] but it is
obvious, from Santorio's description, that it is nothing more than a
circular scale, the index showing, by the figure to which it points, the
length of string remaining unwound upon the axis. We shall, for the
present, postpone the consideration of the invention of pendulum clocks,
and the examination of the different claims to the honour of their first
construction.

At the time of which we are speaking, Galileo was entirely ignorant of
mathematics, the study of which was then at a low ebb, not only in
Italy, but in every part of Europe. Commandine had recently revived a
taste for the writings of Euclid and Archimedes, and Vieta Tartalea and
others had made considerable progress in algebra, Guido Ubaldi and
Benedetti had done something towards establishing the principles of
statics, which was the only part of mechanics as yet cultivated; but
with these inconsiderable exceptions the application of mathematics to
the phenomena of nature was scarcely thought of. Galileo's first
inducement to acquire a knowledge of geometry arose from his partiality
for drawing and music, and from the wish to understand their principles
and theory. His father, fearful lest he should relax his medical
studies, refused openly to encourage him in this new pursuit; but he
connived at the instruction which his son now began to receive in the
writings of Euclid, from the tuition of an intimate friend, named
Ostilio Ricci, who was one of the professors in the university.
Galileo's whole attention was soon directed to the enjoyment of the new
sensations thus communicated to him, insomuch that Vincenzo, finding his
prognostics verified, began to repent his indirect sanction, and
privately requested Ricci to invent some excuse for discontinuing his
lessons. But it was fortunately too late; the impression was made and
could not be effaced; from that time Hippocrates and Galen lay unheeded
before the young physician, and served only to conceal from his father's
sight the mathematical volumes on which the whole of his time was really
employed. His progress soon revealed the true nature of his pursuits:
Vincenzo yielded to the irresistible predilection of his son's mind, and
no longer attempted to turn him from the speculations to which his whole
existence was thenceforward abandoned.

After mastering the elementary writers, Galileo proceeded to the study
of Archimedes, and, whilst perusing the Hydrostatics of that author,
composed his earliest work,—an Essay on the Hydrostatical Balance. In
this he explains the method probably adopted by Archimedes for the
solution of Hiero's celebrated question[8], and shows himself already
well acquainted with the true principles of specific gravities. This
essay had an immediate and important influence on young Galileo's
fortunes, for it introduced him to the approving notice of Guido Ubaldi,
then one of the most distinguished mathematicians of Italy. At his
suggestion Galileo applied himself to consider the position of the
centre of gravity in solid bodies, a choice of subject that sufficiently
showed the estimate Ubaldi had formed of his talents; for it was a
question on which Commandine had recently written, and which engaged at
that time the attention of geometricians of the highest order. Galileo
tells us himself that he discontinued these researches on meeting with
Lucas Valerio's treatise on the same subject. Ubaldi was so much struck
with the genius displayed in the essay with which Galileo furnished him,
that he introduced him to his brother, the Cardinal Del Monte: by this
latter he was mentioned to Ferdinand de' Medici, the reigning Duke of
Tuscany, as a young man of whom the highest expectations might be
entertained. By the Duke's patronage he was nominated, in 1589, to the
lectureship of mathematics at Pisa, being then in his twenty-sixth year.
His public salary was fixed at the insignificant sum of sixty crowns
annually, but he had an opportunity of greatly adding to his income by
private tuition.


FOOTNOTES:

[4] Erythræus, Pinacotheca, vol. i.; Salusbury's Life of Galileo. Nelli,
Vita di Gal. Galilei.

[5] De his quæ diu vivunt. Patavii, 1612.

[6] Comment, in Avicennam. Venetiis, 1625.

[7] Essai sur les Ouvrages de Leonard da Vinci. Paris, 1797.

[8] See Treatise on HYDROSTATICS.




CHAPTER III.

    _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.




CHAPTER IV.

    _Astronomy before Copernicus—Fracastoro—Bacon—Kepler—Galileo's
      Treatise on the Sphere._


THIS period of Galileo's lectureship at Padua derives interest from its
including the first notice which we find of his having embraced the
doctrines of the Copernican astronomy. Most of our readers are aware of
the principles of the theory of the celestial motions which Copernicus
restored; but the number of those who possess much knowledge of the
cumbrous and unwieldy system which it superseded is perhaps more
limited. The present is not a fit opportunity to enter into many details
respecting it; these will find their proper place in the History of
Astronomy: but a brief sketch of its leading principles is necessary to
render what follows intelligible.

The earth was supposed to be immoveably fixed in the centre of the
universe, and immediately surrounding it the atmospheres of air and
fire, beyond which the sun, moon, and planets, were thought to be
carried round the earth, fixed each to a separate orb or heaven of solid
but transparent matter. The order of distance in which they were
supposed to be placed with regard to the central earth was as follows:
The Moon, Mercury, Venus, The Sun, Mars, Jupiter, and Saturn. It became
a question in the ages immediately preceding Copernicus, whether the Sun
was not nearer the Earth than Mercury, or at least than Venus; and this
question was one on which the astronomical theorists were then chiefly
divided.

We possess at this time a curious record of a former belief in this
arrangement of the Sun and planets, in the order in which the days of
the week have been named from them. According to the dreams of
Astrology, each planet was supposed to exert its influence in
succession, reckoning from the most distant down to the nearest, over
each hour of the twenty-four. The planet which was supposed to
predominate over the first hour, gave its name to that day.[17] The
general reader will trace this curious fact more easily with the French
or Latin names than with the English, which have been translated into
the titles of the corresponding Saxon deities. Placing the Sun and
planets in the following order, and beginning, for instance, with
Monday, or the Moon's day; Saturn ruled the second hour of that day,
Jupiter the third, and so round till we come again and again to the Moon
on the 8th, 15th, and 22d hours; Saturn ruled the 23d, Jupiter the
24th, so that the next day would be the day of Mars, or, as the Saxons
translated it, Tuisco's day, or Tuesday. In the same manner the
following days would belong respectively to Mercury or Woden, Jupiter or
Thor, Venus or Frea, Saturn or Seater, the Sun, and again the Moon. In
this manner the whole week will be found to complete the cycle of the
seven planets.

[Illustration: Cycle of the seven planets.]

The other stars were supposed to be fixed in an outer orb, beyond which
were two crystalline spheres, (as they were called,) and on the outside
of all, the _primum mobile_ or _first moveable_, which sphere was
supposed to revolve round the earth in twenty-four hours, and by its
friction, or rather, as most of the philosophers of that day chose to
term it, by the sort of heavenly influence which it exercised on the
interior orbs, to carry them round with a similar motion. Hence the
diversity of day and night. But beside this principal and general
motion, each orb was supposed to have one of its own, which was intended
to account for the apparent changes of position of the planets with
respect to the fixed stars and to each other. This supposition, however,
proving insufficient to account for all the irregularities of motion
observed, two hypotheses were introduced.—First, that to each planet
belonged several concentric spheres or heavens, casing each other like
the coats of an onion, and, secondly, that the centres of these solid
spheres, with which the planet revolved, were placed in the
circumference of a secondary revolving sphere, the centre of which
secondary sphere was situated at the earth. They thus acquired the names
of Eccentrics or Epicycles, the latter word signifying a circle upon a
circle. The whole art of astronomers was then directed towards inventing
and combining different eccentric and epicyclical motions, so as to
represent with tolerable fidelity the ever varying phenomena of the
heavens. Aristotle had lent his powerful assistance in this, as in other
branches of natural philosophy, in enabling the false system to prevail
against and obliterate the knowledge of the true, which, as we gather
from his own writings, was maintained by some philosophers before his
time. Of these ancient opinions, only a few traces now remain,
principally preserved in the works of those who were adverse to them.
Archimedes says expressly that Aristarchus of Samos, who lived about 300
B. C., taught the immobility of the sun and stars, and that the earth is
carried round the central sun.[18] Aristotle's words are: "Most of those
who assert that the whole concave is finite, say that the earth is
situated in the middle point of the universe: those who are called
Pythagoreans, who live in Italy, are of a contrary opinion. For they say
that fire is in the centre, and that the earth, which, according to
them, is one of the stars, occasions the change of day and night by its
own motion, with which it is carried about the centre." It might be
doubtful, upon this passage alone, whether the Pythagorean theory
embraced more than the diurnal motion of the earth, but a little
farther, we find the following passage: "Some, as we have said, make the
earth to be one of the stars: others say that it is placed in the centre
of the Universe, and revolves on a central axis."[19] From which, in
conjunction with the former extract, it very plainly appears that the
Pythagoreans maintained both the diurnal and annual motions of the
earth.

Some idea of the supererogatory labour entailed upon astronomers by the
adoption of the system which places the earth in the centre, may be
formed in a popular manner by observing, in passing through a thickly
planted wood, in how complicated a manner the relative positions of the
trees appear at each step to be continually changing, and by considering
the difficulty with which the laws of their apparent motions could be
traced, if we were to attempt to refer these changes to a real motion of
the trees instead of the traveller. The apparent complexity in the
heavens is still greater than in the case suggested; because, in
addition to the earth's motions, with which all the stars appear to be
impressed, each of the planets has also a real motion of its own, which
of course greatly contributes to perplex and complicate the general
appearances. Accordingly the heavens rapidly became, under this system,

    "With centric and eccentric scribbled o'er,
    Cycle and epicycle, orb in orb;"[20]

crossing and penetrating each other in every direction. Maestlin has
given a concise enumeration of the principal orbs which belonged to this
theory. After warning the readers that "they are not mere fictions which
have nothing to correspond with them out of the imagination, but that
they exist really, and bodily in the heavens,"[21] he describes seven
principal spheres belonging to each planet, which he classes as
Eccentrics, Epicycles, and Concentrepicycles, and explains their use in
accounting for the planet's revolutions, motions of the apogee, and
nodes, &c. &c. In what manner this multitude of solid and crystalline
orbs were secured from injuring or interfering with each other was not
very closely inquired into.

The reader will cease to expect any very intelligible explanation of
this and numberless other difficulties which belong to this unwieldy
machinery when he is introduced to the reasoning by which it was upheld.
Gerolamo Fracastoro, who lived in the sixteenth century, writes in the
following terms, in his work entitled Homocentrica, (certainly one of
the best productions of the day,) in which he endeavours to simplify the
necessary apparatus, and to explain all the phenomena (as the title of
his book implies) by concentric spheres round the earth. "There are
some, not only of the ancients but also among the moderns, who believe
that the stars move freely without any such agency; but it is difficult
to conceive in what manner they have imbued themselves with this notion,
_since not only reason, but the very senses, inform us that all the
stars are carried round fastened to solid spheres_." What ideas
Fracastoro entertained of the evidence of the "senses" it is not now
easy to guess, but he goes on to give a specimen of the "reasoning"
which appeared to him so incontrovertible. "The planets are observed to
move one while forwards, then backwards, now to the right, now to the
left, quicker and slower by turns; which variety is consistent with a
compound structure like that of an animal, which possesses in itself
various springs and principles of action, but is totally at variance
with our notion of a simple and undecaying substance like the heavens
and heavenly bodies. For that which is simple, is altogether single, and
singleness is of one only nature, and one nature can be the cause of
only one effect; and therefore it is altogether impossible that the
stars of themselves should move with such variety of motion. And
besides, if the stars move by themselves, they either move in an empty
space, or in a fluid medium like the air. But there cannot be such a
thing as empty space, and if there were such a medium, the motion of the
star would occasion condensation and rarefaction in different parts of
it, which is the property of corruptible bodies and where they exist
some violent motion is going on; but the heavens are incorruptible and
are not susceptible of violent motion, and hence, and from many other
similar reasons, any one who is not obstinate may satisfy himself that
the stars cannot have any independent motion."

Some persons may perhaps think that arguments of this force are
unnecessarily dragged from the obscurity to which they are now for the
most part happily consigned; but it is essential, in order to set
Galileo's character and merits in their true light, to show how low at
this time philosophy had fallen. For we shall form a very inadequate
notion of his powers and deserts if we do not contemplate him in the
midst of men who, though of undoubted talent and ingenuity, could so far
bewilder themselves as to mistake such a string of unmeaning phrases for
argument: we must reflect on the difficulty every one experiences in
delivering himself from the erroneous impressions of infancy, which will
remain stamped upon the imagination in spite of all the efforts of
matured reason to erase them, and consider every step of Galileo's
course as a triumph over difficulties of a like nature. We ought to be
fully penetrated with this feeling before we sit down to the perusal of
his works, every line of which will then increase our admiration of the
penetrating acuteness of his invention and unswerving accuracy of his
judgment. In almost every page we discover an allusion to some new
experiment, or the germ of some new theory; and amid all this wonderful
fertility it is rarely indeed that we find the exuberance of his
imagination seducing him from the rigid path of philosophical induction.
This is the more remarkable as he was surrounded by friends and
contemporaries of a different temperament and much less cautious
disposition. A disadvantageous contrast is occasionally furnished even
by the sagacious Bacon, who could so far deviate from the sound
principles of inductive philosophy, as to write, for instance, in the
following strain, bordering upon the worst manner of the
Aristotelians:—"Motion in a circle has no limit, and seems to emanate
from the appetite of the body, which moves only for the sake of moving,
and that it may follow itself and seek its own embraces, and put in
action and enjoy its own nature, and exercise its peculiar operation: on
the contrary, motion in a straight line seems transitory, and to move
towards a limit of cessation or rest, and that it may reach some point,
and then put off its motion."[22] Bacon rejected all the machinery of
the _primum mobile_ and the solid spheres, the eccentrics and the
epicycles, and carried his dislike of these doctrines so far as to
assert that nothing short of their gross absurdity could have driven
theorists to the extravagant supposition of the motion of the earth,
which, said he, "we know to be most false."[23] Instances of extravagant
suppositions and premature generalizations are to be found in almost
every page of his other great contemporary, Kepler.

It is with pain that we observe Delambre taking every opportunity, in
his admirable History of Astronomy, to undervalue and sneer at Galileo,
seemingly for the sake of elevating the character of Kepler, who appears
his principal favourite, but whose merit as a philosopher cannot safely
be brought into competition with that of his illustrious contemporary.
Delambre is especially dissatisfied with Galileo, for taking no notice,
in his "System of the World," of the celebrated laws of the planetary
motions which Kepler discovered, and which are now inseparably connected
with his name. The analysis of Newton and his successors has now
identified those apparently mysterious laws with the general phenomena
of motion, and has thus entitled them to an attention of which, before
that time, they were scarcely worthy; at any rate not more than is at
present the empirical law which includes the distances of all the
planets from the sun (roughly taken) in one algebraical formula. The
observations of Kepler's day were scarcely accurate enough to prove that
the relations which he discovered between the distances of the planets
from the sun and the periods of their revolutions around him were
necessarily to be received as demonstrated truths; and Galileo surely
acted most prudently and philosophically in holding himself altogether
aloof from Kepler's fanciful devices and numeral concinnities, although,
with all the extravagance, they possessed much of the genius of the
Platonic reveries, and although it did happen that Galileo, by
systematically avoiding them, failed to recognise some important truths.
Galileo probably was thinking of those very laws, when he said of
Kepler, "He possesses a bold and free genius, perhaps too much so; but
his mode of philosophizing is widely different from mine." We shall have
further occasion in the sequel to recognise the justice of this remark.

In the treatise on the Sphere which bears Galileo's name, and which, if
he be indeed the author of it, was composed during the early part of his
residence at Padua, he also adopts the Ptolemaic system, placing the
earth immoveable in the centre, and adducing against its motion the
usual arguments, which in his subsequent writings he ridicules and
refutes. Some doubts have been expressed of its authenticity; but,
however this may be, we have it under Galileo's own hand that he taught
the Ptolemaic system, in compliance with popular prejudices, for some
time after he had privately become a convert to the contrary opinions.
In a letter, apparently the first which he wrote to Kepler, dated from
Padua, 1597, he says, acknowledging the receipt of Kepler's Mysterium
Cosmographicum, "I have as yet read nothing beyond the preface of your
book, from which however I catch a glimpse of your meaning, and feel
great joy on meeting with so powerful an associate in the pursuit of
truth, and consequently such a friend to truth itself, for it is
deplorable that there should be so few who care about truth, and who do
not persist in their perverse mode of philosophizing; but as this is not
the fit time for lamenting the melancholy condition of our times, but
for congratulating you on your elegant discoveries in confirmation of
the truth, I shall only add a promise to peruse your book
dispassionately, and with a conviction that I shall find in it much to
admire. _This I shall do the more willingly because many years ago I
became a convert to the opinions of Copernicus_,[24] and by that theory
have succeeded in fully explaining many phenomena, which on the contrary
hypothesis are altogether inexplicable. I have arranged many arguments
and confutations of the opposite opinions, _which however I have not yet
dared to publish_, fearing the fate of our master Copernicus, who,
although he has earned immortal fame among a few, yet by an infinite
number (for so only can the number of fools be measured) is exploded and
derided. If there were many such as you, I would venture to publish my
speculations; but, since that is not so, I shall take time to consider
of it." This interesting letter was the beginning of the friendship of
these two great men, which lasted uninterruptedly till 1630, the date of
Kepler's death. That extraordinary genius never omitted an opportunity
of testifying his admiration of Galileo, although there were not wanting
persons envious of their good understanding, who exerted themselves to
provoke coolness and quarrel between them. Thus Brutius writes to Kepler
in 1602:[25] "Galileo tells me he has written to you, and has got your
book, which however he denied to Magini, and I abused him for praising
you with too many qualifications. I know it to be a fact that, both in
his lectures, and elsewhere, he is publishing your inventions as his
own; but I have taken care, and shall continue to do so, that all this
shall redound not to his credit but to yours." The only notice which
Kepler took of these repeated insinuations, which appear to have been
utterly groundless, was, by renewed expressions of respect and
admiration, to testify the value he set upon his friend and
fellow-labourer in philosophy.


FOOTNOTES:

[17] Dion Cassius, lib. 37.

[18] The pretended translation by Roberval of an Arabic version of
Aristarchus, "De Systemate Mundi," in which the Copernican system is
fully developed, is spurious. Menage asserts this in his observations on
Diogen. Laert. lib. 8, sec. 85, tom. ii., p. 389. (Ed. Amst. 1692.) The
commentary contains many authorities well worth consulting. Delambre,
Histoire de l'Astronomie, infers it from its not containing some
opinions which Archimedes tells us were held by Aristarchus. A more
direct proof may be gathered from the following blunder of the supposed
translator. Astronomers had been long aware that the earth in different
parts of her orbit is at different distances from the sun. Roberval
wished to claim for Aristarchus the credit of having known this, and
introduced into his book, not only the mention of the fact, but an
explanation of its cause. Accordingly he makes Aristarchus give a reason
"why the sun's apogee (or place of greatest distance from the earth)
must always be at the north summer solstice." In fact, it was there, or
nearly so, in Roberval's time, and he knew not but that it had always
been there. It is however moveable, and, when Aristarchus lived, was
nearly half way between the solstices and equinoxes. He therefore would
hardly have given a reason for the necessity of a phenomenon of which,
if he observed anything on the subject, he must have observed the
contrary. The change in the obliquity of the earth's axis to the
ecliptic was known in the time of Roberval, and he accordingly has
introduced the proper value which it had in Aristarchus's time.

[19] De Cœlo. lib. 2.

[20] Paradise Lost, b. viii. v. 83.

[21] Itaque tam circulos primi motus quam orbes secundorum mobilium
reverâ in cœlesti corpore esse concludimus, &c. Non ergo sunt mera
figmenta, quibus extra mentem nihil correspondeat. M. Maestlini, De
Astronomiæ Hypothesibus disputatio. Heidelbergæ, 1582.

[22] Opuscula Philosophica, Thema Cœli.

[23] "Nobis constat falsissimum esse." De Aug. Scient. lib. iii. c. 3,
1623.

[24] Id autum eò libentius faciam, quod in Copernici sententiam multis
abhinc annis venerim.—Kepl. Epistolæ.

[25] Kepleri Epistolæ.




CHAPTER V.

    _Galileo re-elected Professor at Padua—New star—Compass of
      proportion—Capra—Gilbert—Proposals to return to Pisa—Lost
      writings—Cavalieri._


GALILEO'S reputation was now rapidly increasing: his lectures were
attended by many persons of the highest rank; among whom were the
Archduke Ferdinand, afterwards Emperor of Germany, the Landgrave of
Hesse, and the Princes of Alsace and Mantua. On the expiration of the
first period for which he had been elected professor, he was rechosen
for a similar period, with a salary increased to 320 florins. The
immediate occasion of this augmentation is said by Fabroni[26], to have
arisen out of the malice of an ill wisher of Galileo, who, hoping to do
him disservice, apprized the senate that he was not married to Marina
Gamba, then living with him, and the mother of his son Vincenzo. Whether
or not the senate might consider themselves entitled to inquire into the
morality of his private life, it was probably from a wish to mark their
sense of the informer's impertinence, that they returned the brief
answer, that "if he had a family to provide for, he stood the more in
need of an increased stipend."

During Galileo's residence at Padua, and, according to Viviani's
intimation, towards the thirtieth year of his age, that is to say in
1594, he experienced the first attack of a disease which pressed
heavily on him for the rest of his life. He enjoyed, when a young man, a
healthy and vigorous constitution, but chancing to sleep one afternoon
near an open window, through which was blowing a current of air cooled
artificially by the fall of water, the consequences were most disastrous
to him. He contracted a sort of chronic complaint, which showed itself
in acute pains in his limbs, chest, and back, accompanied with frequent
hæmorrhages and loss of sleep and appetite; and this painful disorder
thenceforward never left him entirely, but recurred intermittingly, with
greater or less violence, as long as he lived. Others of the party did
not even escape so well, but died shortly after committing this
imprudence.

In 1604, the attention of astronomers was called to the contemplation of
a new star, which appeared suddenly with great splendour in the
constellation Serpentarius, or Ophiuchus, as it is now more commonly
called. Maestlin, who was one of the earliest to notice it, relates his
observations in the following words: "How wonderful is this new star! I
am certain that I did not see it before the 29th of September, nor
indeed, on account of several cloudy nights, had I a good view till the
6th of October. Now that it is on the other side of the sun, instead of
surpassing Jupiter as it did, and almost rivalling Venus, it scarcely
matches the Cor Leonis, and hardly surpasses Saturn. It continues
however to shine with the same bright and strongly sparkling light, and
changes its colours almost with every moment; first tawny, then yellow,
presently purple and red, and, when it has risen above the vapours, most
frequently white." This was by no means an unprecedented phenomenon; and
the curious reader may find in Riccioli[27] a catalogue of the principal
new stars which have at different times appeared. There is a tradition
of a similar occurrence as early as the times of the Greek astronomer
Hipparchus, who is said to have been stimulated by it to the formation
of his catalogue of the stars; and only thirty-two years before, in
1572, the same remarkable phenomenon in the constellation Cassiopeia was
mainly instrumental in detaching the celebrated Tycho Brahe from the
chemical studies, which till then divided his attention with astronomy.
Tycho's star disappeared at the end of two years; and at that time
Galileo was a child. On the present occasion, he set himself earnestly
to consider the new phenomenon, and embodied the results of his
observations in three lectures, which have been unfortunately lost. Only
the exordium of the first has been preserved: in this he reproaches his
auditors with their general insensibility to the magnificent wonders of
creation daily exposed to their view, in no respect less admirable than
the new prodigy, to hear an explanation of which they had hurried in
crowds to his lecture room. He showed, from the absence of parallax,
that the new star could not be, as the vulgar hypothesis represented, a
mere meteor engendered in our atmosphere and nearer the earth than the
moon, but must be situated among the most remote heavenly bodies. This
was inconceivable to the Aristotelians, whose notions of a perfect,
simple, and unchangeable sky were quite at variance with the
introduction of any such new body; and we may perhaps consider these
lectures as the first public declaration of Galileo's hostility to the
old Ptolemaic and Aristotelian astronomy.

In 1606 he was reappointed to the lectureship, and his salary a second
time increased, being raised to 520 florins. His public lectures were at
this period so much thronged that the ordinary place of meeting was
found insufficient to contain his auditors, and he was on several
occasions obliged to adjourn to the open air,—even from the school of
medicine, which was calculated to contain one thousand persons.

About this time he was considerably annoyed by a young Milanese, of the
name of Balthasar Capra, who pirated an instrument which Galileo had
invented some years before, and had called the geometrical and military
compass. The original offender was a German named Simon Mayer, whom we
shall meet with afterwards arrogating to himself the merit of one of
Galileo's astronomical discoveries; but on this occasion, as soon as he
found Galileo disposed to resent the injury done to him, he hastily
quitted Italy, leaving his friend Capra to bear alone the shame of the
exposure which followed. The instrument is of simple construction,
consisting merely of two straight rulers, connected by a joint; so that
they can be set to any required angle. This simple and useful
instrument, now called the Sector, is to be found in almost every case
of mathematical instruments. Instead of the trigonometrical and
logarithmic lines which are now generally engraved upon it, Galileo's
compass merely contained, on one side, three pairs of lines, divided in
simple, duplicate, and triplicate proportion, with a fourth pair on
which were registered the specific gravities of several of the most
common metals. These were used for multiplications, divisions, and the
extraction of roots; for finding the dimensions of equally heavy balls
of different materials, &c. On the other side were lines contrived for
assisting to describe any required polygon on a given line; for finding
polygons of one kind equal in area to those of another; and a multitude
of other similar operations useful to the practical engineer.

Unless the instrument, which is now called Gunter's scale, be much
altered from what it originally was, it is difficult to understand on
what grounds Salusbury charges Gunter with plagiarism from Galileo's
Compass. He declares that he has closely compared the two, and can find
no difference between them.[28] There has also been some confusion, by
several writers, between this instrument and what is now commonly called
the Proportional Compass. The latter consists of two slips of metal
pointed at each end, and connected by a pin which, sliding in a groove
through both, can be shifted to different positions. Its use is to find
proportional lines; for it is obvious that the openings measured by each
pair of legs will be in the same proportion in which the slips are
divided by the centre. The divisions usually marked on it are calculated
for finding the submultiples of straight lines, and the chords of
submultiple arcs. Montucla has mentioned this mistake of one instrument
for the other, and charges Voltaire with the more inexcusable error of
confounding Galileo's with the Mariner's Compass. He refers to a
treatise by Hulsius for his authority in attributing the Proportional
Compass to Burgi, a Swiss astronomer of some celebrity. Horcher also has
been styled the inventor; but he did no more than describe its form and
application. In the frontispiece of his book is an engraving of this
compass exactly similar to those which are now used.[29] To the
description which Galileo published of his compass, he added a short
treatise on the method of measuring heights and distances with the
quadrant and plumb line. The treatise, which is printed by itself at the
end of the first volume of the Padua edition of Galileo's works,
contains nothing more than the demonstrations belonging to the same
operations. They are quite elementary, and contain little or nothing
that was new even at that time.

Such an instrument as Galileo's Compass was of much more importance
before the grand discovery of logarithms than it can now be considered:
however it acquires an additional interest from the value which he
himself set on it. In 1607, Capra, at the instigation of Mayer,
published as his own invention what he calls the proportional hoop,
which is a mere copy of Galileo's instrument. This produced from Galileo
a long essay, entitled "A Defence of Galileo against the Calumnies and
Impostures of Balthasar Capra." His principal complaint seems to have
been of the misrepresentations which Capra had published of his lectures
on the new star already mentioned, but he takes occasion, after pointing
out the blunders and falsehoods which Capra had committed on that
occasion, to add a complete proof of his piracy of the geometrical
compass. He showed, from the authenticated depositions of workmen, and
of those for whom the instruments had been fabricated, that he had
devised them as early as the year 1597, and had explained their
construction and use both to Balthasar himself and to his father Aurelio
Capra, who was then residing in Padua. He gives, in the same essay, the
minutes of a public meeting between himself and Capra, in which he
proved, to the satisfaction of the university, that wherever Capra had
endeavoured to introduce into his book propositions which were not to be
met with in Galileo's, he had fallen into the greatest absurdities, and
betrayed the most complete ignorance of his subject. The consequence of
this public exposure, and of the report of the famous Fra Paolo Sarpi,
to whom the matter had been referred, was a formal prohibition by the
university of Capra's publication, and all copies of the book then on
hand were seized, and probably destroyed, though Galileo has preserved
it from oblivion by incorporating it in his own publication.

Nearly at the same time, 1607, or immediately after, he first turned his
attention towards the loadstone, on which our countryman Gilbert had
already published his researches, conducted in the true spirit of the
inductive method. Very little that is original is to be found in
Galileo's works on this subject, except some allusions to his method of
arming magnets, in which, as in most of his practical and mechanical
operations, he appears to have been singularly successful. Sir Kenelm
Digby[30] asserts, that the magnets armed by Galileo would support twice
as great a weight as one of Gilbert's of the same size. Galileo was well
acquainted, as appears from his frequent allusions in different parts of
his works, with what Gilbert had done, of whom he says, "I extremely
praise, admire, and envy this author;—I think him, moreover, worthy of
the greatest praise for the many new and true observations that he has
made to the disgrace of so many vain and fabling authors, who write, not
from their own knowledge only, but repeat every thing they hear from the
foolish vulgar, without attempting to satisfy themselves of the same by
experience, perhaps that they may not diminish the size of their books."

Galileo's reputation being now greatly increased, proposals were made to
him, in 1609, to return to his original situation at Pisa. He had been
in the habit of passing over to Florence during the academic vacation,
for the purpose of giving mathematical instruction to the younger
members of Ferdinand's family; and Cosmo, who had now succeeded his
father as duke of Tuscany, regretted that so masterly a genius had been
allowed to leave the university which he naturally should have graced. A
few extracts from Galileo's answers to these overtures will serve to
show the nature of his situation at Padua, and the manner in which his
time was there occupied. "I will not hesitate to say, having now
laboured during twenty years, and those the best of my life, in dealing
out, as one may say, in detail, at the request of any body, the little
talent which God has granted to my assiduity in my profession, that my
wish certainly would be to have sufficient rest and leisure to enable
me, before my life comes to its close, to conclude three great works
which I have in hand, and to publish them; which might perhaps bring
some credit to me, and to those who had favoured me in this undertaking,
and possibly may be of greater and more frequent service to students
than in the rest of my life I could personally afford them. Greater
leisure than I have here I doubt if I could meet with elsewhere, so long
as I am compelled to support my family from my public and private
lectures, (nor would I willingly lecture in any other city than this,
for several reasons which would be long to mention) nevertheless not
even the liberty I have here is sufficient, where I am obliged to spend
many, and often the best hours of the day at the request of this and
that man.—My public salary here is 520 florins, which I am almost
certain will be advanced to as many crowns upon my re-election, and
these I can greatly increase by receiving pupils, and from private
lectures, to any extent that I please. My public duty does not confine
me during more than 60 half hours in the year, and even that not so
strictly but that I may, on occasion of any business, contrive to get
some vacant days; the rest of my time is absolutely at my own disposal;
but because my private lectures and domestic pupils are a great
hindrance and interruption of my studies, I wish to live entirely exempt
from the former, and in great measure from the latter: for if I am to
return to my native country, I should wish the first object of his
Serene Highness to be, that leisure and opportunity should be given me
to complete my works without employing myself in lecturing.—And, in
short, I should wish to gain my bread from my writings, which I would
always dedicate to my Serene Master.—The works which I have to finish
are principally—two books on the system or structure of the Universe,
an immense work, full of philosophy, astronomy, and geometry; three
books on Local Motion, a science entirely new, no one, either ancient or
modern, having discovered any of the very many admirable accidents which
I demonstrate in natural and violent motions, so that I may with very
great reason call it a new science, and invented by me from its very
first principles; three books of Mechanics, two on the demonstration of
principles and one of problems; and although others have treated this
same matter, yet all that has been hitherto written, neither in
quantity, nor otherwise, is the quarter of what I am writing on it. I
have also different treatises on natural subjects; On sound and speech;
On light and colours; On the tide; On the composition of continuous
quantity; On the motions of animals;—And others besides. I have also
an idea of writing some books relating to the military art, giving not
only a model of a soldier, but teaching with very exact rules every
thing which it is his duty to know that depends upon mathematics; as the
knowledge of castrametation, drawing up battalions, fortifications,
assaults, planning, surveying, the knowledge of artillery, the use of
instruments, &c. I also wish to reprint the 'Use of my Geometrical
Compass,' which is dedicated to his highness, and which is no longer to
be met with; for this instrument has experienced such favour from the
public, that in fact no other instruments of this kind are now made, and
I know that up to this time several thousands of mine have been made.—I
say nothing as to the amount of my salary, feeling convinced that as I
am to live upon it, the graciousness of his highness would not deprive
me of any of those comforts, which, however, I feel the want of less
than many others; and therefore I say nothing more on the subject.
Finally, on the title and profession of my service, I should wish that
to the name of Mathematician, his highness would add that of
Philosopher, as I profess to have studied a greater number of years in
philosophy than months in pure mathematics; and how I have profited by
it, and if I can or ought to deserve this title, I may let their
highnesses see as often as it shall please them to give me an
opportunity of discussing such subjects in their presence with those who
are most esteemed in this knowledge." It may perhaps be seen in the
expressions of this letter, that Galileo was not inclined to undervalue
his own merits, but the peculiar nature of the correspondence should be
taken into account, which might justify his indulging a little more than
usual in self-praise, and it would have been perhaps almost impossible
for him to have remained entirely blind to his vast superiority over his
contemporaries.

Many of the treatises which Galileo here mentions, as well as another on
dialling, have been irrecoverably lost, through the superstitious
weakness of some of his relations, who after his death suffered the
family confessor to examine his papers, and to destroy whatever seemed
to him objectionable; a portion which, according to the notions then
prevalent, was like to comprise the most valuable part of the papers
submitted to this expurgation. It is also supposed that many were burnt
by his infatuated grandson Cosimo, who conceived he was thus offering a
proper and pious sacrifice before devoting himself to the life of a
missionary. A Treatise on Fortification, by Galileo, was found in 1793,
and is contained among the documents published by Venturi. Galileo does
not profess in it to give much original matter, but to lay before his
readers a compendium of the most approved principles then already known.
It has been supposed that Gustavus Adolphus of Sweden attended Galileo's
lectures on this subject, whilst in Italy; but the fact is not
satisfactorily ascertained. Galileo himself mentions a Prince Gustavus
of Sweden to whom he gave instruction in mathematics, but the dates
cannot well be made to agree. The question deserves notice only from its
having been made the subject of controversy.

The loss of Galileo's Essay on Continuous Quantity is particularly to be
regretted, as it would be highly interesting to see how far he succeeded
in methodizing his thoughts on this important topic. It is to his pupil
Cavalieri (who refused to publish his book so long as he hoped to see
Galileo's printed) that we owe "The Method of Indivisibles," which is
universally recognized as one of the first germs of the powerful methods
of modern analysis. Throughout Galileo's works we find many indications
of his having thought much on the subject, but his remarks are vague,
and bear little, if at all, on the application of the method. To this
the chief part of Cavalieri's book is devoted, though he was not so
entirely regardless of the principles on which his method of measuring
spaces is founded, as he is sometimes represented. This method consisted
in considering lines as made up of an infinite number of points,
surfaces in like manner as composed of lines, and solids of surfaces;
but there is an observation at the beginning of the 7th book, which
shews clearly that Cavalieri had taken a much more profound view of the
subject than is implied in this superficial exposition, and had
approached very closely to the apparently more exact theories of his
successors. Anticipating the objections to his hypothesis, he argues,
that "there is no necessity to suppose the continuous quantities made up
of these indivisible parts, _but only that they will observe the same
ratios as those parts do_." It ought not to be omitted, that Kepler also
had given an impulse to Cavalieri in his "New method of Gauging," which
is the earliest work with which we are acquainted, where principles of
this sort are employed.[31]


FOOTNOTES:

[26] Vitæ Italorum Illustrium.

[27] Almagestum Novum, vol. i.

[28] Math. Coll. vol. ii.

[29] Constructio Circini Proportionum. Moguntiæ, 1605.

[30] Treatise of the Nature of Bodies. London, 1665.

[31] Nova Stereometria Doliorum—Lincii, 1615.




CHAPTER VI.

    _Invention of the telescope—Fracastoro—Porta—Reflecting
      telescope—Roger Bacon—Digges—De
      Dominis—Jansen—Lipperhey—Galileo constructs
      telescopes—Microscopes—Re-elected Professor at Padua for life._


THE year 1609 was signalized by Galileo's discovery of the telescope,
which, in the minds of many, is the principal, if not the sole invention
associated with his name. It cannot be denied that his fame, as the
founder of the school of experimental philosophy, has been in an
unmerited degree cast into the shade by the splendour of his
astronomical discoveries; yet Lagrange[32] surely errs in the opposite
extreme, when he almost denies that these form any real or solid part of
the glory of this great man; and Montucla[33] omits an important
ingredient in his merit, when he (in other respects very justly)
remarks, that it required far less genius to point a telescope towards
the heavens than to trace the unheeded, because daily recurring,
phenomena of motion up to its simple and primary laws. We are to
remember that in the days of Galileo a telescope could scarcely be
pointed to the heavens with impunity, and that a courageous mind was
required to contradict, and a strong one to bear down, a party, who,
when invited to look on any object in the heavens which Aristotle had
never suspected, immediately refused all credit to those senses, to
which, on other occasions, they so confidently appealed. It surely is a
real and solid part of Galileo's glory that he consumed his life in
laborious and indefatigable observations, and that he persevered in
announcing his discoveries undisgusted by the invectives, and undismayed
by the persecutions, to which they subjected him. Plagiarist! liar!
impostor! heretic! were among the expressions of malignant hatred
lavished upon him, and although he also was not without some violent and
foul-mouthed partisans, yet it must be told to his credit that he
himself seldom condescended to notice these torrents of abuse, otherwise
than by good-humoured retorts, and by prosecuting his observations with
renewed assiduity and zeal.

The use of single lenses in aid of the sight had been long known.
Spectacles were in common use at the beginning of the fourteenth
century, and there are several hints, more or less obscure, in many
early writers, of the effects which might be expected from a combination
of glasses; but it does not appear with certainty that any of these
authors had attempted to reduce their ideas to practice. After the
discovery of the telescope, almost every country endeavoured to find in
the writings of its early philosophers traces of the knowledge of such
an instrument, but in general with success very inadequate to the zeal
of their national prepossessions. There are two authors especially to
whom the attention of Kepler and others was turned, immediately upon the
promulgation of the discovery, as containing the germ of it in their
works. These are Baptista Porta, and Gerolamo Fracastoro. We have
already had occasion to quote the Homocentrica of Fracastoro, who died
in 1553; the following expressions, though they seem to refer to actual
experiment, yet fall short of the meaning with which it has been
attempted to invest them. After explaining and commenting on some
phenomena of refraction through different media, to which he was led by
the necessity of reconciling his theory with the variable magnitudes of
the planets, he goes on to say—"For which reason, those things which
are seen at the bottom of water, appear greater than those which are at
the top; and if any one look through two eyeglasses, _one placed upon
the other_, he will see every thing much larger and nearer."[34] It
should seem that this passage (as Delambre has already remarked) rather
refers to the close application of one glass upon another, and it may
fairly be doubted whether anything analogous to the composition of the
telescope was in the writer's thoughts. Baptista Porta writes on the
same subject more fully;—"Concave lenses show distant objects most
clearly, convex those which are nearer, whence they may be used to
assist the sight. With a concave glass distant objects will be seen,
small, but distinct; with a convex one those near at hand, larger, but
confused; _if you know rightly how to combine one of each sort, you
will see both far and near objects larger and clearer_."[35] These words
show, if Porta really was then unacquainted with the telescope, how
close it is possible to pass by an invention without lighting on it, for
of precisely such a combination of a convex and concave lens, fitted to
the ends of an organ pipe by way of tube, did the whole of Galileo's
telescope consist. If Porta had stopped here he might more securely have
enjoyed the reputation of the invention, but he then professes to
describe the construction of his instrument, which has no relation
whatever to his previous remarks. "I shall now endeavour to show in what
manner we may contrive to recognize our friends at the distance of
several miles, and how those of weak sight may read the most minute
letters from a distance. It is an invention of great utility, and
grounded on optical principles, nor is it at all difficult of execution;
but it must be so divulged as not to be understood by the vulgar, and
yet be clear to the sharpsighted." The description which follows seems
far enough removed from the apprehended danger of being too clear, and
indeed every writer who has hitherto quoted it has merely given the
passage in its original Latin, apparently despairing of an intelligible
translation. With some alterations in the punctuation, which appear
necessary to bring it into any grammatical construction,[36] it may be
supposed to bear something like the following meaning:—"Let a view be
contrived in the centre of a mirror, where it is most effective. All the
solar rays are exceedingly dispersed, and do not in the least come
together (in the true centre); but there is a concourse of all the rays
in the central part of the said mirror, half way towards the other
centre, where the cross diameters meet. This view is contrived in the
following manner. A concave cylindrical mirror placed directly in front,
but with its axis inclined, must be adapted to that focus: and let
obtuse angled or right angled triangles be cut out with two cross lines
on each side drawn from the centre, and a glass (_specillum_) will be
completed fit for the purposes we mentioned." If it were not for the
word "_specillum_," which, in the passage immediately preceding this,
Porta[37] contrasts with "_speculum_," and which he afterwards explains
to mean a glass lens, it would be very clear that the foregoing passage
(supposing it to have any meaning) must be referred to a reflecting
telescope, and it is a little singular that while this obscure passage
has attracted universal attention, no one, so far as we are aware, has
taken any notice of the following unequivocal description of the
principal part of Newton's construction of the same instrument. It is in
the 5th chapter of the 17th book, where Porta explains by what device
exceedingly minute letters may be read without difficulty. "Place a
concave mirror so that the back of it may lie against your breast;
opposite to it, and within the burning point, place the writing; put a
plane mirror behind it, that may be under your eyes. Then the images of
the letters which are in the concave mirror, and which the concave has
magnified, will be reflected in the plane mirror, so that you may read
without difficulty."

We have not been able to meet with the Italian translation of Porta's
Natural Magic, which was published in 1611, under his own
superintendence; but the English translator of 1658 would probably have
known if any intelligible interpretation were there given of the
mysterious passage above quoted, and his translation is so devoid of
meaning as strongly to militate against this idea. Porta, indeed,
claimed the invention as his own, and is believed to have hastened his
death, (which happened in 1615, he being then 80 years old,) by the
fatigue of composing a Treatise on the Telescope, in which he had
promised to exhaust the subject. We do not know whether this is the same
work which was published after his death by Stelliola,[38] but which
contains no allusion to Porta's claim, and possibly Stelliola may have
thought it most for his friend's reputation to suppress it. Schott[39]
says, a friend of his had seen Porta's book in manuscript, and that it
did at that time contain the assertion of Porta's title to the
invention. After all it is not improbable that he may have derived his
notions of magnifying distant objects from our celebrated countryman
Roger Bacon, who died about the year 1300. He has been supposed, not
without good grounds, to have been one of the first who recognised the
use of single lenses in producing distinct vision, and he has some
expressions with respect to their combination which promise effects
analogous to those held out by Porta. In "The Admirable Force of Art and
Nature," he says, "Physical figurations are far more strange, for in
such manner may we frame perspects and looking-glasses that one thing
shall appear to be many, as one man shall seeme a whole armie; and
divers sunnes and moones, yea, as many as we please, shall appeare at
one time, &c. And so may the perspects be framed, that things most farre
off may seeme most nigh unto us, and clean contrarie, soe that we may
reade very small letters an incredible distance from us, and behold
things how little soever they be, and make stars to appeare wheresoever
we will, &c. And, besides all these, we may so frame perspects that any
man entering into a house he shall indeed see gold, and silver, and
precious stones, and what else he will, but when he maketh haste to the
place he shall find just nothing." It seems plain, that the author is
here speaking solely of mirrors, and we must not too hastily draw the
conclusion, because in the first and last of these assertions he is, to
a certain extent, borne out by facts, that he therefore was in
possession of a method of accomplishing the middle problem also. In the
previous chapter, he gives a long list of notable things, (much in the
style of the Marquis of Worcester's Century of Inventions) which if we
can really persuade ourselves that he was capable of accomplishing, we
must allow the present age to be still immeasurably inferior to him in
science.

Thomas Digges, in the preface to his Pantometria, (published in 1591)
declares, "My father, by his continuall painfull practises, assisted
with demonstrations mathematicall, was able, and sundry times hath by
proportionall glasses, duely situate in convenient angles, not only
discouered things farre off, read letters, numbered peeces of money,
with the verye coyne and superscription thereof, cast by some of his
freends of purpose, upon downes in open fields; but also, seuen miles
off, declared what hath beene doone at that instant in priuate places.
He hath also sundrie times, by the sunne beames, fired powder and
dischargde ordnance halfe a mile and more distante; which things I am
the boulder to report, for that there are yet living diverse (of these
his dooings) occulati testes, (eye witnesses) and many other matters
farre more strange and rare, which I omit as impertinent to this place."

We find another pretender to the honour of the discovery of the
telescope in the celebrated Antonio de Dominis, Archbishop of Spalatro,
famous in the annals of optics for being one of the first to explain the
theory of the rainbow. Montucla, following P. Boscovich, has scarcely
done justice to De Dominis, whom he treats as a mere pretender and
ignorant person. The indisposition of Boscovich towards him is
sufficiently accounted for by the circumstance of his being a Catholic
prelate who had embraced the cause of Protestantism. His nominal
reconciliation with the Church of Rome would probably not have saved him
from the stake, had not a natural death released him when imprisoned on
that account at Rome. Judgment was pronounced upon him notwithstanding,
and his body and books were publicly burnt in the Campo de Fiori, in
1624. His treatise, De Radiis, (which is very rarely to be met with) was
published by Bartolo after the acknowledged invention of the telescope
by Galileo; but Bartolo tells us, in the preface, that the manuscript
was communicated to him from a collection of papers written 20 years
before, on his inquiring the Archbishop's opinion with respect to the
newly discovered instrument, and that he got leave to publish it, "with
the addition of one or two chapters." The treatise contains a complete
description of a telescope, which, however, is professed merely to be an
improvement on spectacles, and if the author's intention had been to
interpolate an afterwritten account, in order to secure to himself the
undeserved honour of the invention, it seems improbable that he would
have suffered an acknowledgment of additions, previous to publication,
to be inserted in the preface. Besides, the whole tone of the work is
that of a candid and truth-seeking philosopher, very far indeed removed
from being, as Montucla calls him, conspicuous for ignorance even among
the ignorant men of his age. He gives a drawing of a convex and concave
lens, and traces the passage of the rays through them; to which he
subjoins, that he has not satisfied himself with any determination of
the precise distance to which the glasses should be separated, according
to their convexity and concavity, but recommends the proper distance to
be found by actual experiment, and tells us, that the effect of the
instrument will be to prevent the confusion arising from the
interference of the direct and refracted rays, and to magnify the object
by increasing the visible angle under which it is viewed. These, among
the many claimants, are certainly the authors who approached the most
nearly to the discovery: and the reader may judge, from the passages
cited, whether the knowledge of the telescope can with probability be
referred to a period earlier than the commencement of the 17th century.
At all events, we can find no earlier trace of its being applied to any
practical use; the knowledge, if it existed, remained speculative and
barren.

In 1609, Galileo, then being on a visit to a friend at Venice, heard a
rumour of the recent invention, by a Dutch spectacle-maker, of an
instrument which was said to represent distant objects nearer than they
usually appeared. According to his own account, this general rumour,
which was confirmed to him by letters from Paris, was all that he
learned on the subject; and returning to Padua, he immediately applied
himself to consider the means by which such an effect could be produced.
Fuccarius, in an abusive letter which he wrote on the subject, asserts
that one of the Dutch telescopes had been at that time actually brought
to Venice, and that he (Fuccarius) had seen it; which, even if true, is
perfectly consistent with Galileo's statement; and in fact the question,
whether or not Galileo saw the original instrument, becomes important
only from his expressly asserting the contrary, and professing to give
the train of reasoning by which he discovered its principle; so that any
insinuation that he had actually seen the Dutch glass, becomes a direct
impeachment of his veracity. It is certain, from the following extract
of a letter from Lorenzo Pignoria to Paolo Gualdo, that one at least of
the Dutch glasses had been sent to Italy. It is dated Padua, 31st
August, 1609.[40] "We have no news, except the return of His Serene
Highness, and the re-election of the lecturers, among whom Sign. Galileo
has contrived to get 1000 florins for life; and it is said to be on
account of an eyeglass, _like the one which was sent from Flanders to
Cardinal Borghese_. We have seen some here, and truly they succeed
well."

It is allowed by every one that the Dutchman, or rather Zealander, made
his discovery by mere accident, which greatly derogates from any honour
attached to it; but even this diminished degree of credit has been
fiercely disputed. According to one account, which appears consistent
and probable, it had been made for sometime before its importance was in
the slightest degree understood or appreciated, but was set up in the
optician's shop as a curious philosophical toy, showing a large and
inverted image of a weathercock, towards which it was directed. The
Marquis Spinola, chancing to see it, was struck with the phenomenon,
purchased the instrument, and presented it either to the Archduke Albert
of Austria, or to Prince Maurice of Nassau, whose name appears in every
version of the story, and who first entertained the idea of employing it
in military reconnoissances.

Zacharias Jansen, and Henry Lipperhey, two spectacle-makers, living
close to each other, near the church of Middleburg, have both had
strenuous supporters of their title to the invention. A third pretender
appeared afterwards in the person of James Metius of Alkmaer, who is
mentioned by Huyghens and Des Cartes, but his claims rest upon no
authority whatever comparable to that which supports the other two.
About half a century afterwards, Borelli was at the pains to collect and
publish a number of letters and depositions which he procured, as well
on one side as on the other.[41] It seems that the truth lies between
them, and that one, probably Jansen, was the inventor of the
_microscope_, which application of the principle was unquestionably of
an earlier date, perhaps as far back as 1590. Jansen gave one of his
microscopes to the Archduke, who gave it to Cornelius Drebbel, a
salaried mathematician at the court of our James the first, where
William Borelli (not the author above mentioned) saw it many years
afterwards, when ambassador from the United Provinces to England, and
got from Drebbel this account of the quarter whence it came. Lipperhey
afterwards, in 1609, accidentally hit upon the _telescope_, and on the
fame of this discovery it would not be difficult for Jansen, already in
possession of an instrument so much resembling it, to perceive the
slight difference between them, and to construct a telescope
independently of Lipperhey, so that each, with some show of reason,
might claim the priority of the invention. A notion of this kind
reconciles the testimony of many conflicting witnesses on the subject,
some of whom do not seem to distinguish very accurately whether the
telescope or microscope is the instrument to which their evidence
refers. Borelli arrives at the conclusion, that Jansen was the inventor;
but not satisfied with this, he endeavours, with a glaring partiality
which makes his former determination suspicious, to secure for him and
his son the more solid reputation of having anticipated Galileo in the
useful employment of the invention. He has however inserted in his
collections a letter from John the son of Zacharias, in which John,
omitting all mention of his father, speaks of his own observation of the
satellites of Jupiter, evidently seeking to insinuate that they were
earlier than Galileo's; and in this sense the letter has since been
quoted,[42] although it appears from John's own deposition, preserved in
the same collection, that at the time of their discovery he could not
have been more than six years old. An oversight of this sort throws
doubt on the whole of the pretended observations, and indeed the letter
has much the air of being the production of a person imperfectly
informed on the subject on which he writes, and probably was compiled to
suit Borelli's purposes, which were to make Galileo's share in the
invention appear as small as possible.

Galileo himself gives a very intelligible account of the process of
reasoning, by which he detected the secret.—"I argued in the following
manner. The contrivance consists either of one glass or of more—one is
not sufficient, since it must be either convex, concave, or plane; the
last does not produce any sensible alteration in objects, the concave
diminishes them: it is true that the convex magnifies, but it renders
them confused and indistinct; consequently, one glass is insufficient to
produce the desired effect. Proceeding to consider two glasses, and
bearing in mind that the plane glass causes no change, I determined that
the instrument could not consist of the combination of a plane glass
with either of the other two. I therefore applied myself to make
experiments on combinations of the two other kinds, and thus obtained
that of which I was in search." It has been urged against Galileo that,
if he really invented the telescope on theoretical principles, the same
theory ought at once to have conducted him to a more perfect instrument
than that which he at first constructed;[43] but it is plain, from this
statement, that he does not profess to have theorized beyond the
determination of the species of glass which he should employ in his
experiments, and the rest of his operations he avows to have been purely
empirical. Besides, we must take into account the difficulty of grinding
the glasses, particularly when fit tools were yet to be made, and
something must be attributed to Galileo's eagerness to bring his results
to the test of actual experiment, without waiting for that improvement
which a longer delay might and did suggest. Galileo's language bears a
resemblance to the first passage which we quoted from Baptista Porta,
sufficiently close to make it not improbable that he might be assisted
in his inquiries by some recollection of it, and the same passage seems,
in like manner, to have recurred to the mind of Kepler, as soon as he
heard of the invention. Galileo's telescope consisted of a plano-convex
and plano-concave lens, the latter nearest the eye, distant from each
other by the difference of their focal lengths, being, in principle,
exactly the same with the modern opera-glass. He seems to have thought
that the Dutch glass was the same, but this could not be the case, if
the above quoted particular of the _inverted_ weathercock, which belongs
to most traditions of the story, be correct; because it is the
peculiarity of this kind of telescope not to invert objects, and we
should be thus furnished with a demonstrative proof of the falsehood of
Fuccarius's insinuation: in that case the Dutch glass must have been
similar to what was afterwards called the astronomical telescope,
consisting of two convex glasses distant from each other by the sum of
their focal lengths. This supposition is not controverted by the fact,
that this sort of telescope was never employed by astronomers till long
afterwards; for the fame of Galileo's observations, and the superior
excellence of the instruments constructed under his superintendence,
induced every one in the first instance to imitate his constructions as
closely as possible. The astronomical telescope was however eventually
found to possess superior advantages over that which Galileo imagined,
and it is on this latter principle that all modern refracting telescopes
are constructed; the inversion being counteracted in those which are
intended for terrestrial observations, by the introduction of a second
pair of similar glasses, which restore the inverted image to its
original position. For further details on the improvements which have
been subsequently introduced, and on the reflecting telescope, which was
not brought into use till the latter part of the century, the reader is
referred to the Treatise on OPTICAL INSTRUMENTS.

Galileo, about the same time, constructed microscopes on the same
principle, for we find that, in 1612, he presented one to Sigismund,
King of Poland; but his attention being principally devoted to the
employment and perfection of his telescope, the microscope remained a
long time imperfect in his hands: twelve years later, in 1624, he wrote
to P. Federigo Cesi, that he had delayed to send the microscope, the use
of which he there describes, because he had only just brought it to
perfection, having experienced some difficulty in working the glasses.
Schott tells an amusing story, in his "Magic of Nature," of a Bavarian
philosopher, who, travelling in the Tyrol with one of the newly invented
microscopes about him, was taken ill on the road and died. The
authorities of the village took possession of his baggage, and were
proceeding to perform the last duties to his body, when, on examining
the little glass instrument in his pocket, which chanced to contain a
flea, they were struck with the greatest astonishment and terror, and
the poor Bavarian, condemned by acclamation as a sorcerer who was in the
habit of using a portable familiar, was declared unworthy of Christian
burial. Fortunately for his character, some bold sceptic ventured to
open the instrument, and discovered the true nature of the imprisoned
fiend.

As soon as Galileo's first telescope was completed, he returned with it
to Venice, and the extraordinary sensation which it excited tends also
strongly to refute Fuccarius's assertion that the Dutch glass was
already known there. During more than a month Galileo's whole time was
employed in exhibiting his instrument to the principal inhabitants of
Venice, who thronged to his house to satisfy themselves of the truth of
the wonderful stories in circulation; and at the end of that time the
Doge, Leonardo Donati, caused it to be intimated to him that such a
present would not be deemed unacceptable by the senate. Galileo took the
hint, and his complaisance was rewarded by a mandate confirming him for
life in his professorship at Padua, at the same time doubling his yearly
salary, which was thus made to amount to 1000 florins.

It was long before the phrenzy of public curiosity abated. Sirturi
describes a ludicrous violence which was done to himself, when, with the
first telescope which he had succeeded in making, he went up into the
tower of St. Mark, at Venice, in the vain hope of being there entirely
unmolested. Unluckily he was seen by some idlers in the street: a crowd
soon collected round him, who insisted on taking possession of his
instrument, and, handing it one to the other, detained him there for
several hours till their curiosity was satiated, when he was allowed to
return home. Hearing them also inquire eagerly at what inn he lodged, he
thought it better to quit Venice early the next morning, and prosecute
his observations in a less inquisitive neighbourhood.[44] Instruments of
an inferior description were soon manufactured, and vended every where
as philosophical playthings, much in the way in which, in our own time,
the kaleidoscope spread over Europe as fast as travellers could carry
them. But the fabrication of a better sort was long confined, almost
solely, to Galileo and those whom he immediately instructed; and so late
as the year 1637, we find Gaertner, or as he chose to call himself,
Hortensius, assuring Galileo that none could be met with in Holland
sufficiently good to show Jupiter's disc well defined; and in 1634
Gassendi begs for a telescope from Galileo, informing him that he was
unable to procure a good one either in Venice, Paris, or Amsterdam.

The instrument, on its first invention, was generally known by the names
of Galileo's tube, the perspective, the double eye-glass: the names of
telescope and microscope were suggested by Demisiano, as we are told by
Lagalla in his treatise on the Moon.[45]


FOOTNOTES:

[32] Mecanique Analytique.

[33] Histoire des Mathématiques, tom. ii.

[34] "Per duo specilla ocularia si quis perspiciat, altero alteri
superposito, majora multo et propinquiora videbit omnia."—Fracast.
Homocentrica, § 2, c. 8.

[35] Si utrumque recte componere noveris, et longinqua et proxima majora
et clara videbis.—Mag. Nat. lib. 17.

[36] The passage in the original, which is printed alike in the editions
of 1598, 1607, 1619, and 1650, is as follows: Visus constituatur centro
valentissimus speculi, ubi fiet, et valentissimè universales solares
radii disperguntur, et coeunt minimè, sed centro prædicti speculi in
illius medio, ubi diametri transversales, omnium ibi concursus.
Constituitur hoc modo speculum concavum columnare æquidistantibus
lateribus, sed lateri uno obliquo sectionibus illis accomodetur,
trianguli vero obtusianguli, vel orthogonii secentur, hinc inde duobus
transversalibus lineis, ex-centro eductis. Et confectum erit specillum,
ad id, quod diximus utile.

[37] Diximus de Ptolemæi _speculo_, sive _specillo_ potius, quo per
sexcentena millia pervenientes naves conspiciebat.

[38] Il Telescopio, 1627.

[39] Magia Naturæ et Artis Herbipoli, 1657.

[40] Lettère d'Uomini illustri. Venezia, 1744.

[41] Borelli. De vero Telescopii inventore, 1655.

[42] Encyclopædia Britannica. Art. TELESCOPE.

[43] Ibid.

[44] Telescopium, Venetiis, 1619.

[45] De phænomenis in orbe Lunæ. Venetiis, 1612.




CHAPTER VII.

    _Discovery of Jupiter's
      satellites—Kepler—Sizzi—Astrologers—Mæstlin—Horky—Mayer._


AS soon as Galileo had provided himself with a second instrument, he
began a careful examination of the heavenly bodies, and a series of
splendid discoveries soon rewarded his diligence. After considering the
beautiful appearances which the varied surface of the moon presented to
this new instrument, he turned his telescope towards Jupiter, and his
attention was soon arrested by the singular position of three small
stars, near the body of that planet, which appeared almost in a straight
line with it, and in the direction of the ecliptic. The following
evening he was surprised to find that two of the three which had been to
the eastward of the planet, now appeared on the contrary side, which he
could not reconcile with the apparent motion of Jupiter among the fixed
stars, as given by the tables. Observing these night after night, he
could not fail to remark that they changed their relative positions. A
fourth also appeared, and in a short time he could no longer refuse to
believe that these small stars were four moons, revolving round Jupiter
in the same manner in which our earth is accompanied by its single
attendant. In honour of his patron Cosmo, he named them the Medicæan
stars. As they are now hardly known by this appellation, his doubts,
whether he should call them Medicæan, after Cosmo's family, or Cosmical,
from his individual name, are become of less interest.

An extract from a letter which Galileo received on this occasion from
the court of France, will serve to show how highly the honour of giving
a name to these new planets was at that time appreciated, and also how
much was expected from Galileo's first success in examining the heavens.
"The second request, but the most pressing one which I can make to you,
is, that you should determine, if you discover any other fine star, to
call it by the name of the great star of France, as well as the most
brilliant of all the earth; and, if it seems fit to you, call it rather
by his proper name of Henri, than by the family name of Bourbon: thus
you will have an opportunity of doing a thing just and due and proper in
itself, and at the same time will render yourself and your family rich
and powerful for ever." The writer then proceeds to enumerate the
different claims of Henri IV. to this honour, not forgetting that he
married into the family of the Medici, &c.

The result of these observations was given to the world, in an Essay
which Galileo entitled _Nuncius Sidereus_, or the Intelligencer of the
Stars; and it is difficult to describe the extraordinary sensation which
its publication produced. Many doubted, many positively refused to
believe, so novel an announcement; all were struck with the greatest
astonishment, according to their respective opinions, either at the new
view of the universe thus offered to them, or at the daring audacity of
Galileo in inventing such fables. We shall proceed to extract a few
passages from contemporary writers relative to this book, and the
discoveries announced in it.

Kepler deserves precedence, both from his own celebrity, and from the
lively and characteristic account which he gives of his first receiving
the intelligence:—"I was sitting idle at home, thinking of you, most
excellent Galileo, and your letters, when the news was brought me of the
discovery of four planets by the help of the double eye-glass.
Wachenfels stopped his carriage at my door to tell me, when such a fit
of wonder seized me at a report which seemed so very absurd, and I was
thrown into such agitation at seeing an old dispute between us decided
in this way, that between his joy, my colouring, and the laughter of
both, confounded as we were by such a novelty, we were hardly capable,
he of speaking, or I of listening. My amazement was increased by the
assertion of Wachenfels, that those who sent this news from Galileo were
celebrated men, far removed by their learning, weight, and character,
above vulgar folly; that the book was actually in the press, and would
be published immediately. On our separating, the authority of Galileo
had the greatest influence on me, earned by the accuracy of his
judgment, and excellence of his understanding; so I immediately fell to
thinking how there could be any addition to the number of the planets
without overturning my Mysterium Cosmographicum, published thirteen
years ago, according to which Euclid's five regular solids do not allow
more than six planets round the sun."

This was one of the many wild notions of Kepler's fanciful brain, among
which he was lucky enough at length to hit upon the real and principal
laws of the planetary motions. His theory may be briefly given in his
own words:—"The orbit of the earth is the measure of the rest. About it
circumscribe a dodecahedron. The sphere including this will be that of
Mars. About Mars' orbit describe a tetrahedron: the sphere containing
this will be Jupiter's orbit. Round Jupiter's describe a cube: the
sphere including this will be Saturn's. Within the earth's orbit
inscribe an icosahedron: the sphere inscribed in it will be Venus's
orbit. In Venus inscribe an octahedron: the sphere inscribed in it will
be Mercury's. You have now the reason of the number of the planets:" for
as there are no more than the five regular solids here enumerated,
Kepler conceived this to be a satisfactory reason why there could be
neither more nor less than six planets. His letter continues:—"I am so
far from disbelieving the existence of the four circumjovial planets,
that I long for a telescope to anticipate you, if possible, in
discovering two round Mars, (as the proportion seems to me to require,)
six or eight round Saturn, and perhaps one each round Mercury and
Venus."

The reader has here an opportunity of verifying Galileo's observation,
that Kepler's method of philosophizing differed widely from his own. The
proper line is certainly difficult to hit between the mere theorist and
the mere observer. It is not difficult at once to condemn the former,
and yet the latter will deprive himself of an important, and often
indispensable assistance, if he neglect from time to time to consolidate
his observations, and thence to conjecture the course of future
observation most likely to reward his assiduity. This cannot be more
forcibly expressed than in the words of Leonardo da Vinci:[46] "Theory
is the general, experiments are the soldiers. The interpreter of the
works of nature is experiment; that is never wrong; it is our judgment
which is sometimes deceived, because we are expecting results which
experiment refuses to give. We must consult experiment, and vary the
circumstances, till we have deduced general rules, for it alone can
furnish us with them. But you will ask, what is the use of these general
rules? I answer, that they direct us in our inquiries into nature and
the operations of art. They keep us from deceiving ourselves and others,
by promising ourselves results which we can never obtain."

In the instance before us, it is well known that, adopting some of the
opinions of Bruno and Brutti, Galileo, even before he had seen the
satellites of Jupiter, had allowed the possibility of the discovery of
new planets; and we can scarcely suppose that they had weakened his
belief in the probability of further success, or discouraged him from
examining the other heavenly bodies. Kepler on the contrary had taken
the opposite side of the argument; but no sooner was the fallacy of his
first position undeniably demonstrated, than, passing at once from one
extreme to the other, he framed an unsupported theory to account for the
number of satellites which were round Jupiter, and for those which he
expected to meet with elsewhere. Kepler has been styled the legislator
of the skies; his laws were promulgated rather too arbitrarily, and they
often failed, as all laws must do which are not drawn from a careful
observation of the nature of those who are to be governed by them.
Astronomers have reason to be grateful for the theorems which he was the
first to establish; but so far as regards the progress of the science of
inductive reasoning, it is perhaps to be regretted, that the seventeen
years which he wasted in random and unconnected guesses should have been
finally rewarded, by discoveries splendid enough to shed deceitful
lustre upon the method by which he arrived at them.

Galileo himself clearly perceived the fallacious nature of these
speculations on numbers and proportions, and has expressed his
sentiments concerning them very unequivocally. "How great and common an
error appears to me the mistake of those who persist in making their
knowledge and apprehension the measure of the apprehension and knowledge
of God; as if that alone were perfect, which they understand to be so.
But I, on the contrary, observe that Nature has other scales of
perfection, which we cannot comprehend, and rather seem disposed to
class among imperfections. For instance, among the relations of
different numbers, those appear to us most perfect which exist between
numbers nearly related to each other; as the double, the triple, the
proportion of three to two, &c.; those appear less perfect which exist
between numbers remote from, and prime to each other; as 11 to 7, 17 to
13, 53 to 37, &c.; and most imperfect of all do those appear which exist
between incommensurable quantities, which by us are nameless and
inexplicable. Consequently, if the task had been given to a man, of
establishing and ordering the rapid motions of the heavenly bodies,
according to his notions of perfect proportions, I doubt not that he
would have arranged them according to the former rational proportions;
but, on the contrary, God, with no regard to our imaginary symmetries,
has ordered them in proportions not only incommeasurable and irrational,
but altogether inappreciable by our intellect. A man ignorant of
geometry may perhaps lament, that the circumference of a circle does not
happen to be exactly three times the diameter, or in some other
assignable proportion to it, rather than such that we have not yet been
able to explain what the ratio between them is; but one who has more
understanding will know that if they were other than they are, thousands
of admirable conclusions would have been lost, and that none of the
other properties of the circle would have been true: the surface of the
sphere would not be quadruple of a great circle, nor the cylinder be to
the sphere as three to two: in short, no part of geometry would be true,
and as it now is. If one of our most celebrated architects had had to
distribute this vast multitude of fixed stars through the great vault of
heaven, I believe he would have disposed them with beautiful
arrangements of squares, hexagons, and octagons; he would have dispersed
the larger ones among the middle sized and the less, so as to correspond
exactly with each other; and then he would think he had contrived
admirable proportions: but God, on the contrary, has shaken them out
from His hand as if by chance, and we, forsooth, must think that He has
scattered them up yonder without any regularity, symmetry, and
elegance."

It is worth remarking that the dangerous ideas of aptitude and
congruence of numbers had taken such deep and general root, that long
afterwards, when the reality of Jupiter's satellites was incontestably
established, and Huyghens had discovered a similar satellite near
Saturn, he was so rash as to declare his belief, (unwarned by the vast
progress which astronomy had made in his own time,) that no more
satellites would be discovered, since the one which he discovered near
Saturn, with Jupiter's four, and our moon, made up the number six,
exactly equal to the number of the principal planets. Every reader knows
that this notion, so unworthy the genius of Huyghens, has been since
exploded by the discovery both of new planets, and new satellites.

Francesco Sizzi, a Florentine astronomer, took the matter up in a
somewhat different strain from Kepler.[47]—"There are seven windows
given to animals in the domicile of the head, through which the air is
admitted to the rest of the tabernacle of the body, to enlighten, to
warm, and nourish it, which are the principal parts of the μικροκοσμος
(or little world); two nostrils, two eyes, two ears, and a mouth; so in
the heavens, as in a μακροκοσμος (or great world), there are two
favourable stars, two unpropitious, two luminaries, and Mercury alone
undecided and indifferent. From which and many other similar phenomena
of nature, such as the seven metals, &c., which it were tedious to
enumerate, we gather that the number of planets is necessarily seven.
Moreover, the satellites are invisible to the naked eye, and therefore
can exercise no influence on the earth, and therefore would be useless,
and therefore do not exist. Besides, as well the Jews and other ancient
nations as modern Europeans have adopted the division of the week into
seven days, and have named them from the seven planets: now if we
increase the number of the planets this whole system falls to the
ground." To these remarks Galileo calmly replied, that whatever their
force might be, as a reason for believing beforehand that no more than
seven planets would be discovered, they hardly seemed of sufficient
weight to destroy the new ones when actually seen.

Others, again, took a more dogged line of opposition, without venturing
into the subtle analogies and arguments of the philosopher just cited.
They contented themselves, and satisfied others, with the simple
assertion, that such things were not, and could not be, and the manner
in which they maintained themselves in their incredulity was
sufficiently ludicrous. "Oh, my dear Kepler,"[48] says Galileo, "how I
wish that we could have one hearty laugh together. Here, at Padua, is
the principal professor of philosophy, whom I have repeatedly and
urgently requested to look at the moon and planets through my glass,
which he pertinaciously refuses to do. Why are you not here? what shouts
of laughter we should have at this glorious folly! and to hear the
professor of philosophy at Pisa labouring before the grand duke with
logical arguments, as if with magical incantations, to charm the new
planets out of the sky."

Another opponent of Galileo deserves to be named, were it only for the
singular impudence of the charge he ventures to bring against him. "We
are not to think," says Christmann, in the Appendix to his _Nodus
Gordius_, "that Jupiter has four satellites given him by nature, in
order, by revolving round him, to immortalize the name of the Medici,
who first had notice of the observation. These are the dreams of _idle
men_, who love ludicrous ideas better than our laborious and industrious
correction of the heavens.—Nature abhors so horrible a chaos, and to
the truly wise such vanity is detestable."

Galileo was also urged by the astrologers to attribute some influence,
according to their fantastic notions, to the satellites, and the account
which he gives his friend Dini of his answer to one of this class is
well worth extracting, as a specimen of his method of uniting sarcasm
with serious expostulation; "I must," says he, "tell you what I said a
few days back to one of those nativity-casters, who believe that God,
when he created the heavens and the stars, had no thoughts beyond what
they can themselves conceive, in order to free myself from his tedious
importunity; for he protested, that unless I would declare to him the
effect of the Medicæan planets, he would reject and deny them as
needless and superfluous. I believe this set of men to be of Sizzi's
opinion, that astronomers discovered the other seven planets, not by
seeing them corporally in the skies, but only from their effects on
earth,—much in the manner in which some houses are discovered to be
haunted by evil spirits, not by seeing them, but from the extravagant
pranks which are played there. I replied, that he ought to reconsider
the hundred or thousand opinions which, in the course of his life, he
might have given, and particularly to examine well the events which he
had predicted with the help of Jupiter, and if he should find that all
had succeeded conformably to his predictions, I bid him prophecy merrily
on, according to his old and wonted rules; for I assured him that the
new planets would not in any degree affect the things which are already
past, and that in future he would not be a less fortunate conjuror than
he had been: but if, on the contrary, he should find the events
depending on Jupiter, in some trifling particulars not to have agreed
with his dogmas and prognosticating aphorisms, he ought to set to work
to find new tables for calculating the constitution of the four Jovial
circulators at every bygone moment, and, perhaps, from the diversity of
their aspects, he would be able, with accurate observations and
multiplied conjunctions, to discover the alterations and variety of
influences depending upon them; and I reminded him, that in ages past
they had not acquired knowledge with little labour, at the expense of
others, from written books, but that the first inventors acquired the
most excellent knowledge of things natural and divine with study and
contemplation of the vast book which nature holds ever open before those
who have eyes in their forehead and in their brain; and that it was a
more honourable and praiseworthy enterprize with their own watching,
toil, and study, to discover something admirable and new among the
infinite number which yet remain concealed in the darkest depths of
philosophy, than to pass a listless and lazy existence, labouring only
to darken the toilsome inventions of their neighbours, in order to
excuse their own cowardice and inaptitude for reasoning, while they cry
out that nothing can be added to the discoveries already made."

The extract given above from Kepler, is taken from an Essay, published
with the later editions of the _Nuncius_, the object and spirit of which
seem to have been greatly misunderstood, even by some of Kepler's
intimate friends.—They considered it as a covert attack upon Galileo,
and, accordingly, Maestlin thus writes to him:—"In your Essay (which I
have just received) you have plucked Galileo's feathers well; I mean,
that you have shown him not to be the inventor of the telescope, not to
have been the first who observed the irregularities of the moon's
surface, not to have been the first discoverer of more worlds than the
ancients were acquainted with, &c. One source of exultation was still
left him, from the apprehension of which Martin Horky has now entirely
delivered me." It is difficult to discover in what part of Kepler's book
Maestlin found all this, for it is one continued encomium upon Galileo;
insomuch that Kepler almost apologizes in the preface for what may seem
his intemperate admiration of his friend. "Some might wish I had spoken
in more moderate terms in praise of Galileo, in consideration of the
distinguished men who are opposed to his opinions, but I have written
nothing fulsome or insincere. I praise him, for myself; I leave other
men's judgments free; and shall be ready to join in condemnation when
some one wiser than myself shall, by sound reasoning, point out his
errors." However, Maestlin was not the only one who misunderstood
Kepler's intentions: the Martin Horky of whom he speaks, a young German,
also signalized himself by a vain attack upon the book which he thought
his patron Kepler condemned. He was then travelling in Italy, whence he
wrote to Kepler his first undetermined thoughts about the new
discoveries. "They are wonderful; they are stupendous; whether they are
true or false I cannot tell."[49] He seems soon to have decided that
most reputation was to be gained on the side of Galileo's opponents, and
his letters accordingly became filled with the most rancorous abuse of
him. At the same time, that the reader may appreciate Horky's own
character, we shall quote a short sentence at the end of one of his
letters, where he writes of a paltry piece of dishonesty with as great
glee as if he had solved an ingenious and scientific problem. After
mentioning his meeting Galileo at Bologna, and being indulged with a
trial of his telescope, which, he says, "does wonders upon the earth,
but represents celestial objects falsely;"[50] he concludes with the
following honourable sentence:—"I must confide to you a theft which I
committed. I contrived to take a mould of the glass in wax, without the
knowledge of any one, and, when I get home, I trust to make a telescope
even better than Galileo's own."

Horky having declared to Kepler, "I will never concede his four new
planets to that Italian from Padua though I die for it," followed up
this declaration by publishing a book against Galileo, which is the one
alluded to by Maestlin, as having destroyed the little credit which,
according to his view, Kepler's publication had left him. This book
professes to contain the examination of four principal questions
touching the alleged planets; 1st, Whether they exist? 2nd, What they
are? 3rd, What they are like? 4th, Why they are? The first question is
soon disposed of, by Horky's declaring positively that he has examined
the heavens with Galileo's own glass, and that no such thing as a
satellite about Jupiter exists. To the second, he declares solemnly,
that he does not more surely know that he has a soul in his body, than
that reflected rays are the sole cause of Galileo's erroneous
observations. In regard to the third question, he says, that these
planets are like the smallest fly compared to an elephant; and, finally,
concludes on the fourth, that the only use of them is to gratify
Galileo's "thirst of gold," and to afford himself a subject of
discussion.[51]

Galileo did not condescend to notice this impertinent folly; it was
answered by Roffini, a pupil of Magini, and by a young Scotchman of the
name of Wedderburn, then a student at Padua, and afterwards a physician
at the Court of Vienna. In the latter reply we find it mentioned, that
Galileo was also using his telescope for the examination of insects,
&c.[52] Horky sent his performance triumphantly to Kepler, and, as he
returned home before receiving an answer, he presented himself before
his patron in the same misapprehension under which he had written, but
the philosopher received him with a burst of indignation which rapidly
undeceived him. The conclusion of the story is characteristic enough to
be given in Kepler's own account of the matter to Galileo, in which,
after venting his wrath against this "scum of a fellow," whose
"obscurity had given him audacity," he says, that Horky begged so hard
to be forgiven, that "I have taken him again into favour upon this
preliminary condition, to which he has agreed:—that I am to shew him
Jupiter's satellites, AND HE IS TO SEE THEM, and own that they are
there."

In the same letter Kepler writes, that although he has himself perfect
confidence in the truth of Galileo's assertions, yet he wishes he could
furnish him with some corroborative testimonies, which Kepler could
quote in arguing the point with others. This request produced the
following reply, from which the reader will also learn the new change
which had now taken place in Galileo's fortunes, the result of the
correspondence with Florence, part of which we have already
extracted.[53] "In the first place, I return you my thanks that you
first, and almost alone, before the question had been sifted (such is
your candour and the loftiness of your mind), put faith in my
assertions. You tell me you have some telescopes, but not sufficiently
good to magnify distant objects with clearness, and that you anxiously
expect a sight of mine, which magnifies images more than a thousand
times. It is mine no longer, for the Grand Duke of Tuscany has asked it
of me, and intends to lay it up in his museum, among his most rare and
precious curiosities, in eternal remembrance of the invention: I have
made no other of equal excellence, for the mechanical labour is very
great: I have, however, devised some instruments for figuring and
polishing them which I am unwilling to construct here, as they could not
conveniently be carried to Florence, where I shall in future reside. You
ask, my dear Kepler, for other testimonies:—I produce, for one, the
Grand Duke, who, after observing the Medicæan planets several times with
me at Pisa during the last months, made me a present, at parting, worth
more than a thousand florins, and has now invited me to attach myself to
him with the annual salary of one thousand florins, and with the title
of Philosopher and Principal Mathematician to His Highness; without the
duties of any office to perform, but with the most complete leisure; so
that I can complete my Treatises on Mechanics, on the Constitution of
the Universe, and on Natural and Violent Local Motion, of which I have
demonstrated geometrically many new and admirable phenomena. I produce,
for another witness, myself, who, although already endowed in this
college with the noble salary of one thousand florins, such as no
professor of mathematics ever before received, and which I might
securely enjoy during my life, even if these planets had deceived me and
should disappear, yet quit this situation, and betake me where want and
disgrace will be my punishment should I prove to have been mistaken."

It is difficult not to regret that Galileo should be thus called on to
resign his best glasses, but it appears probable that on becoming more
familiar with the Grand Duke, he ventured to suggest that this telescope
would be more advantageously employed in his own hands, than pompously
laid up in a museum; for in 1637 we find him saying, in answer to a
request from his friend Micanzio to send him a telescope—"I am sorry
that I cannot oblige you with the glasses for your friend, but I am no
longer capable of making them, and I have just parted with two tolerably
good ones which I had, reserving only my old discoverer of celestial
novelties which is already promised to the Grand Duke." Cosmo was dead
in 1637, and it is his son Ferdinand who is here meant, who appears to
have inherited his father's love of science. Galileo tells us, in the
same letter, that Ferdinand had been amusing himself for some months
with making object-glasses, and always carried one with him to work at
wherever he went.

When forwarding this telescope to Cosmo in the first instance, Galileo
adds, with a very natural feeling—"I send it to his highness unadorned
and unpolished, as I made it for my own use, and beg that it may always
be left in the same state; for none of the old parts ought to be
displaced to make room for new ones, which will have had no share in the
watchings and fatigues of these observations." A telescope was in
existence, though with the object glass broken, at the end of the last
century, and probably still is in the Museum at Florence, which was
shewn as the discoverer of Jupiter's satellites. Nelli, on whose
authority this is mentioned, appears to question its genuineness. The
first reflecting telescope, made with Newton's own hands, and scarcely
possessing less interest than the first of Galileo's, is preserved in
the library of the Royal Society.

By degrees the enemies of Galileo and of the new stars found it
impossible to persevere in their disbelief, whether real or pretended,
and at length seemed resolved to compensate for the sluggishness of
their perception, by its acuteness when brought into action. Simon Mayer
published his "Mundus Jovialis" in 1614, in which he claims to have been
an original observer of the satellites, but, with an affectation of
candour, allows that Galileo observed them probably about the same time.
The earliest observation which he has recorded is dated 29th December,
1609, but, not to mention the total want of probability that Mayer would
not have immediately published so interesting a discovery, it is to be
observed, that, as he used the old style, this date of 29th December
agrees with the 8th January, 1610, of the new style, which was the date
of Galileo's second observation, and Galileo ventured to declare his
opinion, that this pretended observation was in fact a plagiarism.

Scheiner counted five, Rheita nine, and other observers, with increasing
contempt for Galileo's imperfect announcements, carried the number as
high as twelve.[54] In imitation of Galileo's nomenclature, and to
honour the sovereigns of the respective observers, these supposed
additional satellites were dignified with the names of Vladislavian,
Agrippine, Urbanoctavian, and Ferdinandotertian planets; but a very
short time served to show it was as unsafe to exceed as to fall short of
the number which Galileo had fixed upon, for Jupiter rapidly removed
himself from the neighbourhood of the fixed stars, which gave rise to
these pretended discoveries, carrying with him only his four original
attendants, which continued in every part of his orbit to revolve
regularly about him.

Perhaps we cannot better wind up this account of the discovery of
Jupiter's satellites, and of the intense interest they have at all times
inspired, than in the words of one who inherits a name worthy to be
ranked with that of Galileo in the list of astronomical discoverers, and
who takes his own place among the most accomplished mathematicians of
the present times. "The discovery of these bodies was one of the first
brilliant results of the invention of the telescope; one of the first
great facts which opened the eyes of mankind to the system of the
universe, which taught them the comparative insignificance of their own
planet, and the superior vastness and nicer mechanism of those other
bodies, which had before been distinguished from the stars only by their
motion, and wherein none but the boldest thinkers had ventured to
suspect a community of nature with our own globe. This discovery gave
the holding turn to the opinions of mankind respecting the Copernican
system; the analogy presented by these little bodies (little however
only in comparison with the great central body about which they revolve)
performing their beautiful revolutions in perfect harmony and order
about it, being too strong to be resisted. This elegant system was
watched with all the curiosity and interest the subject naturally
inspired. The eclipses of the satellites speedily attracted attention,
and the more when it was discerned, as it speedily was, by Galileo
himself, that they afforded a ready method of determining the difference
of longitudes of distant places on the earth's surface, by observations
of the instants of their disappearances and reappearances,
simultaneously made. Thus the first astronomical solution of the great
problem of the longitude, the first mighty step which pointed out a
connection between speculative astronomy and practical utility, and
which, replacing the fast dissipating dreams of astrology by nobler
visions, showed how the stars might really, and without fiction, be
called arbiters of the destinies of empires, we owe to the satellites of
Jupiter, those atoms imperceptible to the naked eye, and floating like
motes in the beam of their primary—itself an atom to our sight, noticed
only by the careless vulgar as a large star, and by the philosophers of
former ages as something moving among the stars, they knew not what, nor
why: perhaps only to perplex the wise with fruitless conjectures, and
harass the weak with fears as idle as their theories."[55]


FOOTNOTES:

[46] Venturi. Essai sur les ouvrages de Leo. da Vinci.

[47] Dianoia Astronomica, Venetiis, 1610.

[48] Kepleri Epistolæ.

[49] Kepleri Epistolæ.

[50] It may seem extraordinary that any one could support an argument by
this partial disbelief in the instrument, which was allowed on all hands
to represent terrestrial objects correctly. A similar instance of
obstinacy, in an almost identical case though in a more unpretending
station, once came under the writer's own observation. A farmer in
Cambridgeshire, who had acquired some confused notions of the use of the
quadrant, consulted him on a new method of determining the distances and
magnitudes of the sun and moon, which he declared were far different
from the quantities usually assigned to them. After a little
conversation, the root of his error, certainly sufficiently gross,
appeared to be that he had confounded the angular measure of a degree,
with 69½ miles, the linear measure of a degree on the earth's surface.
As a short way of showing his mistake, he was desired to determine, in
the same manner, the height of his barn which stood about 30 yards
distant; he lifted the quadrant to his eye, but perceiving, probably,
the monstrous size to which his principles were forcing him, he said,
"Oh, Sir, the quadrant's only true for the sky." He must have been an
objector of this kind, who said to Galileo,—"Oh, Sir, the telescope's
only true for the earth."

[51] Venturi.

[52] Quatuor probl. confut. per J. Wedderbornium, Scotobritannum.
Patavii, 1610.

[53] See page 18.

[54] Sherburne's Sphere of Manilius. London, 1675.

[55] Herschel's Address to the Astronomical Society, 1827.




CHAPTER VIII.

    _Observations on the Moon—Nebulæ—Saturn—Venus—Mars._


THERE were other discoveries announced in Galileo's book of great and
unprecedented importance, and which scarcely excited less discussion
than the controverted Medicæan planets. His observations on the moon
threw additional light on the constitution of the solar system, and
cleared up the difficulties which encumbered the explanation of the
varied appearance of her surface. The different theories current at that
day, to account for these phenomena, are collected and described by
Benedetti, and also with some liveliness, in a mythological poem, by
Marini.[56] We are told, that, in the opinion of some, the dark shades
on the moon's surface arise from the interposition of opaque bodies
floating between her and the sun, which prevents his light from reaching
those parts: others thought, that on account of her vicinity to the
earth, she was partly tainted with the imperfection of our terrestrial
and elementary nature, and was not of that entirely pure and refined
substance of which the more remote heavens consist: a third party looked
on her as a vast mirror, and maintained that the dark parts of her
surface were the reflected images of our earthly forests and mountains.

Galileo's glass taught him to believe that the surface of this planet,
far from being smooth and polished, as was generally taken for granted,
really resembled our earth in its structure; he was able distinctly to
trace on it the outlines of mountains and other inequalities, the
summits of which reflected the rays of the sun before these reached the
lower parts, and the sides of which, turned from his beams, lay buried
in deep shadow. He recognised a distribution into something similar to
continents of land, and oceans of water, which reflect the sun's light
to us with greater or less vivacity, according to their constitution.
These conclusions were utterly odious to the Aristotelians; they had
formed a preconceived notion of what the moon ought to be, and they
loathed the doctrines of Galileo, who took delight, as they said, in
distorting and ruining the fairest works of nature. It was in vain he
argued, as to the imaginary perfection of the spherical form, that
although the moon, or the earth, were it absolutely smooth, would indeed
be a more perfect sphere than in its present rough state, yet touching
the perfection of the earth, considered as a natural body calculated for
a particular purpose, every one must see that absolute smoothness and
sphericity would make it not only less perfect, but as far from being
perfect as possible. "What else," he demanded, "would it be but a vast
unblessed desert, void of animals, of plants, of cities and of men; the
abode of silence and inaction; senseless, lifeless, soulless, and stript
of all those ornaments which make it now so various and so beautiful?"

He reasoned to no purpose with the slaves of the ancient schools:
nothing could console them for the destruction of their smooth
unalterable surface, and to such an absurd length was this hallucination
carried, that one opponent of Galileo, Lodovico delle Colombe,
constrained to allow the evidence of the sensible inequalities of the
moon's surface, attempted to reconcile the old doctrine with the new
observations, by asserting, that every part of the moon, which to the
terrestrial observer appeared hollow and sunken, was in fact entirely
and exactly filled up with a clear crystal substance, perfectly
imperceptible by the senses, but which restored to the moon her
accurately spherical and smooth surface. Galileo met the argument in the
manner most fitting, according to one of Aristotle's own maxims, that
"it is foolish to refute absurd opinions with too much curiosity."
"Truly," says he, "the idea is admirable, its only fault is that it is
neither demonstrated nor demonstrable; but I am perfectly ready to
believe it, provided that, with equal courtesy, I may be allowed to
raise upon your smooth surface, crystal mountains (which nobody can
perceive) ten times higher than those which I have actually seen and
measured." By threatening to proceed to such extremities, he seems to
have scared the opposite party into moderation, for we do not find that
the crystalline theory was persevered in.

In the same essay, Galileo also explained at some length the cause of
that part of the moon being visible, which is unenlightened directly by
the sun in her first and last quarter. Maestlin, and before him Leonardo
da Vinci, had already declared this to arise from what may be called
_earthshine_, or the reflection of the sun's light from the terrestrial
globe, exactly similar to that which the moon affords us when we are
similarly placed between her and the sun; but the notion had not been
favourably received, because one of the arguments against the earth
being a planet, revolving like the rest round the sun, was, that it did
not shine like them, and was therefore of a different nature; and this
argument, weak as it was in itself, the theory of terrestrial reflection
completely overturned. The more popular opinions ascribed this feeble
light, some to the fixed stars, some to Venus, some to the rays of the
sun, penetrating and shining through the moon. Even the sagacious
Benedetti adopted the notion of this light being caused by Venus, in the
same sentence in which he explains the true reason of the faint light
observed during a total eclipse of the moon, pointing out that it is
occasioned by those rays of the sun, which reach the moon, after being
bent round the sides of the earth by the action of our atmosphere.[57]

Galileo also announced the detection of innumerable stars, invisible to
the unassisted sight; and those remarkable appearances in the heavens,
generally called nebulæ, the most considerable of which is familiar to
all under the name of the milky way, when examined by his instrument,
were found to resolve themselves into a vast collection of minute stars,
too closely congregated to produce a separate impression upon the
unassisted eye.[58] Benedetti, who divined that the dark shades on the
moon's surface arose from the constitution of those parts which suffered
much of the light to pass into them, and consequently reflected a less
portion of it, had maintained that the milky way was the result of the
converse of the same phenomenon, and declared, in the language of his
astronomy, that it was a part of the eighth orb, which did not, like the
rest, allow the sun's light to traverse it freely, but reflected a small
part feebly to our sight.

The Anti-Copernicans would probably have been well pleased, if by these
eternally renewed discussions and disputes, they could have occupied
Galileo's time sufficiently to detain his attention from his telescope
and astronomical observations; but he knew too well where his real
strength lay, and they had scarcely time to compound any thing like an
argument against him and his theories, before they found him in
possession of some new facts, which they were unprepared to meet,
otherwise than by the never-failing resource of abuse and affected
contempt. The year had not expired before Galileo had new intelligence
to communicate of the highest importance. Perhaps he had been taught
caution from the numerous piracies which had been committed upon his
discoveries, and he first announced his new discoveries enigmatically,
veiling their real import by transpositions of the letters in the words
which described them, (a practice then common, and not disused even at a
much later date,) and inviting all astronomers to declare, within a
certain time, if they had noted any thing new in the heavens worthy of
observation. The transposed letters which he published were—

    "_Smaismrmilme poeta leumi bvne nugttaviras._"

Kepler, in the true spirit of his riddling philosophy, endeavoured to
decypher the meaning, and fancied he had succeeded when he formed a
barbarous Latin verse,

    "_Salve umbistineum geminatum Martia proles_,"

conceiving that the discovery, whatever it might be, related to the
planet Mars, to which Kepler's attention had before been particularly
directed. The reader, however, need not weary himself in seeking a
translation of this solution, for at the request of the Emperor Rodolph,
Galileo speedily sent to him the real reading—

    _Altissimum planetam tergeminum observavi_;

that is, "I have observed that the most distant planet is triple," or,
as he further explains the matter, "I have with great admiration
observed that Saturn is not a single star, but three together, which as
it were touch each other; they have no relative motion, and are
constituted in this form [Symbol: oOo] the middle being somewhat larger
than the lateral ones. If we examine them with an eye-glass which
magnifies the surface less than 1000 times, the three stars do not
appear very distinctly, but Saturn has an oblong appearance, like the
appearance of an olive, thus [Symbol: horizontal 0]. Now I have
discovered a court for Jupiter, and two servants for this old man, who
aid his steps and never quit his side." Galileo was, however, no match
in this style of writing for Kepler, who disapproved his friend's
metaphor, and, in his usual fanciful and amusing strain,—"I will not,"
said he, "make an old man of Saturn, nor slaves of his attendant globes,
but rather let this tricorporate form be Geryon, so shall Galileo be
Hercules, and the telescope his club; armed with which, he has conquered
that distant planet, and dragged him from the remotest depths of nature,
and exposed him to the view of all." Galileo's glass was not of
sufficient power to shew him the real constitution of this extraordinary
planet; it was reserved for Huyghens, about the year 1656, to declare to
the world that these supposed attendant stars are in fact part of a ring
which surrounds, and yet is completely distinct from the body of
Saturn;[59] and the still more accurate observations of Herschel have
ascertained that it consists of two concentric rings revolving round the
planet, and separated from each other by a space which our most powerful
telescopes scarcely enable us to measure.

Galileo's second statement concluded with the remark, that "in the other
planets nothing new was to be observed;" but a month had scarcely
elapsed, before he communicated to the world another enigma,

    _Hæc immatura à me jam frustra leguntur oy_,

which, as he said, contained the announcement of a new phenomenon, in
the highest degree important to the truth of the Copernican system. The
interpretation of this is,

    _Cynthiæ figuras æmulatur mater amorum_,

that is to say,—Venus rivals the appearances of the moon—for Venus
being now arrived at that part of her orbit in which she is placed
between the earth and the sun, and consequently, with only a part of her
enlightened surface turned towards the earth, the telescope shewed her
in a crescent form, like the moon in a similar position, and tracing her
through the whole of her orbit round the sun, or at least so long as she
was not invisible from his overpowering light, Galileo had the
satisfaction of seeing the enlightened portion in each position assume
the form appropriate to that hypothesis. It was with reason, therefore,
that he laid stress on the importance of this observation, which also
established another doctrine scarcely less obnoxious to the
Anti-Copernicans, namely, that a new point of resemblance was here found
between the earth and one of the principal planets; and as the
reflection from the earth upon the moon had shewn it to be luminous like
the planets when subjected to the rays of the sun, so this change of
apparent figure demonstrated that one of the planets not near the earth,
and therefore probably all, were in their own nature not luminous, and
only reflected the sun's light which fell upon them; an inference, of
which the probability was still farther increased a few years later by
the observation of the transit of Mercury over the sun's disc.

It is curious that only twenty-five years before this discovery of the
phases (or appearances) of Venus, a commentator of Aristotle, under the
name of Lucillus Philalthæus, had advanced the doctrine that all the
planets except the moon are luminous of themselves, and in proof of his
assertion had urged, "that if the other planets and fixed stars received
their light from the sun, they would, as they approached and receded
from him, or as he approached and receded from them, assume the same
phases as the moon, which, he adds, we have never yet observed."—He
further remarks, "that Mercury and Venus would, in the supposed case of
their being nearer the earth than the sun, eclipse it occasionally, just
as eclipses are occasioned by the moon." Perhaps it is still more
remarkable, that these very passages, in which the reasoning is so
correct, though the facts are too hastily taken for granted, (the common
error of that school,) are quoted by Benedetti, expressly to shew the
ignorance and presumption of the author. Copernicus, whose want of
instruments had prevented him from observing the horned appearance of
Venus when between the earth and sun, had perceived how formidable an
obstacle the non-appearance of this phenomenon presented to his system;
he endeavoured, though unsatisfactorily, to account for it by supposing
that the rays of the sun passed freely through the body of the planet,
and Galileo takes occasion to praise him for not being deterred from
adopting the system, which, on the whole, appeared to agree best with
the phenomena, by meeting with some which it did not enable him to
explain. Milton, whose poem is filled with allusions to Galileo and his
astronomy, has not suffered this beautiful phenomenon to pass unnoticed.
After describing the creation of the Sun, he adds:—

    Hither, as to their fountain, other stars
    Repairing, in their golden urns draw light,
    And hence the morning planet gilds her horns.[60]

Galileo also assured himself, at the same time, that the fixed stars did
not receive their light from the sun. This he ascertained by comparing
the vividness of their light, in all positions, with the feebleness of
that of the distant planets, and by observing the different degrees of
brightness with which all the planets shone at different distances from
the sun. The more remote planets did not, of course, afford equal
facilities with Venus for so decisive an observation; but Galileo
thought he observed, that when Mars was in quadratures, (or in the
quarters, the middle points of his path on either side,) his figure
varied slightly from a perfect circle. Galileo concludes the letter, in
which he announces these last observations to his pupil Castelli, with
the following expressions, shewing how justly he estimated the
opposition they encountered:—"You almost make me laugh by saying that
these clear observations are sufficient to convince the most obstinate:
it seems you have yet to learn that long ago the observations were
enough to convince those who are capable of reasoning, and those who
wish to learn the truth; but that to convince the obstinate, and those
who care for nothing beyond the vain applause of the stupid and
senseless vulgar, not even the testimony of the stars would suffice,
were they to descend on earth to speak for themselves. Let us then
endeavour to procure some knowledge for ourselves, and rest contented
with this sole satisfaction; but of advancing in popular opinion, or
gaining the assent of the book-philosophers, let us abandon both the
hope and the desire."


FOOTNOTES:

[56] Adone di Marini, Venetiis, 1623, Cant. x.

[57] Speculat. Lib Venetiis, 1585, Epistolæ.

[58] This opinion, with respect to the milky way, had been held by some
of the ancient astronomers. _See_ Manilius. Lib. i. v. 753.

  "_Anne magis densâ stellarum turba coronâ_
  "_Contexit flammas, et crasso lumine candet,_
  "_Et fulgore nitet collato clarior orbis._"

[59] Huyghens announced his discovery in this form: _a a a a a a a c c c
c c d e e e e e g h i i i i i i i l l l l m m n n n n n n n n n o o o o
p p q r r s t t t t t u u u u u_, which he afterwards recomposed into
the sentence. _Annulo cingitur, tenui, plano, nusquam cohærente, ad
eclipticam inclinato_. De Saturni Lunâ. Hagæ, 1656.

[60] B. vii. v. 364. Other passages may be examined in B. i. 286; iii.
565-590, 722-733; iv. 589; v. 261, 414; vii. 577; viii. 1-178.




CHAPTER IX.

    _Account of the Academia Lincea—Del Cimento—Royal Society._


GALILEO'S resignation of the mathematical professorship at Padua
occasioned much dissatisfaction to all those who were connected with
that university. Perhaps not fully appreciating his desire of returning
to his native country, and the importance to him and to the scientific
world in general, of the complete leisure which Cosmo secured to him at
Florence, (for by the terms of his diploma he was not even required to
reside at Pisa, nor to give any lectures, except on extraordinary
occasions, to sovereign princes and other strangers of distinction,) the
Venetians remembered only that they had offered him an honourable asylum
when almost driven from Pisa; that they had increased his salary to four
times the sum which any previous professor had enjoyed; and, finally, by
an almost unprecedented decree, that they had but just secured him in
his post during the remainder of his life. Many took such offence as to
refuse to have any further communication with him; and Sagredo, a
constant friend of Galileo, wrote him word that he had been threatened
with a similar desertion unless he should concur in the same peremptory
resolution, which threats, however, Sagredo, at the same time, intimates
his intention of braving.

Early in the year 1611, Galileo made his first appearance in Rome, where
he was received with marks of distinguished consideration, and where all
ranks were eager to share the pleasure of contemplating the new
discoveries. "Whether we consider cardinal, prince, or prelate, he found
an honourable reception from them all, and had their palaces as open and
free to him as the houses of his private friends."[61] Among other
distinctions he was solicited to become a member of the newly-formed
philosophical society, the once celebrated _Academia Lincea_, to which
he readily assented. The founder of this society was Federigo Cesi, the
Marchese di Monticelli, a young Roman nobleman, the devotion of whose
time and fortune to the interests of science has not been by any means
rewarded with a reputation commensurate with his deserts. If the energy
of his mind had been less worthily employed than in fostering the cause
of science and truth, and in extending the advantages of his birth and
fortune to as many as were willing to co-operate with him, the name of
Federigo Cesi might have appeared more prominently on the page of
history. Cesi had scarcely completed his 18th year, when, in 1603, he
formed the plan of a philosophical society, which in the first instance
consisted only of himself and three of his most intimate friends, Hecke,
a Flemish physician, Stelluti, and Anastasio de Filiis. Cesi's father,
the Duca d'Acquasparta, who was of an arbitrary and extravagant temper,
considered such pursuits and associates as derogatory to his son's rank;
he endeavoured to thwart the design by the most violent and
unjustifiable proceedings, in consequence of which, Cesi in the
beginning of 1605 privately quitted Rome, Hecke was obliged to leave
Italy altogether from fear of the Inquisition, which was excited against
him, and the academy was for a time virtually dissolved. The details of
these transactions are foreign to the present narrative: it will be
enough to mention that, in 1609, Cesi, who had never altogether
abandoned his scheme, found the opposition decaying which he at first
experienced, and with better success he renewed the plan which he had
sketched six years before. A few extracts from the Regulations will
serve to shew the spirit in which this distinguished society was
conceived:—

"The Lyncean Society desires for its academicians, philosophers eager
for real knowledge, who will give themselves to the study of nature, and
especially to mathematics; at the same time it will not neglect the
ornaments of elegant literature and philology, which like a graceful
garment adorn the whole body of science.—In the pious love of wisdom,
and to the praise of the most good and most high God, let the Lynceans
give their minds, first to observation and reflection, and afterwards to
writing and publishing.—It is not within the Lyncean plan to find
leisure for recitations and declamatory assemblies; the meetings will
neither be frequent nor full, and chiefly for transacting the necessary
business of the society: but those who wish to enjoy such exercises will
in no respect be hindered, provided they attend them as accessory
studies, decently and quietly, and without making promises and
professions of how much they are about to do. For there is ample
philosophical employment for every one by himself, particularly if pains
are taken in travelling and in the observation of natural phenomena, and
in the book of nature which every one has at home, that is to say, the
heavens and the earth; and enough may be learned from the habits of
constant correspondence with each other, and alternate offices of
counsel and assistance.—Let the first fruits of wisdom be love; and so
let the Lynceans love each other as if united by the strictest ties, nor
suffer any interruption of this sincere bond of love and faith,
emanating from the source of virtue and philosophy.—Let them add to
their names the title of Lyncean, which has been advisedly chosen as a
warning and constant stimulus, especially when they write on any
literary subject, also in their private letters to their associates, and
in general when any work comes from them wisely and well performed.—The
Lynceans will pass over in silence all political controversies and
quarrels of every kind, and wordy disputes, especially gratuitous ones,
which give occasion to deceit, unfriendliness, and hatred; like men who
desire peace, and seek to preserve their studies free from molestation,
and to avoid every sort of disturbance. And if any one by command of his
superiors, or from some other necessity, is reduced to handle such
matters, since they are foreign to physical and mathematical science,
and consequently alien to the object of the Academy, let them be printed
without the Lyncean name."[62]

The society which was eventually organized formed but a very trifling
part of the comprehensive scheme which Cesi originally proposed to
himself; it had been his wish to establish a scientific Order which
should have corresponding lodges in the principal towns of Europe, and
in other parts of the globe, each consisting of not more than five nor
less than three members, besides an unlimited number of Academicians not
restricted to any particular residence or regulations. The
mortifications and difficulties to which he was subjected from his
father's unprincipled behaviour, render it most extraordinary and
admirable that he should have ventured to undertake even so much as he
actually carried into execution. He promised to furnish to the members
of his society such assistance as they might require in the prosecution
of their respective researches, and also to defray the charges of
publishing such of their works as should be thought worthy of appearing
with the common sanction. Such liberal offers were not likely to meet
with an unfavourable reception: they were thankfully accepted by many
well qualified to carry his design into execution, and Cesi was soon
enabled formally to open his academy, the distinctive title of which he
borrowed from the Lynx, with reference to the piercing sight which that
animal has been supposed to possess. This quality seemed to him an
appropriate emblem of those which he desired to find in his
academicians, for the purpose of investigating the secrets of nature;
and although, at the present day, the name may appear to border on the
grotesque, it was conceived in the spirit of the age, and the fantastic
names of the numberless societies which were rapidly formed in various
parts of Italy far exceed whatever degree of quaintness may be thought
to belong to the Lyncean name. The Inflamed—the Transformed—the
Uneasy—the Humorists—the Fantastic—the Intricate—the Indolent—the
Senseless—the Undeceived—the Valiant—the Ætherial Societies are
selected from a vast number of similar institutions, the names of which,
now almost their sole remains, are collected by the industry of Morhof
and Tiraboschi.[63] The Humorists are named by Morhof as the only
Italian philosophical society anterior to the Lynceans; their founder
was Paolo Mancino, and the distinctive symbol which they adopted was
rain dropping from a cloud, with the motto _Redit agmine dulci_;—their
title is derived from the same metaphor. The object of their union
appears to have been similar to that of the Lynceans, but they at no
time attained to the celebrity to which Cesi's society rose from the
moment of its incorporation. Cesi took the presidency for his life, and
the celebrated Baptista Porta was appointed vice president at Naples.
Stelluti acted as the legal representative of the society, with the
title of procuratore. Of the other two original members Anastasio de
Filiis was dead, and although Hecke returned to Italy in 1614, and
rejoined the Academy, yet he was soon afterwards struck off the list in
consequence of his lapsing into insanity. Among the academicians we find
the names of Galileo, Fabio Colonna, Lucas Valerio, Guiducci, Welser,
Giovanni Fabro, Terrentio, Virginio Cesarini, Ciampoli, Molitor,
Cardinal Barberino, (nephew of Pope Urban VIII.) Stelliola, Salviati,
&c.

The principal monument still remaining of the zeal and industry to which
Cesi incited his academicians is the Phytobasanos, a compendium of the
natural history of Mexico, which must be considered a surprising
performance for the times in which it appeared. It was written by a
Spaniard named Hernandez; and Reccho, who often has the credit of the
whole work, made great additions to it. During fifty years the
manuscript had been neglected, when Cesi discovered it, and employed
Terrentio, Fabro, and Colonna, all Lynceans, to publish it enriched with
their notes and emendations. Cesi himself published several treatises,
two of which are extant; his _Tabulæ Phytosophicæ_, and a Dissertation
on Bees entitled _Apiarium_, the only known copy of which last is in the
library of the Vatican. His great work, _Theatrum Naturæ_, was never
printed; a circumstance which tends to shew that he did not assemble the
society round him for the purpose of ministering to his own vanity, but
postponed the publication of his own productions to the labours of his
coadjutors. This, and many other valuable works belonging to the academy
existed in manuscript till lately in the Albani Library at Rome. Cesi
collected, not a large, but an useful library for the use of the
academy, (which was afterwards augmented on the premature death of
Cesarini by the donation of his books); he filled a botanical garden
with the rarer specimens of plants, and arranged a museum of natural
curiosities; his palace at Rome was constantly open to the academicians;
his purse and his influence were employed with equal liberality in their
service.

Cesi's death, in 1632, put a sudden stop to the prosperity of the
society, a consequence which may be attributed to the munificence with
which he had from the first sustained it: no one could be found to fill
his place in the princely manner to which the academicians were
accustomed, and the society, after lingering some years under the
nominal patronage of Urban VIII., gradually decayed, till, by the death
of its principal members, and dispersion of the rest, it became entirely
extinct.[64] Bianchi, whose sketch of the academy was almost the only
one till the appearance of Odescalchi's history, made an attempt to
revive it in the succeeding century, but without any permanent effect. A
society under the same name has been formed since 1784, and is still
flourishing in Rome. Before leaving the subject it may be mentioned,
that one of the earliest notices that Bacon's works were known in Italy
is to be found in a letter to Cesi, dated 1625; in which Pozzo, who had
gone to Paris with Cardinal Barberino, mentions having seen them there
with great admiration, and suggests that Bacon would be a fit person to
be proposed as a member of their society. After Galileo's death, three
of his principal followers, Viviani, Torricelli, and Aggiunti formed the
plan of establishing a similar philosophical society, and though
Aggiunti and Torricelli died before the scheme could be realized,
Viviani pressed it forward, and, under the auspices of Ferdinand II.,
formed a society, which, in 1657, merged in the famous _Academia del
Cimento_, or Experimental Academy. This latter held its occasional
meetings at the palace of Ferdinand's brother, Leopold de' Medici: it
was composed chiefly, if not entirely, of Galileo's pupils and friends.
During the few years that this society lasted, one of the principal
objects of which was declared to be the repetition and developement of
Galileo's experiments, it kept up a correspondence with the principal
philosophers in every part of Europe, but when Leopold was, in 1666,
created a cardinal, it appears to have been dissolved, scarcely ten
years after its institution.[65] This digression may be excused in
favour of so interesting an establishment as the Academia Lincea, which
preceded by half a century the formation of the Royal Society of London,
and Académie Françoise of Paris.

These latter two are mentioned together, probably for the first time, by
Salusbury. The passage is curious in an historical point of view, and
worth extracting:—"In imitation of these societies, Paris and London
have erected theirs of _Les Beaux Esprits_, and of the _Virtuosi_: the
one by the countenance of the most eminent Cardinal Richelieu, the other
by the royal encouragement of his sacred Majesty that now is. The _Beaux
Esprits_ have published sundry volumes of their moral and physiological
conferences, with the laws and history of their fellowship; and I hope
the like in due time from our Royal Society; that so such as envie their
fame and felicity, and such as suspect their ability and candor, may be
silenced and disappointed in their detractions and expectations."[66]


FOOTNOTES:

[61] Salusbury, Math. Coll.

[62] Perhaps it was to deprecate the hostility of the Jesuits that, at
the close of these Regulations, the Lynceans are directed to address
their prayers, among other Saints, especially to Ignatius Loyola, as to
one who greatly favoured the interests of learning. Odescalchi, Memorie
dell'Acad. de' Lincei, Roma. 1806.

[63] Polyhistor Literarius, &c.—Storia della Letterat. Ital. The still
existing society of Chaff, more generally known by its Italian title,
Della Crusca, belongs to the same period.

[64] F. Colonnæ Phytobasanus Jano Planco Auctore. Florent, 1744.

[65] Nelli Saggio di Storia Literaria Fiorentina, Lucca, 1759.

[66] Salusbury's Math. Coll. vol. ii. London, 1664.




CHAPTER X.

    _Spots on the Sun—Essay on Floating Bodies—Scheiner—Change in
      Saturn._


GALILEO did not indulge the curiosity of his Roman friends by exhibiting
only the wonders already mentioned, which now began to lose the gloss of
novelty, but disclosed a new discovery, which appeared still more
extraordinary, and, to the opposite faction, more hateful than anything
of which he had yet spoken. This was the discovery, which he first made
in the month of March, 1611, of dark spots on the body of the sun. A
curious fact, and one which well serves to illustrate Galileo's
superiority in seeing things simply as they are, is, that these spots
had been observed and recorded centuries before he existed, but, for
want of careful observation, their true nature had been constantly
misapprehended. One of the most celebrated occasions was in the year 807
of our era, in which a dark spot is mentioned as visible on the face of
the sun during seven or eight days. It was then supposed to be
Mercury.[67] Kepler, whose astronomical knowledge would not suffer him
to overlook that it was impossible that Mercury could remain so long in
conjunction with the sun, preferred to solve the difficulty by supposing
that, in Aimoin's original account, the expression was not _octo dies_
(eight days), but _octoties_—a barbarous word, which he supposed to
have been written for _octies_ (eight times); and that the other
accounts (in which the number of days mentioned is different) copying
loosely from the first, had both mistaken the word, and misquoted the
time which they thought they found mentioned there. It is impossible to
look on this explanation as satisfactory, but Kepler, who at that time
did not dream of spots on the sun, was perfectly contented with it. In
1609, he himself observed upon the sun a black spot, which he in like
manner mistook for Mercury, and unluckily the day, being cloudy, did
not allow him to contemplate it sufficiently long to discover his
error, which the slowness of its apparent motion would soon have pointed
out.[68] He hastened to publish his supposed observation, but no sooner
was Galileo's discovery of the solar spots announced, than he, with that
candour which as much as his flighty disposition certainly characterized
him at all times, retracted his former opinion, and owned his belief
that he had been mistaken. In fact it is known from the more accurate
theory which we now possess of Mercury's motions, that it did not pass
over the sun's face at the time when Kepler thought he perceived it
there.

Galileo's observations were in their consequences to him particularly
unfortunate, as in the course of the controversy in which they engaged
him, he first became personally embroiled with the powerful party, whose
prevailing influence was one of the chief causes of his subsequent
misfortunes. Before we enter upon that discussion, it will be proper to
mention another famous treatise which Galileo produced soon after his
return from Rome to Florence, in 1612. This is, his Discourse on
Floating Bodies, which restored Archimedes' theory of hydrostatics, and
has, of course, met with the opposition which few of Galileo's works
failed to encounter. In the commencement, he thought it necessary to
apologize for writing on a subject so different from that which chiefly
occupied the public attention, and declared that he had been too closely
occupied in calculating the periods of the revolutions of Jupiter's
satellites to permit him to publish anything earlier. These periods he
had succeeded in determining during the preceding year, whilst at Rome,
and he now announced them to complete their circuits, the first in about
1 day, 18½ hours; the second in 3 days, 13 hours, 20 minutes; the third
in 7 days, 4 hours; and the outermost in 16 days, 18 hours. All these
numbers he gave merely as approximately true, and promised to continue
his observations, for the purpose of correcting the results. He then
adds an announcement of his recent discovery of the solar spots, "which,
as they change their situation, offer a strong argument, either that the
sun revolves on itself, or that, perhaps, other stars, like Venus and
Mercury, revolve about it, invisible at all other times, on account of
the small distance to which they are removed from him." To this he
afterwards subjoined, that, by continued observation, he had satisfied
himself that these solar spots were in actual contact with the surface
of the sun, where they are continually appearing and disappearing; that
their figures were very irregular, some being very dark, and others not
so black; that one would often divide into three or four, and, at other
times, two, three, or more would unite into one; besides which, that
they had all a common and regular motion, with which they revolved round
with the sun, which turned upon its axis in about the time of a lunar
month.

Having by these prefatory observations assuaged the public thirst for
astronomical novelties, he ventures to introduce the principal subject
of the treatise above mentioned. The question of floating bridges had
been discussed at one of the scientific parties, assembled at the house
of Galileo's friend Salviati, and the general opinion of the company
appearing to be that the floating or sinking of a body depended
principally upon its shape, Galileo undertook to convince them of their
error. If he had not preferred more direct arguments, he might merely
have told them that in this instance they were opposed to their
favourite Aristotle, whose words are very unequivocal on the point in
dispute. "Form is not the cause why a body moves downwards rather than
upwards, but it does affect the swiftness with which it moves;"[69]
which is exactly the distinction which those who called themselves
Aristotelians were unable to perceive, and to which the opinions of
Aristotle himself were not always true. Galileo states the discussion to
have immediately arisen from the assertion of some one in the company,
that condensation is the effect of cold, and ice was mentioned as an
instance. On this, Galileo observed, that ice is rather water rarefied
than condensed, the proof of which is, that ice always floats upon
water.[70] It was replied, that the reason of this phenomenon was, not
the superior lightness of the ice, but its incapacity, owing to its flat
shape, to penetrate and overcome the resistance of the water. Galileo
denied this, and asserted that ice of any shape would float upon water,
and that, if a flat piece of ice were forcibly taken to the bottom, it
would of itself rise again to the surface. Upon this assertion it
appears that the conversation became so clamorous, that Galileo thought
it pertinent to commence his Essay with the following observation on the
advantage of delivering scientific opinions in writing, "because in
conversational arguments, either one or other party, or perhaps both,
are apt to get overwarm, and to speak overloud, and either do not suffer
each other to be heard, or else, transported with the obstinacy of not
yielding, wander far away from the original proposition, and confound
both themselves and their auditors with the novelty and variety of their
assertions." After this gentle rebuke he proceeds with his argument, in
which he takes occasion to state the famous hydrostatical paradox, of
which the earliest notice is to be found in Stevin's works, a
contemporary Flemish engineer, and refers it to a principle on which we
shall enlarge in another chapter. He then explains the true theory of
buoyancy, and refutes the false reasoning on which the contrary opinions
were founded, with a variety of experiments.

The whole value and interest of experimental processes generally depends
on a variety of minute circumstances, the detail of which would be
particularly unsuited to a sketch like the present one. For those who
are desirous of becoming more familiar with Galileo's mode of conducting
an argument, it is fortunate that such a series of experiments exists as
that contained in this essay; experiments which, from their simplicity,
admit of being for the most part concisely enumerated, and at the same
time possess so much intrinsic beauty and characteristic power of
forcing conviction. They also present an admirable specimen of the
talent for which Galileo was so deservedly famous, of inventing
ingenious arguments in favour of his adversaries' absurd opinions before
he condescended to crush them, shewing that nothing but his love of
truth stood in the way of his being a more subtle sophist than any
amongst them. In addition to these reasons for giving these experiments
somewhat in detail, is the fact that all explanation of one of the
principal phenomena to which they allude is omitted in many more modern
treatises on Hydrostatics; and in some it is referred precisely to the
false doctrines here confuted.

The marrow of the dispute is included in Galileo's assertion, that "The
diversity of figure given to any solid cannot be in any way the cause of
its absolutely sinking or floating; so that if a solid, when formed for
example into a spherical figure, sinks or floats in the water, the same
body will sink or float in the same water, when put into any other form.
The breadth of the figure may indeed retard its velocity, as well of
ascent as descent, and more and more according as the said figure is
reduced to a greater breadth and thinness; but that it may be reduced to
such a form as absolutely to put an end to its motion in the same fluid,
I hold to be impossible. In this I have met with great contradictors
who, producing some experiments, and in particular a thin board of
ebony, and a ball of the same wood, and shewing that the ball in water
sinks to the bottom[71], and that the board if put lightly on the
surface floats, have held and confirmed themselves in their opinion with
the authority of Aristotle, that the cause of that rest is the breadth
of the figure, unable by its small weight to pierce and penetrate the
resistance of the water's thickness, which is readily overcome by the
other spherical figure."—For the purpose of these experiments, Galileo
recommends a substance such as wax, which may be easily moulded into any
shape, and with which, by the addition of a few filings of lead, a
substance may be readily made of any required specific gravity. He then
declares that if a ball of wax of the size of an orange, or bigger, be
made in this manner heavy enough to sink to the bottom, but so lightly
that if we take from it only one grain of lead it returns to the top;
and if the same wax be afterwards moulded into a broad and thin cake, or
into any other figure, regular or irregular, the addition of the same
grain of lead will always make it sink, and it will again rise when we
remove the lead from it.—"But methinks I hear some of the adversaries
raise a doubt upon my produced experiment: and, first, they offer to my
consideration that the figure, as a figure simply, and disjunct from the
matter, works no effect, but requires to be conjoined with the matter;
and, moreover, not with every matter, but with those only wherewith it
may be able to execute the desired operation. Just as we see by
experience that an acute and sharp angle is more apt to cut than an
obtuse; yet always provided that both one and the other are joined with
a matter fit to cut, as for instance, steel. Therefore a knife with a
fine and sharp edge cuts bread or wood with much ease, which it will not
do if the edge be blunt and thick; but if, instead of steel, any one
will take wax and mould it into a knife, undoubtedly he will never learn
the effects of sharp and blunt edges, because neither of them will cut;
the wax being unable, by reason of its flexibility, to overcome the
hardness of the wood and bread. And therefore, applying the like
discourse to our argument, they say that the difference of figure will
shew different effects with regard to floating and sinking, but not
conjoined with any kind of matter, but only with those matters which by
their weight are able to overcome the viscosity of the water (like the
ebony which they have selected); and he that will select cork or other
light wood to form solids of different figures, would in vain seek to
find out what operation figure has in sinking or floating, because all
would swim, and that not through any property of this or that figure,
but through the debility of the matter.

"When I begin to examine one by one all the particulars here produced, I
allow not only that figures, simply as such, do not operate in natural
things, but also that they are never separated from the corporeal
substance, nor have I ever alleged them to be stript of sensible matter:
and also I freely admit, that in our endeavours to examine the diversity
of accidents which depend upon the variety of figures, it is necessary
to apply them to matters which obstruct not the various operations of
those various figures. I admit and grant that I should do very ill if I
were to try the influence of a sharp edge with a knife of wax, applying
it to cut an oak, because no sharpness in wax is able to cut that very
hard wood. But yet, such an experiment of this knife would not be beside
the purpose to cut curded milk, or other very yielding matter; nay, in
such matters, the wax is more convenient than steel for finding the
difference depending on the acuteness of the angles, because milk is cut
indifferently with a razor, or a blunt knife. We must therefore have
regard not only to the hardness, solidity, or weight of the bodies
which, under different figures, are to divide some matters asunder; but
also, on the other hand, to the resistance of the matter to be
penetrated. And, since I have chosen a matter which does penetrate the
resistance of the water, and in all figures descends to the bottom, my
antagonists can charge me with no defect; nor (to revert to their
illustration) have I attempted to test the efficacy of acuteness by
cutting with matters unable to cut. I subjoin withal, that all caution,
distinction, and election of matter would be superfluous and
unnecessary, if the body to be cut should not at all resist the cutting:
if the knife were to be used in cutting a mist, or smoke, one of paper
would serve the purpose as well as one of Damascus steel; and I assert
that this is the case with water, and that there is not any solid of
such lightness or of such a figure, that being put on the water it will
not divide and penetrate its thickness; and if you will examine more
carefully your thin boards of wood, you will see that they have part of
their thickness under water; and, moreover, you will see that the
shavings of ebony, stone, or metal, when they float, have not only thus
broken the continuity of the water, but are with all their thickness
under the surface of it; and that more and more, according as the
floating substance is heavier, so that a thin floating plate of lead
will be lower than the surface of the surrounding water by at least
twelve times the thickness of the plate, and gold will dive below the
level of the water almost twenty times the thickness of the plate, as I
shall shew presently."

In order to illustrate more clearly the non-resistance of water to
penetration, Galileo then

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