122 



NATURE 



[April i, 1909 



was the guess of the intelligent Eskimo here men- 

 tioned (p. 201), who from his respect for the 

 prospectors' provision-cans opined that the mysterious 

 phonograpli might be " tinned white man." 



The booli is enlivened by personal incidents and 

 anecdotes, and is abundantly illustrated by well- 

 chosen photographs excellently reproduced. But the 

 cover is ugly both in design and colouring. 



G. W. L. 



A TEXT-BOOK OF PHYSICS. 

 General Physics : an Elementary Text-book for Col- 

 leges. By Dr. Henry Crew. Pp. xi + S22; figures. 

 (New York : The Macmillan Co. ; London : Mac- 

 millan and Co., Ltd., 1908.) Price 12^. net. 



" TX these days of numerous text-books the author, 

 X who dares still further to increase the number, 

 owes to the public, at least an explanation in which 

 he shall set forth his purpose, however far short of 

 accomplishment he may have fallen." 



In these words our author introduces himself to 

 us in his preface; and of the reasons adduced for the 

 present volume the most important is that he has 

 sought " not merely, or even mainly, to impart infor- 

 mation, but to set before the student a large and com- 

 pact body of truth obtained by a method which shall 

 remain for him, throughout life, a pattern and norm 

 of clear and correct thinking." 



Prof. Crew has certainly succeeded in presenting 

 a lively account of modern physics, in so far at least 

 as it can be presented in a series of class lectures 

 in which all experiments are of a qualitative nature 

 only. We regret that he has not done more than 

 this. It is quite possible in very many cases in 

 class lectures to perform quantitative experiments 

 also, and students are never so interested as when 

 such experiments are being performed. There is no 

 suggestion of this in the book before us. This is 

 to be regretted, because, even if in the lectures which 

 the student is privileged to hear qualitative methods 

 are alone presented, yet his text-book should provide 

 him with a detailed account of some of the historical 

 experimental methods by which the present state of 

 science has been attained. We do not quarrel in 

 general with what we find here, but with what is 

 omitted. Open where we may, and it is rare that 

 we find what we hoped. Thus, in connection with 

 Charles's law for gases : — 



" The actual measurement of these quantities is 

 a somewhat difficult matter, requiring many pre- 

 cautions, and may well be reserved for the student's 

 second or third year in physics." 



We are astonished that this should be thought to 

 be advisable. 



Conspicuous gaps also exist in the exposition. 

 After emphasising the fact that speed is the Umitimi 

 value of a ratio of distance over time, and the im- 

 portance of a knowledge of limiting values even in 

 elementary physics, Prof. Crew does not make the 

 slightest effort to impart this knowledge. How easv 

 and mstructive it is to take one or two cases as 

 NO. 2057, VOL. 80] 



illustrations, such as y = K/ or _)' = «/-, and calculate 

 the speeds from them. The student thereby learns 

 something, whereas, at present, the matter is left 

 with an air of mystery hanging over it. 



We are not enthusiastic admirers of D'Alembert's 

 principle; it is correct but confusing, introducing a 

 fictitious equilibrium where equilibrium does not exist. 

 But, at the early stage of instruction covered by 

 the book, to speak of the reversed effective forces as 

 the reaction of the masses against their acceleration 

 immediatelv after having given Newton's law of action 

 and reaction (the reaction acting on a second body) 

 is only to make confusion worse confounded. 



Prof. Crew follows ever5'one else in defining energy 

 as power of doing work. In view of the fact which 

 everybody recognises, that a body may have enor- 

 mous stores of energy and yet have no power of 

 doing work, is it not time that the customary de- 

 finition should be revised? The present writer is 

 accustomed to define it as " that which diminishes 

 when work is done, by an amount equal to the work 

 so done." 



The formula for a simple pendulum is written 

 T = 2Tv//<'/(^' sin e), as though this was the exact form, 

 the usual approximation following it; of course, this 

 is not the case. 



Pascal's theorem for fluid pressure is given as 

 "At any point in a liquid at rest the stress (pressure) 

 is the same in all directions." This is not the prin- 

 ciple which usually goes under the name of Pascal's 

 theorem. 



The subject of magnetism is started with the de- 

 finition, .'\ny body which attracts iron filings is said 

 to be magnetised and is called a magnet. Surely 

 something more satisfactory than this can be found 

 in the wav of a definition. Those of us who have 

 had considerable experience in examining are very 

 familiar with the candidate who presses the passion 

 for the unification of knowledge so far as to con- 

 sider identical all forces of attraction. The present 

 writer has been told by many dozens that we know 

 the earth to be a magnet because if it were not so 

 and we were to jump out of a window we should 

 not fall down. 



Looking back over this review, the writer feels 

 that adverse criticism preponderates in it. He does 

 not wish to convey the idea that the book must be 

 condemned, but to show where it might be improved. 

 He has read it from cover to cover (except the index) ; 

 there is a certain breezy informality about it which 

 is somewhat pleasing, although, to an English ear, 

 a few of the expressions suggest slang. 



Prof. Crew has evidently considerable interest in 

 the historical side of the subject. Every leading 

 ]jrinciple is attributed to its source and is dated. He 

 takes special pains to introduce each section by 

 allusion to facts of familiar experience, and then 

 endeavours out of this " chaos " to produce scientific 

 order. This method serves to stimulate interest, and 

 deserves commendation. 



The book includes the whole range of physics; 

 the part on mechanics (205 pages) bears, perhaps, an 

 excessive ratio to the rest. 



