Moving Force. 227 
indirectly by levers, or other means, or when 
a change of figure is produced, the velocity 
of the pressure being different from that of 
the mass which is moved, this relation is no - 
longer preserved. In cases of that description, 
the sum of the changes produced by the mov- 
ing force, is not in any constant ratio to the 
time of its action. If this statement be cor- 
rect, the relation between the effects of a mov- 
ing force and the time of its action cannot be 
reduced to a general formula—It can only be 
considered as an individual character, or 
property of one class of the phenomena of 
moving force,—a property of great impor- 
tance no doubt, but still not a general pro-_ 
perty. The duration therefore of a moving 
force cannot be taken generally as an element 
in the estimation of its quantity. 
If we attempt to estimate some moving 
forces by their duration, and others by the 
spaces through which the pressure acts,— 
according to particular circumstances which 
may appear to be more favorable to the appli- 
cation of one measure than the other; we 
cannot avoid the inconsistency of sometimes 
concluding that a given quantity of moving 
force may be considered greater or less, 
according to the nature of the effect it is 
intended to produce. 
Ff 2 
