ITS THEORY OF EPICYCLES. 



299 



centre A, while the epicycle uniformly traverses the circle 



A B G D. Now, suppose that 



the star has arrived at H ; it would 



appear to an observer at E to be 



more advanced by the uniform 



movement of all the arc A H ; 



if it be at K, it would appear, on 



the contrary, to be less advanced 



by all the arc A K. At Z the 



star would appear more distant, 



and at T, nearer than if it were at A. 



FIG. 67. The Circle and the 

 Epicycle. 



To explain the other phenomena, such as the stations and 

 retrocessions of the planets, recourse was again had to the 

 epicycles or deferred eccentric circles. By multiplying these 

 it was possible to account for all the angular inequalities in 

 the movements of a planet. It is of importance to note this 

 point, in order to show how very dangerous it is to trust 

 absolutely to mathematics in our search after the truth ; that 

 science which, by the certainty of its demonstrations, nourishes 

 our intellectual pride, and may, therefore, occasionally lull the 

 mind into a false security. The theory of epicycles, from a 

 mathematical point of view, was irreproachable, and it suffi- 

 ciently accounted for the facts which threatened to overthrow 

 the dogma of circular orbits and uniform planetary move- 

 ment. 



But by d-egrees, as observations grew more accurate and 



