104 ESSAYS anp OBSERVATIONS 
limbs preffes forwards both the horfe and the 
{tone ; what is called the reaction of the ftone, 
is not equal to the whole force exerted by the 
horfe; for then indeed there could be no 
progreffion: it is only equal to what is im- 
prefled upon the ftone. 
THE equality of action and reaction in the 
cafe of preflures, is to be underftood in the 
fame manner. When a finger is prefled a- 
gainft any body, the body is faid to reac 
upon the finger, as much as the finger is 
made to act upon the body. If the weight 
of the body be fuftained by the preffure of 
the finger, there will be an active refiftance 
from the power of gravity. And, if the fi- 
gure of the body be violently kept in a bent 
or compreffed ftate, there will be an active 
refiftance from the caufe of cohefion. But — 
if the finger be applied fo as to communicate 
an equal motion to all the parts of the body, 
and without oppofing its gravity ; there will 
be no occafion for imagining, that the body 
really reacts, or actively bears againft the fin- 
ger. The effect indeed upon the finger is 
the fame, as if the body actually preffed up- 
on it; but that effect can eafily be accounted 
for, without having recourfe to fuch a fup- 
pofition. 
