NATURE 



581 



THURSDAY, OCTOBER 11, 1906. 



ELEMENTS OF ELECTRICAL ENCINEEIUNG. 

 Electrical Engineering in Theory and Vraclice. By 



(i. D. Aspinall Parr. Pp. viii + 447; illiislraled. 



(London: Macmillan and Co., 1-Ui.. U)(>().) Price 



\2S. net. 



THIS book is the lirst of two or more voUimi's 

 dcalin^f with {he subject named in (lie lillc. 1 1 

 is introductory, and treats of the elemcnlary (liroi\ 

 .and testing- methods while describint; ihc simpler 

 apparatus used in electrical engineerint;. Direct .and 

 alternating current machinery are to be d<'.ill with in 

 .1 later volume. 



.Magnetism is first considered, then electrostatics. 

 IClectric currents and electromagnetic effects follow, 

 .and in this way the more practical portions of the 

 wairU are approached. Kach chapter ends with a set 

 of examples, chosen, for the most part, from pa|)ers 

 set by recognised authorities. The student who 

 works through these examples after reading each 

 ch.apter will obtain a good grasp of its contents, even 

 though one or two of the examples are perhaps un- 

 fiirtunate. as, for instance, that specially worked out 

 on p. S5, which relates to a rather impossible gener- 

 ■ ilor the voltage of which drops noticeably wiien a 

 high-resi.stance voltmeter is connected across ii> 

 brushes. The author has taken considerable trouble 

 to bring the book up to date, both in the descriptions 

 of apparatus and bv frequent reference to the more 

 iinport.ant of recent papers. 



There is much, however, in the book, ;uid chictlx- 

 i]i its earlier chapters, which to the present writer 

 seems open to criticism. It professes to be a text- 

 book introductory to the subject of electrical engineer- 

 ing. .\s such, its functions are surely to show clearly 

 how the various elementary formulse used by the 

 electrical engineer are derived, and to describe the 

 appliances by which electrical and magnetic quantities 

 .ire measured, and also the simpler commercial appli- 

 cations. Many books have been written which have 

 had this aim, but few have attained it. Either a 

 llieorist writes a text-book which, however perfect 

 llieoretically, is so far removed from actual practice 

 as to be almost useless to the engineer, or a book is 

 written like the present, which is full of useful in- 

 formation, but is not sound theoretically; or perhaps 

 one should say rather that it is incomplete on that 

 side. Rigid proof of fundamental formulce is 

 shirked, and the student loses that confidence in them 

 which always goes with a precise knowledge of the 

 way in which they have been derived. Text-books 

 on electrical engineering, at any rate, should not now 

 be written to which either of the foregoing reproaches 

 can be urged, for the day is gone in which it was 

 questioned whether a sound theoretical training was 

 necessarilv the basis of a practical engineer's Icnow- 

 ledge. 



The present work is quite large enough to deal 

 ilioroughly with the theory without even increasing 

 the space devoted to this part of the subject ; and yet, 

 NO. I93S, VOL. 74] 



when reading il, just where one would expect an 

 exact statement of the w.i\- in which a given formula 

 has been derived, oni- re.ids thai " it can be shown," 

 or that "space will not pi-rmil .1 proof here." Such 

 passages occiu- frequently; for inst.mce, when deriving 

 the magnetic force near a long wire (p. 129) or that 

 in a long solenoid (p. i,ii); or, again, when obtain- 

 ing the relation between hysteresis loss and the area 

 of curves of cyclic magnetisation (p. 147), the pull 

 .along magnetic lines of force (p. 157), the capacity 

 of a condenser (p. 17O or of condensers in series 

 (p. i.So), ,ind the cnergN stored in an inductive circuit 

 (p. 197). It is true thai in one or two of these cases 

 some verv elementary ;ipplication of the calculus 

 would have been required ; but even this may surely 

 now be expected of .any reader to whom the theo- 

 retical portion of the book shall be of any use at all. 

 .\n equivalent graphical proof may frequently be given 

 with advantage instead of the symbolical one, so that 

 even this difficulty may be met. These comments do 

 not appiv to the derivation of the more coinplicated 

 expressions, but only to the derivation of those which 

 form the basis of other formuLf which the engineer 

 may frequently have to use. 



The section entitled " Klectrical Resistance " in- 

 cludes, not only an account of the various standard 

 and testing resist.ances emploved, but also much useful 

 information on insul.aling ni;ileri,ils .-iiid the forms 

 thev take in practice. .\ matt<-r of importance to elec- 

 trical engineers is the subject of contact resistance, 

 and particularlv that occurring with carbon brushes 

 on commutators. Exact information on this point is 

 now available which should find a place in such text- 

 books as the present. .\ few pages might also have 

 been devoted to resist.ances for the absorption of 

 power, and more than .1 casual reference to the use 

 of micanite as an insulator. Considerable space is 

 devoted to the magnetic qualities of iron stampings. 

 One of the best chapters is that on electrical and 

 magnetic instruments, in which the various types now- 

 used in testing and switchboard work are well de- 

 scribed. It mav be remarked, however, that unde\- 

 hot-wire instruments, that of Hartn-iann and Braun, 

 which is the onlv such inslrun-ienl w-idely used, is 

 not described. 



.Although the book is gcner.-illv quite readable, the 

 English is bv no means perfect throughout. Tlie 

 reasoning is here .nid there unsatisfactory, loose 

 language creeps in, or the style becomes diffuse. 

 These are, however, small niatters, which will no 

 doubt be remedied in a later edition. 



The book includes a large number of excellent 

 tables of physical constants and data useful to the 

 engineer, from which much redundant matter has 

 been excluded and modern information put in its 

 place. Such data should always, in the present 

 writer's opinion, be so stated as to give an idea of 

 the percentage accuracy attainable in their measure- 

 ment. To quote the hysteresis loss in tungsten steel 

 .-IS 216,864 ergs per cycle (p. 150), or the specific 

 resistance of paraffin wax as 13,385x10" megohms 

 per inch cube (i). 107), is to give a false in-tpression of 

 the useful .-iccin-.-icy .-ilt.-iinable. Three signific;mt 



11 B 



