A HISTORY OF SCIENCE 



astronomer to the Landgrave of Hesse, and Maestlin, 

 the instructor of Kepler. The Prutenic tables, just 

 referred to, so called because of their Prussian origin, 

 were considered an improvement on the tables of 

 Copernicus, and were highly esteemed by the astrono- 

 mers of the time. The commentary of Rhseticus 

 gives us the interesting information that it was the 

 observation of the orbit of Mars and of the very great 

 difference between his apparent diameters at differ- 

 ent times which first led Copernicus to conceive the 

 heliocentric idea. Of Reinhold it is recorded that 

 he considered the orbit of Mercury elliptical, and that 

 he advocated a theory of the moon, according to which 

 her epicycle revolved on an elliptical orbit, thus in a 

 measure anticipating one of the great discoveries of 

 Kepler to which we shall refer presently. The Land- 

 grave of Hesse was a practical astronomer, who 

 produced a catalogue of fixed stars which has been 

 compared with that of Tycho Brahe. He was assisted 

 by Rothmann and by Justus Byrgius. Maestlin, the 

 preceptor of Kepler, is reputed to have been the 

 first modern observer to give a correct explanation of 

 the light seen on portions of the moon not directly 

 illumined by the sun. He explained this as not due 

 to any proper light of the moon itself, but as light re- 

 flected from the earth. Certain of the Greek philoso- 

 phers, however, are said to have given the same 

 explanation, and it is alleged also that Leonardo da 

 Vinci anticipated Maestlin in this regard. 2 



While various astronomers of some eminence thus 

 gave support to the Copernican system, almost from 

 the beginning, it unfortunately chanced that bv far 



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