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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 PDF (6.7 MB)


Page 245


*-Recent Progress in Theoretical Physics.
two poles of the electro-magnet, bored through for the reception
of the substance and the passage of the light, and N.2 is the anal-
yzer by which the position of the azimuth of the light reaching
it is determined.  When G is a determinate length of "heavy
glass " (a silico-borate of lead), the analyzer requires a rotation
of
6' on producing the electromagnetism, in order to be placed in
the same relation to the azimuth of vibration of the light reaching
it, as it was in, before the circuit was closed. That is, if the posi-
tion of the analvzer is such before the electro-magnetic circuit is
closed, that the field is dark, on closing the circuit, and thus plac-
ing the glass in a strong field of magnetic force, the azimuth of
the polarized light is so changed that a perceptible amount gets
through, and the analyzer must be rotated 60 in order to again cut
it off and render the field dark as before. This angle through
which the light is turned, is, however, in addition to the length of
the stratum of the medium through which it is compelled to pass,
directly proportional to the strength of the current producing the
magnetism (or rather to that resolved part of the magnetic force
produced by the current, which is in the direction of the ray).
The amount of the rotation also depends upon the refractive
energy of the medium subjected to the magnetic strain. The rela-
tion is sometimes stated thus:  "The angular rotation of the plane
of polarization is numerically equal to the amount by which the
magnetic potential increases from the point at which the ray enters
the medium to that at which it leaves it, multiplied by a coeffi-
cient, which, for diamagnetic media (like glass), is generally posi-
tive."  Maxwell.
first and second kind. An elementary discussion of the principal features
of
vortex motion, involving only the simplest Quarternion notions, is given
in
Prof. Clifford's recently published "Elements of Dynamics - Part
I,"
page
191, et seq. Sir Wim. Thompson has also published an extensive paper in the
Trans. of the Royal Soc., Edin. Vol. 8 for 1869, in which many new theories
are established and many illustrations of vortex motions in fluids are given,
by means of real or or ideal electro-magnets variously arranged. A sum-
mary of several of these theories and analogies will be found in Thompson's
" Reprint of Papers on Electro-statics, and Magnetism."-
London,
1872. Aln
earlier ?paper, suggesting the idea of vortex atoms, was published in Vol.
34,
p. 15, of the Phil. Mag., 1867. London, Dublin and Edinburgh.
245


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