Publications of the Astronomical

PUBLICATIONS OF THE

ASTRONOMICAL SOCIETY OF THE PACIFIC

Vol. XLV San Francisco, California, June, 1933 No. 265

GALILEO GALILEI, A PIONEER IN SCIENTIFIC RESEARCH1

By Frederick Slocum

Between 1890 and 1909 the Italian government published a twenty-volume edition of Galileo's works. That edition was quicklv exhausted and a prospectus of a reprint has recently been sent out. This is my excuse for talking about Galileo. Any man whose works have stood the test of three hundred years is worthy of our consideration. Galileo Galilei was born in Pisa in 1564. His father, Vincenzio Galilei, was of noble birth and well educated, especially in Greek, Latin, mathematics, and music. He wrote several books on music, in one of which he declares himself in favor of free and open inquiry, unrestrained by authority and tradi- tion. As we shall see, the son not only indorsed this precept but actually lived up to it. Galileo, as I shall call him, following the Italian custom of using the first name, was the eldest of six children, and the family was very poor, which meant that Galileo would have to work for a living. Vincenzio decided that the boy should follow in his footsteps, and go into the business of selling cloth, but agreed to give him a good education first. At the age of thirteen he was sent to a far-famed monastery near Florence. Here, we are told, he excelled in Greek and Latin language and literature, wrote essays and poems, played well on several instruments, and showed considerable skill as an artist. The father, realizing that all this ability ought not to be wasted on selling cloth, decided to send the boy to the University of Pisa to study medicine. This field was chosen from a purely commercial point of view. Vincenzio hoped, or, perhaps, feared

1 A lecture delivered at California Institute of Technology, April 21, 1933.

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that his son might some day become a professor, and the salaries at the university were differentiated, not according to the ability of the professor, but according to the subject taught. At the top was the professor of Medicine, with a salary equivalent to $2,000. At the bottom was the professor of Mathematics and Natural Science with $65 per year. There were scholarships even in those days, forty of them at the University of Pisa, each entitling the holder to free board and lodging. Galileo applied for one of these, but failed to get it. However, he registered as a student in medicine and attended lectures on philosophy as well as on pre-medical subjects. At that time philosophy included all the natural sciences. These subjects interested Galileo, but he found the lectures dry. Every time he raised a question, the reply invariably was "Magister dixit/' The Magister, of course, was Aristotle, who had been dead for 1,900 years. The lectures on medicine were based on Hippocrates and Galen, and they, too, lived almost as far back. Great men, to be sure, but Galileo wondered if there had been no progress since their day. Let us look for a moment at the development of science up to that time. Starting in Greece, we find a few fragments as early as 900 b.c. Then during the next four hundred years arithmetic and algebra had been well developed, especially by the Egyptians and Arabs. Euclid had written his classic textbook on geometry ; and trigonometry had been invented by Hipparchus of Rhodes. Archimedes had experimented with levers, screws, etc., and had written profusely on various mechanical problems. Hippocrates had studied the symptoms of various diseases, dissected animals, and had almost observed the circulation of the blood. Thaïes, Eudoxus, and Aristarchus had made a good beginning on astronomy. The philosophers dabbled in everything. Pythagoras invented a scheme for explaining the apparent movements of the planets among the stars. He imagined a series of eight glass spheres ; one carrying the stars, and one each for the Sun, the Moon, and the five planets then known. These eight spheres corresponded to the octave in music, and by their relative movements produced the "harmony of the spheres."

Aristotle was a living encyclopedia, undoubtedly one of the greatest men that ever lived. He urged that, in so far as possible, all conclusions should be based on observation and experiment. Unfortunately he did not always practice what he preached and much of his science is very bad. This was especially serious, because of his justly recognized authority in other branches of learning. Here are some samples of Aristotle's science. There is no need to assume an Atlas to support the sky on his shoul- ders, as in the old myths, nor even a whirlwind, for the heavenly bodies are not heavy things like the Earth to need support, and they are not moved by force, but are eternally in motion from the nature of their being.

After discussing his theory of the planetary movements, he says : . . . . all of these movements prove the existence of "Essences," eternal and immovable themselves, who cause these movements. And it has been handed down to us in a mythical way from the most ancient teachers, that these eternal "Essences" are gods. Above all these must be a Prime Mover, who is one, eternal, and enjoys forever the kind of existence which we only experience in our best moments. Upon this Prime Mover depend the whole heaven and all nature.

Aristotle's star pupil, Alexander the Great, founded the first real university, in Alexandria. He built a great library, labora- tories, observatories, etc., and invited scholars from all parts of the world. For six or eight hundred years this was the center of learning of the world. Then came the fanatic Caliph Omar in a.D. 640 and ordered the whole plant to be burned. His idea was that any book that did not agree with the Koran was heretical and should be burned ; any book that did agree with the Koran was superfluous and should be burned; therefore, "spare only the Koran," said Omar. Fortunately, some of the precious works had been copied, some translated into Arabic and other languages, so the loss was not quite total. Out of the wreck was saved Ptolemy's "Mathe- matical System of Astronomy," generally called "The Almagest," and also, unfortunately, his work on Astrology, which is still being used by modern astrologers. The Almagest is an excellent presentation of the state of

astronomical knowledge down to a.d. 150. It contains among many other things an elaborate presentation of the Ptolemaic or geocentric theory of the solar system, which places the Earth at the center with the Moon, Sun, and all the planets revolving

around it. I shall have occasion to refer to this later./ After the Mohammedan conquest of Alexandria came the Dark Ages. Rome had already collapsed and learning was dead or, at least, dormant, and so it remained down to the eleventh century. Then came the Renaissance, with the opening of uni- versities at Rome, Bologna, Pisa, Padua, etc., and finally the Reformation, beginning about the time of the discovery of America. It was during these later years of religious stress that Galileo lived. Now let us return to Pisa. Late one afternoon in the winter of 1581 Galileo was in the Cathedral attending Mass. As it grew dark, the sexton with a long hook drew the hanging chandelier in to the balcony, lighted the candles, and let it swing back into place. Back and forth it swung. Back and forth, and Galileo timed it with his pulse. As the arc through which it swung became shorter, he timed it again and, much to his surprise, got the same count of pulse beats. He returned to his room and set up all sorts of pendulums, long ones and short ones, some with light weights and others heavy. Then he announced the law of the pendulum, that the length is proportional to the square of the time of the swing. He said, "If a long string is suspended so that I can see only the lower end of it, I can tell its length. I would tie a weight on it and start it swinging. Then I would compare the time of swing with the time of a pendulum of one cubit's length, and, in a moment, I can tell the length of the long string within half a hand's breadth." He was still a student of medicine, and so he invented what he called a "pulsilogy," a pendulum whose length could be easily varied so as to swing in unison with the beat of the pulse. Before the end of his first year at Pisa he had attracted the attention of both professors and students and had been dubbed "The Wrangler" because of his habit of arguing with his professors. During the summer the Tuscan court moved from Florence

over to Pisa, and with them came Ostilio Ricci as tutor to the young princes. Galileo met him, and, one day, heard him giving a lesson on Euclid. Galileo was fascinated and begged to be allowed to attend other lessons, but his father forbade him to read mathematics or any of the mathematical sciences. He was still thinking of that $65 a year. However, his orders were of no avail, Galileo mastered Euclid and, with the help of Ricci, plunged into Archimedes. Eventually the study of medicine was dropped. He had discovered, so he says, that "mathematics is the language of nature," and he was interested only in those phenomena that could be related to numbers or described in terms of mathematics. He continued for three years at Pisa and then left, partly, perhaps, on account of friction with his professors, partly on account of lack of funds. He had applied again for a scholarship and had again failed. For the next few years he gave private lessons in mathematics and mechanics. He applied for professorships at Bologna and Padua without success. Later, when his old professor of Mathe- matics at Pisa retired, he applied for a position there and eventually got it, at the age of twenty-five. The appointment was for three years only, but was renewable. The salary was $65 a year, with a reduction for each lecture missed. On account of the sick- ness of his mother and floods in the Arno, he was docked ten per cent the first year. He resumed his researches in mathematics and his experiments in physics and mechanics, inventing the hydrostatic balance, measuring the specific gravity of many substances, study- ing problems on the center of gravity, and starting a systematic investigation of the scientific doctrines of Aristotle. This last, of course, got him into trouble, especially when he performed his experiments in public. It was bad enough to question Aristotle in the classroom, but when he insisted upon drop- ping weights from the top of the Leaning Tower to prove that Aristotle's ideas in regard to falling bodies were all wrong, that was too much. Before his three-year term had expired, he resigned, and, a year later, secured a similar position at Padua at a salary of $180

a year. It was the custom there for members of the faculty as well as students to attend the first lecture of a new professor. Galileo's "inaugural address/' as it was called, won the greatest admiration for its brilliant and eloquent diction as well as for its profound knowledge. He lectured at Padua on falling bodies, accelerated motion, inclined planes, levers, pulleys, screws, sun dials, the celestial sphere, motions of the planets, fortifications, etc. His lectures were not read or dictated, but were, at least apparently, extemporaneous. They were fully illustrated by demonstrations and experiments and there was always opportunity for questions and discussion. This was a decided innova- tion in the college teaching of that date. Students crowded his classroom, and his fame spread throughout Europe. At the end of the first term of his appointment, he was reappointed at a salary of $340. The Senate haggled over this for a long time, and it is not clear whether this increase was finally granted because of his ability and fame, or to help him pay his debts. He had been trying to support his mother, a brother, and two sisters. The sisters had married and their husbands were suing Galileo for the dowries which had not been paid. In granting the increase in salary, the Senate made it clear that this case was not to be a "precedent for every learned and hungry foreigner who might press a similar claim/' Galileo helped out his income by taking private pupils, at times having as many as twenty "living in," to use the technical term for those who boarded with their professors. Some of these were young princes and sons of nobility from various European countries. In 1604 a new star appeared suddenly in the heavens almost as bright as Venus. Some months later Galileo gave three lectures on the star. A thousand people came to the first lecture, and the second and third had to be delivered in the open air, because there was no hall large enough to hold the crowd that came to hear him. He rebuked his hearers for thronging to hear about this novelty, and at the same time ignoring the far more wonderful permanent stars and planets. The appearance of a new star worried the Aristotelians.

Their, master had taught that the Universe is perfect, complete, immutable. It was bad enough to have a new star blaze out. It was much worse to have a man like Galileo call public attention to the fact. Galileo was now forty years old and was devoting more and more time to the study and teaching of astronomy. He confessed to his friends that the more he studied the Almagest, the more convinced he was that the Ptolemaic theory was wrong, and he began to collect observations and arguments to prove his point in support of the Copernican or heliocentric plan. He realized that this was a serious matter. It would displace the Earth from its central position in the Universe and make it one of several insignificant planets revolving around the Sun. And it would make man an infinitesimal speck on this insignificant planet, instead of the great central figure for whom the Universe was created. This was contrary to the teaching of the Church, and the authority of the Church must not be questioned. Copernicus, book on the revolutions of the planets around the Sun had appeared fifty years earlier, but Copernicus was a pious monk. His book was dedicated to the Pope; the cost of printing was borne by a cardinal ; it was written in Latin ; no- body read it, and the author died just as it came from the press. When Bruno, however, among other heresies, taught the Coper- nican theory, he was burned at the stake in Rome. That was in 1600. The new star appeared in 1604, and Galileo came out openly in favor of the Copernican theory in the following year. But Galileo was at Padua in the province of Venice, and Venice was then practically independent of Rome and the Pope. He was becoming more and more famous, and, from the point of view of the Church, more and more dangerous every day. From this time, for several years, he spent his summer vacations at Florence and Pisa as tutor to Prince Cosimo, son of the Grand Duke of Tuscany. Now we come to the familiar story of the telescope. A Dutch spectacle-maker of Middleburg made a toy by gluing two lenses to a stick a few inches long. If you looked through the lenses at a weather cock it appeared enlarged and upside down. Some

Italian travelers saw the toy and mentioned it when they returned home. Galileo heard of it and immediately began to play with lenses. In less than twenty-four hours he had improved upon the Dutch idea. Galileo found a combination of lenses that made the image right side up, and by putting the lenses in the ends of a lead pipe he shut out the stray light from the side, and so got a more brilliant image. News of his invention spread and he was summoned to Venice to show it to the doges. Looking through his optic tube from the campanile of St. Marks, they could see vessels fifty miles away, and they looked as large as they would appear to the naked eye if they were only five miles distant. What a boon in time of war! You could see your enemy and watch his movements long before he could see you. His salary was immediately raised to $1,000 a year and he was appointed to his professorship for life. He made larger and better telescopes, over 200 of them, grinding and polishing most of the lenses himself. His largest instrument had a lens 2¾ inches in diameter and feet focal length. He turned one of his telescopes up to the heavens in 1609. Just imagine being the first man to view the heavenly bodies with a telescope ! Startling discoveries came thick and fast: thousands of stars invisible to the naked eye, star clusters, fuzzy nebulae, the craters of the Moon, spots on the Sun, the rotation of the Sun, four satellites of Jupiter, the phases of Venus, and some peculiarity of Saturn which he was never able to explain. Any one of these discoveries would have made a man famous. There is, of course, a story connected with each one. Take, for example, the discovery of the satellites of Jupiter. In his manuscript notebook we find, under date of January 7, 1610, a sketch showing the planet Jupiter and three stars in line, two on the east, one on the west (see Fig. 1). There was nothing remarkable about that. The sketch simply illustrates Galileo's habit of recording, describing, investigating everything that might be of interest. On the next night he sketched the three stars all on the west side. Jupiter was apparently just moving past them. On the third night he saw two only, and they were back on the east. This puzzled him. Jupiter could not possibly

be moving both ways, and no stars had ever been known to move, at least, by any appreciable amount. The next night was cloudy, but after that he followed them every night, and, by January 13, he was ready to announce that there are four satellites revolving around Jupiter just as the Moon revolves around the Earth, and he named them the "Medi- cean Stars" in honor of the House of Medici of Tuscany. The announcement of this discovery created a sensation. The Aristotelians were naturally embarrassed. Galileo wrote to Kepler in Bohemia : 'Oh, my dear Kepler, how I wish that we could have one hearty laugh together! Here, at Padua, is the principal professor of philosophy, whom I have urgently requested to look through my glass, which he persistently refuses to do. Why are you not here? What shouts of laughter we should have at this glorious folly ! And to hear the professor of philosophy at Pisa laboring before the Grand Duke with logical arguments, as if with magical incantations to charm the new planets out of the sky/' Again I quote from Sizzi, a Florentine, who argues against the discovery thus : There are seven windows in the head, two nostrils, two eyes, two ears, and a mouth; so in the heavens there are seven luminaries, from which and many other similar phenomena of nature such as the seven metals, etc., which it were tedious to enumerate, we gather that the number of planets is necessarily seven. Moreover, the satellites are invisible to the naked eye, and therefore can have no influence on the Earth, and therefore would be useless, and therefore do not exist. Besides, the Jews and other ancient nations as well as modern Euro- peans have adopted the division of the week into seven days and have named them for the seven planets. Now if we increase the number of planets this whole system falls to the ground.

The doubters were soon in a minority. The discovery was verified by others. Yes, more than verified. One Scheiner claimed to have seen five; others as high as twelve. Some of these were probably fixed stars, others purely imaginary. One man, while admitting the motions of the Medicean Stars, questioned whether they were real satellites like the Moon, because their motions were so complicated that it would never be

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possible to trace their orbits or compute their periods. As usual, when Galileo was told that he could not do a thing, he went right ahead and did it. By a clever combination of observation and analysis he soon derived the periods—1.8 days, 3.6, 7.2, and 16.8 days. All, you see, shorter than the length of our month. As the news of Galileo's discoveries spread over Italy there was great excitement. In Florence a public fête was celebrated in his honor. In Venice there was almost a riot when a mob gathered round a man who had one of Galileo's telescopes, all fighting for a chance to look through it. Dukes and cardinals and even kings and queens requested or demanded telescopes. Marie de Medici is described as kneeling on the floor to rest her telescope on the window sill as she looked at the Moon. The account of this incident is concerned chiefly with the lack of queenly dignity and the damage to her royal gown. A message to Galileo from the royal palace in Paris read: "In case you discover any other fine star, call it by the name of the Great Star of France, as well as the most brilliant of all the earth, and, if it seems fit to you, call it rather by his proper name, Henry, than by the family name. Bourbon. Thus you will have an opportunity of doing a thing due and proper in itself, and, at the same time, of rendering yourself and your family rich and powerful for ever/' So far as I know, no star or planet was ever named for Henry IV. Of the other astronomical discoveries I will mention but two, the phases of Venus and the rings of Saturn. According to the Ptolemaic theory, Venus revolved on an epicycle, always between the Earth and the Sun. Since the planets shine only by reflected light, Venus, by that theory, could never show a fully illuminated hemisphere to the Earth. That is, it could never show a phase like the full Moon. Galileo found that it did show such a phase. In fact, it showed all phases—crescent, quarter, and full. At the crescent phase the planet looked large, and at the full phase very small, indicating such a change in distance from the Earth as would result if Venus revolved around the Sun. To Galileo this was the clinching argument in favor of the Copemican system. The same argument was used by Aristotle nineteen cen-

turies before, but on the other side of the debate. He could see no phases on Venus, and therefore claimed that it could not be revolving around the Sun. His logic was good, but his founda- tion weak. Again and again Galileo expressed his great admiration for Aristotle and repeated, in effect, "if the great master were only here I know I could convince him of his errors, but his disciples are hopeless, for they ignore all the progress of 1900 years.^ When Galileo first looked at Saturn he thought it had two satellites, one on each side, symmetrically placed. But, unlike the satellites of Jupiter, they did not appear to revolve around the planet. For years he had been bothered by plagiarists, so he announced his discovery in the form of an anagram of thirty- seven letters. At the request of the Emperor Rudolph II, Galileo finally gave the translation "I have observed that the most distant planet is triple." He continued to observe Saturn and made many sketches of it. Gradually the attendant stars changed their shape. They no longer looked like little dots of light. At one time he described them as ansae, or handles ; again as eara. They became thinner and fainter and finally in 1612 disappeared. We, of course, know now that he was observing the great ring that surrounds Saturn. At first he saw the ring tilted at an appreciable angle, and finally directly on edge, when it was no longer visible in his telescope. Galileo, however, never succeeded in explaining the phenomena. In December, 1612, he writes : Looking at Saturn within these last few days, I found it solitary, without 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, perhaps, the two smaller stars consumed like spots on the Sun? Have they suddenly vanished and fled? Or has Saturn de- voured his own children? Or was the appearance, indeed, fraud and illu- sion, with which the glasses have for so long mocked me and many others who have observed with me? Now, perhaps, the time is come to revive the withering hopes of those who, guided by more profound contemplation, have fathomed all the fallacies of the new observations, and recognised their impossibility. I cannot resolve what to say in a change so strange, so new, so unexpected. The shortness of time, the unexampled occurrence, the weakness of my intellect, the terror of being mistaken, have greatly confounded me.

Later he ventured to predict that the appendages would return, and during the next summer he informed his friends that his prediction had been fulfilled. For eighteen years he lectured, taught private pupils, and carried on his researches at Padua. Among the works that he had wholly or partly finished were two books on the system and structure of the Universe, an immense work full of philosophy, astronomy, and geometry; three books on natural and violent motions ; three books on mechanics ; one on sound and speech ; one on light and color ; one on the tides ; one on the composition of continuous quantity ; one on the movements of animals ; and several on military tactics. In addition to his writings, he had invented various things and had a workshop and several mechanics to manufacture them. There was what he called a military compass ; really a comput- ing device somewhat on the principle of a slide rule. Several thousand of these were made and sold or given away. He also made magnets, magnetic compasses for ships, thermometers, microscopes, and, of course, telescopes. His college duties were not arduous. He says they required only 60 half-hours per year. It was the private teaching that took up most of his time and energy. He was getting tired of this. He longed for freedom to devote all his time to writing and research. By this time the young Tuscan prince, former pupil and ardent admirer of Galileo, had succeeded his father, as Cosimo II, Grand Duke of Tuscany. To him Galileo confessed his ambition to be free to work out his many ideas and hinted that he would be willing to share his fame with the Tuscan court. Cosimo took the hint and invited Galileo to come to Florence as First Mathe- matician of the University of Pisa, and also Philosopher and Mathematician to the Grand Duke of Tuscany. The first part of the title was given so that the university would have to pay him a salary, although he was not to give any lectures, nor even to reside in Pisa. This seemed like an ideal arrangement for Galileo, but his friends at Padua urged him not to accept the invitation. The University of Padua was very liberal. The radical and

the heretic were safe there. The province of Venice was practically independent of the Church. A story is told of two students at their favorite meeting-place, at the Sign of the Ox. After a lively debate, one, Borghese, remarked, "If I were Pope I would excommunicate you and all Venice." The other, Donato, replied, "And if I were Doge of Venice, I would just laugh at your excommunication." Later the first speaker became Pope Paul V and actually did issue a bull excommunicating Venice. Donato became Doge of Venice, and he not only laughed at the bull, but he retaliated by expelling every Jesuit from his province. It was perfectly safe to laugh at a distance, in Venice, but Florence was next door to Rome, and Galileo's friends, knowing that his teachings were considered radical, if not actually heretical, were afraid that he might find his "academic freedom" at least restricted. Again, he had just been appointed "professor for life" at Padua. Was it quite ethical for him to resign immediately? He gave due consideration to the arguments of his friends and then decided to go to Florence. For a while all went well. He was able to devote practically all his time to his telescopic observations, his mechanical researches, and his writing. He gave a few lectures, and we find him occasionally called upon to give advice, as to how to prevent the Arno from overflowing its banks, how best to pump water for irrigation, how to construct a dredge for deepening the har- bor of Pisa. He lived as luxuriously as he desired, was courted and flattered by princes and nobles, and enjoyed a world-wide reputation. He was perfectly aware of the jealousy and hostility of the Jesuits and he knew that his support of the Copernican theory was looked upon as heretical, but his conscience was perfectly clear. He was a really religious man and a devout Catholic. He accepted the authority of the Bible in all matters concerning faith and conduct. As to its statements in regard to scientific matters, he argued that we are so liable to misinterpret their meaning that it is wiser to examine Nature for the truth, and that when direct observation and the Scripture seem to clash, it is because of our fallacious interpretation either of Nature or of the Bible, or of both. Compare this with a statement of the

present Pope Pius XI, as quoted in the New York Times of January, 1932 : "Those who speak of the incompatibility of science and religion either make science say that which it never said or make religion say that which it never taught." Galileo was, in fact, what we would now call a "reconciler.,, He accepted Joshua's miracle, for example, as a literal fact; and he points out how much more easily it could be done on the Copernican theory, by simply stopping the Earth's rotation for a short time, than by stopping the Sun and all the other heavenly bodies as on the old Ptolemaic system, or again by stopping only the Sun and so messing up all astronomy. Up to this time most of the criticism had come from small men. For example, a Dominican priest of Florence preached from Acts I, verse 11, which he slightly misquoted : "Ye men of Galilei! Why stand ye gazing up into the heaven ?" He quoted the familiar references in the Bible to prove that the Earth must be fixed, and closed by reminding his audience that no one was permitted to interpret the Bible in any other sense than that adopted by the Catholic Church. There had been no comment from Rome. He knew, however, that reports of his teaching had been sent in. Finally in 1615 he received a cordial invitation from the Pope, Paul V, to come to Rome and explain his views. This was an opportunity that he had long desired. He felt that he could easily convince the most skeptical of the truth of his theories. The Grand Duke gave him many letters to princes, nobles, and cardinals, sent him to Rome in the royal chair, and instructed the Tuscan ambassador to entertain him at the embassy while he was in Rome. He was right royally received. The church dignitaries vied with the nobles and learned laymen in doing him honor. Galileo showed cardinals and others his telescope, and to as many as would look through it, he showed Jupiter and its moons, and other "celestial novelties." He talked, he harangued, he held forth in the midst of a dozen or more disputants at once, and enjoyed himself immensely. He was a most enthusiastic and successful debater. His

method was to let the opposite arguments be stated as fully and completely as possible, himself aiding, and often adducing the most forcible and plausible arguments against his own views; and then, all having been well stated, to undermine and demolish the whole thing, and to bring out the truth in such a way as to convince all honest minds. He had a long audience with the Pope and the two parted good friends. Apparently all were greatly impressed by what they saw and heard. Cardinal del Monte wrote to Grand Duke Cosimo : Galileo has, during his stay in Rome, given great satisfaction, and I think he must have felt it no less himself, for he had the opportunity of showing his discoveries so well that to all clever and learned men here they seemed no less true and well-founded than astonishing. Were we still living under the ancient republic of Rome, I verily believe there would have been a column on the Capitol erected in his honour.

Galileo would have returned to Florence at the height of his triumph, but he began to hear rumors to the effect that the Holy Office was becoming worried lest the infallibility of the Catholic Church might be involved. Then the question was openly raised as to whether the whole system of Copernicus ought not to be condemned as heretical. Galileo wrote back to Florence : "This new question regards me no more than all those who for the last eighty years have supported those opinions both in public and private, yet, as perhaps I may be of some assistance in that part of the discussion which depends on the knowledge of truths ascertained by means of the sciences which I profess, I, as a zealous and Catholic Christian, neither can nor ought to with- hold that assistance which my knowledge affords." Apparently his efforts were of no avail, for the book of Coper- nicus was put on the forbidden list (that was in 1616. It was removed in 1835), and Galileo himself was ordered never to teach or believe that the Earth moved around the Sun. He left Rome in disgust and returned to Florence. The next few years were perhaps the quietest in his whole life. One of his daughters known as Sister Marie Celeste was a nun in a convent in Arcetri near Florence. She and her father corresponded frequently and most of her letters have been preserved. It is from these that we have learned many of the details of Galileo's life.

A few years later Pope Paul V died and was succeeded by Cardinal Barbarini, who became Urban VIII. This man had been one of Galileo's best friends, so naturally Galileo was de- lighted at his election and immediately began to have hopes that the forbidden edict might be withdrawn. As soon as possible Galileo went to Rome to congratulate his friend. He had many talks with the new Pope and apparently made a good impres- sion, for Urban wrote to the Grand Duke Ferdinand, who had succeeded Cosimo in Tuscany : For We find in him not only literary distinction but also love of piety, and he is strong in those qualities by which Pontifical good will is easily obtainable. And now, when he has been brought to this city to congratulate Us on Our elevation, We have very lovingly embraced him; nor can We suffer him to return to the country whither your liberality recalls him without an ample provision of Pontifical love. And that you may know how dear he is to Us, We have willed to give him this honourable testi- monial of virtue and piety. And We further signify that every benefit which you shall confer upon him, imitating or even surpassing your father's liberality, will conduce to Our gratification.

Encouraged by this, Galileo began at once what has proved to be his most popular work. The Dialogues on the Two Principal Systems of the World. This purports to be a series of four conversations between three characters : Salviati, a Copernican philosopher ; Sagredo, a wit and scholar, keen and critical ; and Simplicio, an Aristotelian philosopher who propounds the stock arguments in favor of the Ptolemaic theory. The conversations are conducted with good temper and fairness, and, discreetly enough, no definite conclusion is arrived at. In the Preface he says that the dialogue on the Copernican side takes up the question purely as a mathematical hypothesis or speculative figment. But the arguments in favor of the Earth's motion around the Sun are so strong and so popularly stated that they did more in a few years to undermine the old system than all that had been written or spoken before. For two years he failed to get permission from the Church Censor to print the work, but finally, possibly either by accident or by carelessness, it was approved and immediately printed. It was perhaps all the more eagerly read because the Church at once sought to suppress it. Galileo writes : "The Holy Office has

forbidden the circulation of my Dialogues. I hear from well- informed persons that the Jesuit Fathers have insinuated in the highest quarters that my book is even more execrable and injurious to the Church than the writings of Luther and Calvin " His friends were most enthusiastic over it. Thus one writes : "I had hardly time to devour your book when it was taken from me and lent from one to another. Today, no sooner do I get it back by main force, than I am obliged to send it to the Commis- sary at Verona, one of our cleverest men, and one who admires you above all the literati of the age." Galileo's enemies tried to convince the Pope that he himself was the character portrayed by Simplicio, the one whose opinions are alternately refuted and ridiculed. It is, of course, in- conceivable that Galileo should thus treat his friend and patron. However, whether the Pope believed it or not, it is certain that his attitude immediately changed. Whether overruled by his cardinals or actuated by some other motive, his favor was completely withdrawn. Galileo was ordered to appear before the Inquisition. He was now seventy years old and very feeble. Volumes have been written on this, one of the most famous trials in history. It dragged on from February to June, 1633. The Inquisitors were a legal body of the Catholic Church. Their function was to crush heresy and maintain the supremacy of the Church. In general they acted without malice, but ef- fectively. They had their regular rules of procedure. They first examined one who was suspected, to determine, if possible, if he was guilty of believing or teaching heretical ideas. If he was found guilty, he must be made to recant. This was accomplished by one or more of the five following stages, at any one of which the victim might recant: (1) the official threat in court; (2) a renewal of the threat at the door of the torture chamber ; (3) the taking inside and showing of the instruments of torture; (4) undressing and binding on the rack; (5) the "Territio realis," either on the rack or perhaps bound to a stake in a public square. During the months of his examination Galileo was well treated. He lived at the Tuscan embassy and was allowed to

drive in the park. On one occasion he was detained by the In- quisitors three days. He may ha*ve spent these days in a dungeon. At the end of these last three days of his "rigorous examination,, he was declared guilty and compelled to recant. Through how many of the stages he went before he gave in, I do not know. There is no evidence that he was ever physically tortured. At some point in the procedure he admitted his guilt and agreed to say anything they wanted him to. The next day clothed as a penitent he was taken to the Con- vent of Minerva, where the cardinals and prelates were assem- bled to pass judgment upon him. He was sentenced, first, to abjuration; second, to formal imprisonment for life; third, to recite the seven penitential psalms every week. This last his daughter, Sister Marie Celeste, did for him. His imprisonment consisted in being confined to the little town of Arcetri where he lived. When he wanted to go to Florence for medical treatment he had to get permission from the Inquisitors. As to the abjuration, that is well known. Copies were ordered posted at all the colleges ; the professors read it before their classes ; priests read it in the churches ; and copies were sent to all of Galileo's friends and to the literati of all Europe. I will read a portion of it. I, Galileo Galilei, son of the late Vincenzio Galilei, of Florence, aged seventy years, being brought personally to judgment, and kneeling before you Most Eminent and Most Reverend Lords, Cardinals, General Inquis- itors of the universal Christian republic against heretical depravity, having before my eyes the Holy Gospels, which I touch with my own hands, swear that I have always believed, and now believe, and with the help of God will in the future believe, every article which· the Holy Catholic and Apostolic Church of Rome holds, teaches, and preaches. But because I have been enjoined by this Holy Office altogether to abandon the false opinion which maintains that the Sun is the centre and immovable, and forbidden to hold, defend, or teach the said false doctrine in any manner, and after it hath been signified to me that the said doctrine is repugnant with the Holy Scripture, I have written and printed a book, in which I treat of the same doctrine now condemned, and adduce reasons with great force in support of the same, without giving any solution, and therefore have been judged grievously suspected of heresy; that is to say, that I have held and believed that the Sun is the centre of the universe and is immovable, and that the Earth is not the centre and is movable; willing, therefore to remove from the minds of your Eminences, and of every Catholic Christian, this vehement suspicion rightfully entertained towards

me, with a sincere heart and unfeigned faith, I abjure, curse, and detest the said errors and heresies, and generally every other error and sect contrary to Holy Church; and I swear that I will never more in future say or assert anything verbally or in writing, which may give rise to a similar suspicion of me; ....

Back in Arcetri, he complained that his head was too busy for his body. He was still keen to work and to write. He com- pleted twenty-five years of systematic observations of the satellites of Jupiter, computed tables of their motions, and the times of their eclipses by the planet. He discovered a method of finding the longitude by these eclipses. In the time of Columbus there was no known method of finding the longitude at sea. He could get his latitude, approximately, but his distance east or west he could only estimate by guessing at the speed of his ship. Prizes were offered by Spain, Portugal, Holland, France, and England for the solution of the longitude problem. Eng- land's prize of 20,000 pounds was eventually paid to the heirs of John Harrison, who made the first reliable chronometer. Galileo submitted his solution to Spain and later to Holland. The Dutch were at once interested and promised to send an ambassador to negotiate with Galileo. The Inquisitors heard of this, and since Galileo had been forbidden to receive visitors, word had to be sent to Holland requesting the ambassador not to come. The method, while theoretically correct, is far inferior in accuracy to methods discovered later, and has never been used at sea. During these later years he wrote his Dialogues on Two New Sciences. These are considered by many to be his most impor- tant work. They form the basis of what we now call mechanics and physics. Remarkable insight is shown in his references to time, space, velocity, acceleration, momentum, gravitation, in- finity, and the infinitesimal. Much of Sir Isaac Newton's work was based upon ideas developed in these Dialogues. In regard to motion Salviati is made to say :

"The present does not seem to be the proper time to investigate the cause of the acceleration of natural motion concerning which various opinions have been expressed by various philosophers, some explaining it by

attraction to the center, others to repulsion between the very small parts of the body, while still others attribute it to a certain stress in the sur- rounding medium which closes in behind the falling body and drives it from one of its positions to another. Now, all these fantasies, and others too, ought to be examined; but it is not really worth while. At present it is the purpose of our Author merely to investigate and to demonstrate some of the properties of accelerated motion (whatever the cause of this acceleration may be)—meaning thereby a motion, such that the momentum of its velocity goes on increasing after departure from rest, in simple pro- portionality to the time, which is the same as saying that in equal time- intervals the body receives equal increments of velocity; and if we find the properties (of accelerated motion) which will be demonstrated later are realized in freely falling and accelerated bodies, we may conclude that the assumed definition includes such a motion of falling bodies and that their speed goes on increasing as the time and the duration of the motion."2

Here is a description of one of his typical laboratory experiments :

"A piece of wooden moulding or scantling, about 12 cubits long, half a cubit wide, and three finger-breadths thick, was taken; on its edge was cut a channel a little more than one finger in breadth; having made this groove very straight, smooth, and polished, and having lined it with parch- ment, also as smooth and polished as possible, we rolled along it a hard, smooth, and very round bronze ball. Having placed this board in a sloping position, by lifting one end some one or two cubits above the other, we rolled the ball, as I was just saying, along the channel, noting, in a manner presently to be described, the time required to make the descent. We repeated this experiment more than once in order to measure the time with an accuracy such that the deviation between two observations never ex- ceeded one-tenth of a pulse-beat. Having performed this operation and having assured ourselves of its reliability, we now rolled the ball only one-quarter the length of the channel ; and having measured the time of its descent, we found it precisely one-half of the former. Next we tried other distances, comparing the time for the whole length with that for the half, or with that for two-thirds, or three-fourths, or indeed for any frac- tion ; in such experiments, repeated a full hundred times, we always found that the spaces traversed were to each other as the squares of the times, and this was true for all inclinations of the plane." .... "For the measurement of time, we employed a large vessel of water placed in an elevated position; to the bottom of this vessel was soldered a pipe of small diameter giving a thin jet of water, which we collected in a small glass during the time of each descent, whether for the whole length of

2 Two New Sciènces of Galileo, p. 166.

the channel or for a part of its length ; the water thus collected was weighed, after each descent, on a very accurate balance; the differences and ratios of these weights gave us the differences and ratios of the times, and this with such accuracy that, although the operation was repeated many, many times, there was no appreciable discrepancy in the results."3

In 1638, at the age of 74, Galileo writes, "Alas ! your dear friend and servant is totally blind. Henceforth this heaven, this Universe, which by wonderful observations I have enlarged a hundred and a thousand times beyond the conception of former ages, is shrunk for me into the narrow space which I myself fill in it. So it pleases God ; it shall therefore please me also/' Viviani, a brilliant young mathematician, begged the honor of being his last disciple. Torricelli and Castelli also came to live with him, and these three took turns in recording his dicta- tions. His son, Vincenzio, was also with him much of the time. To Vincenzio he described a plan for a pendulum clock, with an ingenious escapement. The clock was never made, but Vincenzio's sketch was published and the first really reliable pendulum clocks were built by Huyghens in Holland a few years later (1657). Galileo was now allowed to receive visitors and among others came the poet Milton. His mind was clear almost to the end. In November, 1641, he dictated his commentaries on the theorems of Euclid. This was his last work. He died in January, 1642, at the age of 78. A movement was at once started to erect a great memorial to him in Florence. This, however, was forbidden by the Inquisi- tion. Some even tried to have his remains thrown into the Adriatic, that he might the sooner be forgotten. It was not until fifty years later that it was deemed safe to erect a modest memorial to him. Now, no one goes to Florence without visiting his tomb in Santa Croce, and the Tribuna di Galileo in the Mu- seum of Physics and Natural History. There are impressive statues, too, in Rome, Padua, Venice, Pisa, Milan, London, Ox- ford, Cambridge, and in many other educational centers throughout the world, but by far the greatest and most satisfactory memorial of Galileo is the new complete edition of his writings.

z Ibid., p. 178.

BIBLIOGRAPHY

Le Opere di Galileo Galilei. Edizione Nazionale. (20 vols. 1890-1909) Antonio Favaro, Direttore. Reprint of same. Antonio Garbasso, Direttore. Some of the more recent books in English : Galileo, His Life and Work. J. J. Fahee. Memorials of Galileo Galilei. J. J. Fahie. Two Nezv Sciences of Galileo. Translated by Crew and de Salvio. Galileo, Searcher of the Heavens. Emile Namer. Translated by Sibyl Harris. Galileo. W. W. Bryant. The Private Life of Galileo. Anonymous (Mary Allen-Olney).