CHAP, v.] THE STEREOSCOPE. 279 



CHAPTER V. 



THE STEKEOSCOPE. 



I. VISION IN BELIEF. WHEATSTONE'S REFLECTING STEREOSCOPE. 



WHEN we examine, with the naked eye, a landscape, tree, or monu- 

 ment, we have not simply the sensation of a picture, that is to say, of 

 a flat representation of the objects severally portrayed on our retina. 

 We have, besides this, a clear and lively impression of the relief 

 of the objects, that is, of their unequal distances, and the intervals 

 which separate them; the depth of space is an intuitive sensation 

 resulting from the normal phenomenon of vision. 



Why do paintings never produce the same impressions as the 

 objects themselves, whatever may be the merit of the artist who has 

 created them, however faithful the perspective, the contour, the 

 colouring of the objects, and the lights and shades ? It is a great 

 and rare talent which throws atmosphere into a picture, depth into 

 a landscape ; but even when the artist has succeeded, the idea of 

 relief falls very short of nature. 



It was long before this difference between a flat representation and 

 the real view vision in relief was accounted for. There is, however, 

 a very simple method of solving the problem. If, after observing 

 a foreground with both eyes we examine it with one, either the 

 right or left, the sensation of relievo, of depth, disappears ; or at 

 least it is to a great extent diminished. The landscape itself seems 

 a painting in which the different lines are confused together. This 

 difference between ordinary or binocular and monocular vision, 

 is almost imperceptible for distant objects ; it is greater in propor- 

 tion as the objects are nearer ; it attains a maximum for those in the 

 foreground. 



