66o Journal of Comparative Neurology and Psychology. 



but differently colored objects. They seem to have answered only 

 the first question (as restated above). Our experiments sought for 

 an ansv^er to the second question in the case of the raccoon. 



The objects which were presented to the raccoons to discriminate 

 were thirty-nine of the Milton Bradley colored papers and five of the 

 Hering gray papers of equal (and nearly equal) brightness with 

 certain groups of the colors, as determined by Rood's flicker method. ^° 

 According to their respective brightnesses, these forty -four papers 

 were divided into six groups of six each, one group of five, and three 

 papers of equal brightness with three others were substituted for the 

 latter during a part of the experiments recorded in Table 14. The 

 flicker method as employed by Rood is inexact from the standpoint of 

 human psychology, yet the flicker principle is being employed increas- 

 ingly in color photometry. ^^ 



Our thanks are due to Professor Titchener for retesting for us by 

 the flicker method the first group of colored papers selected and for 

 valuable suggestions with regard to them. We are also indebted to 

 Professor Yerkes for criticism and assistance. 



In order to select our groups of colored papers, we first made fifty 

 Maxwell disks from the successive grays of the Hering series, then 

 ninety disks from the standard colors, the tints, and the shades of 

 the Bradley series. We then selected one of the gray disks, e. g., 

 ISTo. 5, and, under a high illumination of diffused daylight, we com- 

 bined it with an equal area of each of the colored disks in order. The 

 color mixer was made to rotate thirty-three and six-tenths times per 

 second. The observer faced this compound disk of equal parts of the 

 gray and the color at a distance of one meter. If, at this rate of 

 rotation and in this illumination, a colored disk gave no flicker per- 

 ceptible to either of two observers it was assumed to be of equal 

 brightness with the gray. We attempted further to reduce any 

 difference of brightness by testing the raccoons under a much lower 

 illumination than that under which we selected the colors. The 

 colored papers thus selected were afterwards compared as to amount 



"Rood, O. N. On a color system. Amer. Jour, of Sci., vol. 44, pp. 263-270. 

 1892. 



"Titchener, E. B Exp. Psych., vol. 2, Pt. 2, p. 87. 1905. 



