30 



AMES, PKOCTOR AND AMES. 



should be depicted approximately in the way they would be imaged on 

 the retina. This was shown by the obtrusive unnatural appearance of 

 a painting which Blanche Ames and Mr. Ames made in about 1912 

 in which they put in the approximate distortion which exists in the eye 

 but painted all the detail as it appeared while looking directly at it. 

 In later pictures painted by Blanche Ames in which the detail of the 

 distorted features approximated in its characteristics the way it is 

 imaged upon the retina the distortion ceases to be noticeable and gives 

 a pleasing and natural effect. 



Another interesting effect due to distortion results from the fact 

 that objects away from the optical axis are imaged in smaller relative 

 size than those near the axis. This effect is very evident in Figures 

 31(a) and 32(a). In Figure 31(a) taken with the eye lens the statu- 

 ette is much larger relative to the books than it is in Figure 32(a), 

 although the statuette in both pictures is the same size. 



Y\ith a larger angular field this relative difference in size is still 

 greater. In the eye where the field is between four and five times that 

 in the figures the effect is very marked. This is probably the reason 

 why a distant mountain appears so much larger to us when we look 

 at it than it does in a photograph taken with a corrected lens. 



Chapter V. 

 SENSITIVITY OF THE RETINA. 



As stated in the introduction, the character of the picture we get on 

 the retina is determined not only by the kind of image that is formed 

 by the lens system of the eye but also by the nature of the sensitive 

 surface upon which the image falls, that is by the sensitivity of the 

 retina. 



To gain a thorough knowledge of our retinal picture it is necessary 

 therefore to know the sensitivity of the retina in its various parts both 

 to light and to color. 



Unfortunately relatively very little is known as to the sensitivity of 

 the retina as a whole. Considerable is known about the sensitivity of 

 the fovea, i.e., that part of the retina which is on the axis of vision, but 

 very little definite knowledge exists as to the sensitivity of the peri- 

 pheral parts. 



A great deal of work has been done on the limits of the color fields, 

 i.e., as to the limit of obliquity at which different colors are visible. 



