INDUCTIVE EPOCH OF KEPLER. 439 



of the train of thought already noticed. In the 

 beginning of the Mysterium, Kepler had said, " In 

 the year 1595, I brooded with the whole energy of 

 my mind on the subject of the Copernican system. 

 There were three things in particular of which I 

 pertinaciously sought the causes why they are not 

 other than they are ; the number, the size, and the 

 motion of the orbits." We have seen the nature of 

 his attempt to account for the two first of these 

 points. He had also made some essays to connect 

 the motions of the planets with their distances, but 

 with his success in this respect he was not himself 

 completely satisfied. But in the fifth book of the 

 Harmonice Mundi, published in 1619, he says, 

 "What I prophesied two-and-twenty years ago as 

 soon as I had discovered the five solids among the 

 heavenly bodies; what I firmly believed before I 

 had seen the Harmonics of Ptolemy ; what I pro- 

 mised my friends in the title of this book (On the 

 most perfect Harmony of the Celestial Motions'), 

 which I named before I was sure of my discovery ; 

 what sixteen years ago I regarded as a thing to be 

 sought; that for which I joined Tycho Brahe, for 

 which I settled in Prague, for which I have devoted 

 the best part of my life to astronomical contem- 

 plations; at length I have brought to light, and 

 have recognized its truth beyond my most sanguine 

 expectations." 



The rule thus referred to is stated in the third 

 chapter of this fifth book. "It is," he says, "a 



