104 LIFE AND WORKS OF KEPLER. 



upon this hypotliesis, does tlie planet succeed in recognizing its patli ? 

 The expression of its velocity necessarily incliules sines, and admitting 

 even that this soul has a perception of angles, by what mysterious 

 operation, he asks, could it calculate the sines of those angles ? Eecur- 

 ring, finally, to the idea of a magnetic attraction, he is apprehensive of 

 a contlict between the magnetic power and the aninml power. These 

 confused reveries in which the genius of Kepler involves itself, make 

 us involuntarily think of the words we have cited : " Torquchar pane ad 

 /«.s'«^<yVrw;" they add nothing to hisgh)ry; it iinjiorts little that inter- 

 polated among these opinions, which are so many errors, he has for once 

 announced the truth without founding it upon solid reasons. When a 

 traveler seeks his way in the darkness of a rayless night, and hesitating 

 at every step, exclaims anxiously from time to time : Perhaps it is there ! 

 shall we praise his sagacity because he has happened for once to guess 

 right and has then passed on I 



It would be unjust, therefore, to claim for Kepler the discovery of 

 universal attraction, but there is no room for surprise at this. Mechan- 

 ics, scarcely in its infancy, did not enable him, however clear-sighted, 

 to test his ideas on motive forces and to transform them into precise 

 and calculated theories ; the labors of Galileo and of Huyghens were 

 necessary to prepare even Newton for this, his immortal acliievement. 



The studies and meditations of Kepler were often interrupted and 

 constantly troubled by chagrins and embarrassments of every kind. 

 The heirs of Tycho were entitled to a share in the property of the as- 

 tronomic tables which Kepler had promised ; they complained of his 

 deferring their publication while he occupied his time with researches 

 in physics and with empty speculations, while the celebrated astron- 

 omer Lougomontanus constituted himself the organ of their reproaches 

 and unjust suspicions. In a letter, at the outset of which he still treats 

 Kepler as a learned man and a friend of long standing, he accuses him 

 of indulging an immoderate zeal in the refutation of the theories of Tycho, 

 of allowing himself to be diverted from the occupations of his office by 

 the passion, for criticising everything, and of breaking, by attacking the 

 works of his friends, the ties of affection which hound them to him. "If 

 my engagements had permitted," says Longomontanus, "I would have 

 gone to Prague exi)ressly to have an explanation with you ; but," he 

 adds with increasing acrimony, " of what, after all, my dear Kepler, do 

 you so much vaunt yourself? All your researches rest on bases estab- 

 lished by Tycho, in which 30U have changed nothing. You may per- 

 suade the ignorant, but cease to inaintaiu absurdities before those who 

 thoroughly understand the matter. You do not fear to compare the 

 works of Tycho to the muck of the Augean stables, and, like another 

 Hercules, announce yourself ready to cleanse them ; but no one is 

 deceived thereby or prefers you to our great astronomer. Your arro- 

 gance disgusts all sensible ])eople." 



Accusations so remote from truth could not wound Kepler. He 

 despised all this empty objurgation which re-echoed around him. A 

 few notes on the margin of the letter from Longomontanus show in 

 what estimation our philosopher held it. " Pretty abuse," he writes ; 

 and again, " decent phrases, if you please, to disguise your spleen." 

 His reply, in which he declines a useless discussion, displays unbounded 

 kindliness; it enables us to discern the serenity of his mind and moder- 

 ation of his character. "At the moment when I received your militant 

 ejustle, pea<^e had long been made with the son-in-law of Tycho. You 

 and I would resemble, in quarreling, Portuguese and English vessels 

 which should tight in the Indies when peace was already ratified at 



