252 
MOVING FORfE. 
Cases of diftl- tities of motion might be derived from the same quantity of 
docHncs*«f It must be acknowledged that from some expressions 
moving force, of Sir Isaac Newton, in alluding to this and some other cases, 
it might appear, if these expressions are taken individually, 
without reference to his general doctrines, that he supposed a 
variation of force to take place in this case. That supposition 
has been noticed by Mr. Bernoulli with a degree of unfortu- 
nate asperity peculiar to himself, and very inconsistent, it 
must be confessed, with the character by which philosophical 
discussions ought to be distinguished. From the context, how- 
ever, it is obvious, that Sir Isaac Newton could not mean the 
casual expressions in question to be strictly applied as relating 
to variation of force in the cases which he mentions. For, if 
/ 
they can be so applied, they must be indiscriminately applied 
to cases which have no resemblance to each other. The /bree 
which is expended in overcoming the cohesion of pitch*, for 
example, can never be seriously compared w'ith any supposed 
change of jbree in the case under consideration. Yet, accord- 
ing to Mr. Bernoulli’s acceptation. Sir Isaac Newton must 
have meant that there was, in both cases, the same kind of va- 
riation of JoTce. 
If D be a non-elastic body, we shall then, indeed, have a 
variation of the force similar to that which takes place in the 
motion of the pitch. A portion of the force will be expended 
in producing change of figure, and the results after collision 
will exhibit four distinct effects of moving force, namely, a 
change in the progressive motion of D, a change of figure in 
D, a progressive motion in G, and a rotatory motion in A and 
* V 
B'. For D w'ill move on with the velocity — , and its figure 
2 V 
will be changed, G will move on with the velocity — , and A 
V 4 
and B will revolve around G with the velocity — . I'hat is, 
4 
cne-fourth of the original force of D will remain with it after 
collisiofi, one half will have been expended in changing the 
figure 
* See Horsley’s Nevvlou, voI,‘ 4, p. 25^. 
