Moving Force. 197 
the change of figure of M, In the next stage 
of the operation N will have arrived at O’ and 
be at rest ; M will have arrived at 4.5, and will 
have acquired the velocity = And lastly when 
M has arrived at 8’ it will have acquired the ve- 
locity 2. v, and N will have moved back to S” 
and will have re-acquired the velocity > and 
the balls will be at the same distance that they 
' were at first when N struck C.—In explaining 
these facts by the common theory, it is ad- 
mitted that N has communicated to M a 
greater quantity of motion than it had; that 
inconsistency, however, is supposed to be re- 
moved by saying, that the motion of N being 
in the contrary direction, it must be deducted 
from the motion of M, and the remainder will 
be equal to the original motion of N. But 
we know that a body cannot be put in motion, 
in any direction, without force, and as the 
final motion of N, as well as that of M, must 
have been derived from the original force of 
N ; it appears that the motion of N should be 
added to, instead of being deducted from, 
the motion of M, before we can properly 
compare the effects with the force by which 
they have been produced.—tf N had remain- 
ed at rest at O’, M would have been acted 
upon by C till it arrived at 9’, and the whole 
