SCIENCE OF THE SIXTEENTH CENTURY. 89 



Up to Tycho's time astronomers had entertained very erroneous 

 notions concerning comets, holding those bodies to be merely meteors 

 nearer to us than the moon, and engendered within the earth's atmo- 

 sphere. Such having been the opinion of Aristotle, it need hardly be 

 said that all the book philosophers since his time held firmly to it. 

 The comet of 1577 gave Tycho the opportunity of learning some facts 

 concerning these bodies ; and the results gave a rude shock to the com- 

 placency of the Aristoteleans. Tycho found that the comet had no 

 sensible parallax, and this proved that it was situated beyond the region 

 of the moon ; he also made an approximate calculation of the comet's 

 orbit, and the proper motion of the wandering planet proved that the 

 heavenly bodies could not possibly be carried round in the solid crys- 

 talline spheres, which formed the accredited celestial mechanism of 

 the schools. 



The Aristoteleans would not accept these conclusions, and violent 

 opposition was raised, notably by Claramonti, a professor at Pisa, and 

 by a Scotchman named Craig. But as reason and truth were on 

 Tycho's side and could not be overthrown by quotations, his opponents 

 had to resort to personal abuse. 



Thus Tycho shivered into atoms and dissipated into air or rather 

 into vacuous space the huge orbs of impenetrable crystal which had, 

 in men's conceptions, for so many ages majestically revolved about 

 our earth. It had up to this period been thought necessary to fix each 

 planet on one of these immense transparent spheres, which carried 

 it round in its course ; and while these spheres revolved, orb within 

 orb, each in its own circuit, another greater sphere surrounded them 

 bearing the fixed stars ; and, external to all, an immense hollow globe 

 called the primum mobile rolled itself and the included spheres round 

 the central earth every twenty-four hours. 



Tycho did not accept the Copernican system of the world ; but, 

 influenced either by religious scruples resting on the presumed inter 

 pretation of Scripture current in his day, or by some other motive, he 

 proposed a system of his own, which holds an intermediate position 

 between the Copernican and the Ptolemaic. In this the earth is sup- 

 posed to be stationary in the centre, the sun and moon revolving daily 

 about it, while the planets revolved about the sun which, in its motion 

 round the earth was supposed to carry all the planets with it. This 

 theory agreed with, or accounted for, the phenomena as well as the 

 Copernican theory did, and could therefore be equally well used as the 

 basis for calculations. It was, however, vastly inferior in simplicity to 

 the theory of Copernicus, for the supposition of so immense a system 

 revolving about a body of dimensions so insignificant as the earth, 

 presents great difficulties and improbabilities. One of the greatest of 

 these was removed by a modification of the Tychonic doctrine, which 

 consisted in admitting a diurnal rotation for the earth while retaining its 

 central position. Neither of these systems, however, found many sup- 



