The London, Edinburgh and Dublin philosophical magazine and journal of science . ey, described inJ- the Philosophical Magazine [5] xxiv. p. 449, has createdquite a dilemma in the physics of the aether ; for while thegreat body of general evidence tends to show complete inde-pendence of the aether near the earth on the earths motion,this celebrated experiment has been supposed to prove defi- * Communicated by the Author. 24 Mr. W. Sutherland on the Relative iiitely that the earths surface and the adjacent aether have norelative motion. I propose now to show how a slight altera-tion in the point
The London, Edinburgh and Dublin philosophical magazine and journal of science . ey, described inJ- the Philosophical Magazine [5] xxiv. p. 449, has createdquite a dilemma in the physics of the aether ; for while thegreat body of general evidence tends to show complete inde-pendence of the aether near the earth on the earths motion,this celebrated experiment has been supposed to prove defi- * Communicated by the Author. 24 Mr. W. Sutherland on the Relative iiitely that the earths surface and the adjacent aether have norelative motion. I propose now to show how a slight altera-tion in the point of view of the theory of that experiment willmake it appear that, until a special adjustment for sensitive-ness of the optical apparatus has heen made, it is not com-petent to decide as to the relative rest or motion of earth andaath er. For the sake of clearness let us briefly repeat the authorsaccount of the theory of their experiment along with theirdiagram, b and c are two mirrors at right angles to oneanother (fig. 1), and at equal distances D from a a piece of Fie:. glass inclined at 7r/4 to them, and intended to divide a beamof light sa into reflected and transmitted parts going to b andc respectively. Suppose the whole apparatus to be movingin the direction sc with velocity v relative to the aether inwhich the beam of light is moving with velocity Y; thenwhile the reflected beam is going to b and back a is movingto «i, so that the path of the reflected part is abaL, while thatof the transmitted part is acax : at % the former is partlytransmitted and the latter partly reflected to the telescopeunder conditions favourable to the occurrence of ac the beam moves with velocity V—v relative to c,so that the time of traversing ac is J)/(V — v) ; similarly thetime for ca1 is D/(Y + t), and hence ac + cay \V — v V + vj 2D l-t^/V The path of the other beam is taken to be aba1} whose length Motion of the Earth and JEthev. 25 is evidently 2D(1-f?;2/V2
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