174 THE WORLD-ENERGY 



with this result; that the moon must now again cross 

 the earth's path, but this time in advance of the earth 

 itself. 



Thus the moon will once more reach a position, rela- 

 tively to the other bodies, similar to that in which we 

 first found it. 



Evidently, it needs but to pursue this series of move- 

 ments which anyone can figure to himself on paper if 

 he finds it difficult to follow otherwise to see that in 

 their fall toward the sun the earth and moon must inev- 

 itably pursue a curved direction of great complexity, and 

 that they must in this complex movement inevitably fall 

 past the sun. 



At the same time, it is to be remembered that the fall 

 is real. There is, up to a given point, constant decrease 

 in distance between these two bodies and the sun. And 

 that point will inevitably be determined by the rela- 

 tion between two phases of force the centripetal and 

 the centrifugal. So long as the former is greater than 

 the latter, the approach will continue. The moment 

 the latter comes to predominate over the former, that 

 moment the movement toward the center (sun) will be 

 transformed into a movement away from the center. 



What constitutes centrifugal force? The answer has 

 in reality already been given. The mutual attractions 

 of three or more bodies must result in a complex move- 

 ment on the part of each body; the distances passed over 

 by the several bodies being inversely proportional to 

 their masses. And as the multiple attractions render 

 impossible the direct approach of any one body toward 

 any other, the total resultant is the curvilinear move- 

 ment of all. 



