4 GALILEO AND HIS JUDGES. 



the centre, and all the heavenly motions taking place 

 in circles. For this he gives his reasons sound and 

 good reasons for the spherical shape of the Earth ; 

 unsound and mistaken, however, for the denial of the 

 Earth's rotation on its axis, an opinion he evidently 

 knew had been maintained by some persons ; one 

 important argument on this latter head being that if 

 the Earth rotated with the great velocity necessary to 

 carry it round in one day, it would leave the air 

 behind it. He places the Earth (as already said) in 

 the centre, then the Moon as the nearest planet re- 

 volving round it, the next Mercury, then Venus, then 

 the Sun, and beyond these Mars, Jupiter, and Saturn. 

 All moved in circles, but since, with the exception of 

 the Sun and Moon, simple circles would not account 

 for the motions, he supposes small circles in a retro- 

 grade direction forming loops upon the main circle, 

 which he calls epicycles ; undoubtedly following in this 

 respect, Hipparchus, who three centuries before had 

 struck out the same idea. It is curious that Ptolemy's 

 arguments (as above mentioned) show clearly that in 

 his day there were some persons, though their names 

 have perished,* some one or two philosophers 

 endowed with a marvellous insight into Nature, who 

 had guessed at the true solution of the great astro- 

 nomical problem ; but they left no enduring mark 

 on their age. The system of Ptolemy accounted for 



* Kicetas of Syracuse (whose date I am not able to give) seems 

 to have been aware of the diurnal movement of the earth round its 



axis. 



