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Moving Force. 257 
our notions of force from pressure as it is per- 
ceived by the sense of touch, and that in all 
cases where neither the velocity nor the figure 
' of the body pressed is changed by the pres- 
sure, we have only simple pressure balanced by 
pressure, the various combinations of which 
have long ago been explained and demon- 
strated in the most satisfactory manner. 
But in all cases where either the velocity or 
the figure of the body pressed is changed by 
the pressure, we have examples of moving 
force, which may be properly represented by 
a rectangle; of which the pressure forms one 
side, and the space, through which it acts, the 
other side: and however various and compli- 
cated the changes of velocity and of figure may 
appear, they must all be derived from deter- 
minate quantities of moving foree. We may 
have changes of rectilineal velocity in various 
directions, changes of rotatory velocity, and 
changes of figure, all produced at the same 
time by a given quantity of moving force; 
and it is certainly a desirable object to deter- 
mine what portion of that quantity has been 
expended in producing each of these different 
effects. I have endeavoured to show that all 
these changes may be distinctly explained and 
estimated, by examining the pressure and the 
space through which it acts in producing them. 
Kk 
