JIOVINO KORCE, 
303 
fr«e to move In any direction with the slightest impulse j the 
two pegs, O and P, to be similar and equal in every respect, 
and to meet with uniform and equal resistance in penetrating Cj 
the weight of A to be double that of B, the velocity of A raov- 
ling in the direction AC, to behalf that of E, moving in the 
opposite direction BC, and A and B to strike their respective 
pegs at the same instant. The result will be as follows. C 
will remain unmoved^ A and B will be brought to rest in the 
isame time, and the peg P will be found to have penetrated C 
twice as far as it has been penetrated by O. This case appears 
to me to admit of the same explanation as some of those which 
we have already examiivcd. It is considered by many, however, 
to show distinctly, that the forces of A and B arc e«)ual. If 
we confine our attention solely to the circumstance of C remain- 
ing at rest, we must no doubt conclude, that the opposite forces 
of A and B are equal ; but if we attend to all the results of the 
lexperiment, we cannot consistently draw that conclusion. It has 
.often been asserted by the advocates on both sides of this ques- 
ition, that we can judge of forces only by their eftects j yet it has 
■been contended by M. D’Alembert*, and by many other good 
wvriterson dynamics, that the estimation of forces by their total 
.^effects, involves a metaphysical question which ought not to be 
-■mixed with experimental investigations of physical facts. It 
:may be safely affirmed, however, that nothing can be more 
'Strictly grounded upon experiment, than conclusions derived 
'from the examination of mechanical changes of figure. 
This term, as has been already observed, includes every 
ichange of figure which requires moving force, or pressure acting 
I through some portion of space, to produce it. Whether it be 
ithe repulsion or the cohesion of the integrant parts of bodies, or 
the attraction of masses to each other, that is to be overcome, 
.mechanical change of figure is produced ; and we have seen, in 
.various cases which have been examined, the uniform relation 
which subsists between determinable quantities of change of 
:figure, and the moving forces by which they are produced. We 
find 
Cases of 
culty ill till* 
cloctriiii'.s of 
nioviii" foice. 
• Trait£ de Dynjuniqne, Disc. Prelim, p 22. 
