PRELUDE TO THE EPOCH OF HIPPARCHUS. 173 



from west to east, while the wheel, carrying the 

 planet in its motion, moves round its own center. 

 In this way the motion of the wheel about its 

 center, would, in some situations, counterbalance 

 the general motion of the center, and make the 

 planet retrograde, while, on the whole, the wes- 

 terly motion would prevail. Just as if we suppose 

 that a person, holding a lamp in his hand in the 

 dark, and at a distance, so that the lamp alone 

 is visible, should run on turning himself round; 

 we should see the light sometimes stationary, some- 

 times retrograde, but on the whole progressive. 



A mechanism of this kind was imagined for 

 each of the planets, and the wheels of which we 

 have spoken were, in the end, called Epicycles. 



The application of such mechanism to the 

 planets appears to have arisen in Greece about 

 the time of Aristotle. In the works of Plato we 

 find a strong taste for this kind of mechanical 

 speculation. In the tenth book of the " Polity," 

 we have the apologue of Alcinus the Pamphylian, 

 who, being supposed to be killed in battle, revived 

 when he was placed on the funeral pyre, and re- 

 lated what he had seen during his trance. Among 

 other revelations, he beheld the machinery by 

 which all the celestial bodies revolve. The axis 

 of these revolutions is the adamantine distaff which 

 Destiny holds between her knees; on this are 

 fixed, by means of different sockets, flat rings, by 

 which the planets are carried. The order and 



