49* PHILOSOPHICAL TRANSACTIONS. [aNNO I7O8. 



111. An Essay on the Force of Percussion. By IVllUam Richardsov, M. D. 



p. 17. 



Those who maintain that the force of percussion is as the velocity of the 

 striking bodies, when they account for the impressions made in soft bodies (which 

 are found, by experiment, to be as the squares 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 impression will of course be as the time into the velocity, 

 or, which is the same thing, as the square of the velocity. Those who, on the 

 contrary, insist that the force of percussion is in proportion to the squares of 

 velocity, finding from experiment that in soft bodies the velocity after percussion 

 falls short of this estimate, would make us believe, that in compressing the parts 

 of those bodies, a certain degree of force must necessarily be lost, which, being 

 added to what remains after percussion, will sufficiently confirm the truth of 

 their doctrine. How then are these different effects to be accounted for, and in 

 what manner are they to be deduced from the same cause ? This diversity of ap- 

 pearances. Dr. R. has for some time suspected, might proceed from the nature of 

 cohesion : that while the force of percussion produced an effect on the whole 

 mass of matter which receives the stroke, in proportion to the velocity of the 

 impinging body ; it might, at the same time, in separating the cohering parts 

 from each other, produce an effect in proportion to the square of the velocity. 



In order to make a further discovery in this matter, Dr. R. determined first 

 to make experiments on such soft bodies as have a considerable degree af cohe- 

 sion ; and then to try those bodies, when dried and reduced to powder, and by 

 that means deprived of their cohesion ; which experiments, when compared 

 with each other, would give him an insight into this intricate affair, and at the 

 same time disclose that beautiful simplicity, which nature observes in all her 

 operations. His apparatus for making the experiments consists of 4 balls ex- 

 actly spherical, 2 iron branches, and a small lead cistern. The balls are each of 

 them 2 inches in diameter ; 1 are of brass, and 2 of box-wood ; one of each 

 sort is solid, and the other hollow ; that which is hollow is only half the weight 

 of the solid one, and may be opened by means of a screw in the middle. The 

 iron branches are to give the balls their proper directions ; they have each of 

 them a small brass pulley in the fore part, and in the hind part a kind of hook, 

 which fastens them to staples at different heights; one of the branches is, 2 

 inches long, and the other 4 inches, exclusive of pulleys ; by which means the 

 balls when let fall are directed to different parts of the surface they strike upon. 

 The lead cistern is of an oblong form, that the contained matter may, at the 

 same time, receive 2 distinct impressions ; either when balls of different weight 

 are let fall, or the same ball is let fall from different heights ; its length is 6 

 inches, its breadth 4 inches, and its depth 2 inches. 



