194 



NA TURE 



[June 29. 1893 



the subject is taken up the second time. The equations 

 that are given were very useful in the early days when 

 the combinations were first worked out, as they showed 

 what combinations were theoretically possible to produce 

 the desired result. But it is questionable whether these 

 equations are of much use at the present time, or if they 

 are given, it should be clearly explained why equations 

 originally obtained on the assumption that the perme- 

 abihty of iron was constant led to conclusions distinctly 

 valuable in the case of machines intended to produce con- 

 stant pressure, but quite useless for suggesting a method 

 of compounding a dynamo to produce constant current. 



The chapter on lap, wave, and ring winding of arma- 

 tures is most instructive. The original idea of cross 

 connecting the coils of a gramme ring, so as to only 

 r'equire two brushes with a multipolar dynamo, the author 

 attributes to Mr. Mordey, but we were always of opinion 

 that Prof Perry's patent of 1880 contained the first sug- 

 gestion of this now well-known arrangement. 



Chapters xiii., xiv., xv., xvi., xvii.,and xviii.,on "Prac- 

 tical Construction of Armatures," " Commutators, 

 Brushes, and Brush Holders," " Mechanical Points in 

 Design and Construction," " Elements of Dynamo 

 Design," "Arc Lighting Dyijamos," and " Examples of 

 Modern Dynamos," taken in conjunction with the 

 twenty-nine plates at the end of the book, contain a 

 wonderfully compressed, and most admirable, restime of 

 British and foreign practice, and mdke one feel proud 

 that they have been written by an Englishman. 



In Chapter xx.; on electromotors, the laws of maximum 

 activity and maximum efficiency are carefully distin- 

 guished, and it is pointed out that, while Jacobi, Verdet, 

 Miiller, and even Weidemann stumbled, the true ideas of 

 Thomson and Joule were put forth correctly by Achard in 

 January 1879. In 1883 was advocated the proposal to 

 employ a forward lead of the brushes with a motor, and a 

 backward lead with a dynamo, so that the magnetisation 

 of the armature might help instead of opposing that of the 

 fields magnets. With reference to this idea the author 

 says, " The fascinating notion of using the armature to 

 magnetise has proved a failure in practice," a statement 

 undoubtedly true historically, but lacking in prophetic in- 

 spiration, seeiiig that this proposal of May 1883, to utilise 

 instead of counterbalancing the mignetism of the arma- 

 ture is now warmly welcomed in May 1893, after Mr. 

 Sayers has shown how the "destructive sparking" can | 

 be annihilated. 



Chapter xxii., on " The Principles of Alternate Cur- 

 rents," is much too meagre for any one who does not 

 already know more of the subject than is contained in 

 the chapter itself A student reading the book would be 

 inclined either to skip this chapter altogether and go on to 

 the next, on " Alternators," or turn to some other book 

 for what Chapter xxii. professes to give. The account 

 of the construction of alternating current dynamos con- 

 tained in Chapter xxiii. is as comprehensive as the 

 description of the principles in the preceding chapter is 

 meagre. The abstract of Dr. J. Hopkinson's investigation . 

 on the coupling of alternators is , clearly given and 

 easily understood, when the mispript of N A for N H ^ 

 on page 691 i,s,cQrreQted. Thp( device of corpmatating , 

 the current rouod the field of ap alternate current motor, 

 so that wjien, tlxe motor synchronises the excitation is ^ 

 Np. 1235. VOL. 48] 



produced by a pulsating direct current, is due originally 

 to Prof Forbes, and not to Mr. Mordey, as the author 

 states on page 702. 



The author is very perplexingin his naming of alternating 

 currents. He calls the current produced by an ordinary 

 alternator a two phise current, but why we have no idea. 

 At any one moment the current in all parts of the circuit 

 is in one phase ; at different times the current has, of 

 course, every possible phase in succession. The current 

 must therefore be called a one phase current, or a single, 

 current having every possible phase in succession, if the 

 author prefers that ; but there is no more reason to call 

 such a current a two phase current than to call it a 

 twenty-two phase current. When again we come to the 

 arrangement devised by Ferraris, and illustrated in Fig. 

 455 (P^gs 405)) we have two distinct circuits, the currents 

 in which always differ in phase. We have therefore a 

 two phase arrangement. The author however calls this 

 a ^^ four phase transmission." Lastly, however, when 

 there are three circuits in which there are three distinct 

 currents, the phases of which at any one moment are 

 always all three different, the author, for some reasor, is 

 content to call this a "three phase current" like ordinary 

 mortals. 



Chapter xxv., on alternate and direct current trans-, 

 formers, is good, but might be made a little fuller, seeing 

 that so very much work has been carried out on trans- 

 formers during the past few years. The methods of, 

 testing transformers are becoming as important as those^ 

 for "Testing Dynamos and Motors," which forms the, 

 subject of Chapter xxviii. The last chapter, on the 

 " Management of Dynamos," contains many valuable, 

 hints, derived in some cases from the author's own 

 experience. 



The table at the end of the book, headed " Wire Gauge 

 and Amperage Table," we have gazed at with feelings 0% 

 admiration tempered with doubt. Admiration — because,^ 

 if all the columns of numbers given in this table bej 

 correct, then, while we have spent much time experi-. 

 menting and calculating in order to obtain information 

 about the heating of one or two bobbins of wire traversed. 

 by a current, the problem for bobbins wound with all 

 kinds of wire to all sorts of depths up to 4^ inches hasin; 

 some way or other been solved. Doubt — because we, 

 fear that, in solving this problem, some sort of simple, 

 proportion may have taken the place of the complicated- 

 matheinatics which it is necessary to employ on account) 

 of the flow of heat taking place across many layers of; 

 copper and cotton interspersed. 



To say that this book is the best on its subject in thei 

 English language is to say too little, since we know ofinoj 

 book in any other language on the same subject that can, 

 be compared with it. The few peculiarities that we have> 

 drawn attention to must be regarded less in the light of| 

 blemishes than as giving the book individuality, for) 

 we recognise our best friends, when we meet them, byi 

 their characteristic peculiarities. Dr. Thompson's treatise) 

 should be, nay, probably is already, in the hands of every > 

 one who deals with dynamo machinery from an educa ■\ 

 tional or from a mariufacturing point of view. ) > 



It is interesting to notice how the author, in coi^monj 

 with other w;-iters, is unconsciously searching for a goqd/ 

 abbreviation for the important, but somewh?itcumber?omei 



