April 17, 1890] 



NATURE 



561 



SAMPLES OF CURRENT ELECTRICAL 

 LITERATURE."^ 



'X'HESE four books are samples of the different classes 

 ■*■ of text-books of the present day. The first, as its 

 title implies, is intended for workmen actually engaged 

 in the electrical industries, and is therefore of the non- 

 mathematical technical order. The second, on the other 

 hand, is intended for the practical man who is not afraid 

 of a differential equation, and is a very suitable book for 

 a student of one of the higher technical colleges. The 

 third is a mathematical treatise of the University type ; 

 while the fourth is intended for the general public unac- 

 quainted with mathematical or scientific principles, but 

 anxious to learn something about this electricity and its 

 distribution, which are now constantly being referred to 

 even in the daily newspapers. 



Of the four books, the second, on " Absolute Measure- 

 ments in Electricity and Magnetism," is the most valu- 

 able, because the information it contains is correct, and 

 much of it is not to be found in other books. On opening 

 the first book, " Short Lectures to Electrical Artisans," 

 we anticipated seeing how Dr. Fleming had struck out 

 an entirely new line ; but we must confess our disappoint- 

 ment at finding that the author has such a veneration for 

 the authority of antiquity that he felt compelled to com- 

 mence this book with a description of the loadstone. 

 These lectures, we are told in the preface to the first 

 edition, are on "subjects connected with the principles 

 underlying modern electrical engineering," and were 

 delivered " to the pupils and workmen associated with " 

 Mr. Crompton's firm at Chelmsford. We presume, then, 

 that the lectures were intended to enable workmen to 

 make better dynamo machines, electromotors, &c., but 

 as we never yet met with a piece of loadstone in any 

 electrical factory in England or the Continent, we fail to 

 see how the purpose of the lectures was served by their 

 starting with an account of the " native oxide of iron " 

 called the loadstone. Neither the loadstone nor the 

 classical lump of amber, so dear to the hearts of the 

 writers of electrical text-books, are workshop tools. The 

 latter a workman may perhaps come into contact with 

 as a mouthpiece to his pipe, but a piece of loadstone he 

 will probably never even see out of the lecturer's hand. 

 Apart from this academic start. Lecture L is decidedly 

 good ; the author, for example, not merely mentions that 

 an alloy of steel with 12 per cent, of manganese is nearly 

 non-magnetic, but he gives the name and address of the 

 firm from whom manganese steel can be obtained, and 

 he follows the same wise course when explaining how 

 ferro-prussiate photographic paper may be used for 

 obtaining permanent records of magnetic lines of force. 



But why give Rowland's curve connecting permeability 

 and magnetic induction, since later experiments have 

 shown that this curve is quite wrong for large magnetic 

 inductions.? The same mistake is made in Lecture I IL, 

 where it is assumed that for a certain magnetizing force 

 iron becomes saturated, so that no greater induction can 

 be produced, no matter how much the magnetic force is 

 increased. 



Lectures I L and IIL have many blemishes. The ex- 

 pression 50 amperes of current, on p. 24, is misleading ; 

 you cannot have 50 amperes of anything else but current. 

 An ampere is the English name for a unit of current; 

 why, then, put a grave accent over the name 1 One might 

 as well in speaking of so many metres give this last word 

 its French pronunciation.? In justice, however, to Dr. 



' "Short Lectures to Electrical Artisans." 2nd Edition. By J. A 

 Fleming;. (London : E. and F. N. Spon, 1888.) 



"Absolute Measurements in Electriciiy and Magnetism." 2nd Edition 

 Revised and greatly Enlarged. By Andrew Gray. (London : Macmillan 

 and Co.. 1889 ) 



" The Theory and Practice of Absolute Measurements in Electricity and 

 Magnetism. By Andrew Gray. (London: Macmillan and Co., 1888) 

 ,Tr Electricity in Modern Life." By G. W. de Tunzelmann. (London : 

 Walter Scott, i88q.) 



Fleming, we should mention that the use of the grave 

 accent over the word ampere, when used in English, is 

 not peculiar to him. We wish, however, that he had 

 been bold enough to Anglicize this word. In describing 

 the construction of a simple mirror galvanometer, the 

 technical reader ought to have been warned that, unless, 

 in sticking the three magnets on the back of the mirror 

 with shellac varnish, the shellac be put just at the 

 middle only of each magnet, the mirror will be distorted 

 and rendered useless. To say, when speaking of the in- 

 duction of a current in a secondary coil by the starting or 

 stopping of a current in the primary, that the interposition 

 of " a plate of iron prevents it altogether," shows that 

 the author has never tried the experiment. 



On p. 30 is given a picture of the apparatus the 

 author employs for ascertaining the laws of the pro- 

 duction of a current in a coil by the insertion or 

 withdrawal of a magnet. The magnet that is being 

 moved has, judging from the figure, at least looo times 

 the mass of the needle of the galvanometer, which is 

 attached by two very short wires to the coil in which the 

 current is induced. If an electrical artisan were to per- 

 form this experiment with the apparatus placed as in Fig. 

 17 of Dr. Fleming's book, he would probably ascertain 

 the laws of magneto-electric induction with the same 

 amount of accuracy as we once saw obtained at a lecture 

 where the decisive, and applause-producing, swings of 

 the galvanometer needle, on suddenly bringing up the 

 magnet to the coil and removing it again, were certainly 

 produced by the direct action of the magnet on the 

 galvanometer needle, since it was observed at the close of 

 the lecture that one of the wires going from the coil to the 

 galvanometer had never been connected with the galvano- 

 meter terminal. And the same sort of criticism applies 

 to Fig. 28, p. 57, representing the arrangement of ap- 

 paratus for measuring the magnetization of the iron core 

 of an electro magnet by a current passing round its coil. 

 The reader is told that the magnetometer, which is, of 

 course, to be directly affected by the magnetism of the 

 iron bar, is, for some reason unexplained in the book, to 

 be put at a considerable distance from the bar, but he is 

 not warned that the meter used for measuring the current 

 passing round the electro-magnet (and which, of course, 

 ought not to be directly affected by the magnetism of the 

 bar) must on no account be placed, as in this figure, 

 close to the powerful magnet. 



On p. 32 the author says that a core of soft iron "acts 

 like a lens, and concentrates or focusses more lines of 

 force from the magnet on the primary coil through the 

 aperture of the secondary." But this simile with a lens 

 is but a repetition of an old error ; a lens simply bends 

 rays of light, and, so far from adding to the total amount 

 of light, actually slightly diminishes this amount by ab- 

 sorption. A lens for light is like a funnel for a fluid, it 

 directs the stream along a narrow channel, so that while 

 the flow is on the whole diminished by friction the flow 

 along a certain cross-section is much increased. But the 

 insertion of an iron core into a coil traversed by a current 

 vastly increases the total number of lines of force. The 

 solenoid without the iron core is like a cistern with water 

 in it which is being emptied with a pipe full of dirt, 

 through which the water can only trickle ; and the inser- 

 tion of the iron core into the solenoid is like the cleaning 

 out of the pipe, so that the stream of water now becomes 

 vigorous and rapid. Even Dr. Fleming knocks his 

 own simile on the head, for he states 27 pages 

 further on, " The joint effect of the" (iron) " bar and coils 

 is the sum of the effects of each separately." Fancy any- 

 one saying that the joint effect of a lens and a candle was 

 the sum of the effects of each separately. 



We consider it archaic for Dr. Fleming to define the 

 volt for practical men as the E.M.F. generated in one 

 centimetre of wire moving with a velocity of one centimetre 

 per second in a magnetic field of unit force. As well 



