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XVIII. Astronomical Consequences of the Electrical Theory 

 of Matter. Note on Sir Oliver Lodge's Suggestions. By 

 Prof. A. S. Eddington, M.A., F.R.S., Plumian Pro- 

 fessor of Astronomy in the University of Cambridge *. 



IN the Philosophical Magazine for August, p. 81, Sir Oliver 

 Lodge offers an explanation of the celebrated discordance 

 of the motion of the perihelion of Mercury. His explanation 

 is comparatively simple, and on that account will be widely 

 preferred to the recent theory of Einstein, which introduces 

 very revolutionary conceptions, provided that it meets certain 

 other astronomical requirements which seem necessary. In 

 removing the discordance for Mercury, it must not introduce 

 discordances for Venus and the Earth, which at present 

 satisfy gravitational theory. If the explanation breaks down 

 under this further test, the discussion will make prominent a 

 feature of the success of Einstein's theory which has perhaps 

 not been sufficiently emphasized. 



It will be recalled that Lodge nmkes the hypothesis that 

 the extra electrical inertia due to the motion of matter is not 

 subject to gravitation. Hence, for a planet moving in a 

 circular orbit, gravitation remains constant, but the inertia 

 alternately increases and decreases according as the orbital 

 velocity compounds positively or negatively with the uniform 

 motion of the solar system through space. The latter motion 

 is entirely unknown, and any value within reasonable limits 

 may be considered plausible. 



This theory is shown by Lodge to lead to changes in the 

 perihelia and eccentricities of the orbits. He suggests that 

 " through a comparison of the outstanding discrepancies 

 between theory and observation for different planets, if they 

 were definite enough, it might be possible to get some indi- 

 cation of the direction as well as the magnitude of the Sun's 

 true motion through the aether of space." It will be shown 

 that the astronomical data claim to be quite definite enough to 

 follow up the theory in the way he proposes. I give below the 

 present discordances between gravitational theory and obser- 

 vation for the four inner planets f. Here ot is the longitude 



* Communicated by Sir Oliver Lodge. 



t W. de Sitter, ' The Observatory,' vol. xxxvi. p. 297 (1913), with some 

 small corrections taken from ' Monthly Notices' vol. lxxvi. p. 728 (1916). 

 I have transformed the mean evrors there given into probable errors. It 

 may seem strange to those unfamiliar with astronomical practice to find 

 a pure number rh expressed in seconds of arc ; the angle is to be identified 

 with its circular measure. 



