THE STEREOSCOPE : ITS HISTORY. 37 



But how different from the others, both in character and history, 

 is the sense of touch ! Having -with them a common origin, like them 

 it is resident in the outer skin, but it is active alike all over the body ; 

 the touch of the finger-tips may be more delicate than that of the 

 palms, but it is only a quantitative difference. The sense of touch is 

 the fundamental sense. All the other senses have to render their data 

 into its terms before they can be understood by the mind. Animals 

 can live without sight, hearing, taste, or smell, but the presence of the 

 sense of touch seems a necessary condition of animal existence. The 

 other senses are means of self-preservation ; the sense of touch is the 

 manifestation of an animal's existence. 



The senses, then, all originate from the outer covering ; this cov- 

 ering has from the beginning a special sensation from the resistance 

 to external pressure ; this property it retains throughout the animal 

 kingdom. The other sense-organs appear as specialized parts of this 

 universal sense-organ ; morphologically they are only parts of the skin, 

 rendered more sensitive than the normal skin. 



All the evidence seems to point one way, to the conclusion that the 

 other senses are all modifications of the sense of touch. That such is 

 probably the fact seems to be generally admitted. What I have tried 

 to show is our ground for that conclusion, and that what was with 

 Democritus a random speculation is with us fast assuming the nature 

 of a scientific truth. 



- 



THE STEREOSCOPE: ITS HISTORY.* 







By W. LE CONTE STEVENS. 

 I. 



rpHAT a near object of small dimensions presents an aspect slightly 

 -L different to each one of a pair of eyes directed upon it, has been 

 known for more than two thousand years ; but no application of this 

 knowledge was ever made until some time after the beginning of the 

 present century. The analysis of binocular vision is one of the prod- 

 ucts of modern investigation, and the stereoscope is its direct outcome. 

 That vision with two eyes is greatly preferable to what the ancients 

 accorded to Polyphemus is fully appreciated by every one who pos- 

 sesses a pair of healthy visual organs and a stereoscope, but who at 

 any time has been so unfortunate as to suffer a temporary injury that 

 reduces him for a few days to the condition of the classic monocular 

 giant. Familiar as he may be with the truth that the perspective 

 effect of a fine painting is better appreciated when one eye is closed, 



* Expanded from an address before the Photographic Section of the American Insti- 

 tute, delivered March 7, 1882. 



