The Faraday Effect with X-Rays

Voigt's theory for the rotation of the plane of polarization of light by a magnetic field is discussed and one of the equations used by W. Kartschagin and E. Tschetwerikowa who investigated the Faraday effect with x-rays transmitted through ferromagnetic materials, is shown to be inapplicable. The theory for the effect given by Drude is modified for the case of x-ray wave-lengths giving a rotation of $\chi =-\frac{2\pi \mu \mathrm{eIL}}{m{c}^2}$ radians $\mu$ is the refractive index, $I$ is the intensity of magnetization, $l$ the thickness of the material through wich the x-rays are transmitted. The other quantities have their usual meanings. Kartschagin and Tschetwerikowa found evidence suggesting a rotation in the case of x-rays. An experiment was performed which confirmed these suggestions and which checked the equation for $\chi$ given above well within the experimental error. The experimental error was large, but a rotation of the order of 10° was shown to occur for x-rays of wave-length 0.3A transmitted through 0.05 cm of iron in a field of 300 gauss.