NA TURE 



3*3 



THURSDAY, FEBRUARY 3, \\ 



APPLIED MECHANICS, AND THE WAY TO 

 TEACH IT. 



Applied Mechanics : a Treatise for the Use oj Students 

 who ha7>e time to ivork Experimental, Numerical, and 

 Graphic Exercises illustrating the Subject. By John 

 Perry, D.Sc, F.R.S. Pp. v + 678. (London : Cassell 

 and Co., Ltd., 1897.) 



PROFESSOR PERRY'S position in the Department 

 of Science and Art gives him so wide an influence 

 on the teaching of applied mechanics throughout the 

 country, that a book which expounds and exemplifies the 

 method of teaching he approves will be received with 

 keen interest. But the volume before us has no need 

 of any adventitious claim on the attention of readers. 

 Prof. Perry has the knack of throwing his personality 

 into his books. You may not always agree with him : 

 indeed, nothing would distress him more than to find 

 you doing that ; for what is the use of trailing a coat 

 unless a gentleman will be so good as to tread on it ? 

 But, at any rate, you will not find him dull. He holds 

 you alike by what he says and how he says it. You 

 recognise in every chapter the fulness of his knowledge, 

 the ripeness of his experience, the freshness of his 

 methods, the individuality of his style. It is a style 

 which some of us are too steeped in convention to 

 enjoy without qualification. I must myself confess to a 

 measure of distaste for the " Clarendons " which flash out 

 every here and there over the printed page, not in head- 

 lines, but to emphasise words and phrases in the text. 

 And the numerous " asides " about educational methods 

 and other things are oddly placed in a treatise on 

 applied mechanics. But the most critical reader will 

 find his admiration compelled by the immense amount 

 the book contains of excellent matter not found, or not 

 readily found, elsewhere ; and he will admit that the 

 work is pre-eminently alive in every page, and that the 

 author is speaking throughout with a real knowledge of 

 real things. 



Prof. Perry describes it as a treatise for the use of 

 students. I should rather say for the use of teachers, 

 and add that every teacher of mechanics should possess 

 himself of a copy. It is certainly not for beginners. A 

 fairly advanced student will find it very helpful, perhaps 

 as a mine in which to dig rather than as a course to 

 be systematically followed. To the teacher of applied 

 mechanics it will prove invaluable, and through him its 

 influence will, I believe, be far-reaching. 



It is clear enough that Prof. Perry is addressing the 

 teachers at least as much as the taught. Else what 

 mean the frequent homilies on teaching, such as these ? 



" We believe that the principles which an engineer 

 really recollects and keeps ready for mental use are very 

 few. . . . We ought to teach him how to learn for 

 himself. Any child can state Newton's second law of 

 motion, and the other half-dozen all-important principles 

 of mechanics, so as to get full marks in an examination 

 paper ; the engineer knows that the phenomena he deals 

 with are exceedingly complex, and that onl)^ a long 

 experience will enable him to utilise the so easily stated 

 principles " (p. 2). 



" The most important lesson for a beginner, however 

 NO. 1475. VOL. 57] 



he may have studied mathematics and mechanics, and 

 however able he may be as a mathematician, is this — 

 that he must not go on merely assuming that he knows 

 how to do things ; he must know things by actual 

 trial. . . . Teachers will notice that things requiring 

 even a little preparation more than other things will 

 gradually become neglected. . . . When we find our 

 system to be going with clockwork regularity, and we 

 feel no worry, we ought to believe that some change is 

 necessary. If we find that the students are not absorbed 

 in their work, we must understand that we teachers are 

 in fault " (p. 3). 



" If it is possible we try to learn all our mathematics, 

 mechanics, physics, and chemistry from teachers who 

 are engineers. What acquaintance with these subjects 

 we have ought to be a real knowledge, and not the glib 

 pretence which suffices for examinations. . . . To effect 

 this object we must work many numerical and graphical 

 exercises, and try to conquer our contempt for simple 

 laboratory experiments" (p. 3). 



" Our aim is to get students to think, and it is astonish- 

 ing how difficult it is to effect this object. ... In the 

 mechanical laboratory I find that even the dullest student 

 begins to think for himself if he is not too much spoon- 

 fed ; and if his difficulties are not cleared away by some 

 wretched routine system of laboratory work being adopted 

 by cheap laboratory instructors, the fundamental prin- 

 ciples of mechanics will become part of his mental 

 machinery" (p. 56). 



In another passage the author insists, with great truth 

 and force, on the desirability of introducing even ele- 

 mentary students to the fundamental notions and symbols 

 of the calculus at the beginning of their study of applied 

 mechanics. And in another he remarks that " Newton's 

 method, the ' Thomson and Tait method,' is very much 

 to be preferred to any other method of starting in the 

 study of mechanics" ; and adds, "Every engineer ought 

 to have his T and T' (the elementary treatise) a well- 

 thumbed book." 



Chapter xi. opens with these rather oracular sentences: 



" We sometimes assume that our readers know quite 

 well the fundamental principles of mechanics, and then 

 again we assume that they do not. We hope that they 

 agree with us that we are right in proceeding in this 

 way" (p. 242). 



One more passage showing the missionary spirit of the 

 author may be quoted : 



"A student who works such an exercise as this care- 

 fully is getting all sorts of valuable notions, not merely 

 of mechanics but of practical mathematics. Unfor- 

 tunately, twenty academic exercises can be worked out 

 without much thought or trouble to teacher or student, 

 and by the rules of the game this is sufficient for the 

 passing of examinations. For the present, therefore, my 

 advice will be followed by a few earnest students only — 

 the men who want to know, the men who are not merely 

 in search of examination tips, the men who find academic 

 exercises difficult because they think about what they 

 do" (p. 266). 



Like all the rest of the book, these obiter dicta aie 

 full of interest and suggestiveness. With most of what 

 they contend for the present writer heartily agrees. He 

 is disposed, however, to believe that it is not always 

 through excess of thought that men fail even in 

 "academic" examinations. 



One great lesson to be learnt from Prof. Perry is the 

 value of the mechanical laboratory as part of the 

 machinery of teaching. Not merely does he preach 

 this in the passages quoted and in others, but the book 



