A Treatise on Elementary Mechanics. By J. H. Smith, M.A.,
of Gonville and Colas College. (31acmillan.)—Mr. Smith's treatise would seem to be an abridgment and simplification of the subject, based on Mr. Parkinson's treatise. He has accordingly stated the definitions in a concise form, too concise, in some instances, to be exact and clear. His definitions of matter, rest, and motion will illustrate our meaning. Of mechanical principles, or axioms, he tells us little or nothing, in the striking and prominent form that such points should assume when they are to be made the groundwork of all that follows. Again, in regard to force, though he defines it strictly enough, he fails to illustrate his definition sufficiently by forces as they present themselves in nature. In particular, nowhere, as far as we have observed, is friction alluded to from beginning to end ; and yet, as one of those causes which " change or tend to change the state of rest or motion of a body," it surely deserves a passing word of notice, for without it not a creature could stir from its place, not a locomotive machine could be moved an inch, on the face of the earth. He follows Mr. Parkinson in his somewhat cumbrous rendering of Dachayla's proof of the parallelogram of forces; makes that gentleman's treatment of the theory of moments even more uninviting and purposeless, and adopts his impractical description of the common steelyard. We do not instance these as serious drawbacks to his otherwise careful treatise, but rather as a failure to make a step in advance by really simplifying and systematizing the subject for be- ginners. The book has brevity, point, and condensation ; and it may take a creditable place among kindred elementary works on the subject, but it will not supersede them.
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