Sei'tembeb 25, 1908] 



SCIENCE 



411 



identical xerophytic characters occur under a 

 wide range of external conditions that are 

 physiologically equivalent. 



Carlton C. Curtis 



The Principles of Direct-current Elec- 

 trical Engineering. By James E. Barb, 

 A.M.I.E.E., Lecturer in Electrical Engi- 

 neering, rieriot-Watt College, Edinburgh. 

 New York, The Macmillan Company; Lon- 

 don, Whittaker & Co. 1908. Pp. viii + 

 551; 294 illustrations. 



There are several ways in which the gen- 

 eral subject of electrical engineering may be 

 divided for study or treatment in text-books. 

 One very general scheme is first to take up 

 the study of direct-current phenomena as 

 applied to direct-current machinery, then to 

 consider the study of alternating currents and 

 alternating-current machinery, and finally to 

 study the subject of transmission and dis- 

 tribution of power by both direct and alterna- 

 ting currents. A second method of division 

 is to consider direct currents as a special case 

 of periodic currents and to make the general 

 division of the study of generators and re- 

 ceivers between induction apparatus and syn- 

 chronous machines. Here again the subject 

 of transmission and distribution is treated 

 after a study of the machinery of both classes. 

 A third classification consists of dividing the 

 general subject into direct-current engineer- 

 ing and alternating-current engineering, treat- 

 ing under each head the generators, receivers, 

 and systems of distribution utilizing direct 

 currents or alternating currents as the case 

 may be. For those who prefer the third 

 classification the author has prepared a vol- 

 ume on the first division which should find a 

 considerable application in colleges and tech- 

 nical schools. 



The general method of treatment is not 

 diSerent from that used by other authors who 

 prefer to consider direct-current engineering 

 as separate from alternating-current phenom- 

 ena. The first chapter is devoted to a review 

 of the subject of units used, the relation of 

 all practical units to the fundamental units 

 being carefully stated. This ia followed by 



chapters dealing with the laws of the electric 

 circuit and the magnetic circuit, but before 

 the application of these laws to the direct- 

 current generator is taken up in detail a care- 

 fully written chapter on measuring instru- 

 ments, in which the principle of operation 

 and the sources of error of most of the instru- 

 ments in common use are considered, is in- 

 troduced, and this is followed by a brief study 

 of the storage battery, electric lighting and 

 cables. Three chapters are devoted to the 

 direct-current generator, and in these three 

 chapters the author has placed in a logical 

 manner most of the information desired by 

 those not interested directly in the details of 

 designing. The subjects of motors and boost- 

 ers are similarly treated and the book is com- 

 pleted by chapters on testing and electricity 

 control, the final chapter setting forth the 

 general principles involved in the design of 

 the switchboard and of protective apparatus. 

 From the beginning the book deals pri- 

 marily with the principles involved, the de- 

 tails of apparatus being introduced as illus- 

 trations of the manner in which the principles 

 are applied rather than for the purpose of 

 furnishing a catalogue of apparatus. To 

 further aid the student in making application 

 of general principles to calculations, carefully 

 prepared problems with their complete solu- 

 tions are introduced at intervals throughout 

 the text, and similar problems for solution by 

 the students themselves are stated in an ap- 

 pendix. The problems as given are practical 

 and the illustrations of machinery and in- 

 struments are taken from modern practise. 

 The use of two colors in the diagrams of 

 armature windings and other connections 

 should aid the student greatly in his study 

 of the subject. The index of the book is 

 complete enough to make it a ready work of 

 reference. Geo. C. Shaad 



Massachusetts Institute of Technology, 

 June 26, 1908 



fiOIENTIFIO JOURNALS AND ARTICLES 

 The Journal of Experimental Zoology, Vol. 

 v.. No. 4 (June, 1908), contains the follow- 

 ing papers: 



