354 LAPLACE. 



movable particles, would remain at rest although it were 

 impelled equally in every direction. On the other hand, 

 two bodies ought to advance towards each other, since 



O ' 



they would serve the purpose of mutual screens, since 

 the surfaces facing each other would no longer be hit in 

 the direction of their line of junction by the ultra-mun- 

 dane particles, since there would then exist currents, the 

 effect of which would no longer be neutralized by oppo- 

 site currents. It will be easily seen, besides, that two 

 bodies plunged into the gravitative fluid, would tend to 

 approach each other with an intensity which would vary 

 in the inverse proportion of the square of the distance. 



If attraction is the result of the impulse of a fluid, its 

 action ought to employ a finite time in traversing the 

 immense spaces which separate the celestial bodies. If 

 the sun, then, were suddenly extinguished, the earth 

 after the catastrophe would, mathematically speaking, 

 still continue for some time to experience its attractive 

 influence. The contrary would happen on the occasion 

 of the sudden birth of a planet ; a certain time would 

 elapse before the attractive force of the new body would 

 make itself felt on the earth. 



Several geometers of the last century were of opinion 

 that the force of attraction is not transmitted instanta- 

 neously from one body to another ; they even assigned 

 to it a comparatively inconsiderable velocity of propaga- 

 tion. Daniel Bernoulli, for example, in attempting to 

 explain how the spring tide arrives upon our coasts a 

 day and a half after the sizygees, that is to say, a day 

 and a half after the epochs when the sun and moon are 

 most favourably situated for the production of this mag- 

 nificent phenomenon, assumed that the disturbing force 

 required all this time (a day and a half) for its propaga- 



