236 MOVING FORCK. 
Cases of difn- mentj so'it qa'il se mouve uniformement, Buivant, une direc- 
r.ulty in the ,• i / , - . , i 
doctrines of donnee, ics vitesse respectives seront done encore les 
moving force, memes apresle choc. This quotation puts the matter beyond 
dispute. It is plain, Bernoulli, though he makes use of the 
word action, is only speaking of the motion lost or communi- 
cated, and the relative velocities of the bodies ; there is not the 
most distant hint at the change in their absolute forces." 
In addition to this, I would, with great deference, observe, 
that by the term equal actions of the spring, as used above by 
Mr. Maclaurin, pressures only are meant: but M- Ber- 
noulli held that the motion of a body cannot be produced by 
mere pressure. Unless the pressure act through some portion 
of space, no motion can be produced ; and if, together with 
the pressure, we take into consideration the space through 
which the pressure acts, we shall find that, while the motion of 
C lias been transferred to D, the whole force of the spring has 
also been communicated to D. This will become more obvi- 
ous in examining the 8th case. It should be observed, too, that 
when Mr. Maclaurin sets out with supposing the bodies to be 
in motion, and the spiring to be in a compressed state, he refers 
to a previous application of force, of which he takes no farther 
notice, although a part of this previous force is afterwards ex- 
jiended or given out, in producing the changes which he de- 
scribes. 
It is true our researches must be limited chiefiy to relative 
niotiofi“-Of absolute motion we know but little. But is not 
the motion of the space EFGH with the velocity as 1, relative 
motion with regard to some supposed point, as much as tbo 
final motion of D is relative motion ? 
If the compressed spring be disengaged while the bodies 
are at rest, the motion of the bodies is acknowledged to 
be produced by the force of the spring: but when the sp-ice 
EFGH and the bodies are supposed to be put in motion before 
lire spring is disengaged, there is, according to the prevailing 
theory, no motion produced by tire spring. There is merely 
a transfer of motion from C to D, and we have only the .same 
Biotion after, that we had before, the actiou of the spring. 
Is 
