"The starry Galileo with his woes."[1]
But, however powerful be their contrasts, they are not unusual in their
proportions. The balance which has been struck between his days of good
and evil, is that which regulates the lot of man, whether we study it in
the despotic sway of the autocrat, in the peaceful enquiries of the
philosopher, or in the humbler toils of ordinary life.
Galileo Galilei was born at Pisa, on the 15th of February, 1564, and was
the eldest of a family of three sons and three daughters. Under the name
of Bonajuti, his noble ancestors had filled high offices at Florence;
but about the middle of the 14th century they seem to have abandoned
this surname for that of Galileo. Vincenzo Galilei, our author's father,
was himself a philosopher of no mean powers; and though his talents seem
to have been applied only in the composition of treatises on the theory
and practice of music, yet he appears to have anticipated even his son
in a just estimate of the philosophy of the age, and in a distinct
perception of the true method of investigating truth.[2]
The early years of Galileo were, like those of almost all great
experimental philosophers, spent in the construction of instruments and
pieces of machinery, which were calculated chiefly to amuse himself and
his school-fellows. This occupation of his hands, however, did not
interfere with his regular studies; and though, from the straitened
circumstances of his father, he was educated under considerable
disadvantages, yet he acquired the elements of classical literature, and
was initiated into all the learning of the times. Music, drawing, and
painting were the occupations of his leisure hours; and such was his
proficiency in these arts, that he was reckoned a skilful performer on
several musical instruments, especially the lute; and his knowledge of
pictures was held in great esteem by some of the best artists of his
day.
Galileo seems to have been desirous, of following the profession of a
painter: but his father had observed decided indications of early
genius; and, though by no means able to afford it, he resolved to send
him to the university to pursue the study of medicine. He accordingly
enrolled himself as a scholar in arts at the university of Pisa, on the
5th of November, 1581, and pursued his medical studies under the
celebrated botanist Andrew Cæsalpinus, who filled the chair of medicine
from 1567 to 1592.
In order to study the principles of music and drawing, Galileo found it
necessary to acquire some knowledge of geometry. His father seems to
have foreseen the consequences of following this new pursuit, and though
he did not prohibit him from reading Euclid under Ostilio Ricci, one of
the professors at Pisa, yet he watched his progress with the utmost
jealousy, and had resolved that it should not interfere with his medical
studies. The demonstrations, however, of the Greek mathematician had too
many charms for the ardent mind of Galileo. His whole attention was
engrossed with the new truths which burst upon his understanding; and
after many fruitless attempts to check his ardour and direct his
thoughts to professional objects, his father was obliged to surrender
his parental control, and allow the fullest scope to the genius of his
son.
From the elementary works of geometry, Galileo passed to the writings of
Archimedes; and while he was studying the hydrostatical treatise[3] of
the Syracusan philosopher, he wrote his essay on the hydrostatical
balance[4], in which he describes the construction of the instrument,
and the method by which Archimedes detected the fraud committed by the
jeweller in the composition of Hiero's crown. This work gained for its
author the esteem of Guido Ubaldi, who had distinguished himself by his
mechanical and mathematical acquirements, and who engaged his young
friend to investigate the subject of the centre of gravity in solid
bodies. The treatise on this subject, which Galileo presented to his
patron, was the source of his future success.
Through the cardinal del Monte, the brother-in-law of Ubaldi, the
reigning duke of Tuscany, Ferdinand de' Medici, was made acquainted with
the merits of our young philosopher; and, in 1589, he was appointed
lecturer on mathematics at Pisa. By the drudgery of private teaching he
was obliged to add to the small salary of sixty crowns which was
attached to the office.
With this moderate Competency, Galileo commenced his philosophical
career. At the early age of eighteen, when he had entered the
university, he displayed his innate antipathy to the Aristotelian
philosophy. This feeling was strengthened by his earliest inquiries; and
upon his establishment at Pisa, he seems to have regarded the doctrines
of Aristotle as the intellectual prey which, in his chace of glory, he
was destined to pursue. Nizzoli, who flourished near the beginning of
the sixteenth century, and Giordano Bruno, who was burned at Rome in
1600, led the way in this daring pursuit; but it was reserved for
Galileo to track the Thracian boar through its native thickets, and, at
the risk of his own life, to strangle it in its den.
With the resolution of submitting every opinion to the test of
experiment, Galileo's first inquiries at Pisa were directed to the
mechanical doctrines of Aristotle. Their incorrectness and absurdity
soon became apparent; and with a zeal, perhaps, bordering on
indiscretion, he denounced them to his pupils with an ardour of manner
and of expression proportioned to his own conviction of the truth. The
detection of long-established errors is apt to inspire the young
philosopher with an exultation which reason condemns. The feeling of
triumph is apt to clothe itself in the language of asperity; and the
abettor, of erroneous opinions is treated as a species of enemy to
science. Like the soldier who fleshes his first spear in battle, the
philosopher is apt to leave the stain of cruelty upon his early
achievements. It is only from age and experience, indeed, that we can
expect the discretion of valour, whether it is called forth in
controversy or in battle. Galileo seems to have waged this stern warfare
against the followers of Aristotle; and such was the exasperation which
was excited by his reiterated and successful attacks, that he was
assailed, during the rest of his life, with a degree of rancour which
seldom originates in a mere difference of opinion. Forgetting that all
knowledge is progressive, and that the errors of one generation call
forth the comments, and are replaced by the discoveries, of the next,
Galileo did not anticipate that his own speculations and incompleted
labours might one day provoke unmitigated censure; and he therefore
failed in making allowance for the prejudices and ignorance of his
opponents. He who enjoys the proud lot of taking a position in advance
of his age, need not wonder that his less gifted contemporaries are left
behind. Men are not necessarily obstinate because they cleave to deeply
rooted and venerable errors, nor are they absolutely stupid when they
are long in understanding and embracing newly discovered truths.
It was one of the axioms of the Aristotelian mechanics, that the heavier
of two falling bodies would reach the ground sooner than the other, and
that their velocities would be proportional to their weights. Galileo
attacked the arguments by which this opinion was supported; and when he
found his reasoning ineffectual, he appealed to direct experiment. He
maintained, that all bodies would fall through the same height in the
same time, if they were not unequally retarded by the resistance of the
air: and though he performed the same experiment with the most
satisfactory results, by letting heavy bodies fall from the leaning
tower of Pisa; yet the Aristotelians, who with their own eyes saw the
unequal weights strike the ground at the same instant, ascribed the
effect to some unknown cause, and preferred the decision of their master
to that of nature herself.
Galileo could not brook this opposition to his discoveries; and the
Aristotelians could not tolerate the rebukes of their young instructor.
The two parties were, consequently, marshalled in hostile array; when,
fortunately for both, an event occurred, which placed them beyond the
reach of danger. Don Giovanni de' Medici, a natural son of Cosmo, had
proposed a method of clearing out the harbour of Leghorn. Galileo, whose
opinion was requested, gave such an unfavourable report upon it, that
the disappointed inventor directed against him all the force of his
malice. It was an easy task to concentrate the malignity of his enemies
at Pisa; and so effectually was this accomplished, that Galileo resolved
to accept another professorship, to which he had been previously
invited.
The chair of mathematics in the university of Padua having been vacant
for five years, the republic of Venice had resolved to fill it up; and,
on the recommendation of Guido Ubaldi, Galileo was appointed to it, in
1592, for a period of six years.
In 1591, Galileo lost his father, who died at an advanced age, and
devolved upon his eldest son the support of the family. This event,
probably, increased his anxiety to better his situation, and must have
added to his other inducements to quit Pisa. In September, 1592, he
removed to Padua, where he had a salary of only 180 florins, and where
he was obliged to add to his income by the labours of tuition.
Notwithstanding this fruitless occupation of his time, he appears to
have found leisure for composing several of his works, and completing
various inventions, which will be afterwards described. His manuscripts
were circulated privately among his friends and pupils; but some of them
strayed beyond this sacred limit, and found their way into the hands of
persons who did not scruple to claim and publish, as their own, the
discoveries and inventions which they contained.
It is not easy to ascertain the exact time when Galileo became a convert
to the doctrines of Copernicus, or the particular circumstances under
which he was led to adopt them. It is stated by Gerard Voss, that a
public lecture of Mæstlin, the instructor of Kepler, was the means of
making Galileo acquainted with the true system of the universe. This
assertion, however, is by no means probable; and it has been ably shown,
by the latest biographer of Galileo[5], that, in his dialogues on the
Copernican system, our author gives the true account of his own
conversion. This passage is so interesting, that we shall give it
entire.
"I cannot omit this opportunity of relating to you what happened to
myself at the time when this opinion (the Copernican system) began to be
discursed. I was then a very young man, and had scarcely finished my
course of philosophy, which other occupations obliged me to leave off,
when there arrived in this country, from Rostoch, a foreigner, whose
name, I believe, was Christian Vurstisius (Wurteisen), a follower of
Copernicus. This person delivered, on this subject, two or three
lectures in a certain academy, and to a crowded audience. Believing that
several were attracted more by the novelty of the subject than by any
other cause, and being firmly persuaded that this opinion was a piece of
solemn folly, I was unwilling to be present. Upon interrogating,
however, some of those who were there, I found that they all made it a
subject of merriment, with the exception of one, who assured me that it
was not a thing wholly ridiculous. As I considered this individual to be
both prudent and circumspect, I repented that I had not attended the
lectures; and, whenever I met any of the followers of Copernicus, I
began to inquire if they had always been of the same opinion. I found
that there was not one of them who did not declare that he had long
maintained the very opposite opinions, and had not gone over to the new
doctrines till he was driven by the force of argument. I next examined
them one by one, to see if they were masters of the arguments on the
opposite side; and such was the readiness of their answers, that I was
satisfied they had not taken up this opinion from ignorance or vanity.
On the other hand, whenever I interrogated the Peripatetics and the
Ptolemeans (and, out of curiosity, I have interrogated not a a few),
respecting their perusal of Copernicus's work, I perceived that there
were few who had seen the book, and not one who understood it. Nor have
I omitted to enquire among the followers of the Peripatetic doctrines,
if any of them had ever stood on the opposite side; and the result was,
that there was not one. Considering, then, that nobody followed the
Copernican doctrine, who had not previously held the contrary opinion,
and who was not well acquainted with the arguments of Aristotle and
Ptolemy; while, on the other hand, nobody followed Ptolemy and
Aristotle, who had before adhered to Copernicus, and had gone over from
him into the camp of Aristotle; weighing, I say, these things, I began
to believe that, if any one who rejects an opinion which he has imbibed
with his milk, and which has been embraced by an infinite number, shall
take up an opinion held only by a few, condemned by all the schools, and
really regarded as a great paradox, it cannot be doubted that he must
have been induced, not to say driven, to embrace it by the most cogent
arguments. On this account, I have become very curious to penetrate to
the very bottom of the subject."[6]
It appears, on the testimony of Galileo himself, that he taught the
Ptolemaic system, out of compliance with the popular feeling, after he
had convinced himself of the truth of the Copernican doctrines. In the
treatise on the sphere, indeed, which bears his name[7], and which must
have been written soon after he went to Padua, and subsequently to 1592,
the stability of the earth, and the motion of the sun, are supported by
the very arguments which Galileo afterwards ridiculed; but we have no
means of determining whether or not he had then adopted the true system
of the universe. Although he might have taught the Ptolemaic system in
his lectures, after he had convinced himself of its falsehood; yet it is
not likely that he would go so far as to publish to the worlds as true,
the very doctrines which he despised. In a letter to Kepler, dated in
1597, he distinctly states that he _had, many years ago, adopted the
opinions of Copernicus; but that he had not yet dared to publish his
arguments in favour of them, and his refutation of the opposite
opinions._ These facts would leave us to place Galileo's conversion
somewhere between 1593 and 1597; although _many_ years cannot be said to
have elapsed between these two dates.
At this early period of Galileo's life, in the year 1593, he met with an
accident; which had nearly proved fatal. A party at Padua; of which he
was one, were enjoying; at an open window; a current of air, which was
artificially cooled by a fall of water. Galileo unfortunately fell
asleep under its influence; and so powerful was its effect upon his
robust constitution; that he contracted a severe chronic disorder,
accompanied with acute pains in his body, and loss of sleep and
appetite, which attacked him at intervals during the rest of his life.
Others of the party suffered still more severely, and perished by their
own rashness.
Galileo's reputation was now widely extended over Europe; and the
archduke Ferdinand (afterwards emperor of Germany), the landgrave of
Hesse, and the princes of Alsace and Mantua honoured his lectures with
their presence. Prince Gustavus of Sweden also received instructions
from him in mathematics, during his sojourn in Italy; and it has been
supposed that this was the celebrated Gustavus Adolphus.
When Galileo had completed the first period of his engagement at Padua,
he was re-elected for other six years, with an increased salary of 320
florins. This liberal addition to his income is ascribed by Fabbroni to
the malice of one of his enemies, who informed the senate that Galileo
was living in illicit intercourse with Marina Gamba. Without inquiring
into the truth of the accusation, the senate is said to have replied,
that if "he had a family to support, he had the more need of an
increased salary." It is more likely that the liberality of the republic
had been called forth by the high reputation of their professor, and
that the terms of their reply were intended only to rebuke the malignity
of the informer. The mode of expression would seem to indicate that one
or more of Galileo's children had been born previous to his re-election
in 1598; but as this is scarcely consistent with other facts, we are
disposed to doubt the authenticity of Fabbroni's anecdote.
The new star, which attracted the notice of astronomers in 1604, excited
the particular attention of Galileo. The observations which he made upon
it, and the speculations which they suggested, formed the subject of
three lectures, the beginning of the first of which only has reached our
times. From the absence of parallax, he proved that the common
hypothesis of its being a meteor was erroneous, and that, like the fixed
stars, it was situated far beyond the bounds of our own system. The
popularity of the subject attracted crowds to his lecture-room; and
Galileo had the boldness to reproach his hearers for taking so deep an
interest in a temporary phenomenon, while they passed unnoticed the
wonders of creation which were daily presented to their view.
In the year 1606, Galileo was again appointed to the professorship at
Padua, with an augmented stipend of 520 florins. His popularity had now
risen so high, that his audience could not be accommodated in his
lecture-room; and even when he had assembled them in the school of
medicine, which contained 1000 persons, he was frequently obliged to
adjourn to the open air.
Among the variety of pursuits which occupied his attention, was the
examination of the properties of the loadstone. In 1607, he commenced
his experiments; but, with the exception of a method of arming
loadstones, which; according to the report of Sir Kenelm Digby, enabled
them to carry twice as much weight as others, he does not seem to have
made any additions to our knowledge of magnetism. He appears to have
studied with care the admirable work of our countryman; Dr. Gilbert; "De
Magnete," which was published in 1600; and he recognised; in the
experiments and reasonings of the English philosopher; the principles of
that method of investigating truth which he had himself adopted. Gilbert
died in 1603; in the 63d year of his age, and probably never read the
fine compliment which was paid to him by the Italian philosopher:--"I
extremely praise, admire, and envy this author."
In the preceding pages we have brought down the history of Galileo's
labours to that auspicious year in which he first directed the telescope
to the heavens. No sooner was that noble instrument placed in his hands,
than Providence released him from his professional toils, and supplied
him with the fullest leisure and the amplest means for pursuing and
completing the grandest discoveries.
Although he had quitted the service and the domains of his munificent
patron; the grand duke of Tuscany, yet he maintained his connection with
the family, by visiting Florence during his academic vacations, and
giving mathematical instruction to the younger branches of that
distinguished house. Cosmo, who had been one of his pupils, now
succeeded his father Ferdinand; and having his mind early imbued with a
love of knowledge, which had become hereditary in his family, he felt
that the residence of Galileo within his dominions--and still more his
introduction into his household--would do honour to their common
country, and reflect a lustre upon his own name. In the year 1609,
accordingly, Cosmo made proposals to Galileo to return to his original
situation at Pisa. These overtures were gratefully received; and in the
arrangements which Galileo on this occasion suggested, as well as in the
manner in which they were urged, we obtain some insight into his temper
and character. He informs the correspondent through whom Cosmo's offer
was conveyed, that his salary of 520 florins at Padua would be increased
to as many crowns at his re-election; and that he could enlarge his
income to any extent he pleased, by giving private lectures, and
receiving pupils. His public duties, he stated, occupied him only sixty
half-hours in the year; but his studies suffered such interruptions from
the domestic pupils and private lectures, that his most ardent wish was
to be relieved from them, in order that he might have sufficient rest
and leisure, before the close of his life, to finish and publish those
great works which he had in hand. In the event, therefore, of his
returning to Pisa, he hoped that it would be the first object of his
serene highness to give him leisure to complete his works without the
drudgery of lecturing. He expresses his anxiety to gain his bread by his
writings, and he promises to dedicate them to his serene master. He
enumerates, among these books, two on the system of the universe; three
on local motion; three books of mechanics; two on the demonstration of
principles, and one of problems; besides treatises on sound and speech,
on light and colours, on the tides, on the composition of continuous
quantity, on the motions of animals, and on the military art. On the
subject of his salary, he makes the following curious observations:--
"I say nothing," says he, "on the amount of my salary; being convinced
that, as I am to live upon it, the graciousness of his highness would
not deprive me of any of those comforts, of 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 title 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."
During the progress of this negotiation, Galileo went to Venice, on a
visit to a friend, in the month of April or May, 1609. Here he learned,
from common rumour, that a Dutchman, of the name of Jansen, had
presented to prince Maurice of Nassau an optical instrument, which
possessed the singular property of causing distant objects to appear
nearer and larger to the observer. A few days afterwards, the truth of
this report was confirmed by a letter which he received from James
Badovere at Paris, and he immediately applied himself to the
consideration of the subject. On the first night after his return to
Padua, he found, in the doctrines of refraction, the principle which he
sought. He placed at the ends of a leaden tube two spectacle glasses,
both of which were plain on one side, while one of them had its other
side convex, and the other its second side concave, and having applied
his eye to the concave glass, he saw objects pretty large and pretty
near him. This little instrument, which magnified only three times, he
carried in triumph to Venice, where it excited the most intense
interest. Crowds of the principal citizens flocked to his house to see
the magical toy; and after nearly a month had been spent in gratifying
this epidemical curiosity, Galileo was led to understand from Leonardo
Deodati, the doge of Venice, that the senate would be highly gratified
by obtaining possession of so extraordinary an instrument. Galileo
instantly complied with the wishes of his patrons, who acknowledged the
present by a mandate conferring upon him for life his professorship at
Padua, and generously raising his salary from 520 to 1000 florins.
Although we cannot doubt the veracity of Galileo, when he affirms that
he had never seen any of the Dutch telescopes, yet it is expressly
stated by Fuccarius, that one of these instruments had at this time been
brought to Florence. In a letter from Lorenzo Pignoria to Paolo Gualdo,
dated from Padua, on the 31st of August, 1609, it is expressly said,
that, at the re-election of the professors, Galileo had contrived to
obtain 1000 florins for life, which was alleged to be on account of an
eye-glass like the one which was sent from Flanders to the Cardinal
Borghese.
In a memoir so brief and general as the present, it would be out of
place to discuss the history of this extraordinary invention. We have no
hesitation in asserting that a method of magnifying distant objects was
known to Baptista Porta and others; but it seems to be equally certain
that an _instrument_ for producing these effects was first constructed
in Holland, and that it was from that kingdom that Galileo derived the
knowledge of its existence. In considering the contending claims, which
have been urged with all the ardour and partiality of national feeling,
it has been generally overlooked, _that a single convex lens_, whose
focal length exceeds the distance at which we examine minute objects,
performs the part of a telescope, when an eye, placed behind it, sees
distinctly the inverted image which it forms. A lens, twenty feet in
focal length, will in this manner magnify twenty times; and it was by
the same principle that Sir William Herschel discovered a new satellite
of Saturn, by using only the mirror of his forty-feet telescope. The
instrument presented to prince Maurice, and which the marquis Spinola
found in the Dutch optician's shop, performing the part of a
philosophical toy, by exhibiting a magnified and inverted image of a
distant weathercock, must have been a single lens such as we have
mentioned, or an astronomical telescope consisting of two convex lenses.
Upon either of these suppositions, it differed entirely from that which
Galileo constructed; and the Italian philosopher will be justly entitled
to the honour of having invented that form of the telescope which still
bears his name.
The interest which the exhibition of the telescope excited at Venice did
not soon subside: Serturi describes it as amounting almost to phrensy.
When he himself had succeeded in making one of these instruments, he
ascended the tower of St. Mark, where he might use it without
molestation. He was recognised, however, by a crowd in the street; and
such was the eagerness of their curiosity, that they took possession of
the wondrous tube, and detained the impatient philosopher for several
hours, till they had successively witnessed its effects. Desirous of
obtaining the same gratification for their friends, they endeavoured to
learn the name of the inn at which he lodged; but Serturi fortunately
overheard their inquiries, and quitted Venice early next morning, in
order to avoid a second visitation of this new school of philosophers.
The opticians speedily availed themselves of this new instrument.
Galileo's tube,--or the double eye-glass, as it was then called, for
Demisiano had not yet given it the appellation of a _telescope_,--was
manufactured in great quantities, and in a very superior manner. The
instruments were purchased merely as philosophical toys, and were
carried by travellers into every corner of Europe.
The art of grinding and polishing lenses was at this time very
imperfect. Galileo, and those whom he instructed, were alone capable of
making tolerable instruments. It appears, from the testimony of Gassendi
and Gærtner, that, in 1634, a good telescope could not be procured in
Paris, Venice, or Amsterdam; and that, even in 1637, there was not one
in Holland which could show Jupiter's disc well defined.
After Galileo had completed his first instrument, which magnified only
_three_ times, he executed a larger and more accurate one, with a power
of about eight. "At length," as he himself remarks, "sparing neither
labour nor expense," he constructed an instrument so excellent, that it
magnified more than thirty times.
The first celestial object to which Galileo applied his telescope was
the moon, which, to use his own words, appeared as near as if it had
been distant only two semidiameters of the earth. He then directed it to
the planets and the fixed stars, which he frequently observed with
"incredible satisfaction."[8]
The observations which he made upon the moon possessed a high degree of
interest. The general resemblance of its surface to that of our own
globe naturally fixed his attention; and he was soon able to trace, in
almost every part of the lunar disc, ranges of mountains, deep hollows,
and other inequalities, which reflected from their summits the rays of
the rising sun, while the intervening hollows were still buried in
darkness. The dark and luminous spaces he regarded as indicating seas
and continents, which reflected, in different degrees, the incident
light of the sun; and he ascribed the phosphorescence, as it has been
improperly called, or the secondary light, which is seen on the dark
limb of the moon in her first and last quarters, to the reflection of
the sun's light from the earth.
These discoveries were ill received by the followers of Aristotle.
According to their preconceived opinions, the moon was perfectly
spherical, and perfectly smooth; to cover it with mountains, and to
scoop it out into valleys, was an act of impiety which defaced the
regular forms which nature herself had imprinted. It was in vain that
Galileo appealed to the evidence of observation, and to the actual
surface of our own globe. The very irregularities on the moon were, in
his opinion, the proof of divine wisdom: and had its surface been
perfectly smooth, it would have been "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 stripped of all those
ornaments which now render it so various and so beautiful."
In examining the fixed stars, and comparing them with the planets,
Galileo discovered a remarkable difference in the appearance of their
discs. All the planets appeared with round globular discs like the moon;
whereas the fixed stars never exhibited any disc at all, but resembled
lucid points sending forth twinkling rays. Stars of all magnitudes he
found to have the same appearance; those of the fifth and sixth
magnitude having the same character when seen through a telescope, as
Sirius, the largest of the stars, when seen by the naked eye. Upon
directing his telescope to nebulæ and clusters of stars, he was
delighted to find that they consisted of great numbers of stars which
could not be recognised by unassisted vision. He counted no fewer than
_forty_ in the cluster called the _Pleiades_, or _Seven Stars_; and he
has given us drawings of this constellation, as well as of the belt and
sword of Orion, and of the nebula of Præsepe. In the great nebula of
the Milky Way, he descried crowds of minute stars; and he concluded that
this singular portion derived its whiteness from still smaller stars,
which his telescope was unable to separate.
Important and interesting as these discoveries were, they were thrown
into the shade by those to which he was led during an accurate
examination of the planets with a more powerful telescope. On the 7th of
January, 1610, at one o'clock in the morning, when he directed this
telescope to Jupiter, he observed three stars near the body of the
planet; two being to the east and one to the west of him. They were all
in a straight line, and parallel to the ecliptic, and appeared brighter
than other stars of the same magnitude. Believing them to be fixed
stars, he paid no great attention to their distances from Jupiter and
from one another. On the 8th of January, however, when, from some cause
or other[9], he had been led to observe the stars again, he found a very
different arrangement of them: all the three were on the west side of
Jupiter, _nearer one another than before_, and almost at equal
distances. Though he had not turned his attention to the extraordinary
fact of the mutual approach of the stars, yet he began to consider how
Jupiter could be found to the east of the three stars, when only the day
before he had been to the west of two of them. The only explanation
which he could give of this fact was, that the motion of Jupiter was
_direct_ contrary to astronomical calculations; and that he had got
before these two stars by his own motion.
In this dilemma between the testimony of his senses and the results of
calculation, he waited for the following night with the utmost anxiety:
but his hopes were disappointed; for the heavens were wholly veiled in
clouds. On the tenth, two only of the stars appeared, and both on the
east of the planet. As it was obviously impossible that Jupiter could
have advanced from west to east on the 8th of January, and from east to
west on the 10th, Galileo was forced to conclude that the phenomenon
which he had observed, arose from the motion of the stars, and he set
himself to observe diligently their change of place. On the 11th, there
were still only two stars; and both to the east of Jupiter; but the more
eastern star was now _twice as large as the other one_, though on the
preceding night they had been perfectly equal. This fact threw a new
light upon Galileo's difficulties, and he immediately drew the
conclusion, which he considered to be indubitable--"that there were in
the heavens three stars which revolved round Jupiter, in the same manner
as Venus and Mercury revolve round the sun." On the 12th of January, he
again observed them in new positions, and of different magnitudes; and,
on the 13th, he discovered a fourth star, which completed the four
secondary planets with which Jupiter is surrounded.
Galileo continued his observations on these bodies every clear night
till the 22d of March, and studied their motions in reference to fixed
stars that were at the same time within the field of his telescope.
Having thus clearly established that the four new stars were satellites
or moons, which revolved round Jupiter in the same manner as the moon
revolves round our own globe, he drew up an account of his discovery, in
which he gave to the four new bodies the names of the _Medicean Stars_,
in honour of his patron, Cosmo de' Medici, grand duke of Tuscany. This
work, under the title of "Nuncius Sidereus," or the "Sidereal
Messenger," was dedicated to the same prince; and the dedication bears
the date of the 4th of March, only two days after he concluded his
observations.
The importance of this great discovery was instantly felt by the enemies
as well as by the friends of the Copernican system. The planets had
hitherto been distinguished from the fixed stars only by their relative
change of place; but the telescope proved them to be bodies so near to
our own globe as to exhibit well-defined discs; while the fixed stars
retained, even when magnified, the minuteness of remote and lucid
points. The system of Jupiter, illuminated by four moons performing
their revolutions in different and regular periods, exhibited to our
proud reason the comparative insignificance of the globe we inhabit, and
proclaimed in impressive language that globe was not the centre of
the universe.
The reception which these discoveries met with from Kepler is highly
interesting, and characteristic of the genius of that great man. He was
one day sitting idle, and thinking of Galileo, when his friend
Wachenfels stopped his carriage at his door, to communicate to him the
intelligence. "Such a fit of wonder," says he, "seized me at a report
which seemed to be 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. On our parting, I immediately began to think how there could
be any addition to the number of the planets, without overturning my
'Cosmographic Mystery,' according to which Euclid's five regular solids
do not allow more than six planets round the sun. * * * 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 require, _six_ or _eight_ round
Saturn, and perhaps one each round Mercury and Venus."
In a very different spirit did the Aristotelians receive the "Sidereal
Messenger" of Galileo. The principal professor of philosophy at Padua
resisted Galileo's repeated and urgent entreaties to look at the moon
and planets through his telescope; and he even laboured to convince the
grand duke that the satellites of Jupiter could not possibly exist.
Sizzi, an astronomer of Florence, maintained, that as there were only
_seven_ apertures in the head--_two_ eyes, _two_ ears, _two_ nostrils,
and _one_ mouth--and as there were only _seven_ metals, and _seven_ days
in the week, so there could be only _seven_ planets. He seems, however,
to have admitted the visibility of the four satellites through the
telescope; but he argues, that as they are invisible to the naked eye,
they can exercise no influence on the earth; and being useless, they do
not therefore exist.
A _protégé_ of Kepler's, of the name of Horky, wrote a volume against
Galileo's discovery, after having declared, "that he would never concede
his four new planets to that Italian from Padua, even if he should die
for it." This resolute Aristotelian was at no loss for arguments. He
asserted that he had examined the heavens _through Galileo's own glass_,
and that no such thing as a satellite existed round Jupiter. He
affirmed, that he did not more surely know that he had a soul in his
body, than that reflected rays are the sole cause of Galileo's erroneous
observations; and that the only use of the new planets was to gratify
Galileo's thirst for gold, and afford himself a subject of discussion.
When Horky first presented himself to Kepler, after the publication of
this work, the opinion of his patron was announced to him by a burst of
indignation which overwhelmed the astonished author. Horky supplicated
mercy for his offence; and, as Kepler himself informed Galileo, he took
him again into favour, on the condition that Kepler was to show him
Jupiter's satellites; and that Horky was not only to see them, but to
admit their existence.
When the spirit of philosophy had thus left the individuals who bore her
sacred name, it was fortunate for science that it found a refuge in the
minds of princes. Notwithstanding the reiterated logic of his
philosophical professor at Padua, Cosmo de' Medici preferred the
testimony of his senses to the syllogisms of his instructor. He observed
the new planets several times, along with Galileo, at Pisa; and when he
parted with him, he gave him a present worth more than 1000 florins, and
concluded that liberal arrangement to which we have already referred.
As philosopher and principal mathematician to the grand duke of Tuscany,
Galileo now took up his residence at Florence, with a salary of 1000
florins. No official duties, excepting that of lecturing occasionally to
sovereign princes, were attached to this appointment; and it was
expressly stipulated that he should enjoy the most perfect leisure to
complete his treatises on the constitution of the universe, on
mechanics, and on local motion. The resignation of his professorship at
Padua, which necessarily followed his new appointment, created much
dissatisfaction in that university: but though many of his former
friends refused at first to hold any communication with him, this
feeling gradually subsided; and the Venetian senate at last appreciated
the views, as well as the powerful motives, which induced a stranger to
accept of promotion in his native land.
While Galileo was enjoying the reward and the fame of his great
discovery, a new species of enmity was roused against them. Simon Mayer,
an astronomer of no character, pretended that he had discovered the
satellites of Jupiter before Galileo, and that his first observation was
made on the 29th of December, 1609. Other astronomers announced the
discovery of new satellites: Scheiner reckoned five, Rheita nine, and
others found even so many as twelve: these satellites, however, were
found to be only fixed stars. The names of _Vladislavian, Agrippine,
Uranodavian_, and _Ferdinandotertian_, which were hastily given to these
common telescopic stars, soon disappeared from the page of science, and
even the splendid telescopes of modern times have not been able to add
another gem to the diadem of Jupiter.
A modern astronomer of no mean celebrity has, even in the present day,
endeavoured to rob Galileo of this staple article of his reputation.
From a careless examination of the papers of our celebrated countryman,
Thomas Harriot, which baron Zach had made in 1784, at Petworth, the seat
of lord Egremont, this astronomer has asserted[10] that Harriot first
observed the satellites of Jupiter on the 16th of January, 1610; and
continued his observations till the 25th of February, 1612. Baron Zach
adds the following extraordinary conclusion:--"Galileo pretends to have
discovered them on the 7th of January, 1610; so that it is not
improbable that Harriot was likewise the first discoverer of these
attendants of Jupiter." In a communication which I received from Dr.
Robertson, of Oxford, in 1822[11], he informed me that he had examined a
class of Harriot's papers, entitled, "De Jovialibus Planetis;" and that
it appears, from two pages of these papers, _that Harriot first observed
Jupiter's satellites on the 17th of October_, 1610. These observations
are accompanied with rough drawings of the positions of the satellites,
and rough calculations of their periodical revolutions. My friend,
professor Rigaud[12], who has very recently examined the Harriot MSS.,
has confirmed the accuracy of Dr. Robertson's observations, and has thus
restored to Galileo the honour of being the first and the sole
discoverer of these secondary planets.
The great success which attended the first telescopic observations of
Galileo, induced him to apply his best instruments to the other planets
of our system. The attempts which had been made to deprive him of the
honour of some of his discoveries, combined, probably, with a desire to
repeat his observations with better telescopes, led him to announce his
discoveries under the veil of an enigma; and to invite astronomers to
declare, within a given time, if they had observed any new phenomena in
the heavens.
Before the close of 1610, Galileo excited the curiosity of astronomers,
by the publication of his first enigma. Kepler and others tried in vain
to decipher it; but in consequence of the emperor Rodolph requesting a
solution of the puzzle, Galileo sent him the following clue:--
"Altissimam planetam tergeminam observavi."