SEQUEL TO COPEftXICUS. 271 



straight line leading to the centre. He thus showed that he had 

 entertained in his thoughts the hypothesis of the earth's rotation, and 

 was employed in removing the difficulties which accompanied this 

 supposition, by means of the consideration of the composition of 

 motions. 



In like manner we find the question stirred by other eminent men. 

 Thus John Muller of Konigsberg, a celebrated astronomer who died in 

 1476, better known by the name of Regiomontanus, wrote a disserta- 

 tion on the subject " Whether the earth be in motion or at rest," in 

 which he decides ex prqfesso? against the motion. Yet such discus- 

 sions must have made generally known the arguments for the helio- 

 centric theory. 



We have already seen the enthusiasm with which Rheticus, who 

 was Copernicus's pupil in the latter years of his life, speaks of him. 

 " Thus," says he, " God has given to my excellent preceptor a reign 

 without end ; which may He vouchsafe to guide, govern, and increase, 

 to the restoration of astronomical truth. Amen." 



Of the immediate converts of the Copernican system, who adopted 

 it before the controversy on the subject had attracted attention, I shall 

 only add Mastlin, and his pupil, Kepler. Mastlin published in 1588 

 an Ejntome Astronomice, in which the immobility of the earth is 

 asserted; but in 159G he edited Kepler's Mysterium Cosmographicum, 

 and the Narratio of Rheticus : and in an epistle of his own, which he 

 inserts, he defends the Copernican system by those physical reasonings 

 which we shall shortly have to mention, as the usual arguments in this 

 dispute. Kepler himself, in the outset of the work just named, says, 

 " When I was at Tubingen, attending to Michael Masstlin, being dis- 

 turbed by the manifold inconveniences of the usual opinion concerning 

 the world, I was so delighted with Copernicus, of whom he made great 

 mention in his lectures, that I not only defended his opinions in our 

 disputations of the candidates, but wrote a thesis concerning the First 

 Motion which is produced by the revolution of the earth." This must 

 have been in 1590. 



The differences of opinion respecting the Copernican system, of 

 which we thus see traces, led to a controversy of some length and 

 extent. This controversy turned principally upon physical consider- 

 ations, which were much more distinctly dealt with by Kepler, and 

 others of the followers of Copernicus, than they had been by the dis- 



2 Schoneri Opera, part ii. p. 129. 



