$$ 2 7j 28] Eudoxus : Aristotle 29 



scientific Greek astronomers who succeeded him) the 

 spheres were mere geometrical figures, useful as a means 

 of resolving highly complicated motions into simpler 

 elements. Eudoxus was also the first Greek recorded to 

 have had an observatory, which was at Cnidus, but we have 

 few details as to the instruments used or as to the observa- 

 tions made. We owe, however, to him the first systematic 

 description of the constellations (see below, 42), though 

 it was probably based, to a large extent, on rough observa- 

 tions borrowed from his Greek predecessors or from the 

 Egyptians. He was also an accomplished mathematician, 

 and skilled in various other branches of learning. 



Shortly afterwards Callippus ( 20) further developed 

 Eudoxus's scheme of revolving spheres by adding, for 

 reasons not known to us, two spheres each for the sun 

 and moon and one each for Venus, Mercury, and Mars, 

 thus bringing the total number up to 34. 

 '^27. We have a tolerably full account of the astronomical 

 views of Aristotle (384-322 B.C.), both by means of inci- 

 dental references, and by two treatises the Meteorologica 

 and the De Coelo though another book of his, dealing 

 specially with the subject, has unfortunately been lost. He 

 adopted the planetary scheme of Eudoxus and Callippus, 

 but imagined on " metaphysical grounds " that the spheres 

 would have certain disturbing effects on one another, and 

 to counteract these found it necessary to add 22 fresh 

 spheres, making 56 in all. At the same time he treated the 

 spheres as material bodies, thus converting an ingenious^and 

 beautiful geometrical scheme into a confused mechanism.* 

 Aristotle's spheres were, however, not adopted by the 

 leading Greek astronomers who succeeded him, the systems 

 of Hipparchus and Ptolemy being geometrical schemes 

 based on ideas more like those of Eudoxus. 



28. Aristotle, in common with other philosophers of his 

 time, believed the heavens and the heavenly bodies to be 

 spherical. In the case of the moon he supports this belief 

 by the argument attributed to Pythagoras ( 23), namely 

 that the observed appearances of the moon in its several 



* Confused, because the mechanical knowledge of the time was 

 quite unequal to giving any explanation of the way in which these 

 spheres acted on one another. 



