The Motion of the Perihelion of Mercury

Abstract

I AM obliged to Mr. Harold Jeffreys for his friendly criticism (NATURE, April 11, p. 103), but my suggestion was not one of a resisting medium pure and simple, but of a resistance greater at perihelion than aphelion, and therefore synchronous with the planet's orbital period. Mr. Jeffreys will surely admit that a periodic disturbance of this kind, acting parallel to the minor axis of the orbit, would certainly affect the longitude of perihelion, without affecting the eccentricity; though whether the amount of resistance to be expected, say from matter in the Zodiacal light, is sufficient to make the effect appreciable may well be doubted. Moreover, I had not thought of the resisting medium as revolving in a planetary manner. I am inclined to attribute much more importance to my other suggestion based on the electrical theory of matter (Phil. Mag. for August, 1917). Nevertheless, a periodic resistance hypothesis is peculiarly applicable to Mercury, (a) because of its nearness, (b) because of the eccentricity of its orbit.