‘108 On the Measure of 
/ 
Mr. Atwood, in his Treatise on the rectili- 
near motion and rotation of, Bodies, bestowed 
considerable attention on Mr. Smeaton’s ex- 
perinmients and conclusions... He also observes, 
‘that Emerson, and other authors of merit, 
‘have been led into considerable errors, “by 
supposing the momentum of bodies, to be as 
the quantity, of matter into the velocity.*, In 
that he agrees with Mr. Smeaton;. but he 
afterwards concludes, that neither of the mea- 
sures of force are capable of general applica- 
tion, and that for one class. of the effects of 
force, we have no proper measure, 
After discussing various examples, of. force, 
he proceeds as follows: ‘ But the truth is, the 
principle’ (of permanent quantity) obtains not 
according to either of the measures, except in 
particular cases, which may be demonstrated 
as the other properties of forces are from the 
general laws or axioms. 
“In the rectilinear motion of bodies, ac- 
celerated from quiescence, or retarded until 
they ave at fest, the permanency of any given 
quantity of motion is demonstrated from the 
axioms, whether that motion be estimated by 
one measure or the other. 
“In bodies which revolve round fixed axes, 
* Treatise on Rectilinear and Rotatory Motion. Pre- 
face, p. 10. 
