Numbers 10 and 11 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. Numbers 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 0, the green being left at 18. The tests (series 9) immediately indicated discrimination. For series 10 the green was made 64 candle meters, the blue 18, and again there was discrimination. These results were so conclusively indicative of the lack of color vision and the presence of brightness vision, that there appeared 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. TABLE 23 GREEN-BLUE TESTS Brightnesses Different for Human Eye Green 18 candle meters Blue 18 candle meters No. 5 No. 12 DATE SERIES 1906 RIGHT WRONG RIGHT WRONG (GREEN) (BLUE) (GREEN) (BLUE) 1 April 10 6 4 5 5 2 11 5 5 7 3 3 12 6 4 7 3 4 13 4 6 7 3 5 14 7 3 5 5 6 15 4 6 6 4 7 16 6 4 8 2 8 17 5 5 4 6 As it was now evident that the intensity difference was not sufficient to render discrimination easy, the blue was reduced to 0 and the green left at 18. 9 17 7 3 8 2 Now the brightnesses were made, green 64, blue 18, just the reverse of those of series of Table 22.