February 2, 191 1] 



NATURE 



433 



in order that the reader may thoroughly understand 

 the theoretical deductions, and the latter themselves 

 are not always trustworthy. We find a good many 

 quotations with due acknowledgment of articles that 

 have appeared in the Electrical World of New York, 

 and if the author had exercised some care in the selec- 

 tion his book could only have benefited by it. Un- 

 fortunately, however, the necessity of carefully prob- 

 ing the correctness and relevancy of any article before 

 admitting it into his book does not seem to have 

 occurred to the author, and the result is that we find 

 statements in his book which often are quite useless 

 and sometimes even unintelligible. To give only a 

 few examples. On p. 152 is given a formula for the 

 inductance of a solenoid for which an accuracy of 

 half per cent, is claimed, but the author does not say 

 whether the result is obtained in cm. or in Henry. 

 Moreover, the formula is very cumbersome, and no 

 proof is given. On the next page another formula is 

 wrongly quoted from Maxwell, the exponent for the 

 number of turns per cm. length being given as four 

 instead of two. Also in this case the author does not 

 state whether L is obtained in cm. or Henry. 



Another example of the want of criticism on the 

 author's part will be found on p. 32. Here he gives 

 us Mr. H. S. Baker's method of expressing the degree 

 of saturation of the core of an electromagnet. It is 

 as follows :- — Draw a tangent to the magnetisation 

 curve at the point for which the degree of saturation 

 is to be expressed as a ratio. Note the length cut off 

 on the B axis by the point of intersection of this 

 tangent. Then the ratio of this length to the value 

 of B at the selected point gives the degree of satura- 

 tion. Since the characteristic is nearly straight for 

 high values of magnetisation, this method of express- 

 ing saturation leads to the absurd result that Baker's 

 ratio becomes actually smaller for very high degrees 

 of saturation. A rule of this kind is absolutely use- 

 less and even misleading, and a little consideration 

 on the author's part would have shown him that he 

 had better not include it in his book. 



A very bad slip in scientific principles occurs on 

 p. 16. There we are told in an equation that the 

 " Intensity of magnetisation " divided by the magnetic 

 moment gives the " Intensity of the magnetic field." 

 This is quite wrong, for the ratio is simply the in- 

 verse of a volume. Again, on p. 25, we are told that 



■' the relation between the strength of a current in a 

 wire and the intensity of the magnetic field or mag- 

 netising force is expressed by the equation 

 H = o-2l/a." 



This is only true if the wire be infinitely long, but as 

 in what precedes this statement not a word is said 

 about the length of the wire the statement as it stands 

 is misleading, and, in fact, meaningless. 



Some of the terms used are not very familiar to 

 English readers. The author talks of Maxwells, Gil- 

 berts, and Gausses, but these, although used occa- 

 sionally by American writers, have never been sanc- 

 tioned by the international committee on nomencla- 

 ture. There is, moreover, no great necessity for 

 multiplying such terms. It is just as easy to say two 

 megalines as two million Maxwells, or an induction 

 of 15,000 lines as an "induction of 15,000 Gausses." 

 NO. 2153, VOL. 85] 



Why the "Oersted" as representing the magnetic 

 reluctance of "one cubic centimetre of vacuum" 

 should be introduced is also not very apparent. There 

 is perhaps some excuse for the use of such terms in 

 the fact that others have done so before, but the in- 

 troduction of the term " activity " in substitution of 

 the generally used and perfectly understood term 

 "space factor" is surely quite superfluous. It will 

 also puzzle the reader to say what a "water shield," 

 a "stopped solenoid," and a "fringed insulation" are 

 Such technical terms may be convenient for a par- 

 ticular workshop as short instruction to the workman, 

 but a scientific book is not the place to use them. 



On the very important question of heating of coils 

 the information given is rather meagre. All we are 

 told on p. 299 is that a 



" coil of ordinary dimensions may remain in circuit 

 continuously when the applied electrical power does 

 not exceed 050 watt per square inch of superficial 

 radiating surface." 



A curious statement is made on p. 184 as regards 

 the time constant of two coils in parallel. The author 

 says that it is only one-quarter of the value for the 

 coils in series, but he has evidently overlooked the 

 fact that although the inductance is quartered, the 

 resistance is also quartered and therefore the time 

 constant remains the same. Gisbbrt Kapp. 



ANALYSIS OF WINE AND OTHER 

 SPIRITUOUS LIQUORS. 

 Traite cotnplet d'analyse Chimiqiie, appliqti^e aux 

 essais indiistriels. By Prof. J. Post and Prof. B. 

 Neumann. Deuxieme edition Fran^aise, traduite 

 d'apres la troisieme edition allemande. By G. 

 Chenu et M. Pellet. Tome Second. Troisieme 

 Fascicule. Pp. 497-916. (Paris : A. Hermann et 

 Fils, 1910.) Price 13 francs. 



THIS part of Post and Neumann's work deals with 

 alcoholic beverages and some allied products. 

 Chiefly it is concerned with wine and beer, and the 

 original German text has been largely supplemented 

 by details of the French practice in the chemical 

 surveillance of these articles. Thus Gallicised, the 

 work is of special interest for those concerned with its 

 subject, inasmuch as it represents the experience of 

 two great wine-making countries and of one, at least, 

 fgmed also for its beer. 



Dr. P. Kulisch, of Colmar, is responsible for the 

 original section dealing with wines ; but in view of 

 the importance of the subject in France considerable 

 additions have been made by the French translators. 

 The result may therefore be taken to indicate the best 

 practice in the two countries. At the outset are given 

 the definitions of wines and the descriptions of usual 

 manufacturing operations adopted by the International 

 Congress for the Repression of Food Adulteration 

 (Geneva, 1908, and Paris, 1909). Then follow direc- 

 tions for the chemical determinations required during 

 the preparation and fermentation of the grape-juice, 

 and the official methods prescribed in France and in 

 Germany for the analysis of the fermented product. 

 Detailed notice would be unprofitable here ; it must 

 suffice to say that full directions are given for apprais- 

 ing the various vinous constituents. Numerous illus- 



