184 SCIENCE AND THE HUMAN MIND 



entirely unconnected circuit, we have either to 

 suppose an unexplained " action at a distance," or 

 to conceive the intervening space bridged with some- 

 thing through which the effect is transmitted. When 

 Clerk Maxwell in 1865 developed mathematically 

 Faraday's ideas, it became clear that the propaga- 

 tion of electric forces was similar to the propagation 

 of light ; whatever be the means by which one is 

 transferred must also be the means of conveyance of 

 the other. 



Hence the idea of a universal all-pervading aether, 

 which had been accepted owing to the success of the 

 wave theory of light, received a great access of credit, 

 and science entered on what might be described as an 

 aethereal stage. Experiments were made to measure 

 the velocity of the earth " relatively to the aether," 

 and, when it appeared that they were relatively at 

 rest, it was assumed that the earth carried the aether 

 with it in its path, and attempts were made to demon- 

 strate that whirling steel discs dragged the aether with 

 them once more with a negative result. However, 

 a slight change in the dimensions of bodies with 

 change in direction of motion a change too small to 

 be otherwise detected was shown to be enough to 

 explain the discrepancy, and it was universally 

 assumed that time would bring a complete scheme 

 of physics, in which the aether, interpreted in 

 mechanical terms, would form a means of unifying 

 the whole range of phenomena an expectation 

 which, indeed, has since seemed almost on the point 

 of realization. 



Maxwell's theoretical results were verified and 

 interpreted to wider circles by the experiments of 



