72 



NATURE 



[September i6, 1920 



to the community, and this plea is the main object 

 of the present article. The Association should 

 stand not for esoteric, but for exoteric, philo- 

 sophy, and thus bring within its sphere all who 

 believe that . progressive thought, with accurate 

 knowledge, form the only sure foundation upon 

 which man can build a structure that will with- 

 stand the polemic storms of the present and the 

 world shocks which promise to assail it in the 

 future. 



Ewing's " Thermodynamics." 



Thermodynamics for Engineers. By Sir J. A. 

 Evving. Pp. xiii -1-383. (Cambridge: At the 

 University Press, 1920.} Price 305. net. 



ONE of the chief fascinations of thermo- 

 dynamics is the way in which it ramifies 

 into other branches of science, following the mani- 

 fold transformations of energy. The fundamental 

 laws reappear in so many different aspects in rela- 

 tion to the quantities which are the subject of 

 measurement in the different branches, such as 

 chemistry, electricity, radiation, etc., that it 

 affords one of the most interesting standpoints 

 from which to view the growth of natural philo- 

 sophy and to study the correlation of its parts. 

 For the same reason it is difficult for the worker 

 in any one branch to follow the applications of 

 thermodynamics to other subjects with the prin- 

 ciples of which he is unfamiliar ; and he is apt to 

 find that the discussion of his own subject in a 

 general survey is necessarily lacking in the prac- 

 tical details and numerical data which would be 

 required to enable him to make any use of it for 

 his special purpose. Accordingly it is usual in 

 treatises on special subjects, such as steam tur- 

 bines, or petrol motors, or refrigerating machines, 

 to include one or more chapters on the principles 

 of thermodynamics in relation to the subject dis- 

 cussed. This is a very natural compromise, but 

 involves a great deal of repetition of elementary 

 principles, while it frequently fails, owing to 

 limitations of space or lack of generality, in pro- 

 viding a sufficiently solid foundation for furthei 

 research. So much effort has been wasted in the 

 past, and is still being wasted, by inventors and 

 experimentalists, in pursuit of fancied improve- 

 ments which a wider knowledge of thermo- 

 dynamics would have shown to be illusory, that 

 such knowledge should be regarded as an essential 

 part of the equipment of the scientific engineer, 

 however abstract and theoretical it may appeal 

 to the practical man at first sight. 



Among English treatises on thermodynamics, 

 few, if any, appear to have been written primarily 

 NO. 26s i^, VOL. 166I 



from the point of view of the engineer. We are 

 therefore all the more disposed to welcome a book 

 with this object from a master of clear exposition, 

 whose books on kindred subjects are already so 

 well known and appreciated by engineers. The 

 method adopted by the author of the present work 

 is to begin with the elementary notions and their 

 interpretation in practice, and to defer the mathe- 

 matical relations until the reader may be supposed 

 to have become familiar with the fundamental 

 ideas as physical realities, and is presumably able 

 to apply them to practical problems. 



In pursuance of this general scheme, the first 

 six chapters of the book deal with general prin- 

 ciples, explained in the first instance in relation 

 to ideal gases, and then applied to practical 

 problems in discussing the properties of actual 

 fluids, the theory of the steam-engine and of 

 refrigeration, jets and turbines, and internal- 

 combustion engines. Since the general principles 

 of thermodynamics have not changed in the last 

 few years, it naturally follows that most of the 

 material employed in this part of the work is the 

 same as in the author's previous books on "The 

 Steam-engine and Other Heat-engines " and on 

 "The Mechanical Production of Cold." But the 

 material has been rearranged as a connected ex- 

 position of the principles, and brought up to date 

 in minor particulars, such as the adiabatic equa- 

 tion for dry steam, and the effect of supersatura- 

 tion on the discharge through a nozzle. Most of 

 the problems discussed are so well worked out 

 that there is little room for difference of opinion, 

 and so clearly explained that it would be difficult 

 to suggest any improvement. It is only when we 

 come to more recent or debatable problems, espe- 

 cially where the experimental data are still un- 

 certain, that it becomes possible in a few cases to 

 criticise the author's views. 



The importance of devoting adequate considera- 

 tion to the properties of the working fluid as 

 affecting the operation of a heat-engine has been 

 more fully recognised in recent years. Accord- 

 ingly the author has included in the chapter on 

 internal-combustion engines a discussion of the 

 effect of increase of specific heat at high tempera- 

 tures, and has added an appendix on the molecular 

 theory of gases, which should serve as a useful 

 introduction to the theorj' of the variation of 

 specific heat. In discussing this subject the 

 author naturally follows in the main the views ,of 

 his successor at Cambridge, Prof. B. Hopkinson, 

 whose work he did so much to inspire. Prof. 

 Hopkinson 's view that the loss of efficiency, as 

 compared with the ideal air-standard for a given 

 compression-ratio, could be attributed entirely to 

 the increase of specific heat, provides an effective 



