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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
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Page 255

Recent Progress in Theoretical Physics. fundamental equation with which we began this article, and which the experiments of Verdet. so remarkably corroborate. "The disturbance which constitutes light, whatever its physical nature may be, is of the nature of a vector, perpendicular to the direction of the ray. This is proved from the fact of the interfer- ence of two rays of light, which, under certain conditions, pro- duces darkness, combined with the fact of the non-interference of two rays polarized in planes perpendicular to to each other. For, since the interference depends on the angular position of the planes of polarization, the disturbance must be a directed quantity or vector, and since the interference ceases when the planes of polar- ization are at right angles. the vector representing the disturbance must be perpendicular to the line of intersection of these planes, that is, to the direction of the ray. The disturbance, being a vector, can be resolved into compo- nents parallel to x and y, the axis of z being parallel to the direc- tion of the ray. Let e and a' bat these components; then, in the case of a ray of homogeneous circularly-polarized light, = rcos6, ='r sinO, (1) where -nt-qz + a. (2) In these. expressions, r denotes the magnitude of the vector, and O the angle which it makes with the direction of the axis of x. The periodic time, A, of the disturbance is such that nr = 2w. The wave-length, i, of the disturbance is such that q2 = 2w,. The velocity of propagation is n q (3) (4) The phase of the disturbance when t and z are both zero is a- The circularly-polarized light is right-handed or left-handed according as q is negative or positive. polarized light transmitted through magnetized glass, parallel to the lines of magnetizing force, with the same quality, right-handed always or left- handed always, is propagated at different rates, according as its course is in the direction or is contrary to the direction in which a north magnetic pole is drawn; but I believe it can be demonstrated that no other explanation of that fact is possible. Hence it appears that Faraday's optical discovery affords a demonstration of the reality of Ampere's explanation of the ulti- mate nature of magnetism." - SIR WM. THOMPSOoN. 2505

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