208 A SHORT HISTORY OF SCIENCE 



Eleven years later Tycho published a volume on the comet as 

 a part of a comprehensive astronomical treatise which was, how- 

 ever, never completed. About the same time his royal patron 

 died, and the new administration proved less sympathetic with 

 the great astronomer's work and less indulgent with his extrava- 

 gance and personal eccentricities. 



After a series of disagreements, Tycho withdrew from his ob- 

 servatory in 1597, spent the winter in Hamburg, and after nego- 

 tiations with different sovereigns, accepted the invitation of the 

 Emperor Rudolph to settle in Prague in 1599. Here he again 

 organized a staff of assistants, including, to the great advantage 

 of himself and of his science, the young Kepler, but his further 

 progress was prematurely terminated by death in 1601, at the age 

 of 55. 



Tycho's chief services to the progress of astronomy consisted 

 first, in the superior accuracy of his instruments and observations, 

 heightened by repetition and systematic correction of errors; 

 second, in the extension of these observations over a long series of 

 years. In both respects he departed from current practice, and 

 anticipated the modern. In point of accuracy his errors of star- 

 places seem rarely to have exceeded 1' to 2', and he even de- 

 termined the length of the year within one second. While he 

 recomputed almost every important astronomical constant, he 

 accepted the traditional distance of the sun. 



Kepler gave striking evidence later of his confidence in Tycho's 

 accuracy by writing : 



' Since the divine goodness has given to us in Tycho Brahe a most 

 careful observer, from whose observations the error of 8' is shewn in 

 this calculation, ... it is right that we should with gratitude recog- 

 nize and make use of this gift of God. . . . For if I could have 

 treated 8' of longitude as negligible I should have already corrected 

 sufficiently the hypothesis . . . discovered in chapter xvi. But as 

 they could not be neglected, these 8' alone have led the way towards 

 the complete reformation of astronomy, and have made the subject- 

 matter of a great part of this work.' Berry. 



