I9I4.] "A KINETIC THEORY OF GRAVITATION." 127 



earth ; gravity directly, and the retarding force indirectly conspiring 

 toward this result. With the assumed velocity of light for the "gra- 

 vific fluid," Laplace found that the angular acceleration of the moon's 

 motion would be millions of times greater than necessary to account 

 for her known acceleration. 



I have thus outlined Laplace's conception of the mechanism of 

 gravitation, which led to his famous conclusion of virtually infinite 

 velocity of propagation, because I have not met with anything of the 

 sort in modern text books of astronomy or physics ; his startling con- 

 clusion is known to everyone, but his premises are generally for- 

 gotten; and further because I wish to have it clearly in mind for 

 contrast with what is to follow. 



Returning now to the theory of gravitation under discussion: In 

 Fig. 6, E represents the earth and M the moon moving in the dotted 

 line orbit in the direction indicated by the large arrow, both revolv- 

 ing about their common center of gravity C. Instead of showing C 

 well inside the earth's circumference where it belongs, I have shown 

 it outside, so as to enlarge certain details of the diagram and thus 

 avoid confusion of lines. 



The earth and moon are each supposed to cast a spherical energy 

 shadow, or occupy the center of a spherical field of influence, as 

 already indicated, into which the other is pushed by the slightly 

 superior energy-flux coming from beyond it. The strongest push 

 of each is toward the densest part or origin of the shadow of the 

 other. Thus, if earth and moon were stationary, each would be 

 pushed toward the center of mass of the other. But while the 

 shadow, emanating so to speak, from the earth at any instant is being 

 propagated outward to the moon's orbit, the latter will have moved 

 to M', and the earth will have moved to E'. Clearly then, the moon 

 at M' will not be pushed toward E' , but toward E, which is the ori- 

 gin of the shadow into which it is being pushed. The centripetal 

 force M'E may be resolved into the radial component M'E' and the 

 tangential component M'P equal to the displacement of the earth's 

 center from E to E'. Clearly, the force M'P is an accelerating force, 

 and bears the same ratio to gravity at M' that M'P bears to M'E'. 



If the velocity of propagation of the energy shadow equals the 



