Letter | Published:

The Motion of the Perihelion of Mercury

Naturevolume 101page145 (1918) | Download Citation



THE type of resistance suggested by Sir Oliver Lodge (NATURE, April 18, p. 125) is very difficult to visualise. The motion of a planet consists practically of a steady motion in a circle, with a super-imposed free vibration, the amplitude of which is proportional to the eccentricity, and the phase of which depends on the longitude of the perihelion. The hypothesis that the perihelion can be made to move without alteration in the eccentricity is equivalent to assuming that a free vibration can persist in a resisting medium without change of amplitude. It is true that the absolute resistance would be expected to be greater at perihelion than at aphelion, on account of the difference in density at the two points, but this difference contains the eccentricity as a factor, and it is for this reason that the rate of decrease of the eccentricity and the motion of the perihelion would be of the same order of magnitude.

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