.Notices respecting New Books. 519 



The Theory of Commutation. By C. C. Hawkins, M.A. Pp. 1-82. 

 London : ' The Electrician ' Printing & Publishing Co. Ltd., 

 1900. 



The sparkless running of dynamos and motors is one of those 

 extremely complicated problems in which theory has considerably 

 lagged behind practice. It is only quite recently that the vague- 

 ness which characterized all the earlier attempts to deal with this 

 matter theoretically has disappeared, and has given place to a 

 treatment characterized by lucidity and precision. The pamphlet 

 before us is an attempt to expound the present condition of the 

 problem, and is largely based on the valuable work of Arnold and 

 Mie. Although most practical men will be unable to follow the 

 somewhat complicated mathematical treatment, they will find a 

 good deal of interest in the numerous diagrams which graphically 

 exhibit the results of laborious calculations. The discussion of 

 the energy-changes which take place during commutation should 

 prove particularly interesting. The pamphlet is an excellent 

 summary of our present knowledge of this difficult subject. The 

 omission of brackets in connexion with the solidus notation leads 

 to a good deal of ambiguity in some instances, and we hope that 

 this defect will be remedied by the author should another edition 

 be called for. 



Theoretische Betrachtungen iiber die Ergehnisse der Wissenschafilichen 

 Luftfahrten des Deutschen Vereins zur Forderung der Luftschif- 

 fahrt in Berlin. Von Wilhelm von Bezold. Braunschweig : 

 F. Vieweg und Sohn, 1900. Pp. 1-31. 



This pamphlet- is an extract from a large and elaborate treatise 

 giving a full description of the work done by the Deutscher Verein 

 zur Forderung der Luftschiffahrt in Berlin. The pamphlet deals 

 with the scientific value of the data obtained during the various 

 balloon ascents, with the distribution of temperature in a vertical 

 direction, and with the periodic fluctuations of pressure, tempera- 

 ture, and humidity. 



Memoires Originaucc sur la Circulation Generate cle V Atmosphere. 

 Annotes et Commentes par Marcel Beillouin. Paris : Georges 

 Carre et C. Naud, 1900. Pp. xx -f-163. 



This book is a collection of the more important original memoirs 

 relating to the great problem of the circulation of the atmosphere, 

 and includes papers by Halle v (1686), Hadley (1735), Maury 

 (1855), Ferrel (1856-1861), Werner Siemens (1886), M. Moller 

 (1887), Oberbeck (1888), and H. von Helmholtz (1888 & 1889). 

 Some of these memoirs are translated in their entirety, while of 

 others only abstracts are given. M. Brillouin has contributed a 

 most interesting introduction, in which the historical development 

 of the subject and the present state of the problem are clearly set 

 forth. The book is beautifully printed and tastefully bound. 



