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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.
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