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In 1813 Seebeck discovered the polarization of light by tourmaline. That same year Brewster discovered those magnificent bands of colour that surround the axes of biaxal crystals. In 1814 Wollaston discovered the rings of Iceland spar.
'Circular polarization, like circular motion generally, may of course be of two kinds, which differ only in the direction of the motion. Hence if the plate be turned round through 90° we shall see that the bands are shifted in a direction opposite to that in which they were moved at first.
It may be said to partake somewhat of the nature of the magnetization of a bar of steel; for it consists in what we might call the polarization, by an effort of the human will, of a number of parallel lines of astral atoms reaching from the operator to the scene which he wishes to observe.
The motion of ether-particles thus caused may be represented by vibrations, which form the starting-point of light and heat-waves. In quite a similar manner we may also, according to Dr. Siemens, represent the light-phenomenon occurring when an electric current is sent through gases, which always takes place when the maximum of polarization belonging to them is exceeded.
When it is understood that Mental Induction is possible, that is that mental states may be produced by "induction" from others, then we can readily see how a certain rate of vibration, or polarization of a certain mental state, may be communicated to another person, and his polarity in that class of mental states thus changed.
It is here are the Hills of T'ang, the metropolis of Natural Magic perhaps for all the world; and the mind and imagination of China, centered here, were receiving a new polarization; something richer and more luminous was being born. Contemporary with Tao Yuan-ming was Ku Kaichih, the first supreme name in painting.
Every time, however, that we deal with general phenomena which are independent of these special conditions, the parallelism is perfect; and with the waves, we have put in evidence the reflexion, refraction, total reflexion, double reflexion, rotatory polarization, dispersion, and the ordinary interferences produced by rays travelling in the same direction and crossing each other at a very acute angle, or the interferences analogous to those which Wiener observed with rays of the contrary direction.
This want of homogeneity may, according to M. Quincke, be due to the existence of particles suspended in a liquid in contact with another liquid miscible with it and enveloping it as might a membrane, and the phenomena of polarization would thus be quite naturally explained. See Proc. Roy. Soc. A., 23rd July 1906.
That they are identical in all respects cannot of course be the case, for if they were they would act in the same manner upon all instruments, the eye included. The identity meant is such as subsists between one colour and another, causing them to behave alike as regards reflection, refraction, double refraction, and polarization. Let us here run rapidly over the resemblances of light and heat.
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