April 14, 19 10] 



NATURE 



185 



contains narratives by actual travellers, such as those 

 edited by Mr. \\'herry (3) ; these can be used as school 

 readers, or can be set for home reading; this par- 

 ticular set deals with early climbs in the Alps. The 

 second kind takes the form of a special study of a 

 limited area, and the volume on " Cheshire " (4) illus- 

 trates the way in which the pupil may be brought into 

 touch with the work of a specialist ; such books should 

 be in the geographical reference librar}'. These works 

 appear to typify the best efforts of modern teachers of 

 geography. B. C. W. 



ELECTRICAL ENGINEERING. 

 (.1) Electrotechnics. By Dr. John Henderson. Pp. 



xiv+165. (London: Longmans, Green and Co., 



1909.) Price 35. 6d. 

 (2) Practical Testing of Electrical Machines. By 



L. Oulton and N. J. Wilson. Pp. vi+210. (London : 



Whittaker and Co., 1909.) Price 4s. 6d. net. 

 I 'T^HE efficient organisation of students' work in 

 J- an electrical engineering laboratory is a 

 difficult task, and especially so with large elementary 

 classes. Advanced students may be trusted with 

 delicate instruments and left to arrange the necessary' 

 connections by themselves, they require little super- 

 vision, and as their number is small this is easily 

 given. With elementary classes the case is different. 

 It is obviously impossible to let all the men do the 

 same tests simultaneously, since that would require 

 multiplication of apparatus beyond the financial 

 capacity of most institutions. Hence tests of different 

 kinds must go on at the same time, and since the 

 demonstrator cannot personally supervise every one 

 of these different tests from its beginning, it is 

 important that the students should get very clear 

 instructions in print. It is also important so to 

 arrange the tests that they shall, with students of 

 average ability, take about the same time, and to 

 arrange the work generally with the precision of a 

 railway time-table, because otherwise students will 

 drop out of their order and fail to get the full benefit 

 of the course. All this, and the necessity to adapt 

 the work to the class of students attending and to 

 the equipment which happens to be available in any 

 particular institution, tends to make the instruction 

 somewhat cut and dried in character, and this is 

 likely to detract from its educational value. 



The author, who has evidently experience of these 

 difficulties and the way to make the best compromise 

 possible between conflicting requirements, has, in the 

 third volume of this series of physical and electrical 

 engineering laboratory manuals, given us an excel- 

 lent guide to laboratory work of this kind. He does 

 not believe in the use of special apparatus, but very 

 rightly teaches his students to make the tests in the 



boratory very much in the same way that they will 



ive to adopt when they get into practical life, that 

 ~, by the use of ordinary commercial instruments. 



te also adopts the principle that tests must be so 



ranged that only two, or at the outside three, men 



re necessary for any one test. 



The subject-matter is divided into three parts, which 

 roughly correspond to the City and Guilds of London 

 NO. 21 1 1, VOL. 82,] 



syllabus for the "elementary stage" and the "or- 

 dinary grades " of direct and alternating current 

 engineering. We thus get in the first part Ohm's 

 law, the Wheatstone bridge, calibration of instru- 

 ments, fuse testing, some simple magnetic tests, and 

 experiments with a small motor. In the second part 

 we come to heating of wires, potentiometric measure- 

 ments, more advanced magnetic testing, character- 

 istics of dynamos, secondary batteries, photometrj', 

 losses in dynamos, and so on. The third part deals 

 mainly with the fundamental relations of alternating 

 currents, graphic methods of representing these, and 

 some very simple tests on alternators. Transformers 

 and motors are not dealt with. 



In an appendix are given mathematical and phy- 

 sical tables which will be found very useful, not only 

 by the student, but also by the practical engineer. So 

 far as the student is concerned, some of these tables 

 should bring home to him a sense of reality of his 

 work. Students are apt to consider their class-work 

 as something purely scholastic and detached from 

 practical life. If, then, a student, after having in his 

 work found some physical fact such as the fusing 

 current of a certain wire, the E.M.F. of a given 

 cell, or the power per candle required by, say, an 

 Osram lamp, and then turns to the tables at the end 

 of this book to see how his determination agrees with 

 the figures there given, he must get the impression 

 that what he has done in the laboratory has practical 

 importance, and this conviction will give him addi- 

 tional interest and pleasure in his work. 



(2) This book is intended as a guide in testing elec- 

 trical generators and motors. In the preface the 

 authors point out that it is impossible to give " all the 

 theory that the subject entails," and that the reader 

 must therefore also consult some of the many text- 

 books. This is obviously right ; nobody can expect to 

 find in a book which is primarily an instruction how 

 to test the whole of the theory of electrical machines, 

 but some fundamental theories must be given, and in 

 this respect the book falls short of what the reader 

 has a right to expect. The authors give some sort 

 of theory, but it is neither closely reasoned nor always 

 clearly expressed. The latter defect may to some ex- 

 tent be due to their adoption of some terms which 

 give one the impression of being a kind of technical 

 jargon employed in a particular shop or laboratory, 

 though not generally found in scientific books. For 

 instance, if we are told to take a " locked satura- 

 tion " it is not immediately obvious that we have to 

 determine the relation between starting torque and 

 voltage of an induction motor ; nor is it very clear 

 what a "pressed down reading on the scales with the 

 power off " might mean. On p. 34 we read that 

 "C.B. is the leakage current and proportional to the 

 current in the motor." Further that it is "required 

 to overcome the counter E.M.F. due to leakage." 



These are of course merely unfortunate ways of 

 expressing certain ideas which the authors have cor- 

 rectly in their minds, but it is irksome for the reader 

 to have continuously to exercise his ingenuity in order 

 to find out what it is the authors really mean. In 

 some cases this task looks almost hopeless, as, for 



