LIGHT OF DIFFERENT WAVE-LENGTHS BY FISH 



17 



and at the margins of the lens aperture, the curves shown 

 in figure 7 were prepared under the direction of Professor 

 John F. Shepard. He also prepared the following descrip- 

 tion and determinations. The conditions of illumination 



Fig. 8 



Diagram to show the relations of light energy at the center and margin of the 

 lens aperture. 



were as shown in the diagram, figure 8. The effective 

 portion of the Nernst filament used was 28 mm. long. 

 The slit was placed 30 mm. below the filament, and the 

 lens was 188 mm. below the slit. The distance from the 

 lens to the highest portion of the stimulus plate which 

 received illumination was 166 mm. The aperture of the 

 lens was 80 mm. square, and the stimulus plate was 125 



