Chemistry and Physics. 545 



little 16mo volume the author presents in an elementary and semi- 

 popular style the fundamental phenomena and laws of static and 

 current electricity. The practical applications to direct and alter- 

 nating current dynamos and to the problem of power transmission 

 are discussed at some length. Although, in general, the text 

 seems to be as accurate as is consistent with its scope and elemen- 

 tary nature, nevertheless some of the definitions might have been 

 made to conform more closely to scientific rigor. For example, 

 on page 19, the dyne is defined as " . . . that force which, 

 acting steadily in the same direction for a second on the mass of 

 one gram, will give it an acceleration of one cm. per second per 

 second." h. s. u. 



12. Elementary Principles of Electricity and Magnetism for 

 Students in Engineering / by Robert Harrison Hough and 

 Walter Martinus Boehm. Pp. vii, 233, with 95 figures. New 

 York, 1913 (The Macmillan Co.).— " The object of this text is to 

 develop, in logical order, the more important numerical relations 

 existing among the principal quantities employed in electricity 

 and magnetism." " Only those relations which are fundamental 

 to the design of the various machines and instruments used in 

 engineering practice are developed." All of these formulae, 668 

 in number, are collected in a single table immediately preceding 

 the index. A knowledge of mechanics and trigonometry should 

 precede, but analytic geometry and calculus may accompany, the 

 study of this course. Problems, for solution by the student, are 

 collected at the ends of some of the chapters. The numbering of 

 these exercises from 1 to 152 may be deceptive because several 

 gaps exist in the list. In more than one noteworthy instance the 

 authors have substituted their own notation, for certain electrical 

 and magnetic quantities, in place of the accepted and classical 

 symbols. For example, /5 is used to denote magnetic induction 

 instead of B, etc. h. s. u. 



13. Methods of Measuring Electrical Resistance ; by Edwin F. 

 Northrtjp. Pp. xiii, 389, with 162 figures. New York, 1912 

 (McGraw-Hill Book Co.). — Since the author has been engaged in 

 electrical measurement for over twenty years and w r as formerly 

 connected with the Leeds and Northrup Company of Philadel- 

 phia for more than seven years, the expectation of an authorita- 

 tive treatise from his pen is immediately aroused. On careful 

 examination of the text it is found that the most sanguine hopes 

 of the reader are realized and perhaps even exceeded. Some of 

 the methods are new and are described for the first time. North- 

 rup says in the preface : " While it is not claimed that the work 

 is exhaustive, the author has selected for presentation all methods 

 which in his judgment are useful, for commercial tests and 

 measurements, for purposes of instruction in educational institu- 

 tions and for application in technical and research laboratories." 



It seems desirable to show the scope of the volume by giving 

 the headings of some of the chapters, such as : I "Extent, Char- 

 acter and Precision of Electrical Measurement. Theory of 



