____________________
*
The preface (and first chapter) proclaim Kepler's belief in the Copernican system and outline his arguments in favour of it.
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 favoufably 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 VIII, 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; ridenduss 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 froth 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 Galileo had broken 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 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 discove
ries 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 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 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 publication 14 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 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 teacher 16 were described as "that malevolent enemy of honour and of the whole of mankind", "a venomspitting 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-destruction. 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: