December 12, 1907 J 



NATURE 



125 



contents it may be stated that the first five chapters 

 deal with fundamental principles of electricity and 

 mag-netism, the next four with the theory of direct- 

 current dynamos and motors ; these are followed by a 

 single chapter on alternating-current theory, a chapter 

 on transformers, four chapters on alternating-current 

 generators and synchronous motors, and four chapters 

 on induction motors. The book concludes with a few 

 pages devoted to rotary converters, and an appendix 

 on the symbolic method of treating vectors. 



The matter is well arranged and clearly set forth. 

 Considerable space is taken up by the various types of 

 direct-current armature windings, illustrated by several 

 good diagrams, and the important question of spark- 

 ing receives proper attention. 



The treatment of alternating-current generators is 

 good, but it seems questionable whether students 

 should be taught to look upon the magnetising current 

 in the field windings of an alternator as a vector 

 quantity. With this exception the section devoted to 

 the behaviour of such machines on loads with various 

 power factors is excellent, and the discussion of 

 parallel running is particularly clear. Induction 

 motors are considered in the light of the semicircle 

 diagram with a good deal of theoretical elaboration, 

 and single-phase commutator motors are mentioned 

 briefly. 



Taken as a whole, the book will probably strike 

 electrical engineers as being somewhat too theoretical. 

 It does not claim to go beyond the principles of the 

 subject, leaving aside altogether constructional details. 

 There are, however, many items of information which 

 could be given without any trouble, and which would 

 give a greater reality to the student's ideas. Thus, 

 for instance, it seems a pity that a budding electrical 

 engineer should arrive at the end of the book with- 

 out ever having been told, that electrical apparatus 

 must satisfy the requirements of a temperature speci- 

 fication. There should be no need for a man to go 

 through a course of dynamo design to learn this 

 elementary but important fact. 



A word of praise may be given to the translator, who 

 has done his work with marked success ; it is sufficient 

 to say that the book does not read like a translation 

 form the German, and all who have done such work 

 will agree that this is high praise. 



(2) This is another book for the use of students, 

 but it is intended not only for those taking a 

 special electrical course, but also for others studying 

 general engineering. With this object in view, the 

 authors have endeavoured to differentiate between the 

 two classes of readers, by giving in appendices and 

 in several special sections in small type what they 

 call the more elaborate developments of the subject. 

 This seems a good plan, and it is well carried out. 



The authors are professors in Lehigh University, 

 and the book, in consequence, caters especially for 

 the American engineer. Apart from this, the present 

 volume may be thoroughly recommended to students 

 in this country, on account of the practical nature of 

 the information contained therein. For example, the 

 authors are not content with tracing through the pre- 

 liminary theory of the direct-current generator and 

 then leaving the subject at that point, as so many 

 NO. 1989, VOL. ']']'\ 



English text-books do, but they go on to discuss what 

 limits the output of a generator in actual practice, 

 and give a chapter on ratings and guarantees. As 

 a whole, the book is far more in touch with practical 

 conditions than the usual examples of this class of 

 literature. 



The present volume is confined to the study of 

 direct currents, their generation, distribution, and 

 utilisation for lighting. The first part Is devoted 

 to elementary theory, the theory of dynamo machines, 

 the practical aspect of such machinery, including its 

 rating and performance guarantees, its control by 

 switchgear, and its operation alone and in conjunction 

 with storage batteries. The second half contains 

 chapters on distribution and wiring, on photometry 

 and electric lighting, and four appendices on the 

 magnetisation of iron, on characteristic curves, on 

 armature windings, and on problems illustrating the 

 contents of the whole volume. 



The book will no doubt serve its particular pur- 

 pose admirably, but so far as this country is con- 

 cerned it is unfortunate that the slight differences 

 between English and American practice are sufficient 

 to deter many students from purchasing a book of 

 considerable value in its own country. 



OUR BOOK SHELF. 



Modern Lithology, illustrated and defined, for the use 

 of University, Technical, and Civil-Service Stu- 

 dents. By E. H. Adye. Pp. 128. (Edinburgh and 

 London : W. and A. K. Johnston, Ltd., 1907.) 

 Price los. net. 

 The excellent microscopic drawings of rock-sections 

 previously issued by Mr. Adye (see Nature, vol. Ixxi., 

 p. 341), in a work entitled " The Twentieth Century 

 .\tlas of Petrography," prepare us for the present 

 series of sixteen smaller plates, ^^'ith four coloured 

 figures on each, some of them subdivided into two 

 semicircles, we have a wide range of rocks accurately 

 and artistically represented. The drawing and de- 

 scription of thin sections is not strictly "lithology," 

 however "modern" it may be; but Mr. Adye deals 

 with the illustrations clearly in the accompanying text. 

 He also gives a glossary of petrographic terms, which 

 contains many useful references to original papers. 



The definitions of the crystallographic systems are, 

 as often happens In elementary books, far too 

 limited, and would exclude copper pyrites, for 

 example, from the tetragonal system, and hemi- 

 morphite from the orthorhomblc. If, moreover, 

 rhombohedral and hexagonal are to be taken 

 as synonymous, as stated on p. 97, there is 

 no place under the definition given for such common 

 minerals as quartz and calcite. A crystallographic 

 " pyramid " (p. iii) cannot nowadays be regarded as 

 a closed form. The glossary, as a whole, however, is 

 a mine of Information, and every geologist may read 

 it with advantage. "Tachylite," here and on p. 18, 

 should be " tachylyte " ; but this correction has been 

 made again and again without result In geological 

 literature. Few misprints occur ; we notice " Jan- 

 netez," " B6rlckv," " Radanthal," and Galionella. 



There is no strict arrangement in the subjects on 

 the plates, and, as we have hinted, no attempt has 

 been made at writing on lithology In the broad sense. 

 But the book, with its complete index, is a really good 

 companion for those who require guidance in studying 

 the characters presented by thin sections. No small 



