Notices respecting New Books. 535 



the book may be recommended to beginners, particularly as some 

 -numerical exercises are given, and some curves are given to illus- 

 trate the answers ; and the most general case is led up to gradually. 

 We feel, however, that the authors have not taken advantage of 

 their good opportunity. Surely it would have been better to begin 

 by showing the student that in most practical problems d/dt enters 

 in a linear fashion, and if we indicate it by d this symbol may be 

 used like an algebraic quantity. Self-induction means a resistance 

 L0 ; a condenser is represented by a resistance 1/C0 ; and the 

 problem of these eleven chapters is to find 



*( B+u+ es} 



We are sorry to think that the authors mention so very few of 

 the interesting exercises which may be given to students on this 

 subject. 



Chapters xii. and xiii. are devoted to a subject which is rather 

 remote from the previous one; it is one on which they seem to 

 have written original scientiBc papers, — " circuits containing dis- 

 tributed capacity and self-induction." It is unfortunate that a 

 very serious mistake should be made at the beginning. The mis- 

 take leads to the equation 



$£+LC^-RC*=0. 

 dx? dt 2 dt 



Now a very little consideration ought to have shown the authors 

 that the self-induction term must be of the same sign as the re- 

 sistance term. If they had used the symbolical method already 

 referred to, they must have seen that they had only to use K + L0, 

 instead of E in the equation as given by Lord Kelvin originally. 

 We have no time to investigate the amount of error which is 

 introduced by this negative self-induction into the results of the 

 authors, nor even to test their results by those given by Mr. 

 Heaviside (Phil. Mag. January 1887). 



In Part II. there is no attempt to give new matter; students 

 who care for the graphical treatment of this subject will find it 

 sufficiently easy to understand. 



Discussion of the Precision of Measurements, with Examples taken 

 mainly from Physics and Electrical Engineering. By Silas W. 

 Holman, S.B. (176 pages). (Kegan Paul, Trench, Triibner, 

 & Co., Limited.) 



We understand that this is a publication of Prof. Hoi man's notes 

 of a regular course of lectures delivered by him at the Massa- 

 chusetts Institute of Technology. What is the probable accuracy 

 of an experimental result ? What accuracy is essential ? How 



