September 23, 1922] 



NA TURE 



405 



(3) Major Warman deals more narrowly with the 

 agriculturist and is concerned with an account of 

 agricultural co-operation in England and Wales. He 

 is convinced that co-operation is essential to the 

 success of agriculture, and he is able to show that it is 

 beginning to take hold on the rural community. 

 Examples are given of farming societies, egg societies, 

 dairy societies, etc., which are doing good work and 

 have an undoubted future : we should, however, like 

 to have seen some tables showing the amounts of 

 produce handled, the financial turnover, etc. It may 

 be the amounts are not large, but it is desirable that 

 the data should be published. 



(4) Prof. W. Burr discusses a wider problem, the 

 organisation of the whole rural community in contra- 

 distinction to the urban population. It is widely 

 recognised by American writers that the urban and 

 rural communities are distinct, having different needs 

 and requiring different methods of organisation. 

 In this country the rural organisation has grown up 

 through long ages and the urban population is the new 

 problem : in America, however, the rural community 

 is also new, and experts are studying closely the method 

 in which it has developed, and feeling their way to 

 some new organisation. The book is written for 

 students, and it includes lists of questions and " research 

 problems," which space, however, might usefully have 

 been devoted to references to help those who wish to 

 pursue the study of this interesting subject. 



An Ideal Text-book of Physics. 



Cours de physique generate a l' usage des candidats au 

 certificat de Physique generate, au diplome d'lugeni- 

 eur-Eleetricien el a VAgregaiion des Sciences physiques. 

 Par Prof. H. Ollivier. Tome Second : Thermo- 

 dynamique et Etude de l'Energie rayonnante. 

 Deuxieme edition, entierement refondue. Pp. 415. 

 (Paris : J. Hermann, 1922.) 28 francs net. 



FEW examination candidates are likely to base 

 their studies on a book in a foreign language 

 adapted to foreign courses ; and it is therefore un- 

 necessary to consider here the merits of this work for 

 the purpose for which it is primarily intended. It will 

 suffice to say that none but the ablest students could 

 master it unaided. But as an exposition of the funda- 

 mental propositions of mathematical physics, from 

 which those of us who have passed the examination 

 stage may refresh our memories concerning what we 

 once knew, or were officially credited with knowing, 

 the volume exhausts our vocabulary of praise. There 

 are no native works which profess to cover the same 

 range, and few of any merit which cover part of it. 

 NO. 2760, VOL. I 10] 



We usually rely on Winkelmann or Chwolson. The 

 former is far more encyclopaedic, the latter more ex- 

 perimental ; for M. Ollivier gives very few references 

 and only such experimental facts as are necessary to 

 illustrate principles ; but in conciseness, lucidity and 

 accurac\ r they are not to be mentioned in the same 

 breath with our author. Even in completeness he is 

 sometimes superior, for he enters more fully than most 

 authors into some interesting byways of physics, such 

 as luminescence, photometry and astrophysics. 



The treatment is at once original and conservative. 

 The order of historical development is usually aban- 

 doned completely and the subject developed in the full 

 light of our present knowledge. Consequently, the 

 science is presented deductively rather than inductively, 

 the most general principles being stated first and their 

 most important logical consequences (which are of 

 course really their basis) gradually worked out. 

 Whether this reversal of the usual sequence is desirable 

 in teaching may perhaps be questioned, but there is 

 no doubt of its efficacy in summarisation. On the 

 other hand, there are no signs of the modern tendency 

 to seek principles so broad and far-reaching that in 

 gaining generality they almost lose physical signifi- 

 cance. Thus the Boltzmann conception of entropy as 

 probability appears only towards the end of the ex- 

 position of thermodynamics and the Nernst theorem 

 appears mainly in foot-notes. But there is nothing old- 

 fashioned about the book ; if the author does not 

 always pay so much attention as some would wish 

 to the latest work, the reason is clearly a deliberate 

 judgment of value and not mere ignorance. 



But M. Ollivier's supreme merit in our eyes is that 

 he really does write about mathematical physics. He 

 does not give us either a treatise on pure mathematics 

 which neglects the distinction between experiments 

 which can, and those which cannot, be carried out, or 

 a mere collection of familiar formulas with " proofs " 

 which prove nothing but the author's incapacity for 

 accurate thought. He actually tells us how important 

 magnitudes are measured and what is implied by the 

 fact of their measurement ; he realises that to define 

 a magnitude and to say how it is measured are one 

 and the same thing. Yet he does not fall into the 

 opposite vice and weary us with needless pedantry ; 

 many readers will probably appreciate his abandon- 

 ment of the old inadequacies and inaccuracies only by 

 finding that, for the first time, they truly understand. 



However, it is needless to continue in this strain. 

 The present reviewer is not acquainted with the first 

 volume of M. Ollivier's work and must confess that he 

 had never heard of the work until it came into his 

 hands for review. Many others are probably in a 

 similar state of ignorance. The best that he can wish 



