14 AMES, PROCTOR AND AMES. 



appear white, i.e., without colored edges, no matter in what direction 

 or distance the white light point source is from the point in focus. 



As described in Chapter I if instead of a point source edges are used, 

 as a dark object against a light background, the above described 

 diffusions make themselves evident in the form of chromatic edges. 



Figure 15 shows a photograph taken with a lens, which has approxi- 

 mately the same chromatic aberration as the eye, in the same way and 

 of the same objects as described in Figure 7. The lens was focused as 

 described for Figure 11 for yellow at six feet, the objects being three 

 feet away. The combined images are marked by the orange red edges 

 extending over the dark and the blueness of the white along its edges 

 due to the subtraction of the red and yellow light which has diffused 

 over the black. 



Figure 16 is a similar photograph, the focus of the lens remaining the 

 same, the objects being placed at a distance of about twenty feet. In 

 this case the combined images are characterized by the green and blue 

 extending over the dark and the redness of the white along its edges. 



It is regretted extremely that these pictures cannot be reproduced 

 in color as they not only show these characteristics much more clearly, 

 but are very beautiful. 



Figure 17 is similar to Figure 15 taken with a corrected lens. As 

 would be expected from what has been said of Figures 13 and 14 the 

 images taken through the different filters are all diffused to the same 

 extent. As a result the composite picture shows diffused but no 

 colored edges. 



Once one's attention has been called to them, these characteristic 

 chromatic edges in the retinal images are very easily seen. The 

 aberration of the red rays over the dark, characteristic of images of 

 objects which lie inside the focus, was first noticed in the warm color 

 of black specks on a windowpane viewed from a few feet when the eye 

 is focused on the distant sky. All of the characteristic colored edges 

 can be easily seen with the following arrangement. Against the white 

 wall of a room or a piece of cardboard or sheeting put up at the distance 

 of about twenty feet a black object, preferably one that comes down 

 to fine black points, as iron grill work, black wedges of paper will do. 

 At six feet distance put up any small object to focus on in line with the 

 distant objects. At three feet distance in the same line put up another 

 black object preferably like the first. If the eye is kept focused on the 

 object at six feet the dark edges of the near object appear to have a 

 reddish orange tinge next to which the light appears colder or bluer. 

 The edges of the object at twenty feet, in fact the whole surface if the 



