586 



NATURE 



[October 22, 



It is not for the sake of men of science that we desire to 

 see more widely diffused an intelligent appreciation of their 

 work. A celebration like that of last week necessarily brings 

 with it sad as well as happy reflections. "After all," 

 said Bluntschli, the famous jurist, on a like occasion, " it 

 is an end, not a beginning." Prof. Virchow is fresh and 

 vigorous, and the world may still reasonably expect from 

 him much sound work ; but we may be sure that, in 

 responding to congratulations, he had a little of Bluntschli's 

 feeling ; and it is possible that, if he had consulted his 

 own wishes only, he would have preferred to celebrate his 

 seventieth birthday more quietly. But it is good for a 

 nation to express on such occasions the admiration and 

 reverence excited by a long and great career. The mere 

 fact that men desire to honour one whose title to distinc- 

 tion is that he has advanced human knowledge proves 

 that they have interests higher than those of a material 

 character ; and it inevitably tends to deepen and 

 strengthen the best and most enduring of their impulses. 

 We should be glad, therefore, if Englishmen had as 

 strong a wish as Germans to display a hearty apprecia- 

 tion of the triumphs achieved by their great scientific 

 thinkers. That would be the most effectual of all proofs 

 that they had begun, as a people, to understand how 

 momentous is the part which science has played, and 

 must continue to play, in the modern world. 



ELECTRIC LIGHT FITTING-GOOD AND BAD 



WORK. 

 ' Electric Light Fitting: a Hand-book for Working Elec- 

 trical Engineers. By John W. Urquhart. (London : 

 Crosby Lockwood and Son, 1890.) 



THIS book is exactly what it professes to be— a prac- 

 tical book for practical men — and is vastly superior 

 to " Electric Light," by the same author. The detailed 

 instructions given in the first 42 pages, on the erecting, 

 managing, and repairing dynamos, are admirable, and 

 are not to be found in any other book in the English 

 language. The young electrical engineer will find just 

 the information he needs ; how to fit up a large dynamo 

 when received in parts from the makers ; how to prevent 

 the commutator becoming rough in use ; exactly what to 

 do if it be rough ; how to prevent sparking at the brushes ; 

 how to attach a new commutator and make joints in the 

 armature wires ; what to do if the dynamo heats ; and 

 how to get over the various other difficulties met with in 

 the dynamo-room. 



The author, in these early chapters, and indeed 

 throughout the book, uses the , expression "constant 

 current " for direct current ; and although the action 

 of the regulators of the Brush and of the Thomson- 

 Houston constant current dynamos is correctly described, 

 and clear illustrationsgiven of their construction, the reader 

 is left in the dark as to the exact use of these regulators. 

 Or, rather, the only definite statement as to the function of 

 the Thomson-Houston regulator, that it is " for causing 

 the machine to evolve more or less current as required," 

 is certainly much more likely to lead the reader wrong than 

 right. Further, to say that " in Siemens's alternator, or the 

 Ferranti dynamo, Mead ' must be given to the brushes" 

 (an instruction, of course, quite impossible to carry out, as 

 NO. I 147, VOL. 44] 



alternate machines have no commutators, but only col- 

 lecting rings), will probably destroy the correct impression 

 about lead which the practical man may have derived 

 from reading the previous page. 



In spite of these defects, however, chapter i. is excel- 

 lent, but we cannot speak quite as highly of chapter ii., 

 " On Localizing Dynamo Faults,and Observations respect- 

 ing Accumulators." In describing the test for the existence 

 of leakage between the iron framework and the earth, the 

 author makes an error that we have met with before, in 

 stating that a deflection of a galvanometer whose ends 

 are connected respectively with the iron framework and 

 the earth indicates leakage between these two. This is 

 equivalent to saying that a conductor not having the poten- 

 tial of the earth proves that it is in connection with the 

 earth. In the " Hints to Accumulator Attendants" there 

 are some very useful suggestions, but the instructions for 

 deciding when an accumulator is charged confirm the 

 impression we gave when reviewing the author's "Elec- 

 tric Light," that the author had not derived his knowledge 

 of storage cells from a practical acquaintance with them. 

 For he says that they must not be so much discharged that 

 they cease to give any current ; and in the chapter on 

 "Switch Board and Testing Work," that the E.M.F. of ac- 

 cumulators, in discharging, should never be allowed to fall 

 below o"5 volt per cell. Such instructions are about as 

 useful as saying that a horse should not be worked until 

 he dropped, for if accumulators were to be regularly dis- 

 charged until their E.M.F. fell to a value even three times 

 as great as the limit prescribed by Mr. Urquhart, they 

 would be speedily ruined. 



■ Why these two statements about the discharge limit of 

 storage cells should be given in different parts of the book, 

 with information about " Running Dynamos in Parallel,"' 

 the " Periodicity of Alternators," &c., inserted between, 

 we do not know. In a somewhat similar way, the author 

 returns again and again in different parts of the book to the 

 subject of insulation resistance. Each time, no doubt, valu- 

 able information is given ; but why not have put it all to- 

 gether, so that the working electrical engineer could have 

 at once read up the subject, without having to turn up a 

 number of references ? This sort of scattering of informa- 

 tion runs through the whole book, and rather suggests the 

 idea that no very serious attempt was made to sort out in- 

 formation written down by the author as it occurred to him 

 at different times. 



We do not think that the explanation on p. 54. 

 " alternators work according to a 'phase,'" is very lucid, 

 Further on, the author says the number of phases per 

 second is the periodicity, and later that periodicity and 

 phase aie the same thing. On p. 51 we are told "a 

 fall of five volts in a hundred affects the brightness of 

 the lamps," from which a person might easily obtain the 

 wrong impression that a fall of two or three per cent, was 

 not observable, and be astonished when he read, on p. 

 72, " that a fall of five volts in a hundred in the working 

 pressure will cause lamps which burn brightly at a hun- 

 dred volts to become very dull." He would also not be 

 able to reconcile the statement, "upon well- conducted 

 systems the pressure upon the mains is never allowed to 

 vary more than one-half per cent.," with the variation of 



2 per cent, up and 2 per cent, down, which is allowed 

 j by the Board of Trade. Nor is it possible to understand 



