f *7] 
Received November 16 , 1767.' 
III. ^ EJfay on the Force of Percujfion > 
by William Richardfon, M. D. commu~ 
nicated by William Heberden, M. D, 
F. R . S. 
Read Feb. 18,^ TTHEN we confider the extraor- 
W dinary advancement in natural 
philofophy, from the furprifing difcoveries of the 
great Sir Ifaac Newton, and other ingenious men, 
who have followed his example ; it may afford mat- 
ter of the greateft wonder, to find the moft acute 
philofophers ff ill contending, whether the force of 
percuffion be in proportion to the velocity of bodies 
in motion, or the fquares of thofe velocities. 
Sentiments fo oppofite in their nature, and fo 
ftrongly fupported by their refpedive advocates, may 
well make a cautious perfon fufped, that nothing is 
to be difcovered with certainty in the operations of 
nature. In which opinion he may be the more con- 
firmed from this confideration, that the prefen t 
difpute is not about objects far removed from our 
observation, but fuch adions of bodies as do con- 
flantly occur to our fenfes, and which without dif- 
ficulty may be reduced to experiment. 
What then can be the reafon, after fuch variety 
of experiments have been made, why this matter is 
not, before this time, brought to a decifion ? The 
Vol. LVIIL D fault 
