A manual of photographic chemistry, theoretical and practical . or more of these overlap-ping each other; thus the red and yellow spaces intermingledconstitute orange ; the yellow and blue spaces, green. The composition of white light from the seven prismaticcolors may be roughly proved by painting them on the face of 326 OPTICS OF PHOTOGRAPHY. a wheel, and causing it to rotate rapidly; tliis blends them to-gether, and a sort of grayish-white is the result. The white isimperfect, because the colors employed cannot possibly beobtained of the proper tints, or laid on in the exact propor-tions. T
A manual of photographic chemistry, theoretical and practical . or more of these overlap-ping each other; thus the red and yellow spaces intermingledconstitute orange ; the yellow and blue spaces, green. The composition of white light from the seven prismaticcolors may be roughly proved by painting them on the face of 326 OPTICS OF PHOTOGRAPHY. a wheel, and causing it to rotate rapidly; tliis blends them to-gether, and a sort of grayish-white is the result. The white isimperfect, because the colors employed cannot possibly beobtained of the proper tints, or laid on in the exact propor-tions. The decomposition of light is effected in other ways besidesthat already given: First, by reflection from the surfaces of colored bodies. Allsubstances throw off rays of light which impinge upon the re-tina of the eye and produce the phenomena of vision. Coloris caused by a portion only, and not the whole, of the elemen-tary rays, being projected in this way. Surfaces termed whitereflect all the rays ; colored surfaces absorb some and reflect Violet. Fig. 15. others; thus red substances reflect only red rays, yellow sub-stances, yellow rays, etc., the ray which is reflected in all casesdeciding the color of the substance. Secondly, light may be decomposed by transmission throughmedia which are transparent to certain rays, but opaque toothers. Ordinary transparent glass allows all the rays constitutingwhite light to pass; but by the addition of certain metallicoxides to it whilst in a state of fusion, its properties are modi-fied, and it becomes colored. Glass stained by oxide of cobaltis permeable only to blue rays. Oxide of silver imparts a pureyellow tint; oxide of gold or suboxide of copper, a rubyred, etc. PEOPEETIES OF LIGHT. Light possesses a threefold property, viz., heating, illumi-nating, and chemical action, now usually termed properties have up to a recent period been associated with EEFEACTION OF LIGHT. 327 certain rays; for example, the yell
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Keywords: ., bookcentury1800, bookdecade1880, bookidma, booksubjectphotography
