Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume IV (1876-1877)
Davies, J. E.
Report on recent progress in theoretical physics, pp. 241-264 PDF (6.7 MB)
254 Wisconsin Academy of Sciences, Arts, and Letters. by magnetism, " not as giving a 2mechanical explanation of the phe- nomena, but as showing that the phenomena may be explained by equations, which equations appear to be such as ruight possi- blv be deduced frcm some plausible mechanical assumption, although no such assumption has been made." This explanation of what rotatory polarization is, as it occurs in bodies which of themselves rotate the plane of polarization, may Fig. 16. help to an understanding of Fig. 17. the manner in which an /~ " electric current, circulating around a medium through which circularly polarized light is passing, may possi- bly affect the velocity of either circular component of the polarized light, and thus, accord- ing as the direction of the current is with a circular componentt as in Fig. 16, or aqainst it, as in Fig. 17, produce a right-handed or a left-handed rotation, according to the direction in which the current circulates around the medium. Of this latter, Sir Wm. Thompson, in 1856, made the important observation,' which Prof. Clerk Maxwell has elaborated into the "The magnetic influence -on- light, discovered by Faraday, depends on the direction of -motion -of moving particles. For instance, in a medium possess- ing it, particles in a straight line parallel to the lines of magnetic force, dis- placed to a helix round this line as axis, and then projected tangentially with such velocities as to describe circles, will have different velocities, according as their motions are round in one direction (the same as the nominal direc- tion of the galvanic current in the magnetizing coil) or in the contrary direc- tion. But the elastic reaction of the medium must be the same for the same displacements, whatever be the velocities and directions of the particles; that is to say, the forces which are balanced by centrifugal force of the circular motions are equal, while the luminiferous motions are unequal. The absolute circular motions being therefore either equal or such as to transmit equal cen trifugal forces to the particles initially considered, it follows that the lumi- niferous motions are only components of the whole motion; and that a less luminiferous component in one direction; compounded with a motion ex- isting in the medium when transmitting no light, gives an equal resultant to that of a greater luminiferous motion in the contrary direction compounded with the same non-luminous motion. I think it is not only impossible to conceive any other than this dynamical explanation of the fact that circularly-
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