The Sleepwalkers

  "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, O 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 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 unable 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:

  "SMAISMRMILMEPOETALEUMIBUNENUGTTAURIAS."

  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."; * 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

  ____________________

  *

  "There is a red spot in Jupiter which rotates mathematically."

  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 form of heavenly motion.

  IX CHAOS AND HARMONY

  1. Dioptrice

  WE must, for the time being, let Galileo recede into the background, and complete the story of Kepler's life and work.

  Galileo had transformed the Dutch spy-glass from a toy into an instrument of science, but he had nothing to say in explanation of why and how it worked. It was Kepler who did this. In August and September, 1610, while he enjoyed the use of the telescope borrowed from Duke Ernest of Cologne, he wrote within a few weeks a theoretical treatise in which he founded a new science and coined a name for it: dioptrics – the science of refraction by lenses. His Dioptrice 1 is a classic of a strikingly un-Keplerian kind, consisting of a hundred and forty-one austere "definitions", "axioms", "problems" and "propositions" without any arabesque, ornament or mystic flights of thought. 2 Though he did not find the precise formulation of the law of refraction, he was able to develop his system of geometrical and instrumental optics, and to deduce from it the principles of the so-called Astronomical, or Keplerian Telescope.

  In his previous book on optics, published in 1604, Kepler had shown that the intensity of light diminishes with the square of distance; he had explained the principle of the camera obscura, the forerunner of the photographic camera, and the manner in which the spectacles for the short and long-sighted worked. Spectacles had been in use since antiquity, but there existed no precise theory for them. Nor, if it comes to that, did a satisfactory explanation exist for the process of sight – the refraction of the incoming light by the lenses in the eye, and the projection of a reversed image onto the retina – until Kepler's first book on optics. He had modestly called it "a Supplement to Vitellio". 3 This Vitellio, a thirteenth century scholar, had written a compendium of optics mainly based on Ptolemy and Alhazen, and this was the most up-to-date work on the subject till Kepler's advent. One must constantly bear in mind this lack of continuity in the development of science, the immense, dark lowlands extending between the peaks of antiquity and the watershed, to see the achievements of Kepler and Galileo in true perspective.

  The Dioptrice is Kepler's soberest work – as sober as the geometry of Euclid. He wrote it in the same year as his punchdrunk Conversation with the Star Messenger. It had been one of the most exciting years in Kepler's life; it was followed by the blackest and most depressing.

  2. Disaster

  The year 1611 brought civil war and epidemics to Prague; the abdication of his imperial patron and provider; the death of his wife and favourite child.

  Men less prone to astrology would have blamed such a series of catastrophes on the evil influence of the stars; oddly enough, Kepler did not. His astrological beliefs had become too refined for that: he still believed that the constellations influenced the formation of character, and also had a kind of catalysing effect on events; but the cruder form of direct astrological causation he rejected as superstition.

  This made his position at Court even more difficult. Rudolph, sliding from apathy into insanity, was now virtually a prisoner in his citadel. His cousin Leopold had raised an army and occupied part of Prague. The Bohemian Estates appealed for help to his brother Matthias, who had already dispossessed Rudolph of Austria, Hungary and Moravia, and was preparing to take over what was left. Rudolph craved reassurance from the stars; but Kepler was too honest to provide it. In a confidential letter to one of Rudolph's intimate advisers, he explained:

  "Astrology can do enormous harm to a monarch if a clever astrologer exploits his human credulity. I must watch that this should not happen to our Emperor... I hold that astrology must not only be banished from the senate, but also from the heads of all who wish to advise the Emperor in his best interests; it must be kept entirely out of his sight." 4

  He went on to say that, consulted by the Emperor's enemies, he had pretended that the stars were favourable to Rudolph and unfavourable to Matthias; but he would never say this to the Emperor himself, lest he became over-confident and neglected whatever chance there may be left to save his throne. Kepler was not above writing astrological calendars for money, but where his conscience was involved, he acted with a scrupulousness most unusual by the standards of his time.

  On 23 May, Rudolph was forced to abdicate the Bohemian crown; the following January he was dead. In the meantime, Frau Barbara contracted the Hungarian fever, which was followed by attacks of epilepsy and symptoms of mental derangement. When she got better, the three children went down with the pox, which the soldiery had imported. The oldest and youngest recovered; the favourite, six-year-old Friedrich, died. Then Barbara relapsed:

  "Numbed by the horrors committed by the soldiers, and the bloody fighting in the town; consumed by despair of the future and by an unquenchable longing for her lost darling ... in melancholy despondency, the saddest of all states of mind, she gave up the ghost." 5

  It was the first in a series of disasters which weighed down on the last twenty years of Kepler's life. To keep going, he published his correspondence with various scholars on questions of chronology in the age of Christ. Chronology had always been one of his favourite distractions; his theory that Jesus was really born in the year 4 or 5 "B.C." is today generally accepted. Thus he was "marking time" in two meanings of the word; for he had secured himself a new, modest job in Linz, but could not leave Prague while Rudolph was still alive.

  The end came on 20 January, 1612. It was also
the end of the most fertile and glorious period in Kepler's life.

  3. Excommunication

  The new job was that of a Provincial Mathematicus in Linz, capital of Upper Austria – similar to that he had held in his youth in Gratz. He was now forty-one years old, and he stayed in Linz for fourteen years, till he was fifty-five.

  It seemed a depressing come-down after the glories of Prague; but it was not quite as bad as it seemed. For one thing, Rudolph's successor had confirmed Kepler in his title as Imperial Mathematician, which he retained throughout his life. Matthias, unlike Rudolph, had little time for his court astronomer; but he wanted him to be not too far away, and Linz, in his Austrian domain, was a satisfactory solution. Kepler himself was glad to be away from the turmoil of Prague, and to receive a salary from the Austrians which at least he was sure to get. He also had influential patrons among the local aristocracy, the Starhembergs and Liechtensteins; in fact, the job had been specially created for him, carried only theoretical obligations, and left him all the leisure he needed for his work. When the Thirty Years War began with the defenestration of Prague, he could only be thankful to be removed from the focus of events. And when he was offered the succession of Magini in the Chair for Mathematics in Bologna, he wisely refused.

  But nevertheless it was a come-down. " Linz", to Austrians, remains to this day a byword for provincialism. Barbara, whose homesickness for Austria had been one of the reasons for Kepler's choice of Linz, was dead. His desolate loneliness wrung from him one of his self-analytical outcries:

  "... My exaggerated trustingness, display of piety, a clutching at fame by means of startling projects and unusual actions, the restless search for and interpretation of causes, the spiritual anguish for grace..." 6