NEW MECHANICS AND ASTRONOMY. 239 



to Laplace's calculations, at least ten million times as 

 quickly as light, and that consequently it cannot be of 

 electro-magnetic origin. Laplace's result is well known, 

 but its significance is generally lost sight of. Laplace 

 assumed that, if the transmission of gravitation is not 

 instantaneous, its velocity of transmission combines 

 with that of the attracted body, as happens in the case 

 of light in the phenomenon of astronomical aberration, 

 in such a way that the effective force is not directed 

 along the straight line joining the two bodies, but 

 makes a small angle with that straight line. This is 

 quite an individual hypothesis, not very well sub- 

 stantiated, and in any case entirely different from that 

 of Lorentz. Laplace's result proves nothing against 

 Lorentz's theory. 



IL 



Comparison with Astronomical 

 Observations. 



Are the foregoing theories reconcilable with astro- 

 nomical observations? To begin with, if we adopt 

 them, the energy of the planetary motions will be 

 constantly dissipated by the effect of the wave of 

 acceleration. It would follow from this that there would 

 be a constant acceleration of the mean motions of the 

 planets, as if these planets were moving in a resisting 

 medium. But this effect is exceedingly slight, much 

 too slight to be disclosed by the most minute obser- 

 vations. The acceleration of the celestial bodies is 

 relatively small, so that the effects of the wave of 

 acceleration are negligible, and the motion may be 

 regarded as quasi-stationary. It is true that the 



