 PHYSICALann LITERARY. 3; 
to each, by their mutual reaction ; and the 
mt fame mutt ‘happen to hard bodies, if they 
: _ have the fame power of reaction. Ina word, 
~ JT cannot’ diftinguith elafticity from a power 
_ of reaction ; and a hard body differs from an 
elaftic only in this, that the former has no 
‘power of reaction, but only of refiftance, 
A third difficulty is, that, in the bulk of the 
inftances commonly given to illuftrate this 
law, I cannot difcover an equality of action 
_ and reaction, And laftly, what appears the 
moft unfurmountable difficulty is, that, ex- 
cepting the cafe of elafticity now mentioned, © 
and that of fluidity to be mentioned after- 
wards; J have not found a fingle inftance 
of an effect, produced by the action of one 
body upon another, but what may be fairly 
explained by acknowledged principles, lay- 
ing afide altogether this fuppofed equality of 
ation and reaction. And if no fact can be 
condefcended on, to prove the point with 
regard to hard bodies; why fhould we ad- 
apt this as.an univerfal law of motion or of 
matter ? For furely it is irrational to admit of 
any law or principle without evidence. 
‘Turse difficulties will be bett illuftrated 
by going to particulars. And with regard to 
a 
me Sir 
q 
