NATURE 



[November 7, 1907 



The method has its dangers, for it may give cur- 

 rency to vague and inexact doctrines. But here the 

 sparkle of the writing secures the interest without 

 impairing the science. Health is undefined, but the 

 problem of health is mainly how to maintain the fight 

 against malign environment, and " fitness " is largely 

 the capacity to master hostile germs. The discussion 

 of sleep adapts scientific theory to practice, and has 

 many sound hints Of the cold bath it is said, " In 

 general, the value of a cold bath is in inverse pro- 

 portion to its length " (p. 39). Of exercise, the view 

 is that " all mental processes are based upon a simple 

 unit of action or process, in which some one muscle- 

 fibre is a chief factor " (p. 55). Play is preferred. 



The criticism of current superstitions as to exer- 

 cise and training is pointed and conclusive. The 

 cardinal point is the relation of exercise to diet. Dr. 

 (.'avanagh is somewhat dogmatic (p. 60) on the intel- 

 lectual training of women. He assumes too readilv 

 that accepted intellectual standards are a true test of 

 mental capacity even in men. In exercise, walking 

 and running, not any artificial system, are 

 fundamental. " Muscles are not meant to work or 

 be developed individually " (p. 78). 



The discussion of fatigue is highly general, but 

 .■idequate for its purpose. Of clothing a good deal is 

 said in detail, the principle being that " man is 

 homoiothermal," and 98°-4 Fahrenheit is his normal 

 temperature. Clothing is closely criticised from this 

 standpoint. In the other chapters — teeth, eyes, &c. — 

 many hints of experience are embodied, and, though 

 the main facts are well known, every reader will find 

 ihem set forth in a fresh and stimulating way. The 

 chapters on position .md habit are well loaded with 

 good matter. The last chapter points the view that 

 dominates this book and the series it belongs to, 

 namely, that henceforward the physician's true func- 

 tion is to prevent, not to cure, and the profession 

 should be organised accordingly. Altogether, the 

 author succeeds in his effort to be simple, scientific, 

 and vivacious. The aim of the series is to apply 

 scientific medicine to the informing of public opinion, 

 and this volume, within its range, certainly furthers 

 that aim. If looked-for topics are sometimes omitted, 

 they are likely to be found in other volumes. 



OUR BOOK SHELF. 

 Practical Mathematics. By Prof. John Perry, F.R.S. 



Pp. 183. (London : Wyman and Sons, Ltd., 1907.) 



Price 9^. 

 The first edition, a slim little pamphlet price six- 

 pence, was reviewed in these columns about the end 

 of the last century; this new edition begins to show 

 signs of corpulence. 



The pamphlet has raised a crowd of imitators, 

 bulky works on engineering and mathematics, work- 

 shop arithmetic, and general utilitarian and commer- 

 cial theory ; it would be better, for historical interest, to 

 preserve its original size. 



The author has forced the Mathematical Tripos to 

 .•idopt the Slide Rule for numerical computation ; and 

 would do well to follow up by a description of the Hos- 

 pitaller notation of writing derived units, as ft.= and 

 ft." for square and cubic feet, Ib./ft.^ for pressure, 

 NO. I98/I, VOL. ■J'j'\ 



and so on ; no need then for the mathematical 

 Esperanto suggested some years ago. 



The slide-rule hint — " practise with simple num- 

 bers " ; "ask no one to help you" — should be fol- 

 lowed by arithmetical exercises intended to show the 

 learner how to discover the use for himself : such as 

 cube 2, 3, 4, . . . and then extract the cube root; 

 better then to discard all rules, as they can always be 

 re-invented with greater ease than recollected. Con- 

 sidering that the slide rule and logarithm table work 

 to the base 10, the definition of the logarithm 

 in § 8 is — n = log N, if io" = N; not n" = X, which 

 is confusing by its useless generality. 



The practical student Prof. Perry has in view is 

 called upon to work and act, but not to write and 

 explain. His geometry is so very easy, consisting 

 in drawing a few lines by instruments. But if re- 

 quired to give an explanation he would find himself 

 compelled to give six lines or more of tedious defini- 

 tion to one line of demonstration ; he would become 

 Euclidean without knowing it. 



The author enjoys attacking the schoolmaster, who 

 shows certainly many weak points of inherited pre- 

 judice. Prof. Perry looks at geometry from the point 

 of view of everyone becoming an engineer in his turn ; 

 the schoolmaster deals wil:h very few students of that 

 class, and can make out a very good case for Euclid; 

 Greek in Euclid and Euclid in Greek ; and he has 

 an answer ready for the question in the note on 

 p. 8 — "Why not say — delogarize? " — Because the 

 word is a mongrel. 



La Thiorie de la Physique chez les Physiciens cou- 

 temporains. By Abel Rey. Pp. vi4-4i2. (Paris: 

 Felix .'Mean, 190;.) Price 7.50 francs. 

 Recognising the serious discordance between the 

 views of conteinporary physicists upon the true mean- 

 ing- and value of physical theories, the author of this 

 interesting book inquires whether this conflict of 

 opinion justifies the contention of the anti-intellec- 

 tualist philosophers that such theories are purely 

 arbitrary constructions leading, not to completer know- 

 ledge of the world, but merely to more cdective prac- 

 tical control of its course. M. Rey proceeds by an 

 able cross-examination of actual scientific thinkers, 

 classifying them by reference to their attitude towards 

 the post-Newtonian mathematical physics — which 

 assumed the actuality in detail of the molecular 

 machinery that it invoked to explain phenomena. 



In his first group fall Rankine, Mach, Ostwald, and 

 Duhem, who agree in rejecting the ontological pre- 

 tensions of the mechanical theory and in conceiving 

 the various departments of physics as autonomous 

 sciences connected with one another and with 

 mechanics by the notion of energy. British 

 readers will be gratified by the importance which 

 the author attaches here to the work of our 

 countryman — whom he regards as the father of the 

 critical movement — and will welcome his clear account 

 of the views of the brilliant professor of Bordeaux. 

 Next to these M. Rey places Poincare as a critic who 

 corrects rather than rejects the traditional doctrine, 

 accepting its belief that the data of observation in 

 physics are the product of the superposition of an 

 infinite number of elementary phenomena to which 

 the differential equations of theory refer, but recog- 

 nising that its conception of these phenomena as 

 molecules in movement is only a description in one 

 idiom of objective relations that could equally well be 

 rendered in another. Last come the phvsicists (in- 

 cluding most of the British school) who have lost the 

 confidence of the post-Newtonian mechanists rather 

 than their ideals ; who still hold that physical pheno- 

 mena can be explained by the conceptions of 



