related and mutually dependent, that they are convertible, as it were,
into one another, and possess equivalents of power in their action....
This strong persuasion,' he adds, 'extended to the powers of light.'
And then he examines the action of magnets upon light. From conversation
with him and Anderson, I should infer that the labour preceding this
discovery was very great. The world knows little of the toil of the
discoverer. It sees the climber jubilant on the mountain top, but
does not know the labour expended in reaching it. Probably hundreds of
experiments had been made on transparent crystals before he thought of
testing his heavy glass. Here is his own clear and simple description
of the result of his first experiment with this substance:--'A piece of
this glass, about two inches square, and 0.5 of an inch thick, having
flat and polished edges, was placed as a diamagnetic[1] between the
poles (not as yet magnetized by the electric current), so that the
polarized ray should pass through its length; the glass acted as air,
water, or any other transparent substance would do; and if the eye-piece
were previously turned into such a position that the polarized ray was
extinguished, or rather the image produced by it rendered invisible,
then the introduction of the glass made no alteration in this respect.
In this state of circumstances, the force of the electro-magnet
was developed by sending an electric current through its coils, and
immediately the image of the lamp-flame became visible and continued so
as long as the arrangement continued magnetic. On stopping the electric
current, and so causing the magnetic force to cease, the light instantly
disappeared. These phenomena could be renewed at pleasure, at any
instant of time, and upon any occasion, showing a perfect dependence of
cause and effect.'

In a beam of ordinary light the particles of the luminiferous ether
vibrate in all directions perpendicular to the line of progression; by
the act of polarization, performed here by Faraday, all oscillations
but those parallel to a certain plane are eliminated. When the plane
of vibration of the polarizer coincides with that of the analyzer, a
portion of the beam passes through both; but when these two planes
are at right angles to each other, the beam is extinguished. If by any
means, while the polarizer and analyzer remain thus crossed, the plane
of vibration of the polarized beam between them could be changed,
then