VISION AND THE TECHNIQUE OF ART. 35 



The conditions chosen were where the background behind the object 

 at the point of convergence was of an indeterminate nature such as a 

 mass of branches or foliage. The absence of any marked contours 

 under such conditions would not call for the suppression of parts of 

 either retinal image. 



Leaving out the effect of ocular movement and the fusion of doubled 

 images the brain under such conditions may be considered as receiving 

 two superimposed pictures of the object field as seen from each eye. 



To reproduce this effect a camera was devised which, by means of a 

 reflector and half silvered prism, produced superimposed pictures of the 

 landscape as viewed from two points of view, — the distance between 

 which was the same as that between the eyes. The detail' in these 

 pictures superimposed where the axis of the two systems crossed, as 

 the two monocular images do at the point of convergence. The de- 

 tails in all other parts of the pictures were more or less doubled due 

 to the parallax of the two systems. 



Figure 41 shows such a "binocular" photograph. Figure 42 shows 

 an ordinary photograph of the same scene. 



The following characteristics will be noted in the "binocular" 

 picture: 



First, there is a "broadening" of everything in a horizontal direc- 

 tion. At the convergence point this is due to seeing more of the sides 

 of an object. At other points in the scene it is due to the doubling in a 

 horizontal direction resulting from the parallax. This effect of the 

 "broadening" of a scene when viewed binocularly can be noticed by 

 anyone by first observing the scene with one eye and then with two. 



Second, there is an increase in contrast values between the lights 

 and darks in the objects at the convergence point relative to that in 

 other parts of the picture. This is due to the fact that at the con- 

 vergence point the darks and lights superimpose and so reinforce each 

 other while in all other parts of the picture they tend not to superim- 

 pose and so counteract each other. Probably some such effect as this 

 exists in our binocular impression. 



Third, there is a doubling up of the images of objects not at the 

 convergence point, the extent of the separation of the doubled images 

 depending upon their distance from that point. The seeing of objects 

 not at the convergence point in doubled images is supposed to be one 

 of the factors that gives us our idea of relief, the extent of the doubling 

 suggesting the distance of the object from the convergence point. The 

 impression we receive on our mind from these doubled images is differ- 

 ent from that shown in Figure 41 due to the modifying effects of the 



