On the gyration of light by multiplet lines

Abstract

1. In the last few years thee has been a great development of the theory of the intensities of spectral lines, and in its turn this theory has reacted on the general theory of spectra; so that any experimental method which throws new light on the subject has a great importance. It has not apparently been explicitly noticed that a study of the dispersive effect of the rotation of polarised light by a vapour can be made to yield information on the second approximations to the intensities of the ┴ Zeeman components. Since tire difficulties of direct intensity measurement and of obtaining strong magnetic fields must always lie very great, there would seem to lie an advantage in having a method of attach which is, it is true, difficult, but only with the difficulty of a very well-known technique, the study of polarised light. The present work is a theoretical investigation of some of the properties that may be expected to lie found. In a recent paper the present writer worked out some results on the subject using tbs purely mechanical models of the type discussed by Voigt, and obtained the result that any atom which exhibits the Paschen bacf effect should show a similar effect in a magnetic field in regard to the gyration of light, provided that the frequency of this light is not too close to the lines of the multiplet . (Of course light in the immediate neighbourhood will not be affected in this way, but will exhibit the actual Zeeman effect inversely.) In other words, the equation of Becquerel relating the gyratory constant V with the refractive index - n V = e / 2 mc 2 λ dn / dλ will give the normal value of e/m , and all trace of the anomalous Zeeman effect will disappear. If this result is true for a single multiplet, it will remain true in regions where more than one contribute sensibly to the retraction, and will only fail for light of frequency very close to that of one of the multiplets of ths spectrum.