$2 Review of O. Gregory’s Treatise on Mechanics. 
» Chap. 4, treats of the mechanical powers, and contains 
much useful, and interesting matter collected from differ- 
ent sources. The definition of a machine “ that it is any 
thing which serves to augment or regulate moving forces,” 
would be more correct by the omission of the word aug- 
ment. In what machine, has any augmentation of force, m 
a mechanical sense, been produced? Estimating force as 
we do, by the product of mass into velocity, or time the 
reciprocal of the velocity, it will in all cases be diminished 
by the intervention of a machine, on account of its friction 
und the aerial resistance. The advantages of machines con- 
sist in their capacity to alter the components of force, or 
change their direction, or to change the magnitude of the 
factors M, V, T, which compounded constitute the mea- 
sure of force. Thus, when we have a great velocity, and 
little mass, or weight, we may put in motion a great mass, 
or raise a great weight, with velocities, however, in the 
inverse ratio of the masses ; but the force, or product of ve- 
locity into the mass, disregarding friction, &c. will always 
be the same, so that, what we gain in mass or weight is lost 
in velocity. 
_ This and the following chapter, if they had not been too 
much intermixed with unnecessary discussions, and experi- 
ments, we consider as valuable portions of the book. 
The 6th and last Chapter on Statics, is that which treats 
of cords and arches. The subject is difficult, and if the 
author meant to be understood, he should have aimed at a 
good arrangement, and that /ucidus ordo, so essentially ne- 
eessary for the induction of a student into a knowledge of 
this intricate subject. In this he appears to have failed. 
We come now to the very important subject of Dyna- 
ics. This is introduced with remarks, somewhat meta- 
physical, and obscure, and in our opinion unnecessary for 
the subject, as the whole of it is founded on principles of 
common sense, and common experience. It would be dif- 
ficult, indeed, to conceive why Fluxions should be intro- 
duced to prove the fundamental truths of any science, whem 
those of its own are the least evident of any of the branches 
of the mathematics ; this fault, and that of generalization are 
predominant throughout the whole work. We have alrea- 
dy animadverted on the former, and the obscuri its 
symbolic reasoniug, if that can be called reasoning, of which 
