. Biological effects of radiation; mechanism and measurement of radiation, applications in biology, photochemical reactions, effects of radiant energy on organisms and organic products. Radiation; Biology. VISIBLE AND NEAR-VISIBLE RADIATION 171 recently, aluminum mirrors have been developed commercially Avhich exhibit a much higher reflectance over the entire range (better than 80 per cent in the ultra-violet, and exceeding slightly tarnished silver through- out the visible). Quantitative data, however, are not yet available. If a diffusing surface is desired, powders may be applied to a tacky
. Biological effects of radiation; mechanism and measurement of radiation, applications in biology, photochemical reactions, effects of radiant energy on organisms and organic products. Radiation; Biology. VISIBLE AND NEAR-VISIBLE RADIATION 171 recently, aluminum mirrors have been developed commercially Avhich exhibit a much higher reflectance over the entire range (better than 80 per cent in the ultra-violet, and exceeding slightly tarnished silver through- out the visible). Quantitative data, however, are not yet available. If a diffusing surface is desired, powders may be applied to a tacky varnish surface (Fig. 16, shows the reflectance of the various materials).. '2,000 2,400 2,800 4,000 4,400 4800 5,200 5,600 6,000 Wave Length Fig. 17.—Reflectance of commercial paints. (Luckiesch, 47.) In case commercial paints are used, selection may be made in accordance with Fig. 17 (47). SOURCES OF CONTINUOUS EMISSION SUN Despite the extensive development of artificial sources of radiation, even for experimental purposes the sun must be considered a source of primary importance, because of its high intensity and desirable wave- length distribution. The chief difficulties which one encounters in using this source arise from the great variability of the radiation as it reaches the surface of the earth. The causes of this variability are as follows: variation in distance from sun to earth; influence of the earth's atmosphere, affected by altitude or air mass; variability of water vapor and ozone; and the presence of materials due to artificial conditions such as dust and smoke. During a clear summer day at sea level (Washington, D. C), the total solar radiation received on a horizontal surface varies according to the dotted curve in Fig. 18, a record from the October, 1924, Monthly Weather Review by Kimball (43, cf. page 478). A portion of this total radiation is due to scattering from the sky. While the sky radiation attains a maximum at noon, its relative con-
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Keywords: ., bookau, bookcentury1900, booksubjectbiology, booksubjectradiation
