Moving Force: 177 
of two parts, as described in the figure, having 
the ratio to each other of GF*:KI*. If the 
pressure be not uniform, the fluent of the 
pressure into the space will bear the same re- 
lation which DH bears to the sum of the 
products of the masses into the squares of their 
velocities. 
I am quite at a loss to understand why Mr; 
Atwood excluded this case from those in which 
the moving force may be estimated by the 
products of the.masses into the squares of their 
velocities. If, in cases of rotatory motion 
about fixed axes, that principle “ obtains,” as 
he observes, “ without exception,” there can, 
I think, be no exception to its application in 
cases of this description. 
- Having gone through the examples of force 
producing motion from a state of rest, we come 
now to the examination of cases where motion 
is destroyed, or where it is transferred from 
one body to another. 
It was a favorite doctrine with the Cartesians, 
and it was maintained also, though upon quite 
different. principles, by Leibnitz, and John 
Bernoulli, that motion could not be lost; for 
the same quantity of motion, or of force, it 
was said, must be always preserved in the 
world. A similar doctrine, applied to explain 
Zs 
