Notices respecting New Books. 399 



electricity, optics, and acoustics are particularly welcome ; 

 much of the matter contained in them is usually omitted from 

 textbooks. The author has wisely emphasized the broad prin- 

 ciples of the subject and kept them to the forefront ; mathematics 

 has been avoided as far as possible, so that the book can be used by 

 students with little mathematical training. After mastering it, the 

 student should have a clear understanding of the basic principles 

 and be well equipped for the study of more advanced treatises. 



The volume is well illustrated by plates and line diagrams; the 

 excellent photographs by Mr. Gr. A. Clarke, of Aberdeen, illustra- 

 ting the various types of cloud formation may be specially 

 mentioned. It has a very complete index, and is well printed. 



Relativity , the Electron Theory, and Gravitation. By E. Cunning- 

 ham, M.A. Second Edition. Pp. 148. (Longmans & Co. 

 1921.) 



Legons Elementaires sur la Gravitation cVapres la Theorie cV Einstein. 

 By E.M. Lemeray. Pp. 93. (Paris : Gauthier-Villars et C ie . 

 1921.) 



Among the books on Relativity which, despite all the difficulties 

 in cost of production of which we hear so much from the 

 publishing trade, are appearing like "leaves in Yallombrosa," 

 these two deserve very special notice. 



What, distinguishes Mr. Cunningham is his clear straight- 

 forward forcible exposition. We feel that not a word is wasted 

 nor a difficulty slurred over. It breaks no new ground and offers 

 no first-hand criticism, but this makes it especially valuable to 

 the student. 



M. Lemeray's book is also a manual for the student. It is 

 an account of the equations which Einstein use's set forth in 

 the clearest and most precise form and without any extraneous 

 explanations. 



The Mechanism of Life. By James Johnstone, D.Sc. Pp. ix + 



247. (Edward Arnold &"Co. 1921.) 

 The special interest of this book is the author's attempt to bring 

 biology into general line with the recent development of mathe- 

 matics and physics. It might seem a far cry from the principle 

 of relativity to the theory of the elan vital, yet there is nothing 

 extravagant, or in any sense unscientific, in the association which 

 Prof. Johnstone finds between them. The argument is clear and 

 sustained. It begins with an account of the mechanism of the 

 organism and the scheme of its psycho-physical behaviour, drawn 

 largely from Prof. Sherrington's work. It compares the new 

 mechanistic concept with the old Cartesian mechanism, and shows 

 the change which has been brought about by the new physico- 

 chemical concepts and the modern science of energetics. The 

 author then criticises neo- vitalism, particularly the psychoids 

 and entelechies of Driesch, " vestal virgins dedicated to God and 

 barren," and expounds his own " vital " concept that, in living 

 processes the increase of entropy is retarded. 



