120 Presidential Address 



beams which have travelled half with and half against 

 the motion, for many yards; but, after spurious results are 

 allowed for, there is no shift of the bands; proving that the 

 velocity is not affected by so much as one tenth of one per 

 cent, of the velocity of the moving matter. Practically we 

 may say that the Ether of space is never carried forward 

 presumably not even by a planet; for the Fizeau effect, 

 properly interpreted, means the same thing. 



Professor Michelson of Chicago, however, one of the 

 most brilliant experimental physicists in America which 

 is saying a good deal tried a totally different experiment, 

 examining whether light sent to and fro over a fixed dis- 

 tance in the direction of the earth's planetary motion 

 through space, took any longer on its double journey than 

 it did when sent to and fro over the same distance across 

 the motion. The result was likewise negative : no difference 

 could be perceived; though the delicate experiment was 

 performed with the utmost care and skill, and was after- 

 wards repeated still more elaborately by Professor Michel- 

 son and Mr. Morley in collaboration. This negative 

 result, however, is in apparent or superficial opposition 

 to the other negative result : it seemed difficult to suppose 

 that they could both be true. Because if the Ether is not 

 carried forward by the earth at all, it must be relatively 

 streaming past the earth with a speed of many miles per 

 second, as many as 30 sometimes ; and accordingly an effect 

 ought to be obesrved. The negative result of Michelson, 

 therefore, superficially suggests that the Ether in the 

 neighbourhood of the earth is stagnant which in this 

 case is the opposite of stationary i.e. that it clings to the 

 earth and is carried forward by it. Many difficulties 

 would arise if that were true, and the theory of ordinary 

 astronomical aberration would be complicated; the Ether 

 would no longer be behaving as a perfect fluid, but would be 

 exhibiting what is called viscosity. Planets could hardly 

 move through it without resistance, and astronomical 



