The Martyrs of Science, or, The lives of Galileo, Tycho Brahe, and Kepler

Peculiar interest attached to his Life-His Birth-His early studies-His passion for Mathematics-His work on the Hydrostatic Balance-Appointed Lecturer on Mathematics at Pisa-His antipathy to the Philosophy of Aristotle-His contentions with the Aristotelians-Chosen professor of Mathematics in Padua-Adopts the Copernican system, but still teaches the Ptolemaic doctrine-His alarming illness-He observes the new Star in 1604-His magnetical experiments.

The history of the life and labours of Galileo is pregnant with a peculiar interest to the general reader, as well as to the philosopher. His brilliant discoveries, the man of science regards as his peculiar property; the means by which they were made, and the development of his intellectual character, belong to the logician and to the philosopher; but the triumphs and the reverses of his eventful life must be claimed for our common nature, as a source of more than ordinary instruction.

The lengthened career which Providence assigned to Galileo was filled up throughout its rugged outline with events even of dramatic interest. But though it was emblazoned with achievements of transcendent magnitude, yet his noblest discoveries were the derision of his contemporaries, and were even denounced as crimes which merited the vengeance of Heaven. Though he was the idol of his friends, and the favoured companion of princes, yet he afterwards became the victim of persecution, and spent some of his last hours within the walls of a prison; and though the Almighty granted him, as it were, a new sight to descry unknown worlds in the obscurity of space, yet the eyes which were allowed to witness such wonders, were themselves doomed to be closed in darkness.

Such were the lights and shadows in which history delineates

"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 inquiries 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 exercised 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 schoolfellows. This employment 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 C?salpinus, 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, proved the source of his future success in life.

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. As the salary, however, attached to this office was only sixty crowns, he was compelled to enlarge this inadequate income by the additional occupation of private teaching, and thus to encroach upon the leisure which he was anxious to devote to science.

With this moderate competency, Galileo commenced his philosophical career. At the early age of eighteen, when he had entered the university, his innate antipathy to the Aristotelian philosophy began to display itself. 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 on 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 dull when they are long in understanding and slow in 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 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; nor could the Aristotelians 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.

Previous to this event, Galileo had lost his father, who died, in 1591, at an advanced age. As he was the eldest son, the support of the family naturally devolved upon him; and this sacred obligation must have increased his anxiety to better his circumstances, and therefore 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 again 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 M?stlin, 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 discussed. 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 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 inquire 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, in 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 world, 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. The Archduke Ferdinand (afterwards Emperor of Germany), the Landgrave of Hesse, and the Princes of Alsace and Mantua, honoured his lectures with their presence; and Prince Gustavus Adolphus of Sweden also received instructions from him in mathematics, during his sojourn in Italy.

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 overlooked 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 before, 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."

* * *

Cosmo, Grand Duke of Tuscany, invites Galileo to Pisa-Galileo visits Venice in 1609, where he first hears of the Telescope-He invents and constructs one, which excites a great sensation-Discovers Mountains in the Moon, and Forty Stars in the Pleiades-Discovers Jupiter's Satellites in 1610-Effect of this discovery on Kepler-Manner in which these discoveries were received-Galileo appointed Mathematician to Cosmo-Mayer claims the discovery of the Satellites of Jupiter-Harriot observes them in England in October 1610.

In the preceding chapter 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 his 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 projected. 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 had presented to prince Maurice of Nassau an optical instrument, which possessed the singular property of causing distant objects to appear nearer the observer. This Dutchman was Hans or John Lippershey, who, as has been clearly proved by the late Professor Moll of Utrecht,[8] was in the possession of a telescope made by himself so early as 2d October 1608. A few days afterwards, the truth of this report was confirmed by a letter which Galileo received from James Badorere 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.[9]

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; and Sirturus assures us that a Frenchman, calling himself a partner of the Dutch inventor, came to Milan in May 1609, and offered a telescope to the Count de Fuentes. 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 shop of John Lippershey, the spectacle maker of Middleburg, must have been an astronomical telescope consisting of two convex lenses. Upon this supposition, it differed 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, while we must accord to the Dutch optician the honour of having previously invented the astronomical telescope.

The interest which the exhibition of the telescope excited at Venice did not soon subside: Sirturi[10] 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 Sirturi 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 the new instrument. Galileo's tube,-or the double eye-glass, or the cylinder, or the trunk, as it was then called, for Demisiano had not yet given it the appellation of 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 G?rtner, 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 shew Jupiter's disc well defined.

After Galileo had completed his first instrument, which magnified only three times, he executed a larger and a better 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 bore a magnifying power of 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 delight."[11]

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 reverberated from their summits and margins 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 incidental 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 absolutely smooth; and to cover it with mountains, and 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 absolutely 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 varied and so beautiful."

In examining the fixed stars, and comparing them with the planets, Galileo observed 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 nebul? 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 Pr?sepe. In the great nebula of the Milky Way, he descried crowds of minute stars; and he concluded that this singular portion of the heavens 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 his 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,[12] 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 but 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 10th, 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 24th 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 the proud reason of man the comparative insignificance of the globe he inhabits, and proclaimed in impressive language that 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 protegé 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 to 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 so unworthily her sacred name, it was fortunate for science that it found a refuge among 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 in the university of Padua, which was the necessary consequence of his new appointment, created much dissatisfaction: but though many of his former friends refused at first to hold any communication with him, this excitement gradually subsided; and the Venetian senate at last appreciated the feelings, as well as the 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 him. 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[13] 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,[14] he informed me that he had examined a portion 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,[15] 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.

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Galileo announces his discoveries in Enigmas-Discovers the Crescent of Venus-the Ring of Saturn-the Spots on the Sun-Similar Observations made in England by Harriot-Claims of Fabricius and Scheiner to the discovery of the Solar Spots-Galileo's Letters to Velser on the claims of Scheiner-His residence at the Villa of Salviati-Composes his work on Floating Bodies, which involves him in new controversies.

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."

I have observed that the most remote planet is triple.

In explaining more fully the nature of his observation, Galileo remarked that Saturn was not a single star, but three together, nearly touching one another. He described them as having no relative motion, and as having the form of three o's, namely, oOo, the central one being larger than those on each side of it.

Although Galileo had announced that nothing new appeared in the other planets, yet he soon communicated to the world another discovery of no slight interest. The enigmatical letters in which it was concealed formed the following sentence:-

"Cynthi? figuras ?mulatur mater Amorum."

Venus rivals the phases of the moon.

Hitherto, Galileo had observed Venus when her disc was largely illuminated; but having directed his telescope to her when she was not far removed from the sun, he saw her in the form of a crescent, resembling exactly the moon at the same elongation. He continued to observe her night after night, during the whole time that she could be seen in the course of her revolution round the sun, and he found that she exhibited the very same phases which resulted from her motion round that luminary.

Galileo had long contemplated a visit to the metropolis of Italy, and he accordingly carried his intentions into effect in the early part of the year 1611. Here he was received with that distinction which was due to his great talents and his extended reputation. Princes, Cardinals, and Prelates hastened to do him honour; and even those who discredited his discoveries, and dreaded their results, vied with the true friends of science in their anxiety to see the intellectual wonder of the age.

In order to show the new celestial phenomena to his friends at Rome, Galileo took with him his best telescope; and as he had discovered the spots on the sun's surface in October or November 1610, or even earlier,[16] he had the gratification of exhibiting them to his admiring disciples. He accordingly erected his telescope in the Quirinal garden, belonging to Cardinal Bandini; and in April 1611 he shewed them to his friends in many of their most interesting variations. From their change of position on the sun's disc, Galileo at first inferred, either that the sun revolved about an axis, or that other planets, like Venus and Mercury, revolved so near the sun as to appear like black spots when they were opposite to his disc. Upon continuing his observations, however, he saw reason to abandon this hasty opinion. He found that the spots must be in contact with the surface of the sun,-that their figures were irregular,-that they had different degrees of darkness,-that one spot would often divide itself into three or four,-that three or four spots would often unite themselves into one,-and that all the spots revolved regularly with the sun, which appeared to complete its revolution in about twenty-eight days.

Previous to the invention of the telescope, spots had been more than once seen on the sun's disc with the unassisted eye. But even if these were of the same character as those which Galileo and others observed, we cannot consider them as anticipations of their discovery by the telescope. As the telescope was now in the possession of several astronomers, Galileo began to have many rivals in discovery; but notwithstanding the claims of Harriot, Fabricius, and Scheiner, it is now placed beyond the reach of doubt that he was the first discoverer of the solar spots. From the communication which I received in 1822 from the late Dr Robertson, of Oxford,[17] it appeared that Thomas Harriot had observed the solar spots on the 8th of December 1610; but his manuscripts, in Lord Egremont's possession,[18] incontestably prove that his regular observations on the spots did not commence till December 1, 1611, although he had seen the spots at the date above mentioned, and that they were continued till the 18th of January 1613. The observations which he has recorded are 199 in number, and the accounts of them are accompanied with rough drawings representing the number, position, and magnitude of the spots.[19] In the observation of Harriot, made on the 8th December 1610, before he knew of Galileo's discovery, he saw three spots on the sun, which he has represented in a diagram. The sun was then 7° or 8° high, and there was a frost and a mist, which no doubt acted as a darkening glass. Harriot does not apply the name of spots to what he noticed in this observation, and he does not enumerate it among the 199 observations above mentioned. Professor Rigaud[20] considers it "a misapplication of terms to call such an observation a discovery;" but, with all the respect which we feel for the candour of this remark, we are disposed to confer on Harriot the merit of an original discoverer of the spots on the sun.

Another candidate for the honour of discovering the spots of the sun, was John Fabricius, who undoubtedly saw them previous to June 1611. The dedication of the work[21] in which he has recorded his observation, bears the date of the 13th of June 1611; and it is obvious, from the work itself, that he had seen the spots about the end of the year 1610; but as there is no proof that he saw them before October, we are compelled to assign the priority of the discovery to the Italian astronomer.

The claim of Scheiner, professor of mathematics at Ingolstadt, is more intimately connected with the history of Galileo. This learned astronomer having, early in 1611, turned his telescope to the sun, necessarily discovered the spots which at that time covered his disc. Light flying clouds happened, at the time, to weaken the intensity of his light, so that he was able to show the spots to his pupils. These observations were not published till January 1612; and they appeared in the form of three letters, addressed to Mark Velser, one of the magistrates of Augsburg, under the signature of Appelles post Tabulam. Scheiner, who, many years afterwards, published an elaborate work on the subject, adopted the same idea which had at first occurred to Galileo-that the spots were the dark sides of planets revolving round and near the sun.[22]

On the publication of Scheiner's letters, Velser transmitted a copy of them to his friend Galileo, with the request that he would favour him with his opinion of the new phenomena. After some delay, Galileo addressed three letters to Velser, in which he combated the opinions of Scheiner on the cause of the spots. The first of these letters was dated the 4th of May 1612;[23] but though the controversy was carried on in the language of mutual respect and esteem, it put an end to the friendship which had existed between the two astronomers. In these letters Galileo showed that the spots often dispersed like vapours or clouds; that they sometimes had a duration of only one or two days, and at other times of thirty or forty days; that they contracted in their breadth when they approached the sun's limb, without any diminution of their length; that they describe circles parallel to each other; that the monthly rotation of the sun again brings the same spots into view; and that they are seldom seen at a greater distance than 30° from the sun's equator. Galileo likewise discovered on the sun's disc facul?, or luculi, as they were called, which differ in no respect from the common ones but in their being brighter than the rest of the sun's surface.[24]

In the last of the letters which our author addressed to Velser, and which was written in December 1612, he recurs to his former discovery of the elongated shape, or rather the triple structure, of Saturn. The singular figure which he had observed in this planet had entirely disappeared; and he evidently announces the fact to Velser, lest it should be used by his enemies to discredit the accuracy of his observations. "Looking on Saturn," says he, "within these few days, I found it solitary, without the assistance of its accustomed stars, and, in short, perfectly round and defined like Jupiter; and such it still remains. Now, what can be said of so strange a metamorphosis? Are the two smaller stars consumed like the spots on the sun? Have they suddenly vanished and fled? or has Saturn devoured his own children? or was the appearance indeed fraud and illusion, with which the glasses have for so long a time mocked me, and so many others who have often observed with me? Now, perhaps, the time is come to revive the withering hopes of those who, guided by more profound contemplations, have followed all the fallacies of the new observations, and recognised their impossibilities. I cannot resolve what to say in a chance so strange, so new, and so unexpected; the shortness of the time, the unexampled occurrence, the weakness of my intellect, and the terror of being mistaken, have greatly confounded me." Although Galileo struggled to obtain a solution of this mystery, yet he had not the good fortune to succeed. He imagined that the two smaller stars would reappear, in consequence of the supposed revolution of the planet round its axis; but the discovery of the ring of Saturn, and of the obliquity of its plane to the ecliptic, was necessary to explain the phenomena which were so perplexing to our author.

The ill health to which Galileo was occasionally subject, and the belief that the air of Florence was prejudicial to his complaints, induced him to spend much of his time at Selve, the villa of his friend Salviati. This eminent individual had ever been the warmest friend of Galileo, and seems to have delighted in drawing round him the scientific genius of the age. He was a member of the celebrated Lync?an Society, founded by Prince Frederigo Cesi; and though he is not known as the author of any important discovery, yet he has earned, by his liberality to science, a glorious name, which will be indissolubly united with the immortal destiny of Galileo.

The subject of floating bridges having been discussed at one of the scientific parties which had assembled at the house of Salviati, a difference of opinion arose respecting the influence of the shape of bodies on their disposition to float or to sink in a fluid. Contrary to the general opinion, Galileo undertook to prove that it depended on other causes; and he was thus led to compose his discourse on floating bodies,[25] which was published in 1612, and dedicated to Cosmo de Medici. This work contains many ingenious experiments, and much acute reasoning in support of the true principles of hydrostatics; and it is now chiefly remarkable as a specimen of the sagacity and intellectual power of its author. Like all his other works, it encountered the most violent opposition; and Galileo was more than once summoned into the field to repel the aggressions of his ignorant and presumptuous opponents. The first attack upon it was made by Ptolemy Nozzolini, in a letter to Marzemedici, Archbishop of Florence;[26] and to this Galileo replied in a letter addressed to his antagonist.[27] A more elaborate examination of it was published by Lodovico delle Colombe, and another by M. Vincenzo di Grazia. To these attacks, a minute and overwhelming answer was printed in the name of Benedetti Castelli, the friend and pupil of Galileo; but it was discovered, some years after Galileo's death, that he was himself the author of this work.[28]

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