2 14 



NA TURE 



[April 22, 1909 



industrial application of the science is represented by 

 examples of machinery made by French firms, some 

 descriptions of transmission plant and wireless tele- 

 graphy. This short account of the contents will show 

 that the book covers, within its compass of some 430 

 small octavo pages, a wide field, and that for this 

 reason alone anything like exhaustive treatment cannot 

 be expected. Its usefulness is also marred by the 

 defect very frequently found in Continental books of 

 having no index. 



In one respect the book is, however, an improve- 

 ment on other French works on the same subject, and 

 that is the use of mechanical illustrations of electrical 

 phenomena. French men of science have always been 

 adverse to graphic treatment or mechanical analogies. 

 They are content to represent the subject in a purely 

 analytical manner, and although it must be confessed 

 that in elegance of mathematical treatment the French 

 school is supreme, this kind of treatment does not lead 

 so easily to an understanding of the subject as the 

 use of graphic methods and mechanical analogies, 

 which is a characteristic of the English school. Even 

 so highly-trained a mathematician as Maxwell did not 

 disdain the use of some very simple mechanical con- 

 trivance in order to make clear an intricate electrical 

 phenomenon, and since Maxwell's time all English 

 writers and most German have followed this lead. 



Now we find that the author of the book under 

 review has also gone over to the school of Faraday and 

 Maxwell, and uses mechanical analogies to express 

 electrical processes. As a good example of his methods 

 may be taken the vectorial addition of currents illus- 

 trated by the apparatus of Prof. Gaillard, which was 

 primarily designed to illustrate an alternating current 

 of so slow a periodicity that it can be shown by the 

 harmonic movement of a spot of light to a whole class 

 of students (p. 185). Another model to represent 

 three-phase currents and their properties is shown on 

 p. 311. The mechanical representation of the prin- 

 ciple of the inductor alternator, although, strictly 

 ■speaking, not a model, but merely an incomplete 

 machine, should prove useful to beginners. 



The book is, in fact, written for beginners, if we 

 may judge by the omission of many matters of more 

 intricate nature. Thus, after explaining the process 

 of commutation in a general way, the author dis- 

 misses the subject of sparking in a few lines by saying 

 that in modern machines there is hardly any necessity 

 to shift the brushes when the load changes. Nothing 

 is said about commutation by brush resistance or inter- 

 poles, or Deri winding, or Parsons' compensating 

 coils. Again, the short paragraph on inductive drop in 

 a transformer is quite inadequate ; we are told that the 

 drop is from 1 to i^ per cent, in each coil, but not a 

 word is said about the influence of the details of the 

 design on the drop. In the matter of cooling a trans- 

 former, the author is equally superficial ; he merely 

 says that 20 sq. cm. cooling surface per watt lost will 

 produce an admissible temperature rise. Such general 

 statements are perfectly valueless, and, in fact, worse 

 than that, for they are untrue. 



The author seems to have a great aversion to the 

 use of mathematical formula even when they are very 

 simple and convenient. He seems to start from the 

 NO. 2060, VOL. 80] 



supposition that his reader is so much of a beginner 

 that he cannot even grasp the meaning of a very simple 

 analytical expression, and to overcome this imaginary 

 difficulty he uses numerical examples by preference. 

 Most readers will consider this point of view to be 

 wrong in principle. A man who is quite ignorant of 

 even the simplest mathematics had better not attempt 

 to study electrical matters, and if he has the modicum 

 of mathematical knowledge required for the study of 

 such elementary books as that under review, his task 

 is not made easier, but more tedious, if matters that 

 could be presented in three lines of mathematics are 

 worked out in two pages of numerical examples. A 

 striking instance of the cumbersomeness of this method 

 is the deduction of the virtual value of an alternating 

 current given on pp. 174 to 178. Here more than four 

 pages of algebra and arithmetic are used to prove that 

 the virtual current is equal to the crest value divided by 

 the square root of 2. All this could have been shown 

 by a few lines of very simple calculus, or, better still, 

 by Blakesley's graphic method. Gisbert Kapp. 



A GERMAN TEXT-BOOK OF ZOOLOGY. 

 LehrbucJi dcr Zoologic fiir Sfiidierende. By Dr. 

 J. E. V. Boas. Fiinfte vermehrte und verbesserte 

 .\uflage. Pp. x + 668; 603 figs. (Jena: Gustav 

 Fischer, 1908.) Price 12 marks. 



THE fact that Prof. Boas's well-known text-book 

 has now reached its fifth edition speaks volumes 

 for the importance attached to the study of zoology 

 in Germany. The book, although it contains 668 large 

 and closelj'-printed pages, is an elementary one, and 

 is designed especially, as we are told in the preface, 

 for students of medicine, yeterinary science, and 

 forestry. 



German ideas as to the preliminary education of 

 medical students must be very different from those 

 which are held by the medical profession in this 

 country. Perhaps the German students work harder, 

 or it may be that they cover a wider field in a more 

 superficial manner. Dr. Boas's text-book makes us 

 suspect that it is a little of both, and although we 

 think that the subject might well receive more atten- 

 tion from English medical students than it now does, 

 yet we should hardly care to place the present volume 

 in their hands. E.xcellent and interesting as it is in 

 many respects, it appears to us to suffer greatly from 

 over-condensation, from the attempt to cover far too 

 much ground. We miss the detailed anatomical de- 

 scription of types to which English students have 

 become accustomed, and although this can easily be, 

 and we fear frequently is, overdone, it can hardly be 

 altogether dispensed with in an elementary te.xt-book. 

 It is true we find a short description of the .\moeba 

 by way of general introduction to the study of struc- 

 ture and function, but this is the only special type 

 which is at all adequately dealt with. Probably it is 

 intended that the detailed study of types should be 

 undertaken in the laboratory with the aid of a special 

 practical text-book, but we have not noticed any re- 

 ference by the author to the importance of such prac- 

 tical work. 



The book illustrates very clearly the great difficulties 

 which attend the teaching of zoology at the present 



