Abstract

THE experimental and theoretical investigations of the last twenty years have lent a new interest to what, I venture to think, is one of the most fascinating branches of physical optics, namely, the action of an electromagnetic field upon light. The discoveries which have hitherto been made may be classified under four heads: (1) Faraday's experiments, which show that when plane polarised light is transmitted through a transparent magnetised medium, a rotation of the plane of polarisation is produced; (2) Kerr's experiments, which show that the effect of electrostatic force on a transparent medium is to convert it into one which is optically equivalent to a uniaxal crystal whose axis is in the direction of the force; (3) Kerr's experiments on the reflection of plane polarised light at the surface of a magnetised iron reflector, which show that a rotation of the plane of polarisation of the reflected light takes place, which in certain cases is in the same and in others in the contrary direction to that of the amperean current which may be conceived to produce the magnetic force; (4) Kundt's experiments on the reflection of light from magnetised iron, cobalt, and nickel, and also on the transmission of light through thin magnetised films of these metals. There is also another series of experiments by Kundt, in which polarised light is refracted at the upper surface of a plate of glass, is then reflected at the lower surface, and again refracted at the upper surface. The results of these experiments show that the plane of polarisation of the ultimately emergent light is rotated in the contrary direction to that produced by an iron reflector.

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