■562 



NATURE 



[April 17, 1890 



might a kilogramme be defined for a French butcher as 

 the weight of a cubic decimetre of distilled water at 4° C, 

 and the butcher's business be absolutely stopped because 

 he did not possess any distilled water and because the 

 temperature of his shop was 20^ and not 4° C. In fact, 

 Lectures II. and III., although containing a large amount 

 of valuable information, are professorial rather than 

 practical. 



On p. 74 a Ruhmkorfif induction coil is correctly 

 described, but in Fig. 36 on the same page the primary 

 coil, with the vibrating interrupter and four cells in its 

 circuit, is shown as consisting of many convolutions of 

 fine wire, and the secondary of a few turns of thick wire. 

 On p. 83 one centimetre is given as equal to o"0328o87 of 

 afoot — that is, correct io six significant figures — while even 

 in the second edition, " the call " for which " has afforded 

 the opportunity to erase several typographical errors and 

 to remove some other blemishes which had escaped 

 notice and correction in the first edition," the previous 

 statement is immediately followed by the announcement 

 that one inch equals 2 "500 centimetres, an equation which 

 is only correct to two significatit figures, the number ex- 

 pressed correctly to six significant figures being 2"53995. 

 But why not use 2'54oo, the value commonly adopted, and 

 which is correct to four places of decimals 1 As a further 

 example of the want of precision which runs through 

 this book, it may be mentioned that on p. 9 a falling body 

 acquires per second a velocity of 981 centimetres per 

 second. Throughout the whole of p. 85, where the number 

 is frequently mentioijed, the body, as if a little tired 

 cannot get up a velocity of more than 980 centimetres a* 

 second. Proceeding, however, to the next page, the body, 

 like the reader, turns over a new leaf, and hurries up its 

 speed, for it acquires per second a velocity of 981 centi- 

 metres per second all through this page. Further on, 

 however, in the book, the poor falling body gets tired 

 again, for on p. 97 it cannot do more than the 980. On 

 p. 87 we find the statement, " Hence one foot-pound 

 = i'2)S^ joules, or one joule = 7373 foot-pound," whereas 

 a simple division shows that if the first part of the state- 

 ment be correct, the second is not. 



To say that " the work is numerically measured by the 

 product of the displacement and the mean stress estimated 

 in the direction of the displacement" is learned and 

 academical, but might not the poor electrical artisan mix 

 this up with the displacement of the factory hands that 

 usually occurs when there is no stress of work ? 



On p. 99 it is stated that the "E.M.F. of Clark's cell 

 = I "435 true volt," but, as no indication has been given in 

 this book that there is more than one volt, we are left in 

 ignorance of the reason why the volts used to measure 

 the E.M.F. of a Clark's cell have to be so especially true, 

 and why 10''' C.G.S. units, which is the volt that has been 

 previously used, is not good enough for this sort of measure- 

 ment. On looking in the index for the definition of the 

 " Ohm British Asssociation," we find ourselves referred to 

 p. 136, and the reader is left to wonder what is a " B.A.U." 

 of resistance used some forty pages previous to this. 

 Similarly the " Legal Ohm " is spoken of and its value 

 given in terms of a " B.A.U." thirty-seven pages before the 

 reader is told what a " Legal Ohm " is. For this the 

 arrangement of the book and not the index is, of course, 

 to blame. And while on this subject we should like to 

 point out that the indexes of scientific books appear to 

 furnish a conclusive proof of the inherent modesty of 

 scientific writers. Take up some large and important 

 treatise, and turn to the index. There you are told that 

 the book contains almost nothing. On the title-page the 

 publisher may have indiscreetly added after the author's 

 name line after line of small print enumerating the various 

 scientific and unscientific societies to which the author 

 belongs, but in the index all pretension to such a wide 

 acquamtance with science is disclaimed. You may have 

 a distinct recollection of reading in this very book many 



pages on some special subject, but rack your brains as 

 you will to discover under what heading in the index this 

 subject may have been entered, not a reference to it can 

 you find. Accumulators, storage cells, transformers, the 

 volt, voltmeters, &c., seemed likely subjects to be treated 

 on in " Short Lectures to Electrical Artisans," but the 

 index says no ; and it is only by carefully reading 

 through the book that you discover that it contains much 

 valuable information on these very points. We would 

 suggest to the writers of scientific treatises, and also to 

 those who communicate scientific papers to learned 

 societies, that the practical man of to-day cannot possibly 

 afford the time to read through ninety-nine things that 

 he does not want to know about, before he can light 

 on the one thing regarding which he is searching for 

 information. 



In speaking of Messrs. Crompton andKapp's meter, on 

 p. 115, Dr. Fleming says : — 



" The only difficulty which arises in connection with 

 such an instrument as this, is the tendency of a long thin 

 iron wire of this kind to retain strongly residual 

 magnetism and fail to de-magnetize itself, but this effect 

 would only prevent the return of the indicating needle to 

 zero when the current was stopped, but would not prevent 

 the instrument from giving a definite and fixed deflection 

 corresponding to a definite and fixed current passing 

 through the coils." It was no doubt a somewhat delicate 

 task for Dr. Fleming when lecturing to Mr. Crompton's 

 staff to fully criticize Mr. Crompton's meters, but since 

 actual published experiments on some of these meters 

 show that, for the low readings, the apparent value of a 

 given current differs by as much as 10 per cent., depend- 

 ing on whether the current is ascending or descending, 

 we fail to see how the scientific knowledge of any artisans 

 can be improved by their being toldthatnosuch error exists. 



Fig. 50, p. 122, showing the level of the columns of 

 water in stand-pipes attached to a horizontal tube through 

 which water is flowing, was never drawn from an 

 actual apparatus. The author has forgotten that the 

 water has not merely to flow through the horizontal tube 

 h.a, but through the much longer vertical tube CA, and 

 therefore, there is a much greater difference of level 

 between the height of the water in the cistern and in the 

 first stand-pipe, aa', than there is between the level in 

 this stand-pipe and in the next, bb' . If Fig. 50 were 

 correct, it would follow that when a battery of even large 

 internal resistance was sending a considerable current 

 the difference of potentials at its terminals was equal to 

 the E.M.F. of the battery. Not merely, then, is this 

 opportunity lost of explaining to the readers that the 

 difference of potentials at the terminals of a battery may 

 be very much less than the E.M.F., but the information 

 conveyed by the diagram is actually contrary to fact. 



The statement that " Storage cells for lighting purposes 

 cease to give a useful discharge when the electromotive 

 force falls below two volts" is hardly consistent with the 

 fact that, when storage cells are discharged at the current 

 that is considered quite safe by the Electrical Storage 

 Power Company, the E.M.F. for nine-tenths of the 

 period of the discharge is slightly below two volts. 



We have said enough to show that, although the book 

 called "Short Lectures to Electrical Artisans" is written by 

 one who, from his University and factory experience, has 

 a large amount of valuable information at his command, 

 the second edition reads far too much like an uncorrected 

 proof of the first edition ; and instead of the statements it 

 contains possessing weight because they are made in the 

 book, there is an uneasy feeling when reading its pages 

 that any statement may be wrong, and requires to be 

 checked. We trust, however, that the sale of this, the 

 second edition, may be large and rapid, so that the 

 author may have an opportunity of shortly bringing out 

 as a third edition a book more worthy of his acknowledged 

 power. 



