298 ASTRONOMICAL INFALLIBILITY. 



of the circles in which these movements are accomplished ; 

 and that, in this apparent disorder of the phenomena (vegl r^i> 

 vKovovpewiv ruv paivopevut arag/av), nothing really occurs con- 

 trary to their actual immobility (rw oV/ fl-lpim ffupZatvsiv ovdsv 

 dXTiorg/ov O.VTUV rye atdi077}TO$)." 



Now, according to this dogmatic immutability, the straight 

 lines, or radii, which proceed from the revolving star to 

 the centre of the circle, would describe " equal angles in 

 equal times." This is exactly the contrary of the result 

 obtained, as we have seen, by careful observation. 



But this difficulty no more embarrassed the great pontiff 

 of astronomy than a conscientious scruple would perplex 

 the author of a theological dogma. Listen to him : 



" The true cause of these apparent irregularities is explained 

 by two very simple hypotheses. Either the one or the other 

 would account for the phenomena. In fact, if we suppose 

 the movement to occur in a circle described around the 

 centre of the world, and in the plane of the ecliptic, so that 

 the point whence we are looking corresponds with this 

 centre, we must admit either that the planets make their 

 movements equal in non-concentric circles, or that, if these 

 circles are concentric, it is not simply in these circles that 

 they move, but in others, called epicycles, carried through 

 the concentric." * 



Examine Fig. 67. Here A B G D represent the ecliptic, 

 E its centre, and A E G its diameter; Z H T K is the 

 epicycle, in which the planet moves uniformly around the 

 * Ptolemaeus, "Syntaxis Mathematicalis," iii. 3. 



