COLOR BLINDNESS OF CATS 117 



by the animal. Rather they are meant to point out all of the 

 "secondary criteria" by which the animal may discriminate the 

 colored papers. When an animal has confused a color and a 

 gray for some six hundred trials, though quite accustomed to 

 making discriminations, it seems fair evidence that he is unable 

 to discriminate them by secondary criteria, nor even by the 

 primary one, and that they appear the same to him. 



After a confusion had been made between two colors (or a 

 color and a gray) it seemed desirable to define it accurately for 

 the sake of reproducing it at will. This we have done by stating 

 its "flicker equivalent," a term used by Polimanti 3 to avoid any 

 theoretical implication. A comparison of the equivalents we 

 obtained with those of Cole and Long 4 shows that the flicker 

 test reveals any fading of a colored paper and that the Bradley 

 papers, except the violet hues, remain constant for a long time, 

 if kept in darkness when not in use. In determining the flicker 

 equivalents of the colored papers the decision was invariably 

 based on inspection by two observers, and each color was tested 

 with the gray just darker and just lighter than that with which 

 it gave the minimum of flicker, a process which Ives 5 aptly calls 

 "stepping off in various directions." Hence the decision in 

 each case was the result of the comparison of at least three 

 amounts of flicker. The method of determination was that 

 described by Cole and Long (pp. 660-664). When a color gives 

 a slight amount of flicker with each of two consecutive grays 

 it is designated as between the two by giving the numbers of 

 both. Thus Gray 1-2 means a gray which gives a slight amount of 

 flicker when rotated with Hering Gray 1 or Hering Gray 2, a 

 large amount when rotated with Gray 3, but which gives no 

 flicker with those papers which in turn give very slight amounts 

 with Grays both 1 and 2. These intermediate flicker equivalents 

 occur because there are but fifty gray papers with which to 

 test ninety or more colored papers. Cole and Long met this 

 condition by establishing three amounts of flicker between each 

 pair of grays, (p. 662). As we cannot adapt that device to the 



3 Polimanti, O. Ueber die sogennante Flimmer-Photometrie. Zeitschrijt fuer 

 Psychologic vol. 19, 1899, S. 263ff. 



4 Cole, L. W. and Long, F. M. Visual discrimination of Raccoons. Jour, of 

 Comp. Neur. and Psych., vol. 19, 1909, p. 657ff. • 



5 Ives, H. E. Photometry of lights of different colors. Phil. Mag., 1912, p. 858. 



