The Polarization of Light
The importance of the study of polarization was considerably increased when Huygens made the discovery that the two rays, the extraordinary as the ordinary, were completely polarized in planes mutually perpendicular to each other. In passing, it may be mentioned that the above fact forms the basis upon which many pieces of apparatus used in studying polarized light have been designed. It is only necessary to cause one of the rays to be deflected, or removed in some other way, in order for the remaining part of the light which emerges from the crystal to be completely polarized. Several minerals, like tourmaline, possess the property of being able, for transmission, either to diminish the intensity of one of the rays very considerably, or else absorb it entirely. A plate of such a substance constitutes a very simple polarizer; a second similar plate can be used for the analyser.