570 KARL T. WATJGH 



Conclusions: Our results do not indicate any ability to dis- 

 criminate between red and green or between blue and green. The 

 black-eyed mice discriminate between red and white light when 

 they are of equal brightness to the human eye. When the red is 

 made darker the discrimination is slightly improved. When the 

 red is made brighter the discrimination is not so good. The power 

 to discriminate seems to fall away as the brightness of the red 

 relative to the white increases for the human observer. 



PROBLEM 3. PERCEPTION OF FORM 



Apparatus and Method: In these experiments the appar- 

 atus used was the same as that already described in connection 

 with the problem of the discrimination of direct light stimuli, 

 (see p. 557) 



Pieces of black cards were substituted for the liquids in the 

 cells, and in these cards were cut holes of the forms desired for 

 the test. The forms selected were, a circle, 4 cm. in diameter, 

 and an X-shaped figure which was inscribable in a square of 4 cm. 

 diameter (fig. 5). I made these two figures of equal area in 



Fig. 5 Cards for study of perception of form. 



order that difference in the amount of light passing through 

 them might not serve as a condition of discrimination. 



Two incandescent lamps were used as sources of light. Each 

 of these was of 13 candle-power, as tested by the Lufnmer-Brod- 

 hun photometer. The lamps were placed in the light box at a 

 distance of 50 cm. from the apertures. Additional pieces of ground 

 glass were placed against the black cards inside the cells, in order 



