84 Review of O. Gregory’s Treatise on Mechanics. 
~ Chapter 3d, on contripetal forces is taken almost, word 
for word, from Simpson’s Fluxions, with the exception ofa 
proposition, or two, introduced by Mr. Gregory, perhaps 
from some other writer; that in Art. 280, to prove the equal 
velocities at equal distances from the center of bodies de- 
scending in curves, or right lines, isan awkward attempt by 
a blind, and circuitous route to supersede what had been 
done better by Simpson, and infinitely better by Newton. 
Few learners can be made to understand the jumbled solu- 
tion given by our author. id 
Chapter 4th, treats of rotatory motion, aad of the centers 
of Gyration, Oscillation, Percussicn and spontaneous Rota- 
tion, together with other subjects connected with them. We 
find not much to censure, or much to applaud in this, ex- 
cept a more glaring instance of that pedantry, and ostenta- 
tion of learning, of which there are so many in this book. 
After having proved, what is very easily, and evidently 
shown by elementary principles, that the force of bodies, or 
the particles of bodies, in rotatory motion, is as the squares 
of their distances from the.axis of motion; sucha plain Eu- 
clidean ¢emonstration does not appear to have satisfied the 
magnificent ideas of the author, who every where prefers 
demonstrations even of the simplest theorems, if derived 
from the most exalted and obscure source of Analytics. 
Accordingly, we have in Art. 302 a long demonstration de- 
pending on the differential-calculus, and the principles of 
D? Alembert, to show that the force of bodies in rotary mo- 
tion is uly as had been before estimated by the prinei- 
ples of geometry and mechanics. As the differential 
calculus, and D’Alembert’s principles, are founded on these, 
if they have any foundation, it is evident that this proof isa 
mere argumentum in Circu/o and therefore ostentatious, 
and delu-ive. 
Chapter 5th, is a treatise on Percussion founded on the 
principle of its effects arising from a continued, and succes- 
sive action of the particles of the bodies, which undergo 
percussion, and therefore, that it is in itself a kind of 
ure produced in a very small moment of time. On this 
hypothesis, the deductions are made a priori are con- 
ntaneous to those derived from other principles: The 
servatio virium, of Huygenius and Bernauilli, follows easi- 
ly from this doctrine, but all this had been shown with much 
