583 
of Edinburgh, Session 1871 - 72 . 
From Le Sage's fundamental assumptions, given above as nearly 
as may be in his own words, it is, as he says himself, easy to deduce 
the law of the inverse square of the distance, and the law of pro- 
portionality of gravity to mass The object of the present note is 
not to give an exposition of Le Sage’s theory, which is sufficiently 
set forth in the preceding extracts, and discussed in detail in the 
first two books of his posthumous treatise. I may merely say that 
inasmuch as the law of the inverse square of the distance, for every 
distance, however great, would be a perfectly obvious consequence 
of the assumptions, were the gravific corpuscules infinitely small, and 
therefore incapable of coming into collision with one another, it 
may be extended to as great distances as we please, by giving 
small enough dimensions to the corpuscules relatively to the mean 
distance of each from its nearest neighbour. The law of masses 
may be extended to as great masses as those for which observation 
proves it (for example the mass of Jupiter), by making the 
diameters of the bars of the supposed cage-atoms constituting heavy 
bodies, small enough. Thus, for example, there is nothing to pre- 
vent us from supposing that not more than one straight line of a 
million drawn at random towards Jupiter and continued through 
it, should touch one of the bars. Lastly, as Le Sage proves, the 
resistance of his gravific fluid to the motion of one of the planets 
through it, is proportional to the product of the velocity of the 
planet into the average velocity of the gravific corpuscules ; and 
hence by making the velocities of the corpuscules great enough, 
and giving them suitably small masses, they may produce the 
actual forces of gravitation, and not more than the amount of 
resistance which observation allows us to suppose that the planets 
experience. It will be a very interesting subject to examine 
minutely Le Sage’s details on these points, and to judge whether 
or not the additional knowledge gained by observation since his 
time requires any modification to be made in the estimate which he 
has given of the possible degrees of permeability of the sun and 
planets, of the possible proportions of diameters of corpuscules to 
interstices between them in the “ gravific fluid,” and of the possible 
velocities of its component corpuscules. This much is certain, 
that if hard indivisible atoms are granted at all, his principles 
are unassailable ; and nothing can be said against the probability 
