154 



The Dancing Mouse 



R 



FIGURE 21. Ground plan of color 

 discrimination apparatus. E, E, exits 

 from electric-boxes. LB, light-box; 

 R, G, R, filter boxes on carrier; L, left 

 electric-box; /?, .right electric-box; 1C, 

 induction apparatus; C, electric cell; 

 K, key ; 5, millimeter scale. 



green-left, red-right to green- 

 right, red-left was to push the 

 carrier towards the right until 

 the green filter covered the 

 hole on the right at the end of 

 the electric-box. When this 

 had been accomplished the red 

 filter at the left end of the 

 carrier covered the hole on the 

 left at the end of the electric- 

 box. Thus quickly, noiselessly, 

 easily, and without introducing 

 any other change in conditions 

 than that of the interchange of 

 lights, the experimenter was 

 able to shift the positions of 

 his colored lights at will. 



In the tests which are now 

 to be reported, three portions 

 of the spectrum were used : 

 the red end, the blue- violet 

 end, and a middle region, 

 chiefly green. The red light 

 was obtained by the use of a 

 filter which was made by plac- 

 ing two plates of ruby glass in 

 one of the glass boxes, filling the 

 box with filtered water and then 

 sealing it to prevent evapora- 

 tion. The blue- violet was ob- 

 tained by the use of a filter box 

 which contained a 5 per cent 

 solution of copper ammonium 



