He also
proved that the amount of the rotation is proportional to the length
of the diamagnetic through which the ray passes. He operated with
liquids and solutions. Of aqueous solutions he tried 150 and more,
and found the power in all of them. He then examined gases; but
here all his efforts to produce any sensible action upon the
polarized beam were ineffectual. He then passed from magnets to
currents, enclosing bars of heavy glass, and tubes containing
liquids and aqueous solutions within an electro-magnetic helix.
A current sent through the helix caused the plane of polarization to
rotate, and always in the direction of the current. The rotation
was reversed when the current was reversed. In the case of magnets,
he observed a gradual, though quick, ascent of the transmitted beam
from a state of darkness to its maximum brilliancy, when the magnet
was excited. In the case of currents, the beam attained at once its
maximum. This he showed to be due to the time required by the iron
of the electro-magnet to assume its full magnetic power, which time
vanishes when a current, without iron, is employed. 'In this
experiment,' he says, 'we may, I think, justly say that a ray of
light is electrified, and the electric forces illuminated.' In the
helix, as with the magnets, he submitted air to magnetic influence
'carefully and anxiously,' but could not discover any trace of
action on the polarized ray.
Many substances possess the power of turning the plane of polarization
without the intervention of magnetism.
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