Tycho and Kepler

by Kitty Ferguson

  Meanwhile, in the autumn of 1600, Kepler, Barbara, and Regina still waited day after day in the faint hope that a letter from Mästlin would bring an offer from Tübingen. Mästlin’s letter finally reached them in December. There was no job for Kepler in Tübingen, and Mästlin had no advice to give. “Here in Prague6 I have found everything uncertain,” Kepler replied to him, “even my life. The only certainty is staying here until I get well or die.” He continued to write letters to his mentor, pleading for help, but the old man would not reply again for four years. Evidently there was nothing he could do, except, as he had promised in that December letter, to “pray for you7 and yours.”

  Tycho’s frustration and despair were almost equal to Kepler’s. The months were passing with no possibility of going back to Benatky, and he abhorred the work Rudolph asked him to do. Though Tycho had not given up the idea that the movement of the planets and other celestial events somehow influenced life on Earth, he found astrological advice of the sort Rudolph wanted boring and a waste of valuable time. He was particularly ill at ease with the detailed predictions that would have best satisfied a monarch worried about military campaigns, the choice of generals, and the possibility of his own assassination (Rudolph had now reached the age at which his father had been assassinated). For Tycho, who believed that the free will of each human participant mitigated the influence of the stars, producing meaningful predictions about military campaigns, for example, seemed nothing short of ludicrous. Nevertheless, Rudolph was paying the bills, at least theoretically, and Rudolph believed devoutly in astrology. Tycho knew that were he to disabuse the emperor of that belief, he would quickly be out of a job.

  The emperor also wanted advice that was more psychological and political than astrological. At court there were precious few who were politically neutral and could be expected to offer straightforward counsel without a personal agenda. Tycho’s only agenda was getting back to Benatky with sufficient support to continue his work. Rudolph found Tycho’s objectivity invaluable. Tycho thus had no choice but to try to meet Rudolph’s needs and gear himself up to learn whatever he did not already know about dealing with competitors for imperial favor, secret alliances, opportunists hoping to link their careers to his own, and lies, exaggerations, and half-truths designed to thwart an ambition he did not even have

  There was, however, more that needed to be dealt with than the usual affairs of the imperial court that summer and autumn of 1600. Not long after Rudolph summoned Tycho from Benatky, Rudolph suffered a temporary but severe mental collapse. It was not a rational ruler whom Tycho was advising. This was a particularly unfortunate moment for such a breakdown. Though Rudolph was emperor of the Holy Roman Empire, the area that fell under his most direct control was Bohemia, the northwestern part of what is now the Czech Republic—a multiethnic region ruled by a foreign dynasty (Rudolph’s) that had not, even in the best of times, been free of explosive tensions. By the summer of 1600 this diffuse, smoldering enmity had become polarized by the Counter-Reformation and threatened to ignite in a major conflagration.

  Rudolph II was a devout Catholic, but he opposed the more flagrant manifestations of the Counter-Reformation, not only in Bohemia but also in the larger empire. Incidents like the expulsion of Protestants from Graz and Styria represented a tragic failure in Rudolph’s policy of attempting to keep Catholic zealots and Protestants, who actually were in the great majority, from all-out conflict. It was possibly in reaction to that failure in Graz that a mentally unstable Rudolph decided to expel a cloister of Capuchin monks from a residence where he had earlier invited them to live, near the palace. The normal Rudolph was not given to such unexplained acts. The monks accused Tycho of having influenced Rudolph to banish them because their prayers interfered with the black magic he was using to turn base metal into gold. (Had Erik Lange heard this accusation, he would have rushed to Tycho’s side without delay.)

  However much Tycho disliked the work he was doing, it is a tribute to his reawakened skills in the delicate handling of monarchs and the balanced nature of his counsel that he survived Rudolph’s period of madness. Many other powerful men were permanently banished from court. Nor had Tycho contrived to remain on the periphery. He was considered one of Rudolph’s closest advisers. Extensive correspondence survives in which moderate Catholic leaders communicated with him about influencing Rudolph to name his second brother Albrecht as his successor rather than his first brother Matthias, whom they judged to be virulently anti-Protestant.

  On the more positive side, for Tycho, that summer and autumn, he finally received his own long-overdue salary. Also, there was undeniably a part of him that enjoyed moving in the most elite circles at court, having powerful men trust in him and be aware of the emperor’s enthusiasm for him. It was vindication for the treatment he had received in Copenhagen. He also took pleasure in the company of other well-educated people, of whom there were many in Prague. Hoffmann had ordered a copy made of one of the quadrants in Tycho’s Mechanica, and the two men had used it to observe the same solar eclipse Kepler observed from Graz in July.

  For Tycho, another mitigating factor about the move from Benatky to Prague was that he was able to initiate the long-delayed proceedings against Ursus. Tycho had heard that Ursus was seriously ill. The various legal actions Tycho set in motion proceeded much too slowly and inconclusively to satisfy him, for he chafed at the possibility that the man he considered his nemesis, this slippery, underhanded swineherd, would escape punishment by dying. In mid-August Ursus did just that, with Tycho’s lawyers harrying him even as he lay on his deathbed. Ursus had not survived long enough to be, as Tycho reported that the commissioners had promised him, “branded in infamy,8 and beheaded or quartered according to Bohemian law.”

  Hence, by the time the Keplers arrived in Prague, Ursus in the flesh was beyond Tycho’s reach, but Ursus’s book was not, and its very existence was a threat. Tycho told Kepler that he was not so much concerned with “destroying his person,9 whom everyone knows was clownish and vainglorious, but rather his book, stuffed full of so many insults and lies, and restoring the glory and reputation of myself and my associates.” On order of the emperor, the printer sought out all copies that could be found in Prague and consigned them to the flames, and the book was banned throughout the empire. It was an affront to Tycho when the council paid Ursus’s widow three hundred gulden to compensate her for the confiscation of the books. But Tycho could console himself that Rudolph in sound mind would never have let that happen. It was a smaller setback than many suffered as a result of the emperor’s brush with insanity.

  With all the time spent carrying out the move from Benatky to Prague, then from the hostelry to the house, while at the same time dealing with a half-mad emperor, Tycho accomplished little meaningful work in the summer and autumn of 1600, and this situation looked unlikely to improve. Longomontanus left, succumbing to the homesickness that had been drawing Tycho’s Danish assistants and servants back to Denmark. Tycho reluctantly watched the departure of this man who had helped him for so many years and joined him in exile. Tycho had tried hiring various German scholars, none of whom worked out successfully. More in need of analysis and computation than observation, he had been attempting to engage men capable of that sort of work. But in the autumn of 1600 there was no one else but Kepler in Tycho’s employ with whose assistance he could hope to complete his planetary theories in the way he wished.

  The Belvedere, a pavilion in the gardens of the imperial palace in Prague, where Tycho set up his instruments in the autumn of 1600.

  The last of Tycho’s instruments reached Prague in October, at about the time Kepler himself returned. The emperor arranged for Tycho to mount them on the balconies of an ornamental summer-house in the palace grounds, now called the Belvedere. Tycho was bitterly disappointed. He had hoped to use the need to install the instruments in their clifftop bays as an excuse to return to Benatky. From the Belvedere’s south-facing balconies, the emperor’s palace complex blocked off
a good portion of the southwestern sky.

  By New Year 1601, Rudolf’s mental state had improved, and his already high regard for Tycho had increased during the difficult months they had weathered together. When Tycho petitioned for citizenship and nobility for himself and his family in February, the emperor himself sponsored their petition. At last Kirsten and their children enjoyed a status that would permit them to inherit from Tycho and marry nobles of their new homeland. Tycho’s estate was still large, especially if one included back pay from Rudolph (mounting up again), the value of instruments, books, and observations, and the loan (made shortly after he left Denmark) that he was finally calling in from the two young dukes of Mecklenburg. The future of Tycho’s family at last seemed secure.

  On the other hand, his scholarly future looked increasingly bleak. He had been near to having a new Uraniborg the previous spring. Now it seemed he would have to relinquish all hope of that, for Rudolph bought him the same palace he had rejected when he first came to Prague from Denmark. It was undeniably a beautiful house and garden, and an astronomer forced to live in the city could hardly have done better than this hillcrest location. Nevertheless, the mansion still had the same disadvantages that had caused him to turn it down eighteen months earlier: The tower was not large enough, and the location was too accessible to the court, just a few minutes’ walk west of the imperial palace and no time at all in a carriage.

  Again, Tycho’s enjoyment of a splendid, nearly royal lifestyle was an antidote to despair. He moved his library into the house, the three thousand books that had been waiting all this time in Magdeburg. He took smug satisfaction, when spring came, in mentioning in letters inviting former acquaintances and relatives in Denmark to his daughter Elisabeth’s wedding that the summer nuptials would be held in his palace, formerly belonging to the vice chancellor of the empire. The contingent from Denmark was not expected to make an appearance, but it was a triumph to inform them how luxurious and pampered his present situation was and that his daughter was marrying a nobleman.

  Nevertheless, the discouragement of having to move family and research establishment again, not back to Benatky but to this unwanted house, was a serious drain on the fifty-four-year-old Tycho’s energies. During that winter, his friends began to notice that he had lost some of his usual spark and seemed to be resigning himself to old age and declining health. Tycho’s brother Jørgen, who was much younger than he, died in February. Jesensky reported that in the middle of a cheerful conversation Tycho would change the subject to talk about death. Kepler commented in a letter to Mästlin, who was still not answering, that Tycho was acting childish and capricious, though he was “still good-natured,”10 and that Tycho seemed burdened with cares: “He always resembles a lost man, but always somehow extricates himself. His success at this is to be wondered at.” Tycho made some progress reorienting his instruments for their new location, but he did little observing and failed to move ahead at all with the books that he had been working on for many years. Several of these were near completion, and it would not have required a great deal of effort to finish them, but he lacked the energy and interest.

  When Tycho and his family moved to the mansion, the Keplers moved there too. Yet in spite of the difficulty Tycho was having finding good computational help, he wasted Kepler’s talents that winter, partly because Kepler wasn’t at his best—his fever kept returning—but also because Tycho was still paranoid about his observations and not satisfied that he had completely defeated Ursus, even though the man was dead and all known copies of his offensive book had been destroyed. Kepler complained later in a letter to the astronomer Giovanni Antonio Magini that Tycho would show him his “choicest” observations,11 but only “inside his four walls,” and say to him, “Get to work.” If Kepler asked to see observations other than those Tycho set before him, Kepler was told he was being too inquisitive. “If only I could copy12 them quickly enough!” Kepler wrote to Mästlin, and in the same letter mentioned an idea for prising some of the observations out of Tycho: “If you would send him some of your observations, he would, I think send some to you, too, if you ask him to do so. For in spite of all the instability of his character, he is, after all, a man of great benevolence.” Mästlin did not reply.

  As for Kepler’s own astronomy, he spent a little time on some theories about Mercury, Venus, and Mars, discussed them with Tycho, and thought about the orbit of the Moon, but this was not a productive winter. “A fever gripped me,”13 Kepler later recalled. “In the meantime I wrote against Ursus on Tycho’s orders.” In a letter to Mästlin he complained, “Because of this illness14 of mine I am doing nothing but write against Ursus.” Kepler found it distasteful to carry on the dispute after Ursus’s death, but Tycho was still obsessed with proving that he, not Ursus, had invented the Tychonic system. Not only did he want to destroy Ursus’s scientific credibility, to keep him from ever getting credit for it, but he also wanted to discourage others who, he believed, were also guilty of plagiarizing his system. The main current target of Tycho’s fears was a Scotsman named Duncan Liddell, whom Tycho had suspected ever since Liddell visited Hven in 1587 and 1588. Liddell seems to have been completely innocent; over the years he remained a responsible scholar and teacher and one of Tycho’s staunchest supporters, though he kept his distance because of Tycho’s suspicions and hostility.

  Kepler put his feverish head to the task of coming up with something that would satisfy Tycho’s instructions that he “rebut even more clearly15 and more fully than you have done previously Ursus’s distorted and dishonest objections to my invention of the new hypothesis . . . and ascribe the new hypothesis to me, as is right, just as you did before with demonstrable reasoning.” Kepler did not finish his “Defense of Tycho against Ursus”16 that winter and spring. He would resume work on it several years later, but the still unfinished manuscript was not published until 1858. Kepler made the most of a poor assignment. It is one of the finest analyses ever written about scientific methodology, pointing out a difference between the Ptolemaic and Copernican models that was of profound importance to Kepler and that remains even today the primary reason for deciding in favor of Copernicus. In principle, Ptolemaic astronomy was not “incorrect.” It could plot and predict the courses of the heavenly bodies just as correctly as Copernican astronomy. So could the Tychonic model. But, wrote Kepler, “If in their geometrical conclusions17 two hypotheses coincide, nevertheless in physics each will have its own peculiar additional consequence.” In other words, when one began asking the “why” questions, seeking the physical causes for the motion, Ptolemaic and Tychonic astronomy could no longer hold their own. To Kepler, the search for physical causes had become paramount.

  In April, with his health not improved, Kepler interrupted work on this treatise to make another trip back to Graz. Barbara’s father had died, and Kepler needed to salvage whatever he could of his wife’s inheritance. Most of that was tied to estates and useless to the Keplers unless it could be converted into cash. Though the Graz authorities did not block Kepler’s return, in a financial sense the four-month trip was an exercise in futility. Nevertheless, Kepler finally shook off the fever that had afflicted him for nearly a year, and he wrote to Barbara that he was enjoying visiting friends, who everywhere were treating him as a welcome guest.

  Barbara wrote18 that she was not getting as much money from Tycho as he had promised. She could not buy wood for the fire. An angry exchange of letters ensued. Tycho told Kepler to calculate what was owed and he would be paid, but to behave in future more considerately toward his “benefactor” and “have more19 confidence in him.” Kepler bristled at this insinuation that Tycho was giving him charity instead of fair recompense for his work. The contretemps finally ended agreeably, but it was symptomatic of the dissatisfaction Kepler still felt with his working arrangement.

  Kepler kept up with events in Prague through Barbara’s letters, partly written in the Keplers’ own secret code, which would not have helped Tycho’s paranoia if
he had known about it. The most important occasion of the summer was the wedding of Tycho’s daughter Elisabeth to Tengnagel in June. Kepler inquired of Barbara in code whether the bride looked pregnant. Perhaps she did, for Tycho’s grandson was born in late September.

  Though Tycho expressed some displeasure with the young couple prior to the wedding, perhaps because of the pregnancy, he was immensely gratified that his daughter, who in Denmark was not even considered his legitimate child and could never have married into the nobility, was marrying Tengnagel. Although Tycho had previously referred to him as his domesticus, or servant, Tengnagel was a nobleman, a man of great political promise whom Tycho had known and trusted for many years. In this marriage Tycho and his family were repaid a little for the grief and disgrace of Magdalene’s ill-fated betrothal to Gellius. Tycho did everything in his power to make the triumph as public as that embarrassment had been, and the invitation list was long and illustrious. Even Rudolph was invited, though there was no expectation that the reclusive emperor would attend. Tycho’s sister Sophie, who had been intimately involved in Magdalene’s sorrows, hoped to come, but ill health prevented her at the last minute. She had previously begun several journeys to Prague and had to interrupt them midway because of Erik Lange’s recurring disasters. Elisabeth and Tengnagel left after the wedding for the Netherlands along with another of Tycho’s assistants, Johannes Erikson, so when Kepler returned in late August, a healthier, more optimistic, though poorer man, the house by the wall was less crowded.

  By that autumn of 1601 the decision Tycho had been trying to make for nearly a year and a half had taken on greater urgency. His work was not finished and would not be, in his eyes, until there was complete justification of his belief in the Tychonic system. His astronomy would continue to languish, incomplete, with no hope of accomplishing what he had spent a lifetime working toward, unless he finally put his full trust in Kepler. If Tycho was indeed burdened with premonitions that he had not long to live, he surely anticipated that that decision would mean trusting Kepler beyond his death. And—though Tycho had to have recognized that Kepler would put the observations to better use than any other man available—trusting Kepler could not mean trusting him ultimately to support the Tychonic system. Nevertheless, with Ursus buried for more than a year, Tycho at last made the leap of faith and wagered his earthly immortality on Kepler.