. 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 177 Using the darkening of ZnS as a detector, Clark (18, cf. page 246) has observed the ultra-violet, cut off by a microscope slide (see curve 15, Fig. 9) for both daily and seasonal variation at Baltimore, Md. Figure 23 (18) shows the daily fluctuation for clear days at different representative times of the year. It will be noticed on comparison with Fig.
. 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 177 Using the darkening of ZnS as a detector, Clark (18, cf. page 246) has observed the ultra-violet, cut off by a microscope slide (see curve 15, Fig. 9) for both daily and seasonal variation at Baltimore, Md. Figure 23 (18) shows the daily fluctuation for clear days at different representative times of the year. It will be noticed on comparison with Fig. 18 that the ultra-violet rises more sharply to a maximum and then decreases more rapidly than the total radiation, owing to the greater influence of atmospheric Oct Nov. Dec. Jnn. Feb. March April May June Julj( Aug, Sep. Oct. Nov Dec. Jan. Feb. March Apnl Fig. 24.—Seasonal variatioa in ultra-violet radiation. {Zinc sulfide measurements by Clark, 18.) The annual variation in ultra-violet radiation lags somewhat behind that of the total radiation, as will be seen by comparing Clark's values, Fig. 24, with those of Kimball (page 224). The variations in ultra-violet intensity and short-wave-length limit have been attributed by many observers to the absorption of atmos- pheric ozone. According to Dobson (18), the effective depth of ozone in the atmosphere amounts to to cm. at normal temperature and pressure. Figure 25 shows the seasonal fluctuation in effective depth observed by Dobson at Oxford averaged over the years 1925 to 1928, inclusive. The absorption coefficients for ozone under standard condi- tions are given by curve C, upper section of Fig. 2. Corresponding percentage transmissions are given for cm. depth at the right. By shifting this scale up one-half division, one obtains the value for cm. depth. This indicates an effective cut-off in the region of 2900 A, rising. Please note that these images are extracted from scanned page images that
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Keywords: ., bookau, bookcentury1900, booksubjectbiology, booksubjectradiation
