Smithsonian Miscellaneous Collections Volume 71, No. 1 (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. 1920 Excerpt: ...in winter the intensity at noon may drop about. TABLE 290.--Spectral Variation of Sensitiveness as a Function of Intensity. Radiation is easily visible to most eyes from 0.330 M (violet) to 0.770 M (red). At low intensities near threshold values (gray, rod vision) the maximum of spectral sensibility lies near 0.503 ft (green) for 90% of all persons. At higher intensities, after the establishment of cone vision, the max. shifts as far as 0.560 11. Sec Table 297 for more accurate values of sensitiveness after this shift has been accomplished. The ratio of optical sensation to the intensity of energy increases with increasing energy more rapidly for the red than for the shorter wave-lengths (Purkinjc phenomenon); i.e., a red light of equal intensity to the eye with a green one will appear darker as the intensities are equally lowered. This phenomenon disappears above a certain intensity (above 10 millilamberts). Table due to Nutting, Bulletin Bureau of Standards. TABLE 291.--Threshold Sensibility as Related to Field Brightness... rceives with ease and comfort a billion-fold range of intensities. The following data were obtained the eye fully adapted tu the sensitizing field, B, the field flashed off, and immediately the intensity, T, of a test (angular size at eye about 5") adjusted to be just visible. This table gives a measure of the brightness, T, nece to just pick up objects when the eye is adapted to a brightness, B. Intensities are indicated log intensities in i lamberts. Blanchard, Physical Review, it, p. 81, Igis. THE EYE AND RADIATION-TABLE 292.--Heterochrony tic Threshold Sensibility. The following table shows the decrease in sensitiveness of the eye for comparing intensities of different colors. The numbers in the body of the table correspond t...