464 miciielson's recent reseakches on light. 



clinetl about 2^^ to tlie plane of the earth's equator, aud a taugeut to 

 the earth's motion in its orbit makes an anj^le of 23.^° ^vith the plane 

 of the equator. The resultant would be \Yithiu 25° from the equator. 

 The nearer the components are in magnitude, the more nearly would 

 the resultant coincide with the equator. If the apparatus is placed so 

 that the arms point north and east at noon, the eastern arm would coin- 

 cide with the resultant motion of the earth, and the northern arm would 

 be at a right angle to it. The displacement produced by revolving the 

 whole through 9(P should amount to one-twenty fifth of the interval be- 

 tween two fringes. If the proper motion of the solar system is small 

 compared with the velocity of the earth in its orbit, the displacement 

 would be less. Mr. Michelson drew from these experiments the conclu- 

 sion that there was not a suffi(;ient displacement of the fringes to support 

 the theory of aberration, which supposes the lether to move with a cer- 

 tain fraction of the earth's velocity. The displacement however was 

 so small that it easily might have been masked by errors of experiment. 

 Mr. A. Graham Bell supplied Mr. Michelson with the money required 

 for this investigation. 



In 188G, Mr. Michelsou and Mr. Morley published a paper on the in- 

 fluence of the motion of the medium traversed by the light on its ve- 

 locity. Fizeau had made similar experiments. In both cases the in- 

 terfering rays were changed in velocity in opposite ways by tlowing air 

 or water through which they were transmitted. With air having a ve- 

 locity of about 82 feet (25 meters) a second, the effect was so small that 

 it might easily be covered up by errors of experiment; but with water 

 it was measurable, and the result corresponded with the assumption of 

 Fresuel, that the jcther in a moving body is stationary, except the por- 

 tions which are condensed around its particles. In this sense, it may 

 l)e said that the aether is not affected by the motion of the medium which 

 it permeates. For this investigation, which was made possible by a 

 grant from the Bache Fund of the National Academy, Mr. Michelson 

 and Mr. Morley devised a new instrument, called the refractometer. 

 ( ■ornu writes of Michelson's experiments on moving media : " Leur tra- 

 vail concu dans I'esprit le plus eleve execute avec ces puissant moyens 

 d'action que les savants des ]f]tats-Uni8 aimant a deploy er dans les 

 grandes questions scientifiques fait le plus grand honueur a leurs au- 

 teurs." 



In 1887, Professor Michelson published another investigation of the 

 question whether the motion of the earth in its orbit carried its aether 

 with ir. In his previous experiment his apparatus was sensitive to the 

 smallest jars, and it was difficult to revolve it without producing distor- 

 tion of the fringes, and an effect amounting to only one-twentieth of 

 the distance between the fringes might easily be hidden by accidental 

 errors of experiment. In the new experiment the apparatus was placed 

 on a massive rock, which rested on a wooden base, which floated upon 

 mercury, The stoue wa.s 1.5 meters square and 0-.3 of a wet^i" t-lilvlSi 



