A Text-Book of Elementary Mechanics, for the Use of Colleges and Schools

Abstract

THIS is a small-sized book of 290 pages printed in fairly clear type, and bound in an unpleasant-looking cover, and we learn from the preface that it has been prepared to meet the special wants of Yale College instruction. An endeavour has been made to dwell more fully than usual on the principles of the subject, at the same time illustrating these principles in their practical bearings by descriptions of various machines and appliances, while no mathematical knowledge beyond the rudiments of algebra and trigonometry is required. From this it may be presumed that the book is intended for a very elementary class of students, at a lower stage, if passible, than “Poll” men at Cambridge, or else that it aims at assisting self-education by supplying the place of a tutor. An undoubtedly good feature in the book is the collection of examples, some of which are interspersed in the text, and others collected in a body at the end, where the answers are given. The metrical and ordinary units are both employed. These examples are perhaps the only part of the book which would be of any value to teachers in this country. With regard to the main subject-matter of the book, Dynamics is placed first, and Statics follows, with a chapter on the Pendulum at the end. The definitions and the explanation of the principles of the subject, though aiming at fulness and clearness, are not always so satisfactory as might he wished. A tendency to looseness of expression sometimes counter-balances the value of the fuller explanation. To explain solidity we are told that “A solid is characterised by a greater or less degree of rigidity,” which in the absence of a separate definition of rigidity leaves us much where we were before. Again, the definition of a liquid is this, “A liquid is characterised by its mobility; the molecules are free to move about each other, and the liquid takes the shape of any containing vessel,” which is equally true of a gas. The proof of the formula S = ½ft² is clenched by the proposition that “when two sets of variable quantities, which are always equal, simultaneously approach their limits, these limits are equal,” which is suddenly introduced without any explanation of its meaning. This, in a book intended for beginners unacquainted with the idea of a “limit,” would be likely to cause some bewilderment. There is a chapter devoted to Work and Energy, as should be the case with all text-books of mechanics nowadays.

A Text-Book of Elementary Mechanics, for the Use of Colleges and Schools.

By Edward S. Dana, Assistant Professor of Natural in Yale College. (New York: John Wiley and Sons, 1881.)