634 



NA TURE 



[May 20, 1922 



Bulletin that the state of research into animal diseases 

 in the tropics is at present lamentable. 



Affirming that the facilities available in the British 

 Empire in men, laboratory accommodation and equip- 

 ment, are totally inadequate for the interests at stake, 

 the Committee recommends the gradual creation of 

 a cadre of research workers under an advisory organisa- 

 tion of scientific experts. On both scientific and 

 political grounds it is desirable that no demarcation 

 should be drawn between research work in the United 

 Kingdom and that in other parts of the Empire. 



The Committee is of opinion also that, should 

 financial conditions become less stringent, assistance 

 from State funds would be justified towards the creation 

 of one strong Institute to serve the needs of the United 

 Kingdom and possibly of the Empire. In such an 

 institute, research would be made into the comparative 

 aspects of disease as a whole, and workers in different 

 branches of the subject— veterinary, medical, botanical 

 — would be brought into association. 



It is unfortunate that the Committee terminated 

 its labours before the announcement of the gift to 

 the Government by the Rockefeller Foundation of 

 two million dollars for the creation of an Institute of 

 Imperial Hygiene in London. It is understood that 

 the Government has already accepted the responsi- 

 bility of providing staff and maintenance of the Insti- 

 tute when established. Moreover, the "Shakespeare 

 Memorial " site adjoining the area recently acquired for 

 the University of London has been purchased. 



This new development must enhance profoundly the 

 position of London as the post-graduate centre of the 

 Empire. It is understood that the Ministry of Health 

 favours the integration of certain activities of various 

 bodies like the London School of Tropical Medicine 

 with those of the proposed Institute. In view of the 

 enormous advantages which would ensue to the whole 

 science of medicine from the intimate association of 

 research workers in human and animal disease, it is 

 to be hoped that serious efforts will be made to meet 

 the legitimate aspirations of the veterinary profession 

 for better facihties for research and post-graduate 

 study in connection with the new Institute. 



The General Theory of Relativity. 



S-pace— Time— Matter. By Hermann Weyl. Trans- 

 lated from the German by Henry L. Brose. Pp. xi 

 + 330. (London: Methuen and Co., Ltd., 1922.) 

 i8j-. net. 



PROF. WEYL'S work is the standard treatise on 

 the general theory of relativity. It is the most 

 systematic and penetrating book on the subject ; it is 

 also by far the most difficult. The reader must not 

 NO. 2742, VOL. 109] 



expect a helping hand over difficulties which are merely 

 analytical ; only the barest indication of intermediate 

 steps is given in passing from one formula to another. 

 The book is not suitable for a first introduction to the 

 mathematical theory ; but those who have already 

 acquired some familiarity with the methods and mani- 

 pulations required will find here a deeper insight and a 

 more general view of the logical coherence of the theory 

 than is possible in more elementary text-books. We 

 think too that Weyl, more than other continental 

 writers, approaches the outlook natural to an English 

 student. The subtle distinctions between the Cam- 

 bridge and the continental schools survive the revolu- I 

 tion which has overtaken scientific thought. Even \ 

 with Einstein we feel a need to anglicise his mode of 

 thought, and this is still more necessary with some 

 other German writers. But Weyl strikes just the right 

 note for us ; and though he is often too far ahead for 

 us to follow, we pay him the (perhaps doubtful) com- 

 pliment of claiming him as one of our own school of 

 thought. 



In some branches of applied mathematics the 

 analytical methods have obviously no connection with 

 the physical processes. The lunar theory is a notable 

 instance ; we cannot conceive that the processes by 

 which the moon finds out where it ought to be are 

 in any way analogous to those by which the computer 

 solves the same problem. It is part of the charm of 

 Einstein's theory that the mathematical methods cor- 

 respond step by step with physical processes, so that 

 not merely the result but also the form of the analysis 

 is significant. The deeper our comprehension of the 

 mathematical tool (the tensor calculus) the deeper will 

 be our insight into the structure of the world. There 

 are perhaps some who cherish the hope that ultimately 

 simpler mathematical methods of treating these prob- 

 lems will be devised ; but even if this hope were ful- 

 filled the simplification would cost us dearly. If to 

 our minds it seems simpler to solve the problems of 

 Nature for her by methods other than those which she 

 herself follows, that only accentuates our unfittedness 

 to comprehend her processes. In Weyl's treatment 

 the physical significance of each analytical operation 

 is most strongly emphasised. 



A distinctive feature of Weyl's work is his use of the 

 conception of tensor-density in addition to tensor. 

 These differ by a factor ^^g. In any region of the 

 world, we can always choose a system of co-ordinates 

 such that ■\/g=i everywhere; from the analytical 

 point of view the factor is a useless complication which 

 can be omitted without loss of generality, so that tensors 

 and tensor-densities become equivalent. But this com- 

 putational simplification plays havoc with the physical 

 significance of the formulae. Intensity-measures and 



