566 KARL T. WAUCxH 



B. Under direct illumination 



Apparatus: The same as that in problem 1, B, fig. 3. The 

 colors used were red, blue and green, obtained by means of the 

 following ray filters and glasses: 



For green — a saturated solution of nickel nitrate. 



For blue — solution of copper ammonia sulphate. 



For red — pieces of ruby glass placed in the cell. 



The three cells in the. slide between the light box and the experi- 

 ment box were filled with the solutions, the two on the outside 

 containing the same solution. By moving the slide a little to 

 one side, the relative positions of the colors were changed, the 

 one previously on the right now appearing on the left. The cell 

 containing the ruby glass was filled with water in order that by 

 the effect of the refraction it might appear to be the same distance 

 away as the other colors. 



In all, fourteen animals were made use of in this experiment : 



1 The gray and white mouse had pigmented eyes. 



Method: The first two colors used were green and red. One 

 of the electric lamps was moved until the intensities of the two 

 colors appeared equal. Judgment was given on this point by 

 five members of the laboratory, after each had been in the dark- 

 room for five minutes. 



