200 



NATURE 



[December 28, 1899 



seen in etymologies, but also in bizarre analogies as of 

 existence to a tricycle, are salient faults of the book. 

 But Dr. Nicati's obsession by what may be called the 

 fallacy of the graphic formula is its dominant character- 

 istic. In the logical calculus "it is atrociously done," 

 has its adverb expressed by the radical sign ; the anti- 

 Dreyfusard admits fluxional considerations. In Fener- 

 octique^ life is formulated by Cae decorated with arrows, 

 because it arises in the decomposition of matter which 

 has cohesion and other qualities. Pictures on p. 250 are 

 quite exciting. \ 



This sort of inanity throughout makes the writer's 

 charge upon Kant, that he lacks logic in speaking of 

 " empty space," and his attack upon evolution, with a 

 view to substitute "a theory simply evolutionarist," 

 quite devoid of weight. The index is quite excellent. 



H. W. B. 



Kleiner Leitfaden dcr Practischen Physik. Dr. F. 



Kohlrausch. Pp. xix + 260. (Leipzig : Teubner, 



1900.) 

 Every physicist is familiar with Dr. Kohlrausch's 

 " Text-book of Physical Measurements," either m the 

 original or in its English translation. It is not too much 

 to say that it was the foundation of the numerous text- 

 books of practical physics which have since appeared. 

 Owing to the successive additions that have been made, 

 Dr. Kohlrausch feels that it has lost its original character, 

 and now fails to be suitable, as formerly, to the needs of 

 a beginner. This feeling has induced him to prepare 

 the present " Kleiner Leitfaden " by selecting from and 

 otherwise modifying the larger volume. 



In what sense can this new volume be regarded as a 

 book for beginners? One of the most difficult questions 

 for a teacher to solve is : How far ought a student be left 

 to work out his own salvation ? No answer can be given 

 which would be applicable to all students. A youth of 

 keen intelligence only requires outline directions : the 

 details he learns best by finding them out for himself. 

 But such men are exceptions in any laboratory. The more 

 ordmary student will miss a point unless it is explicitly 

 brought before his notice. We think it is to the former 

 class that this book will be most useful. Dr. Kohlrausch 

 has certainly not erred on the side of superabundance of 

 instruction. We think, for example, that it might be 

 found better fitted as a general laboratory manual if a 

 larger number of fully worked out numerical examples 

 were supplied. But as for ourselves, we have only ad- 

 miration for the dignified restraint which is everywhere 

 displayed. This is no cram-book intended to meet the 

 temporary requirements of an examining board ; but it 

 is what the author has aimed to make it — an aid to 

 general culture. 



Further, the volume is well and accurately printed. 

 We have read it through, and only detect one small 

 error. The G Fraunhofer line is, in the diagram on p. 

 I33j apparently identified with the third line in the hydro- 

 gen spectrum ; the difiference between them would only 

 be about a millimetre in the diagram ; but it is a differ- 

 encewhichoughtto be exaggerated rather than diminished, 

 in order to prevent a student running away with a wrong 

 idea. A. W. P. 



Elementary Algebra. By C. H. French and G. Osborn. 



Pp. vii -1-349. (London : J. and A. Churchill, 1899.) 

 This book has been purposely written to help elementary 

 students who have to do much of their study privately, 

 and with this aim in view the authors have avoided as 

 far as possible all technical terms in the explanation of 

 the various theorems. It is possible that there may be a 

 tendency to leave too little for the student to think out 

 for himself by this procedure, but that is matter for indi- 

 vidual opinion. Apart from this, the treatise is excellent 

 in its numerous selections of examples and for the clear 

 arrangement of the various sections. 



NC. 1574, VOL. 61] 



Magnetism and Electricity for Beginners. By H. E. 

 Hadley. Pp. viii-f 327. (London: Macmillan and Co., 

 Ltd., 1899.) 



This little manual is written specially to meet the re- 

 quirements of students preparing for the annual examin- 

 ation of the Science and Art Department, and con- 

 sequently it follows to a considerable extent the lines of 

 the syllabus provided. In many details, however, it very 

 ably satisfies the desirability of providing fuller treat- 

 ment, while a conspicuous and commendable feature is 

 the insertion of many original diagrams and photographs 

 of actual experimental apparatus. 



The general arrangement is to give certain facts or 

 definitions, followed by one or more experiments to be 

 performed for their complete verification, so that in this 

 respect the book may serve very well as an introduction 

 to the electrical side of practical physics. 



The apparatus described is almost entirely simple 

 enough for the average reader to make readily, and the 

 very generous number of illustrations (197) will be very 

 helpful to the clear understanding of the statements made. 



Part i., on magnetism, occupies 103 pages, and all the 

 chief phenomena are illustrated by facsimile reproduc- 

 tions of the fields of force as shown by iron filings or 

 small magnetometers. The explanation of electrical 

 screening is very simply and clearly stated ; in fact, the 

 text is brought up to date as far as is possible in an 

 elementary manual. 



Part ii., statical electricity (106 pages), is specially 

 noticeable for the way in which the usual difficulty of 

 dealing with potential is met by geometrical interpre- 

 tations ; potential-diagrams being given for fields of 

 force, electroscopes, condensers, electrical machines and 

 contact electricity. 



Part iii., voltaic electricity (93 pages), is somewhat 

 terse in style, probably necessarily owing to the number 

 of matters in this part of the subject which need de- 

 scription, but the fundamental points in all the sections 

 are well brought forward. The book is certainly an 

 excellent one for elementary students, and is also likely 

 to form a sound basis on which a teacher may frame his 

 course of lessons. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 



ofN 



manuscripts intended for this or any other part of Naturr. 

 No notice is taken of anonymous communications. \ 



Racial Aspect of Voluntary Enlistment. 



Thp:re is one aspect of our voluntary enlistment system which 

 has never been touched upon so far as I know. It is that by our 

 method the most brave and warlike men of each generation are 

 exposed to far more than the ordinary risks of life, and generally 

 at an age when they have left no descendants. A process of 

 selection has, therefore, been going on in the nation for cen- 

 turies by which, in the long run, the non- fighters, such as com- 

 mercial classes, luxurious people, and any cowards, have more 

 descendants proportionally than the brave and warlike. So 

 that the average opinion is growing more and more unwarlike, 

 less brave, and more inclined for peace at any price. The above 

 selection is brought home to us if we .consider that of those 

 soldiers killed during the last few weeks how few have left two 

 descendants. I foresee two remedies for this state of things, but 

 will not ask for any more of your valuable space. 



R. C. T. Evans. 



9 Heathcote Street, Gray's Inn Road, W.C. 



The Wind during Eclipses of the Sun. 



I WOULD like to draw attention to the importance of ob- 

 servations of the wind in and near the path of a total eclipse of 

 the sun. 



At the Indian eclipse of 1898 I employed at Sahdol, in 



