Section III., 19l:i. [221] Trans. R.S.C. 



The Sensitiveness of the Eye to Light and Color. *^ 



By T. A. Neelin, M.A. 

 Presented by Prof. Frank Allen, Ph. D., F. R.S.C. 



(Read May 28, 1913) 



In an extensive paper on "The Luminous Equivalent of Radiation/' 

 Nutting t thus summarizes some of the more important characteristics 

 of the visual response to radiation: 



I. "Sensibility to Slight Differences in Wave Length, has two 

 pronounced maxima, one in the yellow and one in the green; and two 

 slight maxima in the extreme blue and red. These maxima vary 

 considerably with the individual and probal^ly also with the intensity 

 of the radiation used." 



II. "Sensibility to Radiation of Varying Intensity: 

 Sensibility falls off steadily with increasing intensity. It is approx- 

 imately inversely proportional to the intensity over a wide range. 

 The ratio of optical intensity to intensity of radiation increases more 

 rapidly for red than for blue and green (Purkinje phenomenon).^' 



III. "Sensibility to small Differences in Intensity": 



The least perceptible increment measured as a fraction of the 

 whole is approximately: 



(1) Independent of Intensity {Fechnefs Law). It is about -016 

 for moderate and high intensities and greater for very low and extremely 

 high intensities. 



(2) Independent of Wave Length {Konig's Law) at constant 

 luminosity, extremes again excepted. 



(3) Independent of the Individual." 



With the exception of number I the above characteristics of the 

 visual response to radiation have been verified by several observers. 

 But concerning the sensibility of the retina to slight changes in the 

 wave-length of the light no investigation of a very exhaustive nature 

 appears to have been conducted. Perhaps the best recent data are those 

 due to Dr. Olga Steindler;î but even there a spectrum of only one 

 intensity appears to have been considered. With a view then, in the 

 first place of verifying results already o1)toin':^d bv Stoindlor and others, 



*To be printed also in the Physical Review. 



tP. G. Nutting: Bulletin of the Bureau of Standards, 1908, Vol. 5, No. 2, page 

 265. 



JWien Sitz.: lia, 115, pp. 1-24, 1906. 



