42 2 



NATURE 



[June 2, 192 1 



The volume contains 303 illustrations of 

 machinery in use in the various operations, but 

 few of these, comparatively speaking, are of 

 American origin. Some of the illustrations which 

 are given in diagrammatical sections are of value 

 to the student, whilst many, which are simply pic- 

 tures, convey little or no information as regards 

 working details. In a few cases only are the 

 machines fully described in the text. 



Forty-one pages are devoted to the dyeing of 

 about twenty-five different materials, including 

 leather, paper, furs, feathers, foodstuffs, etc. In 

 this the author has made an attempt to cover a 

 very wide field indeed, but, as stated in the pre- 

 face, he has been able to give only " a brief survey 

 of these interesting fields." Some of the informa- 

 tion given should, nevertheless, be of value to 

 workers. 



In a short review such as this it is unfor- 

 tunately impossible to discuss the contents of the 

 volume more fully. The book certainly deserves 

 the attention of those interested in the dyeing of 

 textiles and other materials. The amount of in- 

 formation which it contains is very considerable, 

 and it is, therefore, safe to assume that at least 

 some parts of its contents will appeal to every 

 reader. J. Huebner. 



Time and Space. 



The Absolute Relations of Time and Space. By 

 Dr. A. A. Robb. Pp. ix + 80. (Cambridge : At 

 the University Press, 1921.) 55. net. 



IN 1914 Dr. Robb published a work entitled 

 "A Theory of Time and Space." Bearing in 

 mind the circumstances of that year, it is not sur- 

 prising to find that the book did not attract a 

 notice commensurate either with the intrinsic im- 

 portance of the subject or with the novelty of the 

 views propounded in it. The short work bearing 

 the above title is introductory to the larger work, 

 and contains a concise statement of the main 

 results embodied in it. The treatment is very 

 different from that of Einstein. In Einstein's 

 theory the emphasis is laid exclusively on the idea 

 of the " relativity " of experience. Dr. Robb, on 

 the other hand, postulates as the basis of his 

 theory an absolute relation — namely, the relation 

 of "before and after." Not only does this relation 

 serve as a physical basis; it is also the founda- 

 tion on which he builds a goodly structure — his 

 purely geometrical theory of time, of which the 

 theory of space forms a part. 



In the first section, devoted to preliminary con- 

 siderations, the author shows by simple illustra- 

 tions the difficulty of giving precise meanings to 

 NO. 2692, VOL. 107] 



apparently simple concepts such as the equality of 

 lengths, and makes clear the close interdependence 

 of time and spatial measurement. The keystone 

 of his work is to be found in his treatment of the 

 problem of identifying the same instant of time 

 at two distinct points of space. In Einstein's 

 theory each observer carries his own local time, 

 and events which are simultaneous to one observer 

 are not necessarily so when compared by the local 

 time of another. Rightly dissatisfied with this 

 view, the author adopts the bold point of view 

 contained in the statement that there is no identity 

 of instants at different places at all. In his own 

 words, " the present instant, properly speakings 

 does not extend beyond here." It follows, then^ 

 that the complete specification of an instant of 

 time requires the use of four co-ordinates 

 {x, y, z, t). 



The author then develops, by means of a system 

 of twenty-one postulates, his four-dimensional geo- 

 metry of time, and this development is character- 

 ised not only by a high degree of originality — 

 particularly evinced in his novel and striking con- 

 cept of conical order — but also by much skill and 

 insight. Elements of time forming a system char- 

 acterised by conical order, the spatial aspect, ex- 

 plicitly introduced in postulate v., becomes a direct 

 consequence of this order. Analytically, after co- 

 ordinates have been introduced, the theory leads 

 to Einstein's restricted relativity. The work is a 

 most valuable and original contribution to a very 

 abstruse and diflficult subject. More satisfactorily 

 grounded than Einstein's theory, its far-reaching 

 results merit the closest study, not only from the 

 physicist, but also from the geometer. To the 

 latter, indeed, it makes a strong appeal, since, as 

 the author points out, the simple asymmetric rela- 

 tion of " before and after " appears to have im- 

 portant advantages over the concept of "linearly 

 between " which has hitherto been mainly used as 

 a basis for systems of geometry. J. F. T. 



Our Bookshelf. 



L' Alimentation et L'Elevage Rationnels du 

 Betail. {Opinions du Prof. A. Mallevre.) By 

 J. E. Lucas. Pp. 466-1- 4.4 {Paris: Librairie 

 Lefran9ois, 1920.) 18 francs. 



The lives of most men of science are divided 

 between teaching and research ; he is indeed for- 

 tunate who can harmonise the duties. The late 

 Prof. Alfred Mallevre, whose premature death in 

 1916 deprived France of a brilliant teacher and 

 keen investigator, seems often to have regretted 

 that his professorial duties left but little leisure 

 for research, and it is sad to read, in the eloquent 

 notice of his career by M. Georges Wery pre- 



