MEASURE OF MOVING FORCE. 151 
tions, directly opposite to each other ; it follows, 
therefore, that when the direction of the motion 
which it actually takes is known, one equation 
only is required to determine this motion in a 
complete manner. 
To calculate the effect of machines in motion, 
M. Poisson gives the following equation of living 
forces :— 
4=mv’—32mk? =z Pdp—/=zQdq. 
Where v represents the velocity of the mass 
m at the end of any given time ¢, & its original 
velocity answering to t=o, P any one of the pres- 
sures applied to cause motion in the machine, and 
Q any one of the resistances to its motion; dp the 
space passed over by P in the direction of its 
force during the time dé, and dq the space pas- 
sed over in the same time by Q, in the direction 
of its force. The integrals to be taken so as to 
vanish at the commencement of the motion. 
The products Pdp and Qdq of which the sums 
are subjected to these integrations have, M. 
Poisson observes, received different denomina- 
tions; and M. Coriolis proposes to call them 
