304 
MOVING FORCE. 
Cases of diffi- find by experience, that when a body in motion is retarded or 
liocni'uos of i^rought to rest, either a change of figure is produced, or a 
niovinn; force, quantity of moving force, equal to that which the body has 
parted with, is communicated to some other body or system of 
bodies. It has been supposed, indeed, that A and B, in the 
' case stated, may be brought to rest without any change of figure 
being produced. That supposition, however, is contradicted by 
universal experience, and in point of fact w'e may, with as 
much consistency, suppose that a body may be put in motion 
without force, as that two bodies moving in opposite direction# 
may destroy each other’s motion without producing change of 
figure. It appears then, that if any metaphysical consideration 
has been improperly mixed with this question, it is the supposed 
possible existence of perfectly hard non*elastic substances. But 
unless we have actual proof of the existence of such substances, 
we can have no evidence derived from experience to justify the 
inference, that A and B may be brought to rest without pro- 
ducing change of figure. When a physical experiment of any 
kind is made, it is generally understood, that unless all the 
results be collected and examined, erroneous conclusions may 
be formed. If an experimenter reject some of the results which 
he obtains, on the supposition, that sometimes they may not 
occur, although in fact they constantly occur in determinate 
quantities, he cannot reasonably demand assent to general con- 
clusions drawn from so partial an examination of the facts. If 
this reasoning be well founded, we cannot reject the considera- 
tion of the changes of figure produced by A and B j and if we 
have no experience of a mechanical change of figure being pro- 
duced without moving force, nor of bodies destroying each 
other’s motion without producing mechanical change of figure, 
we cannot, in the case before us, consistently do otherwise than 
estimate the absolute forces of A and B by the respective 
changes of figure produced by each, 
I shall now conclude my observations with a simple applica- 
tion of the principle which I have endeavoured to support, to the 
resolution of compound moving forces. 
If we suppose BAG (fig'. 22) to be a right angle, and three 
strings, 
