THE 



AMERICAN JOURNAL OF SCIENCE. 



[THIRD SERIES.] 

 ^ 



Art. XXXVI. — On the Relative Motion of the Earth and the 

 Luminiferous Ether ; by Albert A. Michelson and 

 Edward W. Morley.* 



The discovery of the aberration of light was soon followed 

 by an explanation according to the emission theory. The effect 

 was attributed to a simple composition of the velocity of light 

 with the velocity of the earth in its orbit. The difficulties in 

 this apparently sufficient explanation were overlooked until 

 after an explanation on the undulatory theory of light was 

 proposed. This new explanation was at first almost as simple 

 as the former. But it failed to account for the fact proved by 

 experiment that the aberration was unchanged when observa- 

 tions were made with a telescope filled with water. For if the 

 tangent of the angle of aberration is the ratio of the velocity 

 of the earth to the velocity of light, then, since the latter 

 velocity in water is three-fourths its velocity in a vacuum, the 

 aberration observed with a water telescope should be four- 

 thirds of its true value.f 



* This research was carried out with the aid of the Bache Fund. 



fit may be noticed that most writers admit the sufficiency ot the explanation 

 according to the emission theory of light ; while in fact the difficulty is even 

 greater than according to the undulatory theory. For on the emission theory the 

 velocity of light must be greater in the water telescope, and therefore the angle 

 of aberration should be less; hence, in order to reduce it to its true value, we 

 must make the absurd hypothesis that the motion of the water in the telescope 

 carries the ray of light in the opposite direction ! 



Am. Jotra. Sci. — Third Series, Vol. XXXIV, No. 203.— Nov., 1887. 

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