378 SCIENCE PROGRESS 



reference to the important Gibraltar skull, and the translator makes certain 

 passages unintelligible to any except the expert by his ignorance of anatomical 

 terms. The worst instance of this is the use of the expression "third lobe of the 

 brain " (p. 49) for the third frontal gyrus. 



G. Elliot Smith. 



Modern Electrical Theory. By Norman Robert Campbell. [Pp. xii + 400.] 

 Second edition. (Cambridge University Press. Price gs. net.) 



A CAREFUL comparison of this second edition with the first edition (1907) fully 

 confirms the author's statement in the preface that this is really a new book ; even 

 in the places where the work of the last six years has not added to or much affected 

 our knowledge, the book has been rewritten and recast. A mention of some of 

 the remarkable experiments and revolutionary theory of the last six years which are 

 discussed will make it clear how completely a recent book on electrical theory 

 must necessarily differ from one six years old ; reference need only be made to 

 Planck and Einstein's theory of light quanta, Nernst's work on specific heats, the 

 experiments of Barkla, Bragg, and Lane and his collaborators on X-rays, and the 

 principle of relativity. This work is all too recent to have found its way into the 

 text-books, and the papers and pamphlets on it are enormous in number, scattered, 

 and not always particularly clearly written. Whether they are to stand or fall, 

 these modern theories of light and electro-dynamics in general are far too 

 important for any physicist to be able to ignore them, and a book where he can 

 get a general yet correct presentation of them, and find them compared with the 

 older theories, is badly needed, although it may be, probably will be, out of date in 

 another five years. We can congratulate the author both on his courage in 

 attempting such a book, and on the successful result ; for, on the whole, the book 

 gives a presentation of just the nature required by the working physicist, neither 

 too "popular" nor too mathematical. If he shows a disposition to try to bully 

 the reader into an acceptance of every view which has won his own belief, it must 

 be remembered that a certain amount of personal opinion and partisanship is 

 probably necessary to give unity to the book, and to make it the connected 

 presentation it is rather than a mere collection of independent theories and 

 observations. 



The book is now divided into three parts — the electron theory, radiation, and 

 ■electricity and matter. In the first part, besides a good account of the Faraday- 

 Maxwell theory and the electromagnetic theory of dispersion, there is an account 

 of many important matters not treated at all in the standard English books ; 

 especially needed is the chapter on the electronic theory of magnetisation, giving 

 an account of the work of Langevin and Weiss. Elsewhere, in the treatment of 

 conduction, we think the author might point out the difficulty of supposing electrons 

 to be gas-kinetically reflected from atoms and molecules, considering that experi- 

 ment points rather to their being absorbed and subsequently liberated by the 

 molecules, a very different mechanism which, we think, may possibly form the 

 basis of a more complete theory. 



Two chapters in the second part of the book contain an interesting and able 

 discussion of the relative merits of the wave theory and Einstein's corpuscular 

 theory of light, and of the nature of X-rays, in which it is made clear that while 

 modern experiment seems to have conclusively established that X-rays are 

 essentially similar to light, the nature of both light and X-rays is very doubtful. 

 It may be mentioned that Lane's and Bragg's X-ray photographs of 191 2 receive 



