On the Constant P in Observations of Terrestrial Magnetism

Abstract

THE formula for P given by Mr. Rücker (NATURE, vol. xxxvi. p. 508) has evidently been obtained by expanding the usual expression rigorously to terms of the second order; but as the usual expression differs from Gauss's theory by terms of the second order, Mr. Rücker's expansion is necessarily inexact to the same extent, and in fact his second order term has no existence in Gauss's theory.