82 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 atfg*- 

 ment. In what machine, has any augmentation of force, in 

 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 

 and 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 lucidus ordo, so essentially ne- 

 cessary 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- 

 mics. 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, when 

 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 obscurity of its 

 symbolic reasoning, if that can be called reasoning, of which 



