38 ESSAYS ann OBSERVATIONS, 
ftone draws the horfe as much’as the horfe 
the ftone. Were this fo, there could be no 
motion. All I can difcover here, is mere re- 
fiftance in the ftone, oceafioned partly by its 
vis refiflentie, and partly by friction. And 
after this-refiftance is overcome, which fpends 
or exhaufts fo much of the horfe’s {trength; 
the {tone is drawn along with the horfe’s re- 
maining {trength, without any further refift- 
ance. 
WITH regard to gravitation, which is gi- 
ven as another inftance of the equality of ac- 
tion and reaction ; it is very true, that there 
is an equal tendency in every particle of mat- 
ter to every particle ; but I am at'a lofs what 
further can be made of this, than’that fuch 
is the law of gravitation. Why then fhould 
we endeavour to account for this effect by a- 
ny feparate law? I mightadd, that this at 
beft is a doubtful inftance of the mutual ac- 
tions of bodies upon each other. It will 
perhaps, upon examination, be found the 
more fafe opinion, that bodies act not upon 
each other by the power of gravity. But of 
this afterwards. 
KEILL, in explaining this law of na- 
ture, feems to confine it to the percuffion of 
bodies; 
