The Sense of Sight : Color Vision 1 7 1 



TABLE 27 CONTINUED 



Now, as a final test, blue and green glasses were placed over the 

 electric-boxes, the brightness of the two was equalized for the human 

 eye, and the tests of series 18 and 19 were given to No. 2: 



The green was now made much the brighter. 



bright for the human subject, blue 74 candle meters, green 36. 

 Later the brightness of both was first decreased, then increased, 

 in order to ascertain whether discrimination was condi- 

 tioned by the absolute strength of illumination. No evidence 

 of discrimination was obtained with any of the several condi- 

 tions of illumination in seventeen series of ten tests each. 



On the supposition that the animals were blinded by the 

 brightness of the light which had been used in some of the 

 tests, similar tests were made with weaker light. The re- 

 sults were the same. I am therefore convinced that the 

 animals did justice to their visual ability in these experiments. 



Finally, it seemed possible that looking directly at the 

 source of light might be an unfavorable condition for color 

 discrimination, and that a chamber flooded with colored light 

 from above and from one end would prove more satisfactory. 



