On the Constant P in Observations of Terrestrial Magnetism

Abstract

I THINK that on reconsideration Prof. Harkness will admit that it is not I who have fallen into error. If only two observations are made, equations (7) and (8) are identical, and there is no need for the introduction of P₀. In like manner if numerous measurements were available in which the error of observation was nil, any pair would give the same value of L, and P₀ would again be unnecessary. If, however, the equations are affected by errors of observation, and it be agreed that in combining them we may replace the P's by a single quantity, P₀, it must not be arbitrarily defined. Prof. Harkness assumes that in the case of two observations it must be the mean of P and P₁, but he gives no reasons, and he does not state what value he would adopt if the measurements were numerous. The proper course is to determine it by the method of least squares.