Galileo

Front matter

GALILEO GALILEI

CONTENTS.

I. BIRTH AND EDUCATION.

GALILEO.

CHAPTER I.—BIRTH AND EDUCATION.

In the year 1343 one Tommaso Bonajuti, being elected to the Council of Twelve in Florence, changed his family name to Galilei. His grandson, Galileo Galilei, a century later, was a celebrated physician, professor of medicine at the University of Florence, and became chief magistrate of the Republic. This Galileo's brother had a great-grandson Vincenzio, the father of the great Galileo, whose life forms the subject of this volume. We shall consistently drop the surname in our references to him, following a custom of the Italians in speaking of their great men; such as Dante, Raphael, and Michelangelo.

Vincenzio Galilei was a skilful and accomplished musician, with a good knowledge of classics and mathematics, but want of means and the expense of a growing family had sent him into commercial life, and induced him to choose for his eldest son's future career the business of a cloth-dealer, as something of fairly good standing and also lucrative.

This son Galileo was born in Pisa on February 15, 1564, the year that saw the birth of Shakespeare, and his education began in a day-school there with some assistance from his father at times when business did not take him away from Pisa. Vincenzio's help with lessons seems to have been confined to Greek and Latin to the exclusion of mathematics. It may sound odd to modern ears, but there is no doubt of the fact that in those days the objection to the study of mathematics was that it did not pay, as we shall be reminded later on.

At thirteen Galileo was sent to the monastery of Vallombrosa, near Florence, for the conventional classical education, but he only stayed about two years, and was then hurriedly removed by his father, who found him in danger of yielding to the attractions of monastic life, and thus abandoning the career projected for him. The boy showed no special aptitude for business, but had a natural leaning towards mechanics, and like Newton at a later date, made toy machines at an early age. He had inherited a full share of his father's musical ability, and besides theoretical knowledge he learnt to play on various instruments, even surpassing his father's skilful performance on the lute. He showed, moreover, considerable facility in other arts, poetry, and especially drawing and painting, and though his inability to choose an artistic career restricted him almost entirely to criticism, his opinion was greatly valued by several painters of repute. Vincenzio could not be blind to the unsuitability of commercial pursuits for a youth of such accomplishments, and may have regretted what had seemed the necessity in his own case. He therefore abandoned the idea of the cloth trade, and cast about for a paying profession. His own experience taught him that neither mathematics nor music could be regarded as satisfactory from this point of view, and besides, Galileo had so far learnt nothing of mathematics. The choice, possibly influenced by the career of the boy's distinguished namesake, fell on the medical profession, and in his eighteenth year Galileo was sent to the University of Pisa to study under the celebrated physician Andrea Cesalpini, in addition to the usual course in philosophy.

Now Vincenzio himself, as shown in his writings on musical theory, had a rooted objection to taking things on trust, so it is not surprising that Galileo found himself continually at issue with his teachers in philosophy, and thus early struck the keynote of his stormy career. What passed for philosophy in those days had degenerated almost entirely into blind repetition of the statements and doctrines of ancient philosophers, and particularly of Aristotle. But Aristotle and the Greek philosophers generally were not accustomed to put their highly speculative theories to the test of actual experiment, however easy and obvious such experiment might be. They contented themselves with discussions as to what ought to happen according to their preconceived notions of physical laws, rarely attempting to see what does actually happen. Galileo's mind worked in a very different way, and refused to bind or blind itself in such a manner, so he promptly questioned what appeared to be doubtful statements and did not hesitate to contradict if he felt he had a clear case against them. He soon gained such notoriety in this way that he was nicknamed the Wrangler by his fellow-students, and heartily disliked by the professors, who were not only sticklers for tradition, but probably found it less troublesome to rely on memory than on intelligence.

In what we should call his Freshman's term Galileo made his first notable discovery. In the Cathedral of Pisa he noticed a lamp swinging suspended from the roof, and remarked that as the swings died away they did not seem to get slower or quicker. He tested this by counting his pulse-beats, having no other means at hand for measuring time, and found the time of swing to be practically constant. He at once saw that the rule would work both ways, and that a swinging weight would provide a check on the regularity of the pulse, a matter of some importance to the medical profession. Instruments of various patterns which he constructed for this purpose were welcomed with delight by leading doctors, and used under the name of Pulsilogia. All the patterns were founded on the original idea of a pendulum bob, swinging, as is now well known, more quickly as the supporting string was shortened, by drawing it through a hole or winding it round a wheel; so that the length of the string gave a measure of the rapidity of the pulse-beats when the swings were made to coincide with one or more beats. The use of the pendulum for regulating clocks was still in the far future, and it is doubtful whether Galileo ever really made this application, though before his death he seems to have had it in mind.

He was now nearly nineteen, and had still been kept away from mathematics. Some months before his entry into the University his family had returned from Pisa to Florence, and among their friends in that city was a capable mathematician named Ricci, attached to the Tuscan Court as tutor to the grand ducal pages. During Galileo's second year at the University the Court was in residence at Pisa, and Galileo naturally renewed his acquaintance with Ricci. Going to call on him one day he happened to find him lecturing on Euclid to his pupils, and stayed outside an open door to listen without announcing his presence. He was so fascinated by the new ideas, for which his brain must have been pining unawares, that he began to make a practice of secretly listening to Ricci until he plucked up courage to speak to him openly on the subject. After this it was plain enough sailing for a time, for Ricci gladly afforded all assistance in his power. But the inevitable neglect of medical studies, as well as the failure of every application for a free scholarship, convinced Galileo's father that he was not likely to get an adequate return for the crippling expense of his son's university career, which he decided to curtail; so that Galileo gave up any idea of the medical profession and left Pisa without completing his full course.

We thus find Galileo back in Florence at the age of twenty-one, determined to devote himself entirely to mathematics and physics, with the aid of Ricci whenever the Court was in residence at Florence. Meeting with the works of Archimedes he conceived a profound admiration for that philosopher, and was dissatisfied with the vague accounts generally given of the solution of the celebrated problem always associated with the word "Eureka". This, it will be remembered, consisted in the detection of the presence of inferior metal in the Crown of Hiero, tyrant of Syracuse, without any injury to the crown, the weight of the crown being equal to that of the gold provided by Hiero. Archimedes found that the crown displaced more water than an equal weight of pure gold did, and calculated the extent of the goldsmith's fraud. Galileo set himself to consider how this calculation must have been performed, and constructed his Hydrostatic Balance for this purpose. This instrument, called "la Bilancetta," had some resemblance to a steelyard. Galileo also devoted himself to the determination of the centre of gravity in solids of different forms, and this work with the pulsilogia and bilancetta attracted the attention of the Marquis del Monte, who, being himself a competent mathematician, formed a just estimate of the young man's capabilities, and strongly recommended him to the Grand Duke of Tuscany, but without any immediate success.

The necessity of an income of some kind in default of medical fees, compelled Galileo to obtain pupils in mathematics and mechanics, and naturally he applied for every vacant mathematical professorship to be found. After failing to secure such an appointment at Bologna (1587), Padua (1588), Pisa (1588), and Florence (1588)—though the Pisa appointment was in the gift of the Grand Duke—he was on the point of going to the East in 1589 to "seek his fortune" in the company of a friend, when the Pisa professorship again fell vacant, and he secured the post with a salary of about five shillings a week. We cannot wonder at Vincenzio's poor opinion of mathematics as a means of livelihood, especially as the professor of medicine received more than thirty times as much. The position, however, was worth much more than its meagre official salary, as it naturally brought Galileo more pupils and probably raised his fees.

II. University Professorships

CHAPTER II.—UNIVERSITY PROFESSORSHIPS.

Galileo, having thus acquired some economic security, threw himself with increased ardour into the investigations that he loved, and set to work systematically to test by experiment everything in Aristotle's mechanics. The stirring in men's minds which produced the Reformation had already caused a few isolated attempts to replace dogma by proof, but no one previously had made such determined assaults on the "peripatetic" stronghold. No sooner did Galileo find any rebutting experiment than he promptly pilloried the discredited dogma, exposing it in his lectures. Once more, therefore, he drew upon himself the enmity of those professors who had objected to his sceptical attitude as a student. The best-known instance of the success of his campaign is that associated with the celebrated Leaning Tower of Pisa. According to Aristotle the velocity of falling bodies is proportional to their weight, so that a weight of a hundred pounds would fall a hundred times as fast as a weight of one pound. Galileo asserted that but for the resistance of the air, which varies with the size and shape of the body, both would fall at the same rate. The parapet of the Leaning Tower offered a very convenient opportunity of testing the point. The experiment was tried by Galileo, and in the event the heavy weight beat the light weight by about two inches. Curiously enough, many of his opponents claimed the victory for Aristotle, as the heavy weight fell more quickly than the light one, and Galileo caustically pointed out that they were trying to make his two inches cover up Aristotle's ninety-nine yards, the amount by which the heavy weight should have won the race to the ground on Aristotle's hypothesis.

It was at this period that Galileo produced one of his literary efforts in the form of a burlesque, "In Abuse of Gowns," ridiculing the University ordinance which compelled professors to wear their gowns on all outdoor occasions as well as when lecturing. Various sonnets and other effusions would also appear to have been written during his first professorship.

A combination of circumstances arose to cut short even the three years for which Galileo had received his appointment. The feeling of nearly all his colleagues was against him; he was mulcted of part of his miserable stipend for any accidental failure to lecture; moreover, he had undertaken to help in the support of his brother and sisters, the eldest of whom, Virginia, was married in 1591, Galileo pledging himself to provide her dowry. Perhaps most important of all was the animosity of Giovanni dei Medici, the Grand Duke's natural son, an engineer and architect who designed a big dredging machine to clear Leghorn harbour. Galileo reported to the Grand Duke, after examining the model at his request, that it was useless, as indeed proved to be the case. These causes combined proved sufficient to induce Galileo to resign his post and return to Florence, where he found himself, his father having died soon after Virginia's marriage, almost entirely responsible for the daily wants of his mother and the two younger sisters; his brother Michelangelo had been trained as a musician but did not yet contribute anything to the family exchequer. A more lucrative post was imperatively required, and the Padua professorship being still vacant, as it had been when Galileo applied for it in 1588, four years before, he obtained the support of his friend the Marquis del Monte, and through his aid and that of his friends succeeded in securing the post against the rivalry of the man who had defeated him for the Bologna professorship. He was appointed for four years certain at a salary three times as great as he had received at Pisa, roughly £40 a year. Besides this increase, the greater number of students at Padua meant a much larger income from pupils. For their benefit he wrote a great number of treatises (some of which have been lost, as they were for a long time only in manuscript), treating of such diverse subjects as fortifications, the geometry of the sphere, and mechanics, that is to say, the lever, the pulley, and the screw, including that of Archimedes for raising water. In this was the first development of the principle that what is gained in power is lost in speed, the foundation of equilibrium conditions. In his first summer at Padua Galileo and two friends went to sleep in a cool or perhaps poisonous draught from a cavern, with fatal effects soon afterwards, except in Galileo's case, though his previously strong constitution did not save him from acute chronic disorder.

Some three years later he invented the geometrical and military compass, known to us as the sector, for mechanically solving a great many problems, and this with other similar inventions met with such practical success that he started a workshop in his house and employed a staff of mechanics to make them under his personal supervision. Some of the ideas were plagiarised by Simon Mayer (or Marius) under cover of another man's name, but Galileo had no difficulty in proving priority.

The four years of the appointment had stretched to six years, as was contemplated by the conditions, and Galileo carried on for a seventh year without raising any question. His friends then pestered the Doge on his behalf for an increase of salary, pointing out that his Bologna rival was now receiving more than Galileo, and succeeded in having the appointment secured for a second six year period with a salary of £70 approximately. He now had a wide European reputation as a teacher, and among those who came to Padua for his lectures were the Archduke Ferdinand, afterwards Emperor of Germany, and several other princes. Harvey, the discoverer of the circulation of the blood, probably attended a course of Galileo's lectures. The next step was a move into a large house for the accommodation of resident pupils. Galileo looked after the catering himself and made practically no profit on the housekeeping. There was a large garden to which he added extra ground with vines, and in the cultivation of which he took a considerable share.

Apparently Galileo marked the occasion of his increase of salary by setting up an establishment for a Venetian lady by whom he had three children within the next few years, but at the same time he had to bear the increasing burden of the maintenance of the other members of his family, of which he had now for some years been the head. His brother was continually sponging on him, and even when Galileo succeeded in getting him established in good positions as Court Musician, first in Poland and afterwards in Bavaria, it was Galileo who had to advance the money for an expensive outfit, hardly any of which did Michelangelo ever repay. Virginia's husband caused fresh trouble by threatening to bring an action against Galileo for the unpaid balance of his wife's dowry, and another sister Livia was married in 1601, her brothers guaranteeing her dowry, which meant that the whole responsibility for this also fell upon Galileo. It may be urged in palliation of the irregular nature of Galileo's private household that no wife would have allowed so much to be spent in such ways, but that he felt bound to take his father's place, whatever the cost. It was in 1601 that he began to earn additional fees by undertaking the tuition during the holidays, which he usually spent at Florence, of the Grand Duke's son, Cosmo, both of whose parents held Galileo in high esteem, the Grand Duke regarding him as the greatest mathematician in Christendom, while the Grand Duchess Cristina believed him the greatest of astrologers. In spite of the vogue of this pseudo-science, it is difficult to suppose that Galileo had any real faith in astrology, though he did not refuse to cast horoscopes, just as he lectured on Ptolemy's system after he became a convinced Copernican.

In 1602 Galileo invented his air-thermometer which was not perfected until some years after his death. Two years later the sudden appearance of a bright new star in Ophiuchus provided him with a new interest, and he lectured on it in the great hall of the University. The ordinary lecture rooms were frequently unable to hold the large numbers of students who flocked to hear the new ideas propounded by Galileo, and it is said that sometimes even the great hall was insufficient, so that he had to lecture in the open air. Galileo's conclusions about the new star, though not now acceptable, included at any rate the fact that it was as distant as other stars and not an atmospheric phenomenon. The suggestion that it belonged to the region regarded by the Aristotelians as perfect and unchangeable led to direct conflict, and Galileo openly argued in favour of the theory of Copernicus against that of Ptolemy, who had followed Aristotle. His third term of six years began in 1604, but there was as before delay on the part of the Venetian Council. Once more, in spite of the objections urged by some, among which his irregular household was not forgotten, a fresh increase of salary was voted, partly on the very ground of his increasing family. On the whole he was very well treated by the republic, his salary, which now amounted to about £115, being higher than that of any previous mathematical professor, and his new doctrines being permitted without any protest from the Council.

The next new subject attacked was magnetism. Galileo admired the work of Gilbert of Colchester, the famous author of "De Magnete," whose habit of mind was very similar to that of Galileo in its reliance upon experiment and its bold speculations. Galileo invented an armature for increasing the lifting power of a "loadstone," finding that small magnets were more efficient than large ones, and that when shaped specially they could be made to support a mass of iron weighing some forty times their own weight.

III. Galileo's Telescope

CHAPTER III.—GALILEO'S TELESCOPE.

We now come to the most important epoch in Galileo's career. In 1609, being at Venice, he heard for the first time of the invention of a telescope the previous year in Flanders, and at once determined to think the matter out to see whether he could find the principle of construction. He soon succeeded in fitting two lenses in a tube, so that objects viewed through it were magnified, and his second attempt was still more satisfactory. His success was speedily reported to the Venetian Council, who summoned him to exhibit his spy-glass, which was already much more efficient than the Flanders one, besides which it showed objects upright whereas the first telescopes inverted them. The Doge wished to possess one, and Galileo promptly offered to present the one with which the Council had been so pleased, and when he had taken it to the palace he was complimented on the efficient manner in which he had served the State for seventeen years, and informed that instead of waiting until his third term of office had expired, the Council had determined to raise his salary at once to nearly double what it had been at the last augmentation, and to confirm the appointment for life at the new salary of 1000 florins, or about £220.

It is considered by some that Galileo's discovery is greatly discounted by the previous success in Holland, but as the latter was due to a pure accident, while Galileo's was by design, others will be inclined to give him the greater credit, reserving an even higher meed of praise for one who deliberately invents a contrivance of great importance without any previous hint as to its possibility. The aperture of the Doge's telescope was about 13/4 inches. It was the second instrument of its kind, but has been lost. Its magnifying power was 3 diameters, and it showed objects 22 miles distant on the earth. On his return to Padua he made a third telescope with a power of 8 diameters, soon followed by a fourth with a power of 20 diameters. This instrument he turned towards the sky, observing the moon and Jupiter, and soon found opportunity on a visit to Florence to show it to his old pupil Cosmo, now Grand Duke, since the death of Ferdinand early in the year. It is interesting to note that three weeks before Ferdinand's death Galileo had cast his horoscope at the request of the Grand Duchess, and promised many more years of life.

Early in 1610 came the fifth telescope, magnifying more than 30 diameters. With this Galileo began his series of astronomical discoveries, except that of the appearance of the moon, begun with the fourth telescope, and shown by its means to the young Grand Duke the previous year. In his tract, the "Sidereus Nuncius" (or Sidereal Messenger), printed at Venice in the same year, he announced the first fruits of his search with the new instrument; first the diversified surface of the moon, with many markings not visible to the naked eye; mountains four or five miles high, and the "earthshine," which he attributed to its true cause; next, the great number of stars revealed by the telescope in clusters, including the true structure of the Milky Way. The planets, moreover, which in his fourth telescope were seen to differ from stars, in showing discs instead of points of light, yielded fresh surprises to the fifth telescope. It was on January 7, 1610, that with this instrument directed towards Jupiter Galileo first saw three bright objects close to the planet. Repeated observation proved that these, with a fourth, which must have been on the first night hidden by the planet, were moons revolving round Jupiter. This conclusion was reached in a very few weeks, and Galileo gave the newly discovered bodies the name of "Medicean stars" in compliment to the Grand Duke and his three brothers.

Meanwhile Galileo had fitted up a workshop for the manufacture of telescopes, finding, however, that only about one in ten of his object glasses was good enough to show the "Medicean stars". The demand for the new instrument was great, as Galileo's telescopes were much more efficient than any to be procured elsewhere, so that his workmen, who made also hundreds of his other instruments, geometrical compasses, hydrostatic balances, air thermometers, magnets, and so on, were kept busy, though Galileo ground all his lenses himself until his sight failed. It was some time before the superiority of other forms of telescope for very high magnifying power was realised. Galileo's principle still survives in field glasses, where the power is not high and when the inverting effect of the astronomical telescope is inconvenient, especially as the erecting eyepiece involves loss of light. The Grand Duke Cosmo II. asked for the telescope with which these discoveries were made, but Galileo, though he at once consented, nevertheless kept it for his own use, ostensibly only on loan. Its focal length was 52/ feet and aperture 24/ inches.

During the earlier part of 1610 more than a hundred telescopes, accompanied by copies of the "Sidereus Nuncius," were sent to princes and learned men of Italy, France, Flanders, and Germany, and the French Court in particular, where Marie dei Medici was queen, desired to bespeak for the King, Henry of Bourbon, the privilege of giving his name to the next striking discovery in the heavens. Many savants, however, refused to accept Galileo's discoveries, some even declining to look through a telescope, rather than risk seeing something in whose existence they would not believe. Galileo did not at this time state openly in the "Sidereus Nuncius" the conclusion to which his discoveries had driven him, namely, that the earth moves round the sun, and not the sun round the earth. He spoke of it and lectured about it, not realising how he would be affected by the furious outcry against it. Kepler, the greatest astronomer of the time, accepted everything in full confidence, though the mystic numbers in which he delighted were liable to be upset by such new discoveries. Simon Marius (Mayer) claimed priority in the discovery of Jupiter's moons, as he had previously claimed it in the case of the proportional compass, but there is no doubt that both claims were fraudulent. In the endeavour to increase his list of discoveries and comply with the earnest wish of the Italian Queen of France, Galileo next turned his attention to Saturn. He found no satellite, but under the imperfect definition of his telescope he noted that the planet appeared triple, the appearance being caused, as was discovered later, by the ring projecting on both sides of the ball. To avoid the chance of being again accused of adopting other people's discoveries, he published this one in the form of a jumble of letters, which when sorted out, would spell the words:—

"Altissimuni Planetam Tergeminum Observavi," meaning, "I have found the furthermost planet (Saturn at that time, as Uranus and Neptune were not yet discovered) to be triple," the fact of the matter being that the imperfect definition of his telescope caused the ring of Saturn, which was then open as viewed from the earth, to resemble companion stars, one each side of the central ball. These attendant objects gradually diminished in apparent size, and after two years disappeared altogether, the ring being then edgeways as seen from the earth. This occurs every fourteen years, though naturally the fact was quite unknown to Galileo, and he was very much taken aback at the vanishing of the new objects, which suggested to him a reference to the Greek myth of Saturn swallowing his children. He predicted their reappearance and observed them again as the ring widened out. Later he realised the dark space on each side of the ball between it and the ring, but, as he gave no indication of having grasped the significance of this appearance, it is probable that he did not really understand it. The true explanation was discovered some years after his death, by Huygens, with a telescope of magnifying power of 100 diameters. It is needless to emphasise the additional annoyance caused to the Aristotelians by this new evidence of change in the "immutable" heavens.

To Galileo himself the successive discoveries and the controversies they aroused brought a large increase of students and pupils from all directions, and his teaching work grew to such an extent that he could find very little time for original research. He felt that after twenty years he had had enough of this labour and was desirous of finding more leisure. He had gratefully accepted the life-appointment at Padua, but was only too ready to relinquish it when an opportunity of escape was offered. His great European reputation made it seem desirable to the Tuscan Court to attach him permanently to the Grand Ducal service, and negotiations were opened between Galileo and the Duke's Secretary of State. Galileo stated plainly how irksome he found the necessity of spending so much time on pupils on account of his family expenses, and even the amount of lecturing required, though this was not very great. He also said how many inventions he had in mind, many of them only of use to princes making war; he enumerated books in contemplation, some of them already in hand, on the structure of the universe, on local motion, on mechanics, on sound and speech, on light and colours, on the tides and other subjects, besides works on military science, manœuvres, fortification, etc. In addition to these and other proposed reprints and publications, he pointed out how much time he wanted for observation of the Medicean stars in order to construct tables of their motion, and for other astronomical pursuits. The result of the negotiations was his nomination by Cosmo II. as First Mathematician of the University of Pisa, and also Philosopher and Mathematician to the Grand Duke, but with no obligation to lecture nor to live at Pisa.

IV. Discovery of Sun-spots

CHAPTER IV.—DISCOVERY OF SUN-SPOTS.

It now appeared that Galileo had everything in his favour, a good permanent salary and abundant leisure for his favourite pursuits, with the support of a powerful prince. But the event proved that this was a very bad exchange for the Padua post, and it was not very long before the philosopher must have begun to regret leaving the one government in Italy where he would have been perfectly safe. Before Galileo entered its service, the Venetian republic, finding that the Jesuits were scheming to obtain control of education, starting with a school of their own, had decreed that no Jesuit should be allowed to teach in its territory. On the intervention of the Pope, who supported the Jesuit cause by laying Venice under an interdict, the senate retorted by expelling the Jesuits altogether. In no other part of Italy was absolute freedom of thought possible.