214 On the Measure of 
be estimated by the product of the mass into 
its progressive velocity, the change of figure, 
as well as the rotatory motion, must be left 
wholly unaccounted for. 
If the more complicated cases of this des- 
cription, where the force is neither communi- 
cated in the directions of the centres of gravity 
nor in those of the centres of gyration, be 
examined on the same principles by which E 
have attempted to explain the fifth case and 
the case before us, it will be found, that the 
force expended in producing change of figure, 
added to that which is exhibited in the 
motion of the bodies after collision, will 
always be equal to the original force of the 
striking body. 
Having stated, more fully perhaps than is 
consistent with the due limits of a paper of 
this kind, various opinions and explanations 
relating to the examples of force which I have 
offered to the consideration of this society; I 
wish to observe, that the terms, pressure,— 
foree,—moving force,—momentum, &c. are 
used, by different authors, and sometimes 
even by the same author, with various mean- 
