November 9, 1899] 



NATURE 



27 



From the facts of optics we deduce the existence of an 

 icthereal medium, which according to Fresnel's view is 

 discontinuous. (A good account is given in this section 

 of the struggle between the corpuscular and undulatory 

 theories.) The dispersion of light as interpreted by 

 Cauchy lends support to the discontinuity of the 

 medium. 



Unfortunately, the luminiferous aether cannot be made 

 to explain gravitation. The author discusses some of 

 the theories of gravitation, such as that of Lesage. More- 

 over, the elastic asther which transmits light cannot 

 account for electro-magnetic actions. Prof. Mannequin 

 also finds difficulties in the electro-magnetic theory of 

 light ; these appear to rest, i however, not on any im- 

 possibility of accounting for optical phenomena on the 

 electro-magnetic theory, but on the irreconcilable differ- 

 ences in the properties of the aether as originally invented 

 to explain light and those of the electro-magnetic asther. 



In this way we arrive at a multiplicity of irreconcilable 

 aethers as well as a multiplicity of irreconcilable atoms. 



The necessity and the contradictions of atomistic 

 explanations of nature having thus been brought out, the 

 author concludes his first book as follows ; — 



"Why should atomism be found everywhere in modern 

 science to such an extent that it is, as it were, its vital 

 principle, if its contradictions were final, and if they had 

 not their last reason in the very substance of a reality 

 which only appears to us under the obscure veils of 

 space and time, but which perhaps will reveal its law to 

 him who will seek it above extension and duration, or in 

 a word above the appearances which science analyses?" 



We are thus led to the purely metaphysical part of 

 the work, which it would be out of place to attempt to 

 discuss here. The final chapter, however, sums up the 

 conclusions arrived at. Science will never attain to the 

 mdivisible towards which she seems to be incessantly 

 marching ; if she did reach it, she would be unable to ex- 

 plain nature by means of it. Our difficulties vanish if we 

 render to the atom its true sense— the element, definite 

 but always complex, with a minimum of extension in 

 space and a minimum also of dynamical attributes. 

 And instead of seeing in it the real individual stripped of 

 all activity and of all quality, all that we ought to see in 

 it »s the work of the mind pursuing in space the reduction 

 without end of phenomena which, though pure appear- 

 ances, are appearances which have their basis in reality. 



There can be no question of the interest and import- 

 ance of a philosophical examination of the foundations 

 of science such as M. Mannequin has attempted. 



Me has, we think, exaggerated the inconsistencies of 

 the "atoms" postulated for different purposes. So 

 long as we do not imagine that we have ever to deal 

 with absolute indivisible structureless atoms the con- 

 tradictions do not exist. Most of us would agree with 

 M. Mannequin as to the barrenness of any system of 

 absolute atomism. 



There is no reference in the book to any of the more 

 direct methods in which matter is proved to have a 

 discontinuous structure, and by which an estimate is 

 obtained of the size of the molecules ; such methods as 

 are described in Lord Kelvin's lecture on the size of 

 atoms (Popular Lectures and Addresses), This is surely 

 a serious omission. 



NO. 1567, VOL. 61] 



OUR BOOK SHELF. 

 Elements of Physics. By Menry Crew. Pp. xiv -f- 347. 



(London : Macmillan^nd Co., Ltd. New York : The 



Macmillan Company, 1899.) 

 The writer of this review possesses a collection of text- 

 books of physics written during the first half of this 

 century, all the volumes put together occupying a length 

 of about six feet on his book shelves. Me sometimes 

 wonders where a future collector would find the space 

 for all the text-books written now, when professors who 

 have not written their own text-books are beginning to 

 be rare curiosities. The proportion of books, however, 

 that possess any originality has not increased, and may 

 be put down, roughly speaking, as one in ten. The rest 

 may be good because they have been inspired by good 

 books, but there is a dreary similarity between them. 



It would be ungracious to make these remarks while 

 reviewing one of the average class of productions, and it 

 must therefore at once be stated that Mr. Crew's volume 

 cannot help striking the reader at once as having been 

 the result of a good deal of thought, both in wording and 

 arrangement. The book is very elementary. I think it 

 is customary in this country to enter somewhat more 

 fully into many parts of the subject, even in a first 

 course. On the other hand, it treats of several matters 

 which it is customary to omit, and it is on this point 

 that we wish specially to commend the volume. 



I note with great satisfaction a general chapter on waves, 

 before the special consideration of sound waves is entered 

 upon, also the introduction — at an early stage — of the 

 wave theory of light. The great amount of time which, 

 owing to examination requirements, we are forced — often 

 against our will — to devote to geometrical optics, would 

 much more usefully be spent in explaining (as the writer 

 seems to do) the elements of diffraction and interference. 



It is, further, a satisfaction to see frequent allusions to 

 the phenomena of every-day life, and this feature might 

 have been still further extended by including, for 

 instance, some reference to the principal meteorological 

 phenomena. No doubt very often the most com- 

 mon occurrences are most difficult to explain, and 

 it may be impossible to give to elementary students 

 a satisfactory explanation of, e.g., the rainbow or 

 the blue colour of the sky. But unless the attempt 

 be made the students generally carry away the im- 

 pression that what they learn in the lecture room belongs 

 to a different part of their existence from what they can 

 see and observe outside the college buildings. The book 

 begins with mechanical and kinematical principles, in- 

 cluding among other matters the consideration of har- 

 monic oscillation and a well-considered chapter on the 

 properties of matter. 



Altogether it forms an admirable introduction to the 

 study of physics. The only criticisms I should like to 

 make, refer to some of the illustrations ; but as the book 

 only suffers to a slight extent from the prevailing epi- 

 demic of bad illustration caused by the spreading microbe 

 of cheap processes of reproduction, we must be satisfied 

 and say no more about it. Arthur Schuster. 



A Laboratory Outline of General Chemistry. By 

 Alexander Smith. Pp. 88. (Chicago : Kent Chemical 

 Laboratory of the University of Chicago, 1899.) 

 This book comes with a strong claim to attention. I 

 is an untrammelled attempt to lay down a course of 

 practical chemistry in an educational and scientific 

 spirit, and the author's introduction sounds a pleasing 

 note. 



Much thought, care, and experience are embodied in 

 the work, and though no claim to originality of material 

 is made there are a good many things included that are 

 fresh to books on practical chemistry The author 

 makes some very just remarks on the difficult question 

 of the correlation of lecture and laboratory work, and it 



