568 



NATURE 



[January 23, 19 13 



it differs from the ordinary text-book scarcely ex- 

 presses the truth of the matter. It is so often 

 found that a new book on physics merely consists 

 of previous works plus a few modifications and 

 additions. Here, however, internal evidence 

 makes it perfectly clear from page to page that 

 the author is indeed the author. 



The book is a very good one indeed, and should 

 find a large sale among those students of physics 

 who need in a single volume a treatment of the 

 subject rather more than elementary. It is true 

 that in many places the illustrations of physical 

 principles used verge on the ludicrous, and that 

 the mode of expression often seems out of place, 

 Ijut the redeeming feature is that the illustrations 

 are excellent. It may be said, in fact, that 

 by reason of the frequent recourse to everyday 

 occurrences as constituting examples of various 

 physical phenomena this book is chiefly note- 

 worthy. A few of them, notably those connected 

 witii physiological processes, may, perhaps, be 

 beyond the average student, but the author has 

 evidently introduced them for the special benefit of 

 students of medicine. One undesirable feature 

 may be mentioned in conclusion, namely, the fact 

 that the author has attempted in several places to 

 conduct algebraic calculations in words instead 

 of symbols, the result being that the reasoning, 

 although correct, is very difficult to grasp. 



(4) This is a combined theoretical and practical 

 text-book intended for schools, and to be covered 

 normally on a three-years' course. In most 

 respects it resembles the usual school-book. It 

 is, however, a good plan to describe in one volume 

 the methods of doing experiments and the 

 theoretical treatment of the principles involved. 



(5) The author of this book has produced a 

 useful record of much of the experimental work 

 which has been done on electrolysis, and interprets 

 the results upon the theory of ionisation. He 

 claims that the simple theory, although admittedly 

 inapplicable to concentrated solutions, yet may 

 afford a basis to which modifications may be made, 

 just as did Mariotte's and Gay-Lussac's laws for 

 gases. The subject is divided into four sections, 

 namely, the constitution of electrolytes, their con- 

 ductivity, contact potential, and electrical energy. 

 .\ considerable number of tables are given record- 

 ing numerical values of such quantities as heats of 

 ionisation and conductivities of acid solutions of 

 various strengths. 



(6) In a book having the reputation of the late 

 Prof. Drude's "Optics," the chief interest in the 

 appearance of the third edition is attached to the 

 modifications and additions introduced. Such a 

 Ijook would be hard to improve, and might easily 

 be spoilt. Prof. Gehrcke has wisely refrained 



NO. 2256, VOL. 90] 



from making any serious alterations, and the 

 additions are few in number, the principal 

 being a short description of Stokes's theory of 

 aberration and a paragraph or so on the photo- 

 chemical effect on gases. The treatise is still 

 Drude's "Optics," and will continue to merit the 

 high place it already holds in physical science. 



(7) This volume has been written for the use of 

 students of electrical engineering. It consists of 

 the treatment of magnetism and electricity, first 

 of all from the theoretical point of view, and then 

 in connection with its various applications. The 

 mathematical treatment is quite elementary — it is, 

 in fact, based on Deschanel's " Natural Philo- 

 sophy," so far as the purely theoretical part is 

 concerned, many of the diagrams also being repro- 

 duced from that treatise. A series of tables of 

 constants and various questions and exercises add 

 to the value of the book, which appears to be 

 well fitted for its purpose. 



OUR BOOKSHELF. 



La Ceinciitazionc dell' Acciaio. By Dr. Frederico 

 Giolitti. Pp. xi + 506. (Torino : Unione Tipo- 

 grafico-Editrice Torinese, 1912.) 

 In the present work, Prof. Giolitti has collected 

 together the important experimental results ob- 

 tained by his fellow-workers during the last four 

 years relative to the cementation of steel. At 

 the same time, he has presented an exhaustive 

 review of the subject from its scientific and tech- 

 nical aspects. The chemical nature of the process 

 of cementation (in which term case-hardening is 

 included) has been the subject of many con- 

 troversies, and it cannot be said that the mechan- 

 ism of the transport of carbon is even now 

 understood. Prof. Giolitti subjects the extensive 

 literature of the question to a critical review, which 

 does not appear to omit any work of importance, 

 English and German memoirs being examined as 

 thoroughly as those in Italian and French. This 

 part of the book might, perhaps, have been some- 

 what condensed by the omission of repetitions, 

 but it forms an excellent source of reference for 

 a class of facts of great importance for the general 

 theory of metallic alloys. The chapter in which 

 the results of previous investigations are summed 

 up scarcely gives sufiTicient attention to the fact, 

 now fully established, that carbon diffuses in the 

 solid as a carbide, and not in the free state. 



The author's own researches, which occupy 

 the larger pari of the book, deal mainly with the 

 specific influences of carburising gases (hydro- 

 carbons and carbon monoxide, alone or in the 

 presence of solid carbon) in the process of cement- 

 ation. Details are given of the experimental con- 

 ditions employed, and of the technical processes 

 based on the experiments. The methods are of 

 great scientific as well as technical interest as 

 examples of the application of a purely physico- 

 chemical studv of et|uilibri\ini to an industrial 



