536 SCIENCE PROGRESS 



Taut the theory and explanations are sometimes not quite clear enough. In 

 the first part of the book no explanation is given as to when an electroscope 

 shows density or when it shows potential (called degree of electrification), and 

 the capacity of the electroscope is not mentioned. The second part of the 

 book, on dynamic electricity, covers a large field, and the treatment is rather 

 inadequate. Very little space is devoted to magnetism, and this subject is 

 only treated qualitatively. Throughout the book, which is written in the first 

 person, Prof. Kolbe seems rather unorthodox in his choice of terms. For instance, 

 •''for the sake of clearness" he substitutes "fall of current" for "fall of potential," 

 .and uses " current intensity " for " current." Several of the terms used must 

 be unfamiliar to English students - for instance, positive and negative electricity 

 are called electricity of the first kind and electricity of the second kind, and 

 the middle of a mass of lodestone where no iron filings cling is called the 

 .zone of indifference. The treatment throughout is unmathematical — in fact, the 

 book is intended for those whose mathematical equipment is small. The practice, 

 however, of dealing with subjects such as Hertzian waves and Radium rays in 

 a text-book before defining, say, the moment of a magnet, is unusual. To 

 an inexperienced lecturer without access to other books the details of many 

 •of the experiments should be of use, but the book is not one which can be 

 recommended to a student entering upon a study of electricity and magnetism. 



R. W. Forsyth. 



Experimental Elasticity. By G. F. C. Searle, M.A., F.R.S. [Pp. xvi. + 183.] 



(Cambridge University Press. $s. net.) 

 The volume is the first of a series of text-books on Practical Physics which the 

 author proposes to publish. The usefulness of books of this type is obvious, and 

 this one will doubtless supply the demand in the particular subject with which it 

 •deals. 



It is divided into three sections. The first deals with the definitions of the 

 •elastic constants and the elements of the theory of elasticity. Some problems 

 having a bearing on the experimental work are solved in the second chapter ; and 

 the third contains descriptions and directions for the performance of some fourteen 

 experiments on elasticity. 



The student thus finds in one text-book both the method of carrying out the 

 experiment and the theory involved in it. This is certainly a distinct advantage. 

 In each case the apparatus is carefully described, and copious details as to 

 experimental difficulties and means of surmounting them are given. Besides this, 

 ■examples of the best method of recording observations and results are shown, and 

 the description of each experiment concludes with a practical example based on 

 actual measurements made either by Mr. Searle himself or his colleagues. 



The book concludes with a series of notes, the last of which—" Hints on 

 Practical Work in Physics" — deserves the careful attention of students. The 

 author rightly insists that good work is only possible when observations are 

 carefully made and all neatly recorded at once, all calculations, however simple, 

 being carried out after the completion of the experiment. 



This work should prove very useful not only to the students of physics them- 

 selves, but also to those whose duty it is to prepare experiments for them and 

 instruct them in the use of apparatus. 



A. O. Rankine. 



