THE STEREOSCOPE. 



530 



each eye sees both ; of these four pictures, two unite to form 

 one, which gives the impression of solidity, while the two others are 

 flat, and so faint as to interfere little if the attention is directed to 

 the central one. 



Stereoscopic views of various objects, produced by photography, 

 may now be had in great variety and at moderate prices. The 

 fig. 295 gives two binocular pictures, in which the difference 

 between the right and left picture is very obvious. A represents 



FIG. 295. 



three concentric circles behind one another ; B is a ten-sided 

 pyramid. The -two binocular pictures of the six-sided column in 

 fig. 292 would, if viewed by means, of a stereoscope, similarly com- 

 bine to give the appearance of solidity. 



Two impressions of printed lines, or of a drawing, which are 

 perfectly alike will appear as a single impression, if they are placed 

 side by side and viewed in the stereoscope like two binocular 

 pictures. But if some portions in one impression are a little 

 more to the left, while the corresponding portions in the other 

 impression stand more to the right, these portions will appear 

 either higher or lower than the rest. Thus in the following two 

 impressions, when looked at by the stereoscope, the 1st, 3rd, and 5th 

 lines appear depressed, while the 2nd, 4th, and 6th lines appear raised. 



