A WEEKLY ILLUSTRATED JOURNAL OF SCIENCE 



" To the solid ground 

 Of Nature trusts the mind which builds for aye." — Wordsworth. 



TWO TEXT-BOOKS ON MECHANICS. 

 An Introduction to the Design of Beams, Girders, 



and Columns in Machines and Structures, with 



Examples in Graphic Statics. By W. H. Atherton. 



Pp. xiv + 236. (London : Charles Griffin and Co., 



Ltd., 1905.) Price 6s. net. 

 Mechanics for Engineers, a Text-book of Intermediate 



Standard. By Arthur Morley. Pp. xi + 282. 



(London : Longmans, Green and Co., 1905.) Price 



js. net. f 



A/| R. ATHERTOX'S book is for engineering 

 * ' 1 students whose mathematical knowledge does 

 not include the calculus, and such readers will find 

 it a very useful source of information. 



The style is very unconventional — a trait which is 

 rather helpful than otherwise — but occasionally the 

 disregard of grammatical niceties and the ordinary- 

 rules of composition is carried too far. 



The author does not trouble himself in the least 

 about discussions as to absolute and gravitation units 

 of force and the so-called " engineer's unit of mass " 

 (which is about 32.2 pounds). He is a practical 

 engineer, as is sufficiently obvious from the words, 

 " There are only two units of force that will be of 

 much use to us — namely a pound for light work and 

 a ton for heavy work "; but there is a suggestion of 

 an ancient conundrum about his statement, " So far 

 as we are concerned, force is measured in terms of 

 some unit of weight, as that of a ton of iron." 

 Chapter vi. contains a good exposition of the theory 

 of the bending of beams, together with some useful 

 cautions and explanations of certain discrepancies 

 between theory and practice. The moments of resist- 

 ance of beams of various cross-sections are all calcu- 

 lated by elementary non-calculus methods. The 

 calculation of moment of inertia (the absurdity of 

 which term the author very properly emphasises) is 

 made in the same manner. It would be a great help 

 to students — even to those who can use the calculus 

 NO 1879, VOL. 73] 



— to give the particle rule for calculating all moments 

 of inertia with reference to a triangular (and thence 

 any polygonal) area ; the moment of inertia of a 

 triangular area about any axis whatever can be calcu- 

 lated by replacing the triangle by three equal particles 

 at the middle points of the sides, their masses being 

 represented by -|A, where A = area of triangle. 



While the whole of the book will be found useful, 

 the chapter on the comparative strengths of tubes of 

 various forms may be specially mentioned. 



Mr. Morley 's work differs from that above noticed 

 in excluding all technical knowledge and terms, so 

 that it is suitable to all students of dynamics, whether 

 engineers or not. It does not employ a knowledge 

 of calculus, its range being covered by algebra and 

 elementary trigonometry, and its scope being that of 

 the London intermediate engineering examination 

 and that for the A.M.I.C.E. The work adopts the 

 plan of founding the science of force on Newton's 

 axiom ii., so that kinetical principles precede the 

 treatment of equilibrium (statics). The great import- 

 ance of the direct application of the principles of 

 momentum and energy is recognised at the outset 

 by supplying a large number of excellent examples of 

 these principles, so that the work is thoroughly 

 modern in conception and method. There is a large 

 and commendable use of squared paper diagrams for 

 calculating velocities, forces, work, &c, in cases in 

 which these are variable according to other than the 

 mosl simple laws. 



The poundal is, happily, not employed, but the 

 " engineer's unit of mass " is adopted in order to 

 save the definition of force, viz. " force is the rate 

 of change of momentum." It is doubtful if many 

 students are helped by this device, or if they really 

 understand what they are doing when they say that 

 the mass of a body is W ' g. We must confine our- 

 selves to a few brief observations on a work which 

 we commend very highly. Is not a " knot " a speed 

 — a geographical mile per hour? The newspapers 

 sometimes speak of " 20 knots an hour," so does the 

 author (p. 20). It is a pity that he speaks of 

 " accelerating forces " (p. 43, &c), because it is 



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