The Sense of Sight : Color Vision 159 



Numbers 10 and n exhibited no preference for either of 

 these colors in the series of 20 tests which preceded the 

 training tests, and neither of them gave evidence of ability 

 to discriminate as the result of ten series of training tests. 

 In this case, again, the behavior of the animals was as strongly 

 against the inference that they can tell green from blue as 

 are the records of choices which appear in the table. Granted, 

 that they are unable to discriminate green from blue when 

 these colors are of about the same brightness for the human 

 eye, what results when they differ markedly in brightness? 

 Table 23 furnishes a definite answer to this question. Num- 

 bers 5 and 12 were given eight series of green-blue tests 

 with each light at 18 candle meters. Little, if any, evidence 

 of discrimination appeared. Then, on the supposition that 

 the difference was not great enough for easy discrimination, 

 the blue light was reduced almost to o, the green being left 

 at 1 8. The tests (series 9) immediately indicated discrimi- 

 nation. For series 10 the green was made 64 candle meters, 

 the blue 18, and again there was discrimination. These re- 

 sults were so conclusively indicative of the lack of color 

 vision and the presence of brightness vision, that there ap- 

 peared to be no need of continuing the experiment further. 



Accepting provisionally the conclusion that the dancers 

 cannot tell green from blue except by brightness differences, 

 we may proceed to inquire whether they can discriminate 

 other colors. Are green and red distinguishable? 



Green-red discrimination now was tested by a method 

 which it was hoped might from the first prevent dependence 

 upon brightness. The light in the light-box on the left was 

 so placed that it had a value of 18 candle meters, that in the 

 light-box on the right so that it had a value of 1800 candle 

 meters. Neither light was moved during the first four series 

 of the green-red tests which were given to Nos. 151 and 152. 



