132 DISSERTATION SECOND. [parti. 



a severe blow to the physicks of Aristotle, which regarded 

 comets as meteors generated in the atmosphere. His ob- 

 servation of the new star in 1572, was no less hostile to 

 the argument of the same philosopher, which maintained, 

 that the heavens are a region in which there is neither 

 generation nor corruption, and in which existence has 

 neither a beginning nor an end. 



Yet Tycho, with this knowledge of astronomy, and 

 after having made observations more numerous and accu- 

 rate than all the astronomers who went before him, con- 

 tinued to reject the system of Copernicus, and to deny 

 the motion of the earth. He was, however, convinced 

 that the earth is not the centre about which the planets 

 revolve, for he had himself observed Mars, when in oppo- 

 sition, to be nearer to the earth than the earth was to the 

 sun, so that, if the planets were ranged as in the Ptole- 

 iuaick system, the orbit of Mars must have been within 

 the orbit of the sun. He therefore imagined the system 

 still known by bis name, according to which the sun moves 

 round the earth, and is at the same time the centre of the 

 planetary motions. It cannot be denied, that the phe- 

 nomena purely astronomical may be accounted for on this 

 hypothesis, and that the objections to it are rather derived 

 from physical and mechanical considerations, than from the 

 appearances themselves. It is simpler than the Ptole- 

 maick system, and free from its inconsistencies ; but it is 

 more complex than the Copernican, and, in no respect, 

 affords a better explanation of the phenomena. The true 

 place of the Tychonick system is between the two former; 

 an advance beyond the one, and a step short of the other ; 

 and such, if the progress of discovery were always perfectly 

 regular, is the place which it would have occupied in the 

 history of the science. If Tycho had lived before Co- 

 pernicus, his system would have been a step in the ad- 



