Artificial double refraction, due to æolotropic distribution, with application to colloidal solutions and magnetic fields

In 1902 Majorana described some new effects observed on placing in a uniform magnetic field certain solutions of dialysed iron, such as that of Bravais. The solution was found to become doubly refracting like a positive or negative uniaxal crystal, with its axis parallel to the lines of magnetic force. A formal theory of the phenomena given by Voigt consisted in adding to the ordinary electrical equations terms of the second order, representing the action of the magnetic field upon the natural vibrations of the medium. Previously to these experiments, Kerr had obtained a negative double refraction in submitting to a magnetic field a medium composed of pure water containing invisibly fine particles of Fe3O4, his explanation of the effect being that the particles might be supposed to join together into filaments along the lines of magnetic force.