32 



AMES, PROCTOR AND AMES. 



the fovea. The amount brighter that blue light of different wave 

 length appears is shown in Figure 38. 



This greater peripheral intensity of blue is probably primarily due 

 not so much to the difference in sensitivity of the retina in the two 

 regions as to the absorption of blue light at the fovea by the yellow 

 spot. The yellow spot lies over the fovea, covering an angular area of 

 about six degrees horizontally and four vertically. Its effect is to 

 absorb light of short wave lengths, i.e., blue. 



The effect on our retinal picture of this difference in sensitivity is to 

 cause those parts which are outside the yellow spot to appear more 



Sensitiveness oi 1he T^e-Tiwi 



10° from fovea to 

 that" oi Mellow staot near tVvc 



\t of \iell< 

 1 f 



ova. a.. 



Cooo 



Figure 38. Curve showing ratio of sensitivity of the retina 10° from the 

 fovea to that at the fovea. 



blue. This effect was very evident to Dr. Proctor and Mr. Ames 

 while measuring the astigmatic fields for blue light, the blue light ap- 

 pearing many times brighter when it was a few degrees off the axis 

 than when looked at directly. The sensation is also commonly experi- 

 enced in the falling off of the apparent blueness of something one sees 

 out of the side of the eye when one turns to observe it directly. 



To approximate this effect photographically a yellow spot of approx- 

 imately the proper absorption and of about six degrees in angular size 

 was put in the middle of the blue focal plane filter which with a red and 

 green filter was used to take three color photographs. The exposure 



