H2 Revietb of 0. Gttgoi^y^s Trtatist on Mechanics» 



Cabinets of the Lyceum and Dr. Mitchill. 

 Length exclusive of the margin 2.6 Breadth LO 

 Length including the margin 3.0 Breadth 2.2 

 Shell oblong Oval, coated with a coarse, green, rough 

 epidermis, closely adhering to the shell, and concealing the 

 whole, except a small part of the carinated center of the 

 back, in which the shell appears black, smooth and shin- 

 ing ; Colour, under the epidermis and on the inside, pure 

 ivory white ; margin more than half as broad as the shell, 

 thickly studded with unequal, irregular, white, round head- 

 ed spines. Animal pale green : inner margin lighter colour 

 than the animal. 



Remarks^. 



The spines are white, in the specimen figured, or white 

 with a black center : but the native colour is black or dark 

 amethystine, and the white is a calcarious accretion, which 

 appears to be a microscopick Cellepore. 



New-York, March 3, 1823. 



MATHEMATICS. 



Art. X. — ^ Treatise of Mechanics, theoretical, practical 

 and descriptive : by Olinthus Gregory, LL. D. — 3 

 vols. 8vo. London, 1815. 



(Communicated.) 



The science of mechanics, whether considered in its the- 

 ory as a subject of curious and refined speculations, calcu- 

 lated for the learned, ingenious, and contemplative, or in 

 practice as contributing to the conveniences and elegancies 

 of life, and the wealth of nations, may be ranked the first 

 and most important of all human acquirements. What 

 Lord Bacon says of all true philosophy, is eminently appli- 

 cable to this branch of it, " that it enlarges the powers of 

 man, and extends his dominion in nature." By it, her 

 most refractory and opposing powers have been subdued, 



