[ 4*8 ] 
admitting this Principle, no Argument can be drawn 
from it by one Party, that will be of any Service to 
convince the other. 
But as this Principle is chiefly made ufe of in 
reafoning upon Experiments made with [Springs, 
many of which have been produced by both Parties, 
in Support of their Opinions, it may be worth while 
more particularly to confider. What Right there is 
on the one Side to impofe this Principle, and what 
Reafons may be given on the other for rejeding it. 
When one End of a Spring, wholly unbent, leans 
againft an immoveable Support, and the oppofite 
End is ftruck upon by a Body in Motion, which, 
bending the Spring to fome certain Degree, does 
thereby lofe its whole moving Force ; the moving 
Force of the Body may be confidered as the Caufe 
of bending the Spring; and the Bending of the 
Spring may be looked upon as the Effed of that 
Caufe, which is wholly fpent and confumed in pro- 
ducing it. 
Now if two unequal Bodies, moving with une- 
equal Velocities, ftrike in this manner upon two equal 
Springs, and each of them bend the Spring it ftrikes 
upon, exadly to the fame Degree; and by fo doing, 
the moving Force of each Body be intirely con- 
fumed; Here, fay the Leibnitian Writers, are two 
equal Effeds produced ; for the Springs are equal, 
and are now equally bent ; and the moving Forces, 
which are the Caufes of thofe Effeds, are wholly 
confumed in producing them ; and therefore, by vir- 
tue of the Principle above laid down, thofe Caufes 
muft be equal ; that is, the moving Forces of the two 
Bodies muft be equal. 
But 
