Notices respecting New Boohs. 463 



point of view of an observer who is moving along with the 

 charge e, the phenomenon is merely one of ordinary electro- 

 static repulsion and the test electron should experience no 

 change in velocity in the X direction but should be accelerated 

 merely in the Y direction. 



If, however, we divide equation (12) by (13) we obtain 



F '=^'? F ,> .••... (14) 



which agrees with equation (5), the necessary relation for 

 zero acceleration in the X direction. The application of 

 equation (5) thus removes a discrepancy which could not be 

 accounted for in anv system of mechanics in which force and 

 acceleration are in the same direction. 



Summary. 

 For non-Newtonian mechanics, it has been pointed out 

 that force and the acceleration it produces are not in general 

 in the same direction. A definite relation (equation 5) has 

 been derived connecting the components of force parallel and 

 perpendicular to the acceleration. For a special problem. 

 the application of this relation has removed an apparent 

 discrepancy between the predictions based on the electro- 

 magnetic theory and on the principle of relativity. 



Ann Arbor, Mich. 

 March 25th, 1911. 



XLV. Notices respecting N T ew Boohs. 

 The Principles of Electric Wave Telegraphy and Telephony. Bv 

 Prof. J. A. Fleming, D.Sc, F.R.S. Second Edition. Pp. xviii 

 + 906. With Illustrations. (London : Longmans, Green & Co. 

 1910.) 

 A LTIIOUGH it is only five years since the first edition of this 

 ■£*- book appeared, yet, so vast have been the developments since 

 its appearance, that this new edition is almost a new book. Those 

 who are acquainted with Professor Fleming's previous treatises 

 will be prepared for a masterly exposition of electric wave 

 telegraphy ; but he surpasses himself in his presentation of this 

 subject. Xo one is better qualified than he for the task. Xot 

 onlv is he intimate with the mathematical and theoretical side of 

 the subject ; but he has for many years been in close contact with 

 and has himself contributed largely to the rapid developments 

 which have taken place both on the theoretic and experimental 

 sides. It is impossible to do justice to this book in the space at 

 our disposal — the enumeration of the headings of the chapters 

 would almost exhaust it. The characteristic feature is the happy 

 combination of theory with 'experiment, each being dealt with 

 in an encyclopaedic manner. For example, twelve pages deal with 



