160 THE LIMITATIONS OF SCIENCE 



ether which would annul the effect the motion of the 

 earth should produce; but it was shown that unless the 

 ether remains absolutely at rest worse difficulties re- 

 sult. Then the bold assumption was made, often 

 called the Fitzgerald-Lorentz effect, that the dimen- 

 sions of bodies in motion were so changed by their 

 motion as to neutralize the effect of the earth's motion 

 on the phenomena of light. Every body would, accord- 

 ing to this idea, grow shorter, the faster it moved; 

 and would flatten out to a disc of no thickness if it 

 could attain a speed equal to the velocity of light. 



One of the results of this criticism of mechanics has 

 been to change profoundly our hypothesis of the ether. 

 As is well known, the early conception of the ether was 

 a kind of material substance possessing properties in- 

 compatible with those of any other kind of matter. A 

 large part of the effort of theorists down to the middle 

 of the nineteenth century was devoted to inventing 

 attributes for it which would enable it to fulfill its func- 

 tion as the medium for the transmission of light. At 

 this time, Faraday discovered an effect in electricity 

 which required an entire change in our ideas of the 

 ether. When he found that static electric charges and 

 forces were dependent on the characteristics of the 

 material substance in which electrified bodies were im- 

 mersed, and when later Maxwell predicted and Hertz 

 showed experimentally that electro-magnetic energy 

 passed through vacuous space, and that this form of 



