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~—~854 ; 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 
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- 
