Gravitation and Light 341 



of the cosmos, in no case leaping across intermediate elements as 

 action at a distance would imply. The early stage of formulation 

 of the confused notion of relativity is the postulate that position 

 and change of position are purely relative: the final solution is to 

 abolish the idea of immediate ^m/e change of position altogether. 

 But that does not imply that a portion of the cosmos can evolve 

 itself without constant interference from all the rest. 



To a question as to what is gained by absorbing gravitation in 

 space an answer would be that it need make no difference as regards 

 gravitation ; but if other relations of an assumed space- time fourfold 

 (e.g. stress-tensor theory) have to go in also in a simple way, it 

 may be convenient or even necessary to assist them by choosing 

 a space which requires some alterations of the recognised laws of 

 gravitation and, if these suggested discrepancies are verified, that 

 may presumably have a claim to be the real type of space. The 

 aim is not primarily to reduce gravitation to a quality of space, — 

 perhaps is not even relativity, which has evaporated, — but is to get 

 it out of Newtonian space and time into the mixed space-time 

 fourfold which was strongly suggested by the form of the Max- 

 wellian electrodynamic relations of free space, and would make 

 that scheme valid for great velocities of convection beyond ex- 

 perience, even up to the speed of light. 



An expansion of the Einstein ideas on general relativity has 

 been worked out by H. Weyl {Ann. der Physik, 59, 1919) in which 

 a further metric scale of vector character appears to be imposed 

 on a non-uniform space-time, which has here been itself ascribed 

 to the imposition of a Gauss- Riemann metric on the formless 

 spacial threefold that is inherent in the mind. There would seem 

 to be no formal obstacles to such piling up of metric upon metric, 

 in an unlimited play of thought. 



The physical analysis perhaps not very remote to this new 

 elaboration of metric is, as I think Prof. Schouten remarks, a 

 theory of an elastic aether in which at each point p, q, ... a vector 

 displacement ^, 17, ... of the element of the medium is supposed, 

 involving a strain and an elastic stress determined in terms of 

 the strain by assigned laws. Only it is to be remembered that 

 time is now in a fourth dimension, in which the historical world- 

 process is all spread out once for all; so that the feature of elastic 

 wave propagation becomes a static relation. The idea that the 

 single fundamental electric vector is represented by a superposed 

 metric is thus correlative with the usual dynamical hypothesis 

 that electric force is a stress in an aether. It thus affords another 

 illustration of this kind of speculation: the interlacing of space 

 and time for purposes of electrodynamics having upset the his- 

 torical development of dynamical principles on a Newtonian basis 

 of separate space and time, order has to be re-constituted by 



