December 2, 1920] 



NATURE 



431 



siderations. Only in this way is it possible to 

 bring- in the new ideas and the new light which 

 alone make research successful. 



The reception of the scheme by the younger 

 scientific workers has been very satisfactory, and 

 the responsible authorities of the institutes have 

 been in the gratifying position of finding excellent 

 candidates for their posts. At no time in the last 

 twenty years have the research institutes been 

 better staffed than now. 



Provision has also been made for the creation 

 of a link between the university and the research 

 service. The Ministry of Agriculture awards 

 scholarships of the value of 2oo2. per annum to 

 men and women, possessing an honours degree or 

 equivalent qualification, who are desirous of 

 entering the service. The successful candidates 

 ore attached to whichever institutes they may 

 prefer, and have their opportunity in the event of 

 a vacancy occurring. They will, however, usually 

 find other scholarship holders at the institutes — 

 1 85 1 Exhibitioners, various university scholars, 

 and other post-graduate workers also waiting for 

 posts — and they can hope for appointments only 

 if they happen to be the best of the available 

 candidates. 



Thus the scheme provides for selection from the 

 universities of the most promising young men and 

 women for research work; it allows of a proba- 

 tionary pyiod in which each candidate can show 

 his or her fitness for the work; it affords per- 

 manent posts for those finally chosen ; it gives 

 increments of salary commensurate with the value 

 imparted by experience; and for the highly gifted 

 worker it affords prospects of promotion to posts 

 which, considering their freedom from routine 

 duties and from worries, must be regarded as dis- 

 tinctly good. The scheme is economical and 

 effective; it works with the minimum of friction 

 and without interference with the individual re- 

 search worker; and it may confidently l)c recom- 

 mended as a model to other Government Depart- 

 ments which are concerned with the promotion of 

 scientific research. 



Philosophy of Relatiyity. 



The General Principle of Relativity: In its Philo- 

 sophical and Historical Aspect. By Prof. 

 H. Wildon Carr. Pp. x-t-iG5. (London: 

 M.icmillan and Co., Ltd., 1920.) Price 7s. 6d. 

 net. 



PROF. WILDON CARR has produced in this 

 little volume a really valuable book. There 

 in hiatus in the current expositions of the 

 NO. 2666, VOL. 106] 



principle of relativity. Its significance and im- 

 portance had been clearly set forth in their bear- 

 ing on mathematical physics. But the doctrine 

 had not been connected with its position in the 

 history of general philosophical thought. This 

 Prof. Carr has now done, and with great know- 

 ledge of philosophy. 



After explaining the old difficulties, he shows 

 how Descartes and Leibniz had partially recog- 

 nised their origin. The exposition of the dis- 

 cussions by each of these thinkers is lucid and 

 informing. In particular, there is an admirable 

 explanation of the Leibnizian theory of monads, 

 and of how Leibniz was driven to its adoption. 

 Both philosophers were mathematicians of great 

 eminence. They saw that the explanation of 

 matter must come after that of movement, and 

 could not precede it. Extension was not 

 "stuff." The explanation of gravitation given 

 by Newton follows. The book goes on to 

 deal with the difficulties that led to Einstein's 

 revision of the whole of the Newtonian hypo- 

 thesis of space and time as absolutely existing 

 frameworks. The special principle of relativity 

 is then explained, and it is shown that the general, 

 or later, Einstein principle is simply a full state- 

 ment of what is implied in its earlier form. The 

 first dealt with a definite phenomenon — the velo- 

 city of light. The second extends the explana- 

 tion to the laws of Nature generally. There is 

 no longer a particular finite velocity taken to be a 

 constant and limiting one. As soon as 'we extend 

 the special case of relativity to non-uniform and 

 rotational systems of motion, the doctrine of equi- 

 valence between the experience of the observer 

 taken to be at rest, and the experience of the 

 observer in another system relatively to which the 

 observer taken to be at rest is regarded as being 

 in motion, becomes apparent. The explanation 

 of the possibly non-Euclidean character of space 

 systems, and of the necessity of correlating 

 observations by adequate formulae of transforma- 

 tion, becomes clear. The idea of pure objectivity 

 disappears. Mind appears as relating the centre 

 of a universe which is no longer infinite in the 

 sense given to the word as applied to New- 

 tonian space. For the observer is not a fixed 

 point existing at a fixed instant. "Space and 

 time are not containers, nor arc they contents; 

 they arc variants. Thev rhantre ns my system of 

 reference changes." 



One of the difficult i»'s i-Npcriiim-d in reading 

 even Flinstein himself is the lack of a thorough- 

 going connection of his principle with the new 

 character really given by it to space and time. 

 They arc discussed ns thotigh they remained 

 changed, not in kind, hut in degree only, .uul 



