. The Family tutor . one of the plates aboutthe ray as an axis. Light is also polarized when passedobliquely through a bundle of plates ofthin glass, or mica, arranegd as in theFig. 12. The reflection of light from thesurface of various substances is alsoproductive of polariza-tion at an angle whichis peculiar to each sub-stance, and hence calledthe angle of polariza-tion. This angle on glassis found to be 56° phenomena of po-larized light are amongthe most attractive andimportant in the scienceof optics, but theirstudy would lead usaway from our presentobject. Chemical Rays.—Besides th
. The Family tutor . one of the plates aboutthe ray as an axis. Light is also polarized when passedobliquely through a bundle of plates ofthin glass, or mica, arranegd as in theFig. 12. The reflection of light from thesurface of various substances is alsoproductive of polariza-tion at an angle whichis peculiar to each sub-stance, and hence calledthe angle of polariza-tion. This angle on glassis found to be 56° phenomena of po-larized light are amongthe most attractive andimportant in the scienceof optics, but theirstudy would lead usaway from our presentobject. Chemical Rays.—Besides the rays oflight in the solar spectrum which we havealready noticed, and the rays of heat whichwe shall presently consider, there is stillanother class of rays, which, while theyhave a greater refrangibility than theviolet, are also found by the delicateexperiments of Herschel to be present inevery part of the solar spectrum; they havebeen sometimes called the chemical rays,from tlie powerful eifect which they pro-. duce in chemical combinations. Theyact in a manner altogether independent ofthe rays of heat. Chlorine and hydrogengases are made to combine by them withexplosive energy, while in difiuse lightthe union of these gases is slow and quiet. Many metallic salts are changed to adarker colour by their action, as thechloride and iodide of silver, facts whichhave been beautifully applied in the artsof photography by sensitive papers, and ofthe daguerreotype. The last depends onthe sensitiveness of the iodide of silver tothe action of the chemical or more lumi-nous rays of the sun. This power in thenon-luminous rays has been variouslydesignated by the terms actinism, tithoni-city, and energia. The accompanying diagram will enable
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