CUVJER . 



Pig. 1. CUVIER. 



THE STEREOSCOPE. 



1. Surprising effect of the instrument explained. 2. Causes of visual 

 perspective and relief. 3. Effects of binocular parallax. 4. Example 

 of the bust of Cuvier. 5. Principle of the stereoscope. 6. Origin of 

 the name. 7. Wheatstone's reflecting stereoscope. 8. Sir David 

 Brewster's lenticular stereoscope. 9. Method of obtaining stereoscopic 

 pictures. 10. How the effects of relief are produced. 11. Natural 

 relief greatly exaggerated. 



1. THE surprise excited by the impressions of perspective and 

 relief produced by the stereoscope have never, as we think, been 

 fully or adequately explained. This emotion of astonishment does 

 not merely arise, as is commonly supposed, from the fact that 

 such impressions are stronger than those produced by the best 

 executed drawings or paintings, but that, paradoxical as it may 

 seem, they are actually in many cases stronger and more vivid, 

 than any which could be produced by the objects themselves. In 

 a word, the stereoscope has the property of exaggerating the 

 natural effects of perspective and relief. To comprehend this it 

 will only be necessary to revert for a moment to the principles 

 upon which the effects of vision are based. 



The mind judges of the relative position, form, and magnitude 

 of visible objects, by comparing their apparent outlines and 

 varieties of light and shade, with previously acquired impressions 

 of the sense of touch. The knowledge that such and such visual 

 appearances and optical effects are produced by certain varieties 

 of form, position, and distance having been already acquired, it 

 substitutes with the quickness of thought the cause for the effect. 

 The continual repetition of such acts, which are necessarily re- 

 peated as often as the sense of vision is exercised, and the extreme 

 rapidity with which all such mental operations are performed, 



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