Continuity 57 



light that the velocity of light is not 

 an absolute thing, but is dependent on 

 the speed of the source. With corpuscu- 

 lar light there is nothing to observe ; with 

 wave light there is something, but we 

 cannot observe it. 



But if the whole solar system is moving 

 through the ether I see no reason why 

 the relative ether drift should not 

 be observed by a differential residual 

 effect in connection with Jupiter's satel- 

 lites or the right and left limbs of the 

 sun. The effect must be too small to 

 observe without extreme precision, but 

 theoretically it ought to be there. In- 

 asmuch however as relative motion of 

 matter with respect to the observer is 

 involved in these effects, it may be held 

 that the detection of a uniform drift of 

 the solar system in this way is not con- 

 trary to the Principle of Relativity. It 

 is contrary to some statements of that 

 Principle; and the cogency of those 

 statements breaks down, I think, when- 

 ever they include the velocity of light; 

 because there we really have something 



