The Sense of Sight : Color Vision 1 6 1 



necessary to alter the conditions of the experiment. The 

 only criticism of the above method of excluding brightness 

 discrimination, of which I could think, was that the red at no 

 time had been brighter than the green. In other words, that 

 despite a value of 1800 candle meters for the red and only 

 1 8 candle meters for the green, the latter still appeared the 

 brighter to the mouse. To meet this objection, I made the 

 extreme brightness values i and 1800 candle meters in some 

 of the later series, of which the results appear in Table 24. 

 From day to day different degrees of brightness were used, 

 as is indicated in the second column of the table. Instead 

 of having first one color and then the other the brighter, 

 after the fourth series I changed the position of the lights 

 each time the position of the filters was changed ; hence, the 

 table states a certain brightness value for each color instead 

 of for each electric-box. 



Series 5 to 14 so clearly indicated discrimination, that it 

 seemed necessary to devise some other means than that of 

 changing the brightnesses of the colored lights themselves 

 to test the assumption that the animals were choosing the 

 brighter light. I therefore removed the light filters so that the 

 colors which had been present as conditions of discrimination 

 were lacking, and arranged the apparatus so that first one box, 

 then the other, was illuminated the more brightly. The pur- 

 pose of this was to discover whether as the result of their 

 green-red training the mice had acquired the habit of choos- 

 ing uniformly either the lighter or the darker box. One 

 series was given under the conditions of illumination specified 

 in Table 24 with the result that the brighter box was chosen 

 eight times in ten by No. 151 and every time by No. 152. 

 Since neither of these individuals had previously been trained 

 by white-black tests to go to the white, and since, furthermore, 

 the dancers usually manifest a slight preference for the lower 



