188 On the Measure of 
~ objected to by all those who hold that the pro- 
duct of the mass into its velocity is the proper 
measure of the force of.a body in motion. 
They contend that‘ all the experiments 
which are usually brought to determine the 
impressions made upon soft bodies, as snow, 
clay, &c. are absolutely unfit for the purpose.” 
That “ the circumstances, which take place 
in the production of these effects, are such as 
-we can never discover.” And that ‘ ‘the 
directions in which the particles recede, the 
velocities. they acquire, their mutual actions 
upon one another, and lastly, the time, in 
which these effects are performed, are all 
beyond the reach of computation,” * 
To this it may be replied, that if only the 
pressure and the space through which it has 
acted be determined, it would be quite super- 
fluous to enter into any farther computation 
cof the cireumstances above enumerated, in 
order to estimate the quantity of mechanical 
force expended in producing the impression. 
For, whatever may have been the relative 
directions, velocities or mutual actions of the 
particles during the time that the impression 
was making, no internal motion remains after 
the impression is completed; and the force 
* D:. Milner. Philos, Trans, 1778. p. 353. 
