Moving Force. 209 
whole impression will be produced by gradual 
pressure. —In estimating the force in this case; 
a practical man thinks of nothing but the 
quantity of mechanical force—or the pressure 
into the space—necessary to raise the prism 
to the given height; and as the same quantity 
of force will always raise it-to the same height; 
he concludes'that the same effect must always 
be produced by its fall, although the times 
in which these equal effects are produced 
may be very different. If instead of a piece 
of clay, we place a much harder substance— 
a block of iron for example—under the 
prism, we shall have an impression produced 
on the prism as well as on the block; and, 
unless the centre of motion be ofa very: per- 
manent kind, we shall, when the block is 
placed near to A, have a change of figtire in 
that centre also. But still if all these changes 
of figure could be accurately measured, by the 
pressure and the space expended in producing 
each of them, their sum would be equal to the 
whole change of figure produced on the clay, 
or'on any other comparatively soft substance, 
placed under P. There are many very com= 
plicated cases of this kind,—such as the biam= 
mering and rolling of metals, which may, I 
apprehend, be all distinctly sc: al upon 
the same principles. 
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