312 EPOCHS IN THE HIST011Y OF THE CONTEMPLATION OP 



to be fastened as if nailed. ( 478 ) Geminus the Rhodian, a 

 cotemporary of Cicero's,, doubted the constellations being 

 all in the same plane ; some, he thought, were higher and 

 some lower. This manner of representing the heaven of the 

 fixed stars was transferred to the planets ; and thus arose 

 the theory of the excentric intercalated spheres of Eudoxus, 

 Menaechmus, and Aristotle who invented retrograding 

 spheres. After a century, the acute mind of Apollonius 

 caused the theory of epicycles, a construction which 

 adapted itself more easily to the representation and calcula- 

 tion of the motions of the planets, to supersede the solid 

 spheres. Whether, as Ideler believes, it was not until after 

 the establishment of the Alexandrian Museum, that philoso- 

 phers began to regard " a free movement of the planets in 

 space as possible," whether previously to that period the 

 intercalated transparent spheres, (27 according to Eudoxus, 

 55 according to Aristotle), as well as the epicycles which 

 passed from Hipparchus and Ptolemy to the middle ages, 

 were generally regarded, not as actual solid substances 

 having material thickness, but simply as ideal abstractions, 

 I refrain here from any attempt to decide historically, 

 greatly as I incline to the latter view. 



It is more certain, that in the middle of the 1 6th century, 

 when the theory of the 77 homocentric spheres of the learned 

 Polyhistor, Girolamo Fracastoro, was received with applause, 

 and when, subsequently, the opponents of Copernicus sought 

 for every means of supporting the system of Ptolemy, the 

 representation of the existence of solid spheres, circles 

 and epicycles, which had been particularly favoured by the 

 fathers of the Church, was still extremely prevalent. Tycho 

 Brahe expressly boasts, that by his considerations on the 



