Tycho and Kepler (37 page)

Though Kepler may have felt invisible and slighted, Tycho had not forgotten
this young scholar who looked so ill at ease at his dinner table. Kepler did not realize, may never have realized, the lingering consequences of the foolish letter he had written Ursus. Kepler’s future probably hung at the moment less on his mathematical skills and possible scholarly value than on Tycho’s hope of using him as a weapon against Ursus, and his lingering unease about the possibility
that Kepler might secretly be Ursus’s ally. Though many of Tycho’s acquaintances had advised him that he was making too much of the Ursus affair, Tycho could not let it go. That was both fortunate and unfortunate for Kepler. It meant Tycho had to go out of his way to keep Kepler at Benatky, under his own watchful eye, but it also meant that Tycho was extremely reluctant to allow Kepler to see the
observations.

Kepler had not yet reached his full potential as a mathematician or interpreter of observations, but that potential had been sufficiently evident from
Mysterium
(Tycho had called the polyhedral theory “quite a brilliant speculation”)
⁶
for Tycho to realize, even before he met Kepler in person, that, properly harnessed with regard to wilder flights of fancy, Kepler might be the
assistant who could interpret the Mars observations and discover ways to show that the Tychonic system was correct. Though his Mars parallax campaign had so far been a failure, Tycho’s letters from Benatky in 1600 and 1601 show that he had not given up hoping that he—rather than Copernicus and certainly rather than Ursus—might be celebrated for generations to come as the man who provided the true
breakaway from Ptolemaic astronomy and set the course for the future. It had to have seemed
the
worst luck and damnable irony that Kepler, who might have served him so well in this effort, should at the same time represent a double threat. Allowing him to see the precious observations might be tantamount to giving them away to Ursus. Or, just as threatening, it might end in confirmation of Copernicus’s
system rather than Tycho’s. However, paranoia or no paranoia—and in spite of his knowledge that Kepler, at present, preferred Copernicus—Tycho was short of assistants and desperately needed someone with Kepler’s gifts. “An astronomical treasure accumulated by the expenditure of sweat and money over so many ears,” Tycho lamented, was going to waste.

Kepler himself clearly recognized Tycho’s
great need for him, which made the older man’s secretiveness all the more puzzling. “Tycho has the best observations—that
⁷
is to say the materials to put up the building—and he has the workers. He is lacking only one thing, the master builder who can make use of all that. Although he is clearly of an extremely architectonic mind, the variety and the depths of the truths with which he is dealing
are hindering Tycho, because he is approaching the age of an old man. His mind and all his powers are weakened and are going to be weakened more in a few years so that he will hardly be able to carry out everything alone.”

No doubt with terrible misgivings, the old dragon decided to loosen his grip on his hoard just a bit, and Kepler found himself with an assignment. Tycho put him to work—”by
divine providence,” as Kepler later described it—on the Mars observations under the supervision of Longomontanus, who had rejoined Tycho only about two and a half weeks before Kepler came. Kepler reported that Tycho “saw that I possess
⁸
a daring mind [and] thought the best way to deal with me would be to give me my head, to let me concentrate on the observations of one single planet, Mars.” He
would of course be working only as assistant to an assistant, but Longomontanus was almost certainly the most gifted astronomer at Benatky besides Tycho himself. He was a warmhearted, well-meaning, unpretentious man, a favorite with Tycho and his family. Furthermore, Tycho usually had his assistants work in pairs. When Kepler asked Tycho whether he could use the true Sun, rather than the center of
Earth’s orbit, as the reference point for Mars’s orbit, and Tycho agreed, Kepler found himself floundering with the mathematics. It was Longomontanus who pointed out a clever technique that Tycho had outlined in a private handbook for his assistants.

Kepler still felt frustrated. He had thought he would be working on his own theories here, not just Tycho’s. In order to move ahead with them,
he needed time off from Tycho’s projects, and he needed data on
all
the planets, not just Mars. “I thought I would
⁹
later also get the other observations,” he said, but that did not happen. He was not finding answers at Benatky to the questions that most intrigued him.

Tycho soon recognized that it made no sense to have his two most able assistants both working on the Mars observations. Kepler
was more than capable of carrying on the work on his own. By now Tycho had had a little experience with Kepler in person, which must have confirmed both the good and the bad (as Tycho perceived them) that
Tycho
had discerned when he read
Mysterium
. Kepler was at least as gifted as Longomontanus and a better writer. (Tycho praised his “well-rounded way
¹⁰
of expression.”) Furthermore, Tycho knew
of no other assistant available who was better equipped to analyze his observations and find out whether they validated the Tychonic system. “Tycho was pleased
¹¹
with this work I did,” wrote Kepler. “He said that he himself had been occupied with similar [work], but liked to avoid the complicated calculations and learn of other people’s views.” However, by allowing Kepler to be his “master builder,”
taking the road to discovering whether he was right, Tycho would also be opening the possibility of learning he was wrong, and having the world learn it. His most valuable trump card was that he
alone
had observations—and the means to make more—that could prove or disprove
any
current theory.
^fn1
This was an advantage he would forfeit if he gave someone as skilled and perceptive, and independent,
as Kepler the key to the treasure house. But it was a dubious advantage to a man who had spent a lifetime looking for real answers.

Tycho was not yet prepared to give Kepler full access to his observations, but it was nevertheless a significant step when he reassigned Longomontanus to a project Longomontanus had begun earlier, the lunar theory, and allowed Kepler to analyze the Mars observations
without further supervision. Tycho could do little to avert the danger that the young man, intentionally or, worse yet, honestly, might analyze the data and find it supporting Copernicus, not Tycho. But Tycho was running out of options. He did take a rather lame precaution with regard to the threat of Ursus. He extracted a written pledge from Kepler that he would never reveal any of Tycho’s
secrets.

The tragedy of Tycho’s paranoia was that there was definitely at least a part of him that liked Kepler, appreciated his talent as perhaps no other but Mästlin could, and longed to have him as friend and colleague.
Had
there been no Ursus, and had Tycho been more open-minded about the Copernican system, the time they spent together might have been a supremely happy and productive time
for them both. Instead, Kepler became increasingly out of sorts and unraveled that spring. He had arrived at Benatky with confidence in his own abilities and in the importance of his ideas. Tycho obviously had the intellectual capacity to value these, and also the wherewithal to save the Keplers from their intolerable position in Graz. Yet here was no sympathetic mentor, no secure and rewarding
job, only an aloof, suspicious curmudgeon and a hand-to-mouth existence. Kepler had always been vulnerable to the opinion of others. When he was younger, he had written about himself, “My greatest worries
¹²
are not how to live, not my external appearance, not hurt, not joy, not work itself, but the opinion of other people of me, which I wish only to be good. Whence comes this foolishness about
‘being seen’?” How distressing must have been the image of himself he saw reflected in Tycho’s eyes, and the confusing way it shifted between liking and suspicion.

As the days passed, Kepler found there was, after all, some progress he could make at Benatky on his own theories. The Mars observations alone
were
sufficient for work on his hypothesis that a force from the Sun moves the planets.

He was looking for some hint in the geometry of Mars’s movements that it was responding to a force coming from the Sun, and encouragement was not long in coming. He found, as he had suspected, that the only way he could make sense of Mars’s orbit, as it was showing up in Tycho’s observations, was to take into account the actual position of the Sun rather than using the center of Earth’s orbit
as his reference point. This use of the “true” Sun made sense if the Sun was the source of Mars’s motion.

Next Kepler used the Mars observations in an innovative way to study Earth’s orbit. In writing
Mysterium
, when he had been using older observations, Kepler had been forced to admit, reluctantly, that his idea that the Sun was the source of the movements of the planets
seemed
not to work
for Earth. Using Tycho’s observations, he found that it
did
work. Earth like the other planets sped up as it came nearer the Sun and slowed down as it moved farther away. This was a particularly significant and welcome breakthrough.

When Tycho learned of Kepler’s findings, he was not happy about them, and he raised objections. Here, as he had feared, was the Copernican system rearing its ugly
head. Furthermore, he, like Mästlin, disapproved of Kepler’s insistence that in order to develop planetary theory one must find the physical causes of the motion.

Ironically, success only added to Kepler’s frustration. Having caught a glimpse of what he might be able to accomplish with Tycho’s data, he also became aware of how extensive the research project was that he had begun. Kepler concluded,
“If I don’t want
¹³
to be deprived of the purpose of my travel, I have two choices. Either I copy his observations for my purpose (he is not going to accept that, and rightly, because these are the treasure he has spent his whole life and fortune on) or I find some way to stay and complete my own work.” That meant trying to formalize his position at Benatky.

Kepler was to all intents and purposes
Tycho’s guest. Tycho had not regularized his position in any way, given him a contract, or even talked about long-term employment. The situation for Kepler’s family back in Graz continued to be precarious. It was almost unthinkable that they should stay there, yet with no promise of regular financial support, Kepler could not drag Barbara away from her home and her extended family and ask her
to forfeit her property. She would, Kepler knew, be even more likely than he to go mad in this clifftop beehive where men and women whose language she did not speak held all power and her husband did not even draw a salary. Kepler desperately needed a job commitment. He let Tycho know of his distress.

Tycho chose to interpret Kepler’s requests for a contractual arrangement as a lack of trust
in his honor and reliability. From Tycho’s perspective there was, in fact, much to be said for letting this tense young
man
depart. He was not the good-natured, warmhearted man that Longomontanus was; he had had to be excused from the observation rota because of poor eyesight; his theories were eccentric; and he continued to lean toward Copernicanism. Furthermore, Tycho was not in a good position
to make salary promises. Support from the treasury for the renovation was proving to be undependable, and Tycho had yet to see a gulden of the salary that Rudolph had promised him.

However, for Tycho, the moment of truth had arrived. He knew that validation of the Tychonic system could come only through skilled analysis of the observations, and Kepler had the potential to do the analysis.
If Tycho wanted an authentic victory, and not merely the hollow, negative one of having no one able to gainsay him, he needed Kepler. Rising above the irritation of Kepler’s complaints, he acted to try to remedy Kepler’s problems. At the beginning of March, he wrote to Hoffmann, the man who had brought Kepler to Prague the previous January, suggesting that Hoffman meet him and Kepler to discuss Kepler’s
job position. While that meeting was being arranged, contract negotiations between Kepler and Tycho sputtered on, taking place through a variety of intermediaries, including Longomontanus. Kepler became more unhappy with each passing day. In his lifetime he endured many crises and indignities that would be sufficient to drive most men to distraction, yet only that spring at Benatky did his
equanimity and good sense completely desert him. By his own report, he had a temper, but it had seldom been evident in public. In these tense days, he let it get the better of him several times at Tycho’s dinner table.

Kepler grew so impatient, waiting for a reply from Hoffmann, that he took it on himself to lay out in writing the terms of employment he would accept. When Longomontanus suggested
he moderate his demands, he submitted an only slightly revised memorandum. The demands were not unreasonable, but they were irksome to Tycho. They included permission for Kepler to go into Prague when he chose, though not to stay long; time off during the day for family affairs to compensate for having to work night hours; a guarantee of
relief
from observing duties, since his poor eyesight and
lack of skill made him worthless at that anyway; Sundays and holidays off; and assurance that anything Tycho wished to publish under Kepler’s name (such as an opinion of Ursus) would have to be at Tycho’s expense and subject to Kepler’s approval. Much more of a stumbling block were Kepler’s demands that he have a salary both from Tycho and the emperor, that he be allowed to spend every day after
noon on his own projects, and that he and his family be given a house separate from the castle. The house was particularly important to Kepler. “Tycho’s house is very cramped,”
¹⁴
he wrote. “The turmoil of his family is great. I do not want to mix my family with them, because they are used to silence and modesty.”