AND THEORY OF THE HEAVENS. 107 



that we know; and I do not understand by what system 

 this could be harmonized with a body whose mass 

 exceeds all the rest, unless this motion itself is to be 

 regarded as the effect of that attraction which this 

 heavenly body exercises according to the ratio of that 

 same mass. If the axial rotation were the effect of an 

 external cause, then Mars ought to have a more rapid 

 rotation than Jupiter ; for the same moving force moves 

 a smaller body more than a larger one. And it would 

 justly astonish us, seeing that all movements decrease as 

 they are further from the centre, that the velocities of 

 the rotations should increase with the same distances, 

 and in the case of Jupiter could be even two and a 

 half times quicker than that of its annual movement. 



As we are therefore forced to recognize in the daily 

 rotations of the planets the very same cause which is 

 the universal source of motion in nature namely, 

 Attraction this mode of explanation will authenticate its 

 correctness by the natural claim of its fundamental con- 

 ception, and by such unforced inferences from it. 



But if the formation of a body does itself produce the 

 rotation round its axis, then all the orbs of the universe 

 must have this rotation. Why, then, has the moon not got 

 it j for the moon, according to some (although erroneously) 

 seems to derive that sort of rotation by which it always 

 turns the same side to the earth rather from a preponder- 

 ance of one hemisphere than from an actual motion of 

 revolution? May it not, in fact, have formerly turned 

 more rapidly round its axis, and by some unassigned causes 

 which gradually diminished it this motion has been 

 brought to this small and proportioned remainder? We 

 have only to solve this question in regard to one of 



