Notices respecting New Books. 235 
lying a number of methods for “ separating ” the lcsses, viz., that 
the frictional torque is independent of the speed, is entirely 
erroneous, as has been shown by Dettmar’s careful investigations 
on this subject ; hence methods based on this assumption must be 
more or less valueless. Further, it must be remembered that in 
order to arrive at the normal working value of the frictional torque, 
the machine must be kept running for at least two or three hours— 
a fact not even alluded to by Dr. Fleming. We presume that the 
last chapter of the book was already in the press when Mr. Behrend’s 
important paper on the differential method of testing allernators 
appeared, as no reference to it is made by the author. 
In concluding this brief review of an important contribution to 
electrical literature, we may say that the present volume bears on 
it the stamp of the author’s exceptional gift of clear exposition, 
and that it forms most interesting as well as instructive reading 
for the electrical engineer. | 
Light Waves and Their Uses. By A. A. MicuEtson. (Being 
vol. iii. of the Second Series of the Decennial Publications of 
the University of Chicago.) Chicago: The University of 
Chicago Press. 1903. Pp. 166. Price $2-00. 
A cLEAR and simple account of the application of interference 
methods to various physical measurements, written by the leading 
authority on the subject, is sure to meet with a warm welcome 
from all students of physical science. There is a singular charm 
about this first-hand account of the subject, pervaded as it is with 
the glow of enthusiasm which has animated the author in his extra- 
ordinarily difficult and brilliant researches. The book, which is 
based on a series of eight lectures on ‘“‘ Light Waves and their 
Uses” delivered by Professor Michelson in the spring of 1899 at 
the Lowell Institute, is free from mathematical technicalities, and 
should prove quite intelligible to the general reader. 
Le Point Critique des Corps Purs. Par EB. Marutas, Professeur de 
Physique &@ la Faculté des Sciences de UUniversité de Toulouse. 
Paris: C. Naud. 1903. Pp. vin-+ 255. 
At the Paris International Physical Congress of 1900, Professor 
Mathias presented a paper on “ Methods of Determining the 
Critical Constants.” ‘lhis paper may be found in Vol. I. of the 
Rapports. The volume now before us is an expansion of the article 
in the Rapports, with important modifications and additions, and 
forms a most complete and useful monograph on what must be 
regarded as a somewhat neglected branch of science. 
The book is divided into ten chapters. The first chapter gives 
an account of Andrews’ classical theory, Chapter II. deals with 
what the author terms the phenomenon of Cagniard-Latour, which 
consists in the disappearance of the meniscus separating the gaseous 
from the liquid phase at a temperature bclow tke critical temperature. 
