SEQUEL TO THE EPOCH OF HIPPARCHUS. 235 



and referred them to the earth alone; and thus 

 the apparent eccentricities which he had to account 

 for, were the compound result of the Eccentricity 

 of the Earth's orbit, and of the proper Eccentricity 

 of the orbit of the Planet. He explained this 

 result by the received mechanism of an eccentric 

 Deferent, carrying an Epicycle; but the motion 

 in the Deferent is uniform, not about the center 

 of the circle, but about another point, the Equant. 

 Without going further into detail, it may be 

 sufficient to state that, by a combination of 

 Eccentrics and Epicycles, he did account for the 

 leading features of these motions; and by using 

 his own observations, compared with more ancient 

 ones, (for instance, those of Timocharis for Venus,) 

 he was able to determine the Dimensions and 

 Positions of the Orbits (j). 



I shall here close my account of the astrono- 

 mical progress of the Greek School. My purpose 

 is only to illustrate the principles on which the 

 progress of science depends, and therefore I have 

 not at all pretended to touch upon every part 

 of the subject! Some portions of the ancient the- 

 ories, as for instance, the mode of accounting for 

 the motions of the moon and planets in latitude, 

 are sufficiently analogous to what has been ex- 

 plained, not to require any more especial notice. 

 Other parts of the Greek astronomical knowledge, 

 as, for instance, their acquaintance with refraction, 

 did not assume any clear or definite form, and can 



