OP ARTS AND SCIENCES. 397 



direction is inclined about 26° to the plane of the earth's equator, and 

 a tangent to the earth's motion in its orbit makes an angle of 20?,° 

 with the plane of the equator. The resultant would be within 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 coincide with the resultant motion of the earth, 

 and the northern arm would be at a right angle to it. The displace- 

 ment produced by revolving the whole apparatus through 90° should 

 amount to ^V °f the interval between 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 conclusion that there was not a suffi- 

 cient displacement of the fringes to support the theory of aberration, 

 which supposes the ether to move with a certain 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 inves- 

 tigation. 



In 1886, Mr. Michelson and Mr. Morley published a paper on the 

 influence of the motion of the medium traversed by the light on its 

 velocity. Fizeau had made similar experiments. In both cases the 

 interfering rays were changed in velocity in opposite ways by flowing 

 air or water through which they were transmitted. With air having 

 a velocity 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 Fresnel, that the ether in a moving body is stationary, 

 except, the portions which are condensed around its particles. In this 

 sense, it may be said that the ether 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. Cornu writes of Michelson's experiments on 

 moving media : " Leur travail cone.ii dans l'esprit le plus eleve Exe- 

 cute* avec ces puissant moyens d'action que les savants dea Ktats-l nis 

 aimant a deployer dans les grandes questions scientifiques fait Le plus 

 grand honneur a leurs auteurs." 



In 1887, Professor Michelson published another investigation of 

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

 ether with it. In his previous experiment his apparatus was sensitive 



