208 On the Measure of 
call it, of collision; the resulting velocities 
and directions of the bodies, after collision, 
cannot be determined. . 
‘have selected the case which I have stated, 
(as I have selected all the rest,) as being the 
most simple of its kind; and the solution 
which I have offered is also simple; being 
derived from examining the pressures and the 
spaces through which they act in producing: 
the motion of A. 
The 12th example is stated for the purpose 
of showing that, in cases where quantity of 
motion in one direction forms no part of the 
subject to be considered, there is in the colli- 
sion of non-elastic bodies a positive loss of 
force, in whatever way it may be reckoned, 
and if that loss be estimated by examining the 
pressures and the spaces through which they 
act, a change of figure, corresponding to the 
force which has been expended, will be found. 
The 13th case was propesed to me by my 
friend Mr. Dalton, to whose candid encou- 
ragement I have been much indebted in the 
prosecution of this enquiry. It is stated in 
order to show that the same effect is produced 
by the same force, whether it act by gradual 
pressure or by sudden percussion.—lf the 
piece of clay be placed so near to A as to 
touch the prism when it begins to fall, the 
