light, FitzGerald proceeded to extend it so as to take account of a closely related phenomenon. In 1876 J. Kerr[1] had shown experimentally that when plane-polarized light is regularly reflected from either pole of an iron electromagnet, the reflected ray has a component polarized in a plane at right angles to the ordinary reflected ray. Shortly after this discovery had been made known, FitzGerald[2] had proposed to explain it by means of the same term in the equations which accounts for the magnetic rotation of light in transparent bodies. His argument was that if the incident plane-polarized ray be resolved into two rays circularly polarized in opposite senses, the refractive index will have different values for these two rays, and hence the intensities after reflexion will be different; so that on recompounding them, two plane-polarized rays will be obtained—one polarized in the plane of incidence, and the other polarized at right angles to it.
The analytical discussion of Kerr's phenomenon, which was given by FitzGerald in his memoir of 1879, was based on these ideas; the most essential features of the phenomenon were explained, but the investigation was in some respects imperfect.[3]
A new and fruitful conception was introduced in 1879–1880, when H. A. Rowland[4] suggested a connexion between the magnetic rotation of light and the phenomenon which had been discovered by his pupil Hall.[5] Hall's effect may be regarded
- ↑ Phil. M (5) iii (1877), p. 321.
- ↑ Proc. R. S. xxv (1877), p. 447; FitzGerald's Scient. Writings, p. 9.
- ↑ Cf. Larmor's remarks in his Report on the Action of Magnetism on Light, Brit. Assoc. Rep., 1893; and his editorial comments in FitzGerald's Scientific Writings. Larmor traced to its source an inconsistency in the equations by which FitzGerald had represented the boundary-conditions at an interface between the media. FitzGerald had indeed made the mistake, similar to that which was so often made by the earlier writers on the elastic-solid theory of light, of forgetting that when a medium is assumed to be incompressible, the condition of incompressibility must be introduced into the variational equation of motion (as was done supra, p. 172). Larmor showed that when this correction was made, new terms (resembling the terms in p, supra, p. 172) made their appearance; and the inconsistency in the equations was thus removed.
- ↑ Amer. Jour. Math. ii, p. 354, iii, p. 89; Phil. Mag. xi (1881), p. 254.
- ↑ Cf. p. 327.
