Figure 8 — Sketch of dark cabinet and stimulus box. The colored bands are ad- 

 mitted through windows W, W and \\\ They pass to the mirrors MS M 

 and M^ and thence to the plaster-paris surfaces of the stimulus boxes .SS S 

 and S-. The small diagram shows the details of the construction of the " satu- 

 ration box." The ground glass surface S^ receives monochromatic light from 

 the speculum mirror above and white light from the tungsten miniature F, 

 below. 



