12 



CORA D. REEVES 



d. Apparatus for Regulation of the Intensity and Distribution of Light. 



A plano-convex cylindrical lens (Yerkes 1903) 20 cm. long and 10 cm. wide, with 

 a radius of curvature of 12.5 cm., was divided crosswise into halves. One of these 

 was fitted into the frame at the bottom of the lamphouse in each side (SL in figs. 

 2, 4). The Nemst lamps are placed at the principal foci of the lenses with the 

 glowers parallel to and above the long axis of the lenses. In this position the cylin- 

 drical lenses serve to parallelize the light rays in the direction indicated in figure 4. 

 As the walls of the aquarium are black, the diverging rays which strike them at the 

 sides of the stimulus plates (see fig. 5) are so little reflected as to be scarcely visible. 

 But as the margins of these areas remain parallel they vary only in brightness not 

 in shape. Their variation in brightness will be the same as the variation of the 

 stimulus patches depending upon the slit-width. By this method no direct light 

 from the glowers reaches the floor of the aquarium, and though the whole of each 

 stimulus plate (S in fig. 2) is not illuminated, the patches of light on the two are 

 exactly the same in shape and size. They are rectangular 12.3 cm. by 11.6 cm., 

 and their edges are always sharp and straight across the plates. 



To regulate the light intensity a slit is used (figs. 2, 4, 5). The slit consists of 

 two steel plates and a narrow steel frame which is the size of the inside cross-sec- 



FiG. 5 



Cross-section of one-half of lamphouse through Nemst glower along line uv in 

 figure 1. 



A'^, Nemst glower. 

 0, slit opening. 

 RF, ray filter in kit ki. 

 SL, cylindrical lens. 

 S, stimulus plate of opal ground glass. 

 W, groove in which the frame for the slit slides in and out 



