DYNAMICAL ILLUSTRATIONS OF THE MAGNETIC AND THE HELIÇOIDAL ROTATORY EFFECTS OF TRANSPARENT BODIES ON POLARIZED LIGHT

The elastic reaction of a homogeneously strained solid has a character essentially devoid of all heliçidal and of all dipolar asymmetry. Hence the rotation of the plane of polarization of light passing through bodies which either intrinsically possess the heliçidal property (syrup, oil of turpentine, quartz crystals, &c), or have the magnetic property induced in them, must be due to elastic reactions dependent on the heterogeneousness of the strain through the space of a wave, or to some heterogeneousness of the luminous motions dependent on a heterogeneousness of parts of the matter of lineal dimensions not infinitely small in comparison with the wave length. An infinitely homogeneous solid could not possess either of those properties if the stress at any point of it was influenced only by parts of the body touching it; but if the stress at one point is directly influenced by the strain in parts at distances from it finite in comparison with the wave length, the heliçoidal property might exist, and the rotation of the plane of polarization, such as is observed in many liquids and in quartz crystals, could be explained as a direct dynamical consequence of the statical elastic reaction called into play by such a strain as exists in a wave of polarized light.