C 18 ] 
fault cannot be in the experiments themfelves, the 
chief of which have been often repeated, and that 
in the mod accurate manner : it muft, therefore, be 
in the ufe which has been made of them, in the 
eroundlefs inferences which have been drawn from 
o 
them* 
Thofe who have wrote belt on this fubjeCt (whe- 
ther in fupport of the velocities, or the fquares of 
velocities) feem to me to have inferred more from 
the principle they maintain than what they bring 
fufficient arguments to juftify ; by which means they 
blend truth with error, and the more they endeavour 
to illuftrate their refpedtive do&rines, the more they 
render them perplexed and confufed. For the truth 
of what I have advanced, I appeal to the two fol- 
lowing inftances. 
Thofe who maintain that the force of percuffion 
is as the velocity of the (hiking bodies, when they 
account for the impreffions made in foft bodies (which 
are found, by experiment, to be as the fquares of 
the velocities), inform us, that the time ought to 
be taken into the account ; which being as the 
velocity of the impinging body, the impreffion will 
of courfe be as the time into the velocity, or (which 
is the fame thing) as the fquare of the velocity. 
But this, in my mind, is to affert more than what 
can be clearly demonftrated : for as a&ion and re- 
action are equal, the more forcibly one body aCts 
upon another, the greater muft be the refinance it 
meets with ; and whatever be the time of its aCting, 
fuppofing its force to be given, the effeCt produced 
muft (till remain the lame. 
To 
