The Red (C) Line of Hydrogen and the Zeeman Effect

Abstract

FOR some months we have been engaged in an investigation of the effect of a magnetic field on the more conspicuous lines of certain elementary gases, including the case of helium referred to by Prof. Gray and Dr. Stewart in your issue of November 21. We have employed a very fine echelon grating of twenty-six plates by Hilger. One observation that we have already made is, perhaps, of sufficient interest to deserve mention in your columns. The red (C) line of hydrogen was unmistakably divided before the application of the magnetic field. A reference to Michelson's papers on the application of interference methods to spectroscopic measurements showed that he had announced the red hydrogen line to be a very close double as long ago as 1887. A more detailed examination of the visibility curve is given in the Philosophical Magazine for September, 1892, from which it appears that the curve is practically the same as that due to a double source, whose components have the intensity ratio 7:10, and in each of which the light is distributed according to the exponential law resulting from Maxwell's theory of velocities. The distance between the components is given as 1·4 × 108 millim., so that it should be well within the power of the echelon as at present constructed to resolve the line.