Popular Astronomy Volume N . 18 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1910 Excerpt: ...affects the nerves composing the retina of the eye. These waves express themselves as different colors. Average daylight or so-called sunlight is a clearer and whiter light than that from any artificial lighting source thus far perfected. When allowed to fall upon a prism, however, it is immediately seen that this white light is composed of seven visible and easily distinguished colors, namely; red, orange, yellow, green, blue, indigo and violet in varying proportions. These colors are the seven fundamental or visible spectral colors which form a part of the total radiation from the Sun. This wave radiation or emission from the Sun affects the human sight only in that portion of the spectrum between the red and blue limits. The so-called infra-red and ultra-violet extremes of the spectrum, which lie on either side of these values of red and blue, form the larger portion of the radiation from artificial sources and due to their wave lengths they are lost to view. It can readily be shown that the most efficient illuminant would be one in which all of the radiation properly proportioned as to color would occur between the limits of red and blue and therefore would be visible. Daylight is composed of varying proportions of the seven visible colors. The greatest variation in the quality of daylight may be attributed to the varying percentages of these fundamental colors. In all forms of daylight a certain relationship exists between its different component colors. A relation remaining practically the same under most conditions is that the amount of blue light in nature is maximum while the red is minimum. Such a relation of the fundamental colors can be likewise noted in all growths in which the reds are produced to a less degree while the blues and violets are ...