TABLES 292-295. 



THE EYE AND RADIATION. 



TABLE 292. He tero chroma tic Threshold Sensibility. 



257 



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 to the line marked T/B of Table 291. The intensity of the field was 

 probably between 10 and 100 millilamberts (25 photons). 



TABLE 293. Contrast or Photometric Sensibility. 



For the following table the eye was adapted to a field of o.i millilambert and the Sensitizing field flashed off. A 

 neutral gray test spot (angular size at eye, 5 X 2.5) the two halves of which had the contrast indicated (\ transparent, 

 $ covered with neutral screen of transparency = contrast indicated) was then observed and the brightness of the 

 transparent part measured necessary to just perceive the contrast after the lapse of the various times. One eye only 

 used, natural pupil. Blanchard, Physical Review, n, p. 88, 1918. Values are log brightness of brighter field in 

 millilamberts. 



TABLE 294. Glare Sensibility. 



When an eye is adapted to a certain brightness and is then exposed suddenly to a much greater brightness, the 

 latter may be called glaring if uncomfortable and instinctively avoided. Observers naturally differ widely. The data 

 are the means of three observers, and are log brightnesses in millilamberts. The glare intensity may be taken as roughly 

 1 700 times the cube root of the field intensity in millilamberts. Angle of glare spot, 4. Blanchard, Physical Review, 

 loc. cit. 



TABLE 295. Rate of Adaptation of Sensibility. 



This table furnishes a measure of the rate of increase of sensibility after going from light into darkness, and the 

 values were obtained immediately from the instant of turning off the sensitizing field. Both eyes were used, natural 

 pupil, angular size of test spot, 4.9, viewed at 35 cm. Blanchard, loc. cit. Retinal light persists only 10 to 20 m when 

 one has been recently in darkness, then in a dimly lighted room; it persists fully an hour when a subject has been in 

 bright sunlight for some time. A person who has worked much in the dark "gets his eyes" quicker than one who has 

 not, but his final sensitiveness may be no greater. 



SMITHSONIAN TABLES. 



