SOURCE: "Kepler and Galileo," in The Sleepwalkers. A History of Man's Changing Vision of the Universe, The Macmillan Company, 1959, pp. 352-78.

[In the following excerpt, Koestler gives a frank and detailed account of Galileo's life and work, attempting to sepaàrate fact from legend. He gives particular attention to Galileo's professional relationship with Kepler and his struggle with the authorities of the Roman Catholic Church.]

1. A Digression on Mythography

It was indeed a new departure. The range and power of the main sense organ of homo sapiens had suddenly started to grow in leaps to thirty times, a hundred times, a thousand times its natural capacity. Parallel leaps and bounds in the range of other organs were soon to transform the species into a race of giants in power—without enlarging his moral stature by an inch. It was a monstrously one-sided mutation—as if moles were growing to the size of whales, but retaining the instincts of moles. The makers of the scientific revolution were individuals who in this transformation of the race played the part of the mutating genes. Such genes are ipso facto unbalanced and unstable. The personalities of these "mutants" already foreshadowed the discrepancy in the next development of man: the intellectual giants of the scientific revolution were moral dwarfs.

They were, of course, neither better nor worse than the average of their contemporaries. They were moral dwarfs only in proportion to their intellectual greatness. It may be thought unfair to judge a man's character by the standard of his intellectual achievements, but the great civilizations of the past did precisely this; the divorce of moral from intellectual values is itself a characteristic development of the last few centuries. It is foreshadowed in the philosophy of Galileo, and became fully explicit in the ethical neutrality of modern determinism. The indulgence with which historians of science treat the Founding Fathers is based on precisely that tradition which the Fathers introduced—the tradition of keeping intellect and character as strictly apart as Galileo taught us to separate the "primary" and "secondary" qualities of objects. Thus moral assessments are thought to be essential in the case of Cromwell or Danton, but irrelevant in the case of Galileo, Descartes or Newton. However, the scientific revolution produced not only discoveries, but a new attitude to life, a change in the philosophical climate. And on that new climate, the personalities and beliefs of those who initiated it had a lasting influence. The most pronounced of these influences, in their different fields, were Galileo's and Descartes'.

The personality of Galileo, as it emerges from works of popular science, has even less relation to historic fact than Canon Koppernigk's. In his particular case, however, this is not caused by a benevolent indifference towards the individual as distinct from his achievement, but by more partisan motives. In works with a theological bias, he appears as the nigger in the woodpile; in rationalist mythography, as the Maid of Orleans of Science, the St. George who slew the dragon of the Inquisition. It is, therefore, hardly surprising that the fame of this outstanding genius rests mostly on discoveries he never made, and on feats he never performed. Contrary to statements in even recent outlines of science, Galileo did not invent the telescope; nor the microscope; nor the thermometer; nor the pendulum clock. He did not discover the law of inertia; nor the parallelogram of forces or motions; nor the sun spots. He made no contribution to theoretical astronomy; he did not throw down weights from the leaning tower of Pisa, and did not prove the truth of the Copernican system. He was not tortured by the Inquisition, did not languish in its dungeons, did not say "eppur si muove"; and he was not a martyr of science.

What he did was to found the modern science of dynamics, which makes him rank among the men who shaped human destiny. It provided the indispensable complement to Kepler's laws for Newton's universe: "If I have been able to see farther," Newton said, "it was because I stood on the shoulders of giants." The giants were, chiefly, Kepler, Galileo and Descartes.

2. Youth of Galileo

Galileo Galilei was born in 1564 and died in 1642, the year Newton was born. His father, Vincento Galilei, was an impoverished scion of the lower nobility, a man of remarkable culture, with considerable achievements as a composer and writer on music, a contempt for authority, and radical leanings. He wrote, for instance (in a study on counter-point): "It appears to me that those who try to prove an assertion by relying simply on the weight of authority act very absurdly."¹

One feels at once the contrast in climate between the childhoods of Galileo and our previous heroes. Copernicus, Tycho, Kepler, never completely severed the navel-cord which had fed into them the rich, mystic sap of the Middle Ages. Galileo is a second-generation intellectual, a second-generation rebel against authority; in a nineteenth century setting, he would have been the Socialist son of a Liberal father.

His early portraits show a ginger-haired, short-necked, beefy young man of rather coarse features, a thick nose and conceited stare. He went to the excellent Jesuit school at the Monastery of Vallombrosa, near Florence; but Galileo senior wanted him to become a merchant (which was by no means considered degrading for a patrician in Tuscany) and brought the boy home to Pisa; then, in recognition of his obvious gifts, changed his mind and at seventeen sent him to the local university to study medicine. But Vincento had five children to look after (a younger son, Michelangelo, plus three daughters), and the University fees were high; so he tried to obtain a scholarship for Galileo. Although there were no less than forty scholarships for poor students available in Pisa, Galileo failed to obtain one, and was compelled to leave the University without a degree. This is the more surprising as he had already given unmistakable proof of his brilliance: in 1582, in his second year at the University, he discovered the fact that a pendulum of a given length swings at a constant frequency, regardless of amplitude.² His invention of the "pulsilogium", a kind of metronome for timing the pulse of patients, was probably made at the same time. In view of this and other proofs of the young student's mechanical genius, his early biographers explained the refusal of a scholarship by the animosity which his unorthodox anti-Aristotelian views raised. In fact, however, Galileo's early views on physics contain nothing of a revolutionary nature.³ It is more likely that the refusal of the scholarship was due not to the unpopularity of Galileo's views, but of his person—that cold, sarcastic presumption, by which he managed to spoil his case throughout' his life.

Back home he continued his studies, mostly in applied mechanics, which attracted him more and more, perfecting his dexterity in making mechanical instruments and gadgets. He invented a hydrostatic balance, wrote a treatise on it which he circulated in manuscript, and began to attract the attention of scholars. Among these was the Marchese Guidobaldo del Monte who recommended Galileo to his brother-in-law, Cardinal del Monte, who in turn recommended him to Ferdinand de Medici, the ruling Duke of Tuscany; as a result, Galileo was appointed a lecturer in mathematics at the University of Pisa, four years after that sanie University had refused him a scholarship. Thus at the age of twenty-five, he was launched on his academic career. Three years later, in 1592, he was appointed to the vacant Chair of Mathematics at the famous University of Padua, again through the intervention of his patron, del Monte.

Galileo remained in Padua for eighteen years, the most creative and fertile years of his life. It was here that he laid the foundations of modern dynamics, the science concerned with moving bodies. But the results of these researches he only published towards the end of his life. Up to the age of forty-six, when the Messenger from the Stars was sent into the world, Galileo had published no scientific work.⁴ His growing reputation in this period, before his discoveries through the telescope, rested partly on treatises and lectures circulated in manuscript, partly on his mechanical inventions (among them the thermoscope, a forerunner of the thermometer), and the instruments which he manufactured in large numbers with skilled artisans in his own workshop. But his truly great discoveries—such as the laws of motion of falling bodies and projectiles—and his ideas on cosmology he kept strictly for himself and for his private correspondents. Among these was Johannes Kepler.

3. The Church and the Copernican System

The first contact between the two Founding Fathers took place in 1597. Kepler was then twenty-six, a professor of mathematics in Gratz; Galileo was thirty-three, a professor of mathematics in Padua. Kepler had just completed his Cosmic Mystery and, profiting from a friend's journey to Italy, had sent copies of it, among others, "to a mathematician named Galileus Galileus, as he signs himself'.⁵

Galileo acknowledged the gift in the following letter:

Your book, my learned doctor, which you sent me through Paulus Amberger, I received not a few days but merely a few hours ago; since the same Paulus informed me of his impending return to Germany, I would be ungrateful indeed not to thank you at once: I accept your book the more gratefully as I regard it as proof of having been found worthy of your friendship. So far I have only perused the preface of your work, but from this I gained some notion of its intent [The preface (and first chapter) proclaim Kepler's belief in the Copernican system and outline his arguments in favour of it.], and I indeed congratulate myself on having an associate in the study of Truth who is a friend of Truth. For it is a misery that so few exist who pursue the Truth and do not pervert philosophical reason. However, this is not the place to deplore the miseries of our century but to congratulate you on the ingenious arguments you found in proof of the Truth. I will only add that I promise to read your book in tranquility, certain to find the most admirable things in it, and this I shall do the more gladly as I adopted the teaching of Copernicus many years ago, and his point of view enables me to explain many phenomena of nature which certainly remain inexplicable according to the more current hypotheses. I have written [conscripsi] many arguments in support of him and in refutation of the opposite view—which, however, so far I have not dared to bring into the public light, frightened by the fate of Copernicus himself, our teacher, who, though he acquired immortal fame with some, is yet to an infinite multitude of others (for such is the number of fools) an object of ridicule and derision. I would certainly dare to publish my reflections at once if more people like you existed; as they don't, I shall refrain from doing so.

There follow more polite affirmations of esteem, the signature "Galileus Galileus", and the date: 4 August, 1597.⁶

The letter is important for several reasons. Firstly, it provides conclusive evidence that Galileo had become a convinced Copernican in his early years. He was thirty-three when he wrote the letter; and the phrase "many years ago" indicates that his conversion took place in his twenties. Yet his first explicit public pronouncement in favour of the Copernican system was only made in 1613, a full sixteen years after his letter to Kepler, when Galileo was forty-nine years of age. Through all these years he not only taught, in his lectures, the old astronomy according to Ptolemy, but expressly repudiated Copernicus. In a treatise which he wrote for circulation among pupils and friends, of which a manuscript copy, dated 1606, survives,^6a he adduced all the traditional arguments against the earth's motion: that rotation would make it disintegrate, that clouds would be left behind, etc., etc.—arguments which, if the letter is to be believed, he himself had refuted many years before.

But the letter is also interesting for other reasons. In a single breath, Galileo four times evokes Truth: friend of Truth, investigating Truth, pursuit of Truth, proof of Truth; then apparently without awareness of the paradox, he calmly announces his intention to suppress Truth. This may partly be explained by the mores of late Renaissance Italy ("that age without a superego" as a psychiatrist described it); but taking that into account, one still wonders at the motives of his secrecy.

Why, in contrast to Kepler, was he so afraid of publishing his opinions? He had, at that time, no more reason to fear religious persecution than Copernicus had. The Lutherans, not the Catholics, had been the first to attack the Copernican system—which prevented neither Rheticus nor Kepler from defending it in public. The Catholics, on the other hand, were uncommitted. In Copernicus' own day, they were favourably inclined towards him—it will be remembered how Cardinal Schoenberg and Bishop Giese had urged him to publish his book. Twenty years after its publication, the Council of Trent re-defined Church doctrine and policy in all its aspects, but it had nothing to say against the heliocentric system of the universe. Galileo himself, as we shall see, enjoyed the active support of a galaxy of Cardinals, including the future Urban Vill, and of the leading astronomers among the Jesuits. Up to the fateful year 1616, discussion of the Copernican system was not only permitted, but encouraged by them—under the one proviso, that it should be confined to the language of science, and should not impinge on theological matters. The situation was summed up clearly in a letter from Cardinal Dini to Galileo in 1615: "One may write freely as long as one keeps out of the sacristy."⁷ This was precisely what the disputants failed to do, and it was at this point that the conflict began. But nobody could have foreseen these developments twenty years earlier, when Galileo wrote to Kepler.

Thus legend and hindsight combined to distort the picture, and gave rise to the erroneous belief that to defend the Copernican system as a working hypothesis entailed the risk of ecclesiastical disfavour or persecution. During the first fifty years of Galileo's lifetime, no such risk existed; and the thought did not even occur to Galileo. What he feared is clearly stated in his letter: to share the fate of Copernicus, to be mocked and derided; ridendus et explodendum—"laughed at and hissed off the stage" are his exact words. Like Copernicus, he was afraid of the ridicule both of the unlearned and the learned asses, but particularly of the latter: his fellow professors at Pisa and Padua, the stuffed shirts of the peripatetic school, who still considered Aristotle and Ptolemy as absolute authority. And this fear, as will be seen, was fully justified.

4. Early Quarrels

Young Kepler was delighted with Galileo's letter. On the first occasion when a traveller left Gratz for Italy, he answered in his impulsive manner:

Gratz, October 13, 1597.

Your letter, my most excellent humanist, which you wrote on August 4, I received on September 1; it caused me to rejoice twice: first because it meant the beginning of a friendship with an Italian; secondly, because of our agreement on the Copernican cosmography.… I assume that if your time has permitted it, you have by now become better acquainted with my little book, and I ardently desire to know your critical opinion of it; for it is my nature to press all to whom I write for their unvarnished opinion; and believe me, I much prefer even the most acrimonious criticism of a single enlightened man to the unreasoned applause of the common crowd.

I would have wished, however, that you, possessed of such an excellent mind, took up a different position. With your clever secretive manner you underline, by your example, the warning that one should retreat before the ignorance of the world, and should not lightly provoke the fury of the ignorant professors; in this respect you follow Plato and Pythagoras, our true teachers. But considering that in our era, at first Copernicus himself and after him a multitude of learned mathematicians have set this immense enterprise going so that the motion of the earth is no longer a novelty, it would be preferable that we help to push home by our common efforts this already moving carriage to its destination.… You could help your comrades, who labour under such iniquitous criticism, by giving them the comfort of your agreement and the protection of your authority. For not only your Italians refuse to believe that they are in motion because they do not feel it; here in Germany, too, one does not make oneself popular by holding such opinions. But there exist arguments which protect us in the face of these difficulties.… Have faith, Galilii, and come forward! If my guess is right, there are but few among the prominent mathematicians of Europe who would wish to secede from us: for such is the force of Truth. If your Italy seems less advantageous to you for publishing [your works] and if your living there is an obstacle, perhaps our Germany will allow us to do so. But enough of this. Let me know, at least privately if you do not want to do it in public, what you have discovered in support of Copernicus.…

Kepler then confessed that he had no instruments, and asked Galileo whether he had a quadrant sufficiently precise to read quarter-minutes of arc; if so, would Galileo please make a series of observations to prove that the fixed stars show small seasonal displacements—which would provide direct proof of the earth's motion.

Even if we could detect no displacement at all, we would nevertheless share the laurels of having investigated a most noble problem which nobody has attacked before us. Sat Sapienti.… Farewell, and answer me with a very long letter.⁸

Poor, naïve Kepler! It did not occur to him that Galileo might take offence at his exhortations, and regard them as an implied reproach of cowardice. He waited in vain for an answer to his exuberant overtures. Galileo withdrew his feelers; for the next twelve years, Kepler did not hear from him.

But from time to time unpleasant rumours reached him from Italy. Among Kepler's admirers was a certain Edmund Bruce, a sentimental English traveller in Italy, amateur philosopher and science snob, who loved to rub shoulders with scholars and to spread gossip about them. In August 1602, five years after Galile o had broke n off their correspondence, Bruce wrote Kepler from Florence that Magini (the professor of astronomy at Bologna) had assured him of his love and admiration of Kepler, whereas Galileo had admitted to him, Bruce, having received Kepler's Mysterium, but had denied this to Magini.

I scolded Galileo for his scant praise of you, for I know for certain that he lectures on your and his own discoveries to his pupils and others. I, however, act and shall always act in a manner which serves not his fame, but yours.⁹

Kepler could not be bothered to answer this busybody, but a year later—21 August, 1603—Bruce wrote again, this time from Padua:

If you knew how often and how much I discuss you with all the savants of Italy you would consider me not only an admirer but a friend. I spoke with them of your admirable discoveries in music, of your studies of Mars, and explained to them your Mysterium which they all praise. They wait impatiently for your future works.… Galileo has your book and teaches your discoveries as his own.… ¹⁰

This time Kepler did answer. After apologizing for the delay and declaring himself delighted with Bruce's friendship, he continued:

But there is something about which I wish to warn you. Do not form a higher opinion of me, and do not induce others to do so, than my achievements are able to justify.… For you certainly understand that betrayed expectations lead eventually to contempt. I wish in no way to restrain Galileo from claiming, what is mine, as his own. My witnesses are the bright daylight and time.¹¹

The letter ends with "Greetings to Magini and Galileo".

Bruce's accusations should not be taken seriously. In fact, the opposite is true: the trouble with Galileo was not that he appropriated Kepler's discoveries—but that he ignored them, as we shall see. But the episode nevertheless sheds some additional light on the relations between the two men. Though Bruce cannot be trusted on points of fact, the inimical attitude of Galileo to Kepler emerges clearly from Bruce's letters. It fits in with the fact that he broke off the correspondence, and with later events.

Kepler, on the other hand, who had good reason to be offended by Galileo's silence, could easily have been provoked by Bruce's scandal-mongering into starting one of those juicy quarrels between scholars which were the order of the day. He was suspicious and excitable enough, as his relations with Tycho have shown. But towards Galileo he always behaved in an oddly generous way. It is true that they lived in different countries and never met personally; but hatred, like gravity, is capable of action at a distance. The reason for Kepler's forbearingness was perhaps that he had no occasion to develop an inferiority complex towards Galileo.

The year after the Bruce episode, in October 1604, a bright new star appeared in the constellation Serpentarius. It caused even more excitement than Tycho's famous nova of 1572, because its appearance happened to coincide with a so-called great conjunction of Jupiter, Saturn and Mars in the "fiery triangle"—a gala performance that occurs only once in every eight hundred years. Kepler's book De Stella Nova (1606) was primarily concerned with its astrological significance; but he showed that the nova, like the previous one, must be located in the "immutable" region of the fixed stars, and thus drove another nail into the coffin of the Aristotelian universe. The star of 1604 is still called "Kepler's nova" [John Donne referred to Kepler's nova when he wrote (To the Countesse of Huntingdon): Who vagrant transitory Comets sees, [/] Wonders, because they are rare: but a new starre [/] Whose motion with the firmament agrees, [/] Is miracle, for there no new things are].

Galileo, too, observed the new star, but published nothing about it. He gave three lectures on the subject, of which only fragments are preserved; he, too, seems to have denied the contention of the Aristotelians that it was a meteor or some other sublunary phenomenon, but could not have gone much further, since his lectures in defence of Ptolemy were still circulated two years later.¹²

Between 1600 and 1610, Kepler published his Optics (1604), the New Astronomy (1609) and a number of minor works. In the same period, Galileo worked on his fundamental researches into free fall, the motion of projectiles, and the laws of the pendulum, but published nothing except a brochure containing instructions for the use of the so-called military or proportional compass. This was an invention made in Germany some fifty years earlier,¹³ which Galileo had improved, as he improved a number of other gadgets that had been known for a long time. Out of this minor publication¹⁴ developed the first of the futile and pernicious feuds which Galileo was to wage all his life.

It began when a mathematician named Balthasar Capra in Padua published, a year after Galileo, another brochure of instructions for the use of the proportional compass.¹⁵ Galileo's Instructions were in Italian, Capra's in Latin; both referred to the same subject, which interested only military engineers and technicians. It is very likely that Capra had borrowed from Galileo's Instructions without naming him; on the other hand, Capra showed that some of Galileo's explanations were mathematically erroneous, but again without naming him. Galileo's fury knew no bounds. He published a pamphlet Against the Calumnies and Impostures of Balthasar Capra, etc. (Venice 1607), in which that unfortunate man and his teacher¹⁶ were described as "that malevolent enemy of honour and of the whole of mankind", "a venom-spitting basilisque", "an educator who bred the young fruit on his poisoned soul with stinking ordure", "a greedy vulture, swooping at the unborn young to tear its tender limbs to pieces", and so on. He also obtained from the Venetian Court the confiscation, on the grounds of plagiarism, of Capra's Instructions. Not even Tycho and Ursus had sunk to such fish-wife language; yet they had fought for the authorship of a system of the universe, not of a gadget for military engineers.

In his later polemical writings, Galileo's style progressed from coarse invective to satire, which was sometimes cheap, often subtle, always effective. He changed from the cudgel to the rapier, and achieved a rare mastery of it; while in the purely expository passages his lucidity earned him a prominent place in the development of Italian didactic prose. But behind the polished façade, the same passions were at work which had exploded in the affair of the proportional compass: vanity, jealousy and self-righteousness combined into a demoniac force, which drove him to the brink of self-destuction. He was utterly devoid of any mystical, contemplative leanings, in which the bitter passions could from time to time be resolved; he was unable to transcend himself and find refuge, as Kepler did in his darkest hours, in the cosmic mystery. He did not stand astride the watershed; Galileo is wholly and frighteningly modern.

5. The Impact of the Telescope

It was the invention of the telescope which brought Kepler and Galileo, each travelling along his own orbit, to their closest conjunction. To pursue the metaphor, Kepler's orbit reminds one of the parabola of comets which appear from infinity and recede into it; Galileo's as an eccentric ellipse, closed upon itself.

The telescope was, as already mentioned, not invented by Galileo. In September 1608, a man at the annual Frankfurt fair offered a telescope for sale which had a convex and a concave lens, and magnified seven times. On 2 October, 1608, the spectacle-maker Johann Lippershey of Middleburg claimed a licence for thirty years from the Estates General of the Netherlands for manufacturing telescopes with single and double lenses. In the following month, he sold several of these, for three hundred and six hundred gilders respectively, but was not granted an exclusive licence because in the meantime two other men had claimed the same invention. Two of Lippershey's instruments were sent as a gift by the Dutch Government to the King of France; and in April 1609, telescopes could be bought in spectacle-makers' shops in Paris. In the summer of 1609, Thomas Harriot in England made telescopic observations of the moon and drew maps of the lunar surface. In the same year, several of the Dutch telescopes found their way to Italy and were copied there.

Galileo himself claimed in the Messenger from the Stars that he had merely read reports of the Dutch invention, and that these had stimulated him to construct an instrument on the same principle, which he succeeded in doing "through deep study of the theory of refraction". Whether he actually saw and handled one of the Dutch instruments brought to Italy is a question without importance, for once the principle was known, lesser minds than Galileo's could and did construct similar gadgets. On 8 August, 1609, he invited the Venetian Senate to examine his spy-glass from the tower of St. Marco, with spectacular success; three days later, he made a present of it to the Senate, accompanied by a letter in which he explained that the instrument, which magnified objects nine times, would prove of utmost importance in war. It made it possible to see "sails and shipping that were so far off that it was two hours before they were seen with the naked eye, steering full-sail into the harbour",¹⁷ thus being invaluable against invasion by sea. It was not the first and not the last time that pure research, that starved cur, snapped up a bone from the warlords' banquet.

The grateful Senate of Venice promptly doubled Galileo's salary to a thousand scudi per year, and made his professorship at Padua (which belonged to the Republic of Venice) a lifelong one. It did not take the local spectacle-makers long to produce telescopes of the same magnifying power, and to sell in the streets for a few scudi an article which Galileo had sold the Senate for a thousand a year—to the great amusement of all good Venetians. Galileo must have felt his reputation threatened, as in the affair of the military compass; but, fortunately, this time his passion was diverted into more creative channels. He began feverishly to improve his telescope, and to aim it at the moon and stars, which previously had attracted him but little. Within the next eight months he succeeded, in his own words: "by sparing neither labour nor expense, in constructing for myself an instrument so superior that objects seen through it appear magnified nearly a thousand times, and more than thirty times nearer than if viewed by the natural powers of sight alone."

The quotation is from Sidereus Nuncius, the Messenger from the Stars, published in Venice in March 1610. It was Galileo's first scientific publication, and it threw his telescopic discoveries like a bomb into the arena of the learned world. It not only contained news of heavenly bodies "which no mortal had seen before"; it was also written in a new, tersely factual style which no scholar had employed before. So new was this language that the sophisticated Imperial Ambassador in Venice described the Star Messenger as "a dry discourse or an inflated boast, devoid of all philosophy".¹⁸ In contrast to Kepler's exuberant baroque style, some passages of the Sidereus Nuncius would almost qualify for the austere pages of a contemporary "Journal of Physics".

The whole booklet has only twenty-four leaves in octavo. After the introductory passages, Galileo described his observations of the moon, which led him to conclude:

that the surface of the moon is not perfectly smooth, free from inequalities and exactly spherical, as a large school of philosophers considers with regard to the moon and the other heavenly bodies, but that, on the contrary, it is full of irregularities, uneven, full of hollows and protuberances, just like the surface of the earth itself, which is varied everywhere by lofty mountains and deep valleys.

He then turned to the fixed stars, and described how the telescope added, to the moderate numbers that can be seen by the naked eye, "other stars, in myriads, which have never been seen before, and which surpass the old, previously known stars in number more than ten times." Thus, for instance, to the nine stars in the belt and sword of Orion he was able to add eighty others which he discovered in their vicinity; and to the seven in the Pleiades, another thirty-six. The Milky Way dissolved before the telescope into "a mass of innumerable stars planted together in clusters"; and the same happened when one looked at the luminous nebulae.

But the principal sensation he left to the end:

There remains the matter which seems to me to deserve to be considered the most important in this work, namely, that I should disclose and publish to the world the occasion of discovering and observing four planets, never seen from the very beginning of the world up to our own times.

The four new planets were the four moons of Jupiter, and the reason why Galileo attributed to their discovery such capital importance he explained in a somewhat veiled aside:

Moreover, we have an excellent and exceedingly clear argument to put at rest the scruples of those who can tolerate the revolution of the planets about the sun in the Copernican system, but are so disturbed by the revolution of the single moon around the earth while both of them describe an annual orbit round the sun, that they consider this theory of the universe to be impossible.

In other words, Galileo thought the main argument of the anti-Copernicansto be the impossibility of the moon's composite motion around the earth, and with the earth around the sun; and further believed that this argument would be invalidated by the composite motion of the four Jupiter moons. It was the only reference to Copernicus in the whole booklet, and it contained no explicit commitment. Moreover, it ignored the fact that in the Tychonic system all the planets describe a composite motion around the sun and with the sun around the earth; and that even in the more limited "Egyptian" system at least the two inner planets do this.

Thus Galileo's observations with the telescope produced no important arguments in favour of Copernicus, nor any clear committal on his part. Besides, the discoveries announced in the Star Messenger were not quite as original as they pretended to be. He was neither the first, nor the only scientist, who had turned a telescope at the sky and discovered new wonders with it. Thomas Harriot made systematic telescopic observations and maps of the moon in the summer of 1609, before Galileo, but he did not publish them. Even the Emperor Rudolph had watched the moon through a telescope before the he had heard of Galileo. Galileo's star maps were so inaccurate that the Pleiades group can only be identified on them with difficulty, the Orion group not at all; and the huge dark spot under the moon's equator, surrounded by mountains, which Galileo compared to Bohemia, simply does not exist.

Yet when all this is said, and all the holes are picked in Galileo's first published text, its impact and significance still remain tremendous. Others had seen what Galileo saw, and even his priority in the discovery of the Jupiter moons is not established beyond doubt^18a; yet he was the first to publish what he saw, and to describe it in a language which made everybody sit up. It was the cumulative effect which made the impact; the vast philosophical implications of this further prizing-open of the universe were instinctively felt by the reader, even if they were not explicitly stated. The mountains and valleys of the moon confirmed the similarity between heavenly and earthly matter, the homogeneous nature of the stuff from which the universe is built. The unsuspected number of invisible stars made an absurdity of the notion that they were created for man's pleasure, since he could only see them armed with a machine. The Jupiter moons did not prove that Copernicus was right, but they did further shake the antique belief that the earth was the centre of the world around which everything turned. It was not this or that particular detail, but the total contents of the Messenger from the Stars which created the dramatic effect.

The booklet aroused immediate and passionate controversy. It is curious to note that Copernicus' Book of Revolutions had created little stir for half a century, and Kepler's Laws even less at their time, while the Star Messenger, which had only an indirect bearing on the issue, caused such an outburst of emotions. The main reason was, no doubt, its immense readability. To digest Kepler's magnum opus required, as one of his colleagues remarked, "nearly a lifetime"; but the Star Messenger could be read in an hour, and its effect was like a punch in the solar plexus on those grown up in the traditional view of the bounded universe. And that vision, though a bit shaky, still retained an immense, reassuring coherence. Even Kepler was frightened by the wild perspective opened up by Galileo's spyglass: "The infinite is unthinkable," he repeatedly exclaimed in anguish.

The shock-waves of Galileo's message spread immediately, as far as England. It was published in March 1610; Donne's Ignatius was published barely ten months later,¹⁹ but Galileo (and Kepler) are repeatedly mentioned in it:

I will write [quoth Lucifer] to the Bishop of Rome:
He shall call Galileo the Florentine to him …

But soon, the satirical approach yielded to the metaphysical, to a full realization of the new cosmic perspective:

Man has weav'd out a net, and this net throwne
Upon the Heavens, and now they are his owne …

Milton was still an infant in 1610; he grew up with the new wonders. His awareness of the "vast unbounded Deep" which the telescope disclosed, reflects the end of the medieval walled universe:

Before [his] eyes in sudden view appear
The secrets of the hoary Deep—a dark
Illimitable ocean, without bound,
Without dimension …²⁰

6. The Battle of the Satellites

Such was the objective impact on the world at large of Galileo's discoveries with his "optick tube". But to understand the reactions of the small, academic world in his own country, we must also take into account the subjective effect of Galileo's personality. Canon Koppernigk had been a kind of invisible man throughout his life; nobody who met the disarming Kepler, in the flesh or by correspondence, could seriously dislike him. But Galileo had a rare gift of provoking enmity; not the affection alternating with rage which Tycho aroused, but the cold, unrelenting hostility which genius plus arrogance minus humility creates among mediocrities.

Without this personal background, the controversy which followed the publication of the Sidereus Nuncius would remain incomprehensible. For the subject of the quarrel was not the significance of the Jupiter satellites, but their existence—which some of Italy's most illustrious scholars flatly denied. Galileo's main academic rival was Magini in Bologna. In the month following the publication of the Star Messenger, on the evenings of 24 and 25 April, 1610, a memorable party was held in a house in Bologna, where Galileo was invited to demonstrate the Jupiter moons in his spy-glass. Not one among the numerous and illustrious guests declared himself convinced of their existence. Father Clavius, the leading mathematician in Rome, equally failed to see them; Cremonini, teacher of philosophy at Padua, refused even to look into the telescope; so did his colleague Libri. The latter, incidentally, died soon afterwards, providing Galileo with an opportunity to make more enemies with the much quoted sarcasm: "Libri did not choose to see my celestial trifles while he was on earth; perhaps he will do so now he has gone to Heaven."

These men may have been partially blinded by passion and prejudice, but they were not quite as stupid as it may seem. Galileo's telescope was the best available, but it was still a clumsy instrument without fixed mountings, and with a visual field so small that, as somebody has said, "the marvel is not so much that he found Jupiter's moons, but that he was able to find Jupiter itself." The tube needed skill and experience in handling, which none of the others possessed. Sometimes, a fixed star appeared in duplicate. Moreover, Galileo himself was unable to explain why and how the thing worked; and the Sidereus Nuncius was conspicuously silent on this essential point. Thus it was not entirely unreasonable to suspect that the blurred dots which appeared to the strained and watering eye pressed to the spectacle-sized lens, might be optical illusions in the atmosphere, or somehow produced by the mysterious gadget itself. This, in fact, was asserted in a sensational pamphlet, Refutation of the Star Messenger,²⁰ published by Magini's assistant, a young fool called Martin Horky. The whole controversy about optical illusions, haloes, reflections from luminous clouds, and about the unreliability of testimonies, inevitably reminds one of a similar controversy three hundred years later: the flying saucers. Here, too, emotion and prejudice combined with technical difficulties against clear-cut conclusions. And here, too, it was not unreasonable for self-respecting scholars to refuse to look at the photographic "evidence" for fear of making fools of themselves. Similar considerations may be applied to the refusal of otherwise open-minded scholars to get involved in the ambiguous phenomena of occult seances. The Jupiter moons were no less threatening to the outlook on the world of sober scholars in 1610, than, say, extra-sensory perception was in 1950.

Thus, while the poets were celebrating Galileo's discoveries which had become the talk of the world, the scholars in his own country were, with very few exceptions, hostile or sceptical. The first, and for some time the only, scholarly voice raised in public in defence of Galileo, was Johannes Kepler's.

7. The Shield Bearer

It was also the weightiest voice, for Kepler's authority as the first astronomer of Europe was uncontested—not because of his two Laws, but by virtue of his position as Imperial Mathematicus and successor to Tycho. John Donne, who had a grudging admiration for him, has summed up Kepler's reputation "who (as himselfe testifies of himselfe) ever since Tycho Brahe's death hath received it into his care, that no new thing should be done in heaven without his knowledge."²¹

The first news of Galileo's discovery had reached Kepler when Wackher von Wackenfeld called on him on or around 15 March, 1610. The weeks that followed he spent in feverish expectation of more definite news. In the first days of April, the Emperor received a copy of the Star Messenger which had just been published in Venice, and Kepler was graciously permitted "to have a look and rapidly glance through it". On 8 April, at last, he received a copy of his own from Galileo, accompanied by a request for his opinion.

Galileo had never answered Kepler's fervent request for an opinion on the Mysterium, and had remained equally silent on the New Astronomy. Nor did he bother to put his own request for Kepler's opinion on the Star Messenger into a personal letter. It was transmitted to Kepler verbally by the Tuscan Ambassador in Prague, Julian de Medici. Although Kepler was not in a position to verify Galileo's disputed discoveries, for he had no telescope, he took Galileo's claims on trust. He did it enthusiastically and without hesitation, publicly offering to serve in the battle as Galileo's "squire" or "shield bearer"—he, the Imperial Mathematicus to the recently still unknown Italian scholar. It was one of the most generous gestures in the sour annals of science.

The courier for Italy was to leave on 19 April; in the eleven days at his disposal Kepler wrote his pamphlet Conversation with the Star Messenger in the form of an open letter to Galileo. It was printed the next month in Prague, and a pirated Italian translation appeared shortly afterwards in Florence.

It was precisely the support that Galileo needed at that moment. The weight of Kepler's authority played an important part in turning the tide of the battle in his favour, as shown by Galileo's correspondence. He was anxious to leave Padua and to be appointed Court Mathematician to Cosimo de Medici, Grand Duke of Tuscany, in whose honour he had called Jupiter's planets "the Medicean stars". In his application to Vinta, the Duke's Secretary of State, Kepler's support figures prominently:

Your Excellency, and their Highnesses through you, should know that I have received a letter—or rather an eight-page treatise—from the Imperial Mathematician, written in approbation of every detail contained in my book without the slightest doubt or contradiction of anything. And you may believe that this is the way leading men of letters in Italy would have spoken from the beginning if I had been in Germany or somewhere far away.²²

He wrote in almost identical terms to other correspondents, among them to Matteo Carosio in Paris:

We were prepared for it that twenty-five people would wish to refute me; but up to this moment I have seen only one statement by Kepler, the Imperial Mathematician, which confirms everything that I have written, without rejecting even an iota of it; which statement is now being reprinted in Venice, and you shall soon see it.²³

Yet, while Galileo boasted about Kepler's letter to the Grand Duke and his correspondents, he neither thanked Kepler nor even acknowledged it.

Apart from its strategical importance in the cosmological battle, the Conversation with the Star Messenger is without much scientific value; it reads like a baroque arabesque, a pattern of amusing doodles around the hard core of Galileo's treatise. It starts with Kepler voicing his hope that Galileo, whose opinion matters to him more than anybody's, would comment on the Astronomia Nova, and thereby renew a correspondence "laid aside twelve years ago". He relates with gusto how he had received the first news of the discoveries from Wackher—and how he had worried whether the Jupiter moons could be fitted into the universe built around the five Pythagorean solids. But as soon as he had cast a glance at the Star Messenger, he realized that "it offered a highly important and wonderful show to astronomers and philosophers, that it invited all friends of true philosophy to contemplate matters of the highest import.… Who could be silent in the face of such a message? Who would not feel himself overflow with the love of the Divine which is so abundantly manifested here?" Then comes his offer of support "in the battle against the grumpy reactionaries, who reject everything that is unknown as unbelievable, and regard everything that departs from the beaten track of Aristotle as a desecration.… Perhaps I shall be considered reckless because I accept your claims as true without being able to add my own observations. But how could I distrust a reliable mathematician whose art of language alone demonstrates the straightness of his judgement? …"

Kepler had instinctively felt the ring of truth in the Star Messenger, and that had settled the question for him. However. much he may have resented Galileo's previous behaviour, he felt committed "to throw himself into the fray" for Truth, Copernicus and the Five Perfect Solids. For, having finished the Promethean labours of the New Astronomy, he was again steeped in the mystic twilight of a Pythagorean universe built around cube, tetrahedra, dodecahedra, and so on. They are the leitmotif of his dialogue with the Star Messenger; neither the elliptical orbits, neither the First nor the Second Law, are mentioned even once. Their discovery appeared to him merely as a tedious detour in the pursuit of his idee fixe.

It is a rambling treatise, written by a hurried pen which jumps from one subject to another: astrology, optics, the moon's spots, the nature of the ether, Copernicus, the habitability of other worlds, interplanetary travel:

There will certainly be no lack of human pioneers when we have mastered the art of flight. Who would have thought that navigation across the vast ocean is less dangerous and quieter than in the narrow, threatening gulfs of the Adriatic, or the Baltic, or the British straits? Let us create vessels and sails adjusted to the heavenly ether, and there will be plenty of people unafraid of the empty wastes. In the meantime, we shall prepare, for the brave sky-travellers, maps of the celestial bodies—I shall do it for the moon, you Galileo, for Jupiter.

Living in an atmosphere saturated with malice, Professors Magini, Horky, and even Maestlin, could not believe their ears when they heard Kepler singing Galileo's praises, and tried to discover some hidden sting in the treatise. They gloated over a passage in which Kepler showed that the principle of the telescope had been outlined twenty years before by one of Galileo's countrymen, Giovanni Della Porta, and by Kepler himself in his work on optics in 1604. But since Galileo did not claim the invention of the telescope, Kepler's historical excursion could not be resented by him; moreover, Kepler emphasized that Della Porta's and his own anticipations were of a purely theoretical nature "and cannot diminish the fame of the inventor, whoever it was. For I know what a long road it is from a theoretical concept to its practical achievement, from the mention of the antipodes in Ptolemy to Columbus' discovery of the New World, and even more from the two-lensed instruments used in this country to the instrument with which you, 0 Galilee, penetrated the very skies."

In spite of this, the German envoy in Venice, Georg Fugger, wrote with relish that Kepler had "torn the mask off Galileo's face",²⁴ and Francis Stelluti (a member of the Lincean Academy) wrote to his brother: "According to Kepler, Galileo makes himself out to be the inventor of the instrument, but more than thirty years ago Della Porta described it in his Natural Magic … And so poor Galileo will look foolish."²⁵ Horky also quoted Kepler in his much read pamphlet against Galileo, whereupon Kepler immediately informed Horky that "since the demands of honesty have become incompatible with my friendship for you, I hereby terminate the latter",²⁶ and offered Galileo to publish the rebuke; but when the youngster relented, he forgave him.

These reactions indicate the extent of dislike for Galileo in his native Italy. But whatever hidden irony the scholars had imputed to Kepler's Dissertatio, the undeniable fact was that the Imperial Mathematicus had expressly endorsed Galileo's claims. This persuaded some of Galileo's opponents, who had previously refused to take him seriously, to look for themselves through improved telescopes which were now becoming available. The first among the converts was the leading astronomer in Rome, the Jesuit Father Clavius. In the sequel, the Jesuit scholars in Rome not only confirmed Galileo's observations, but considerably improved on them.

8. The Parting of the Orbits

Galileo's reaction to the service Kepler had rendered him was, as we saw, complete silence. The Tuscan Ambassador at the Imperial Court urgently advised him to send Kepler a telescope to enable him to verify, at least post factum, Galileo's discoveries which he had accepted on trust. Galileo did nothing of the sort. The telescopes which his workshop turned out he donated to various aristocratic patrons.

Four months thus went by, Horky's pamphlet was published, the controversy had reached its peak, and so far not a single astronomer of repute had publicly confirmed having seen the moons of Jupiter. Kepler's friends began to reproach him for having testified to what he himself had not seen; it was an impossible situation.^26a On 9 August, he again wrote to Galileo:

… You have aroused in me a great desire to see your instrument so that at last I too can enjoy, like yourself, the spectacle of the skies. For among the instruments at our disposal here the best magnifies only ten times, the others hardly thrice.… ²⁷

He talked about his own observations of Mars and the moon, expressed his indignation at Horky's knavery; and then continued:

The law demands that everybody should be trusted unless the contrary is proven. And how much more is this the case when the circumstances warrant trustworthiness. In fact, we are dealing not with a philosophical but with a legal problem: did Galileo deliberately mislead the world by a hoax? …

I do not wish to hide from you that letters have reached Prague from several Italians who deny that those planets can be seen through your telescope.

I am asking myself how it is possible that so many deny [their existence], including those who possess a telescope … Therefore I ask you, my Galileo, nominate witnesses for me as soon as possible. From various letters written by you to third persons I have learnt that you do not lack such witnesses. But I am un-able to name any testimony except your own.… ^27a

This time Galileo hurried to answer, evidently scared by the prospect of losing his most powerful ally:

Padua, August 19, 1610.

I have received both your letters, my most learned Kepler. The first, which you have already published, I shall answer in the second edition of my observations. In the meantime, I wish to thank you for being the first, and almost the only, person who completely accepted my assertions, though you had no proof, thanks to your frank and noble mind.²⁸

Galileo went on to tell Kepler that he could not lend him his telescope, which magnified a thousandfold, because he had given it to the Grand Duke who wished "to exhibit it in his gallery as an eternal souvenir among his most precious treasures". He made various excuses about the difficulty of constructing instruments of equal excellence, ending with the vague promise that he would, as soon as possible, make new ones "and send them to my friends". Kepler never received one.

In the next paragraph, Horky and the vulgar crowd came in for some more abuse; "but Jupiter defies both giants and pygmies; Jupiter stands in the sky, and the sycophants may bark as they wish". Then he turned to Kepler's request for witnesses, but still could not name a single astronomer; "In Pisa, Florence, Bologna, Venice and Padua, a good many have seen [the Medicean stars] but they are all silent and hesitate." Instead, he named his new patron, the Grand Duke, and another member of the Medici family (who could hardly be expected to deny the existence of stars named after them). He continued:

As a further witness I offer myself, who have been singled out by our University for a lifelong salary of a thousand florins, such as no mathematician has ever enjoyed, and which I would continue to receive forever even if the Jupiter moons were to deceive us and vanish.

After complaining bitterly about his colleagues "most of whom are incapable of identifying either Jupiter or Mars, and hardly even the moon", Galileo concluded:

What is to be done? Let us laugh at the stupidity of the crowd, my Kepler.… I wish I had more time to laugh with you. How you would shout with laughter, my dearest Kepler, if you were to hear what the chief philosophers of Pisa said against me to the Grand Duke.… But the night has come and I can no longer converse with you.…

This is the second, and last, letter which Galileo ever wrote to Kepler.²⁹ The first, it will be remembered, was written thirteen years earlier, and its theme-song had been the perversity of philosophers and the stupidity of the crowd, concluding with the wistful remark "if only more people like Kepler existed". Now, writing for the first time after these thirteen years, he again singled out Kepler as a unique ally to laugh with him at the foolishness of the world. But concerning the quandary into which his loyal ally had got himself, the letter was as unhelpful as could be. It contained not a word on the progress of Galileo's observations, about which Kepler was burning to hear; and it made no mention of an important new discovery which Galileo had made, and which he had communicated, about a fortnight earlier, to the Tuscan Ambassador in Prague.³⁰ The communication ran as follows:

SMAISMRMILMEPOETALEUMIBUNENUGTTAURPAS.

This meaningless sequence of letters was an anagram made up from the words describing the new discovery. The purpose behind it was to safeguard the priority of the find without disclosing its content, lest somebody else might claim it as his own. Ever since the affair of the proportional compass, Galileo had been very anxious to ascertain the priority of his observations—even, as we shall hear, in cases where the priority was not his. But whatever his motives in general, they can hardly excuse the fact that he asked the Tuscan Ambassador to dangle the puzzle before the tantalized eyes of Kepler, whom he could not suspect of intending to steal his discovery.

Poor Kepler tried to solve the anagram, and patiently transformed it into what he himself called a "barbaric Latin verse": "Salve umbistineum geminatum Martia proles"—"Hail, burning twin, offspring of Mars."³¹ He accordingly believed that Galileo had discovered moons around Mars, too. Only three months later, on 13 November, did Galileo condescend to disclose the solution—not, of course, to Kepler, but to Rudolph, because Julian de Medici informed him that the Emperor's curiosity was aroused.

The solution was: "Altissimum planetam tergeminum observavi"—"I have observed the highest planet [Saturn] in triplet form". Galileo's telescope was not powerful enough to disclose Saturn's rings (they were only seen half a century later by Heuygens); he believed Saturn to have two small moons on opposite sides, and very close to the planet.

A month later, he sent another anagram to Julian de Medici: "Haec immatura a me jam frustra legunturoy"—"These immature things I am searching for now in vain". Once again Kepler tried several solutions, among them: "Macula rufa in Jove est gyratur mathem, etc." ["There is a red spot in Jupiter which rotates mathematically."] then wrote to Galileo in exasperation:

I beseech you not to withhold from us the solution for long. You must see that you are dealing with honest Germans … consider what embarrassment your silence causes me.³²

Galileo disclosed his secret a month later—again not directly to Kepler, but to Julian de Medici: "Cynthiae figuras aemulatur mater amorum"—"The mother of love [Venus] emulates the shapes of Cynthia [the moon]." Galileo had discovered that Venus, like the moon, showed phases—from sickle to full disc and back—a proof that she revolved around the sun. He also considered this as proof of the Copernican system—which it was not, for it equally fitted the Egyptian or the Tychonic system.

In the meantime, Kepler's dearest wish: to see for himself the new marvels, was at last fulfilled. One of Kepler's patrons, the Elector Ernest of Cologne, Duke of Bavaria, was among the select few whom Galileo had honoured with the gift of a telescope. In the summer of 1610, Ernest was in Prague on affairs of state, and for a short period lent his telescope to the Imperial Mathematicus. Thus from 3 August to 9 September, Kepler was able to watch the Jupiter moons with his own eyes. The result was another short pamphlet, Observation-Report on Jupiter's Four Wandering Satellites,³³ in which Kepler confirmed, this time from first-hand experience, Galileo's discoveries. The treatise was immediately reprinted in Florence, and was the first public testimony by independent, direct observation, of the existence of the Jupiter moons. It was also the first appearance in history of the term "satellite" which Kepler had coined in a previous letter to Galileo.³⁴

At this point the personal contact between Galileo and Kepler ends. For a second time Galileo broke off their correspondence. In the subsequent months, Kepler wrote several more letters, which Galileo left unanswered, or answered indirectly by messages via the Tuscan Ambassador. Galileo wrote to Kepler only once during this whole period of the "meeting of their orbits": the letter of 19 August, 1610, which I have quoted. In his works he rarely mentions Kepler's name, and mostly with intent to refute him. Kepler's three Laws, his discoveries in optics, and the Keplerian telescope, are ignored by Galileo, who firmly defended to the end of his life circles and epicycles as the only conceivable from of heavenly motion.

Notes

¹ F. Sherwood Taylor, Galileo and the Freedom of Thought (London, 1938), p. 1.

² This is strictly true for small angles only, but sufficient for practical purposes of time-measurement. The correct law of the pendulum was discovered by huygens.

The Candelabra still shown at the Cathedral of Pisa, whose oscillations are alleged to have given Galileo his idea, was only installed several years after the discovery.

³ His manuscript treatise De Motu, written about 1590, and privately circulated, certainly deviates from Aristotelian physics, but by subscribing to the entirely respectable theory of impetus which had been taught by the Paris school in the fifteenth century and by several of Galileo's predecessors and contemporaries. Cf. A. Koyre, Etudes Galileennes (Paris, 1939).

⁴ About his technical treatise on the proportional compass, see below.

⁵ Letter to Maestlin, September 1597, G.W., Vol. XIll, p. 140 seq.

⁶ G.W., Vol. XIII, p. 130 f.

^6aTrattato della Sfera, Opera, Ristampa della Ediz. Nazionale (Florence, 1929-39), Vol. ll, pp. 203-255. Henceforth "Opere" refers to this edition, except when marked "Ed. F. Flora", which refers to the handier selection of works and letters in one volume, published in 1953.

⁷ Quoted by Sherwood Taylor, op. cit., p. 85.

⁸ G.W., Vol. XIII, p. 144 seq.

⁹ G.W., Vol. XIV, p. 256.

¹⁰ Ibid., p. 441.

¹¹ Ibid., p. 444 f.

¹² It is surprising to read that Prof. Charles Singer attributes the discovery that the nova of 1604 had no parallax to galileo, and moreover, passing in silence over Tycho's classic book on the nova of 1572, writes:

New stars when previously noticed had been considered to belong to the lower and less perfect regions near the earth. Galileo had thus attacked the incorruptible and interchangeable heavens and had delivered a blow to the Aristotelian scheme, wellnigh as serious as the experiment on the tower of Pisa (sic)." (Ch. Singer, A Short History of Science to the Nineteenth Century, Oxford, 1941, p. 206.)

Since that experiment is also legendary, Prof. Singer's comparison contains an ironic truth; but this triple misstatement is characteristic of the power of the Galileo myth over some eminent historians of science. Prof. Singer also seems to believe that Galileo invented the telescope (op. cit., 217), that in Tycho's system "the sun revolves round the earth in twenty-four hours carrying all the planets with it" (ibid., p. 183), that Kepler's Third Law was "enunciated in the Epitome Astronomiae" (ibid., p. 205), etc.

¹³ Cf. Zinner, op. cit., p. 514.

¹⁴Le Operazioni delle Compasso Geometrico e Militare, Padova, 1606; Opere 11, pp. 362-405.

¹⁵Usus et Fabrica Ciriui Cuiusdam Proporziones, Padova, 1607; Opere 11, pp. 425-511.

¹⁶ Capra's teacher was the distinguished astronomer Simon Marius (1573-1624), discoverer of the Andromeda Nebula, with whom Galileo later became involved in another priority quarrel. See [The Sleepwalkers: A History of Man's Changing Vision of the Universe, by Arthur Koestler, The Macmillan Company, 1959], p. 468.

¹⁷ Letter to B. Landucci, quoted by [Karl von] Gebler, Galileo Galilei and the Roman Curia, London, 1879, p. 19.

¹⁸ George Fugger (a member of the famous banker's family) in a letter to Kepler, 16.4.1610, G.W., Vol. XVI, p. 302.

^18a Cf Zinner, op. cit., p. 345 f

¹⁹ This refers to the first, Latin edition.

²⁰Paradise Lost, book ii, 1. 890.

^20aPeregrinatio contra Nuncium Sydereum, Mantua, 1610.

²¹Ignatius his Conclave.

²²Opere, ed. F. Flora, Milano-Napoli, 1953, p. 887 seq.

²³ Ibid., p. 894 seq.

²⁴ 28.5.1610, G.W., Vol. XVI, p. 314.

²⁵ Quoted by E. Rosen, The Naming of the Telescope, New York, 1947.

²⁶ Letter to Horky, 9.8.1610, G.W., Vol. XVI, p. 323.

^26a G.W., "Poor Kepler is unable to stem the feeling against Your Excellency, for Magini has written three letters, which were confirmed by 24 learned men from Bologna, to give effect that they had been present when you tried to demonstrate your discoveries … but failed to see what you intended to show them." M. Hasdale to Galileo, 15.4 and 28.4 1610, G.W., Vol. XVI, pp. 300 f, 308.

²⁷ G.W., Vol. XVI, p. 319 seq.

^27a It was probably this letter which lead Prof. de Santillana to the erroneous statement: "it took even Kepler, always generous and open-minded, a whole five months before rallying to the cause of the telescope.… His first Dissertatio cum Nuncio sidereo, of April, 1610, is full of reservations." (Dialogue on the Great World Systems, Chicago, 1937, p. 98 n.) Kepler's reservations referred, as we saw, to the priority of the invention of the telescope, not to Galileo's discoveries with it.

²⁸ G.W., Vol. XVI, p. 327 seq.

²⁹ Except for a short note of introduction to Kepler, which Galileo gave a traveller seventeen years later, in 1627. Opere XIII, p. 374 f.

³⁰ [Karl von] Gebler, op. cit., p. 24.

³¹ At least, that seems to be the meaning. The word "unmbistineum" does not exist and may either be derived from "ambustus", burnt up, or "umbo"=boss, projection.

³² 9.1.1611, G.W., Vol. XVI, p. 356 seq.

³³Narratio de Observatis a se quatuor lovis sattelitibus erronibus.

³⁴ 25.10.1610, G.W., Vol. XVI, p. 341.

Works Cited

… Kepler, Johannes. Johannes Kepler, Gesammelte Werke. Edited by W. van Dyck and Max Caspar. Munich, 1938-.…

Zinner, E. Entstehung und Ausbreitung der Copernicanischen Lehre. Erlangen, 1943.