LIGHT OF DIFFERENT WAVE-LENGTHS BY FISH 



19 



Intensity at P=K 



/I09 



w + 6.38 



188 



Reducing- Intensity at P=K 



[218\/(218)2 + 1600]dz 



[(40+z)2 + (218)- + 1600p 

 109 



w -h 6.38 



188 



109 



— w + 6.38 



188 



48374 dz 



[z2+80z+50724P 



109 

 — w + 6.38 



188 



For the limiting case when the slit is removed, 



14 



The intensity at 0=K 



The intensity at P==K 



2182dz 



(218= +z2)2 

 — 14 



14 



[218\/218- + 1600]dz 



[2182 + 1600 + (40 tz)2]2 

 — 14 



From these determinations the curves of figure 7 are plotted. 



The curve " Point " (fig. 7) shows the intensities of 

 light at the center of the lens aperture for different widths 

 of the slit, while the curve " Point P " shows the intensi- 

 ties of the light for point P, in figure 8, at the border of 

 the lens aperture, for different slit-widths. The intensities 

 are expressed on the ordinate by means of an arbitrary 

 scale. It is to be noted that there is less difference in the 

 light distribution between the center and the margin with 

 a wider or with a narrower slit width than with a slit of 

 24 cm. Whenever a stimulus plate is illuminated without 

 the use of the slit, or with any width in excess of 35 mm. 

 the light passing through the lens aperture at its center 

 will be as 100 per cent to 90 at the border. From the 

 graph (fig. 7) it is plain that when the slit width is 24 mm. 

 this difference in intensity will be maximum or the ratio 

 will be as 100 to 71, and the difference between the center 

 and the margin will be less with narrower slit widths. In 



