NATURE 



49 



THURSDAY, MAY 15, 1890. 



THE ALTERNA TE CURRENT TRANSFORMER. 

 The Alternate Current Transformer in Theory and 



Practice. By J. A. Fleming, M.A., D.Sc. Vol. I. 



"The Induction of Electric Currents." Pp. 479- 



(London : The Electrician Printing and Publishing 



Company, Limited, 1889.) 



THE alternating current has of late years sprung into 

 great commercial importance, and accordingly 

 the laws regulating its flow, long known to a few, are 

 becoming recognized and assimilated by the many. The 

 behaviour of alternating currents is so vastly more com- 

 plex than anything which had to be dealt with in the 

 time-honoured chapter of the text-book concerning 

 " divided circuits " for the case of steady currents, that 

 a new literature has arisen, and a number of half-accepted 

 new terms have been coined. 



It is evidently with the aim of making accessible to 

 average readers the greater portion of this subject that 

 Dr. Fleming has put together the above-named book. 



The volume is distinctly a compilation, a rcchaiiffce of 

 recent work, though it consists partly of a reprint of the 

 author's own articles in the Electrician, and it is a com- 

 pilation of a very useful kind. It brings together a 

 quantity of floating information collected with a keen 

 scent for practically useful items, as well as for topics of 

 contemporary interest. 



It is hardly a book to be recommended to the student 

 as a logical treatise. The proof of the laws is a second- 

 ary consideration, and though proofs are indicated, it is 

 more to link them on to other things than really to justify 

 and deduce them. In fact the book has the air of being 

 hastily written ; but the facts are there, whether deduced 

 rigorously or not, and the practical man, for whom it is 

 written, will not be hkely to find fault. In several in- 

 stances, however, it can be claimed that the presentation 

 of doctrines is as clear as could be wished and as the 

 ability of the author would lead us to expect. Students 

 will undoubtedly bQ glad of a book which contains so 

 much useful information only accessible otherwise with 

 difficulty. 



The early part of the book, dealing with the modern 

 treatment of magnetism, hysteresis, and the Hke, is fairly 

 good, but is probably now superseded by some still more 

 recent articles by Prof. Ewing himself. The next portion, 

 on simply periodic currents, is very instructive. In it Lord 

 Rayleigh's investigation of the laws of branching for 

 alternating currents is incorporated, and the result applied 

 to determine the correcting factor for a watt-meter ; a clear 

 explanation being given of why it is so difficult to measure 

 the average power of an alternating current. Some of 

 Mr. Blakesley's geometrical representations are also uti- 

 lized ; and the whole circumstances of a simply alternating 

 current are very clearly explained. 



Then comes an abstract of some of the too-long-buried 

 researches of Prof. Henry, which the recent publication of 

 his memoirs by the Smithsonian Institution has brought 

 into prominence. 



A brief account of the experimental investigations of 

 Masson and Breguet, Blaserna, Helmholtz, on transient 

 Vol. xlii.— No. 1072. 



currents, of Hughes on the induction balance and on the 

 throttling effect of iron wire, follows ; together with the 

 Maxwell-Rayleigh-Heaviside theory of the same. 



We then come to the main subject of the book— the 

 laws of mutual induction and the theory of induction 

 coils or transformers. Here the author enters into very 

 instructive detail, showing how to deal with transformers 

 containing iron, and incorporating the researches of 

 Hopkinson, Forbes, Sumpner, Ferraris, and Kapp, as 

 well as the general theories of Maxwell and Lord 

 Rayleigh. 



A chapter headed " The Dynamical Theory of Current 

 Induction " follows, wl\erein Prof. Garnett's summary of 

 Maxwell's electro-magndtic ether models is reproduced ; 

 some instructive explanations of many Maxwellian ideas 

 is given in a much clearer and more elementary form 

 than is frequent ; some experiments and articles of the 

 present writer are incorporated ; and lastly, Mr. Tunzel- 

 mann's abstract of Hertz's papers is reprinted once more. 

 It is to be regretted that we have not the advantage of a 

 fresh abstract and discussion of these papers by Dr. 

 Fleming himself. So much in Hertz's papers was con- 

 fessedly crude and tentative that it would have been 

 much more satisfactory to have had a real digest from 

 a contemporary point of view, instead of the useful but 

 now out-of-date summary with which most persons were 

 already familiar. 



Perhaps also it may without offence be suggested that 

 a free use of quotation marks in this last chapter, pos- 

 sibly in other chapters also, would not have been out of 

 place. One is a little startled to find whole paragraphs 

 and diagrams incorporated into a book without rather 

 more explicit statement concerning their origin. I may 

 instance pp. 380, 408, 409, among others, as having 

 struck me personally with some surprise, though very 

 likely the feeling was unjustifiable. 



It may be useful if I record such trifling slips as I have 

 noticed. Quite possibly some are not erroneous at all. 

 On p. 7 the assertion is made that Faraday "came to 

 see that that which he had denominated the clectrotonic 

 state is really the amount of electro-magnetic momentum 

 which the circuit possesses." As a matter of history this 

 is surely incorrect ? And is there any evidence for the 

 statement on p. 2, that Faraday's failure to obtain 

 current induction in 1825 and 1828 was because his 

 galvanometer circuit was not closed? It seems very 

 improbable. At the bottom of p. 67 the argument 

 seems to me incorrect and confusing. In the diagram 

 on p. 140 current should appear as a factor in the 

 lengths OB, BA, &c. On the top of p. 145, there is no 

 need for L and N to be both zero in order that the watt- 

 meter factor, F, may equal unity ; it is sufficient if the 

 time constant of the fine wire shunt alone vanishes. Cn 

 p. 209 a p is twice dropped out of an equation. On 

 p. 253 the statement is made "that we may regard 

 the inductance of a conductor as an efi'ect which is due 

 to the fact that the current takes time to penetrate into 

 the conductor"— a statement which is by no means true. 

 And two pages on we read, " as the frequency of alterna 

 tion is increased, the resultant self-induction of the circuit 

 is lessened, but [? so that] although the true resistance 

 is increased, the impedance may be diminished on the 

 whole." It may, however, be more truly asserted that no 



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