506 SCIENTIFIC THOUGHT. 



a kind of deception, gave to perfectly flat surfaces the 

 vivid appearance of depth and distance. And here we 

 may note, in passing, how it was almost entirely left 

 to foreign thinkers to utilise this remarkable invention 

 for the benefit of the theory of vision and the science 

 of psycho-physics ; l Whewell having characteristically 

 omitted this epoch-making fact, as in his well-known 

 history he omitted to notice many other contemporary 

 British contributions to science. 



Philosophers, who are accustomed to find hidden 

 problems where ordinary persons only see common-sense, 

 had already approached the question of the genesis of our 

 space perception from two definite points of view, which 

 we may, for the sake of convenience, identify with the 

 names of Kant and Herbart. The genetic view associ- 

 ated by the physiologists with the name of Kant, and 

 supposed to have been prepared by Locke, Berkeley, and 

 Hume, was this, that what we know of external things 

 depends upon the peculiarities of our own perceiving 



1 Sir Charles Wheatstone (1802- [ original researches in optics, it has 



1875), to whom several inventions I been found that ancient as well as 



of equal scientific and practical more recent philosophers had ap- 



interest are due, invented the proached the subject very closely ; 



mirror - stereoscope in 1833. A | and many references are given in 



notice of it was given in Mayo's | the new edition of the ' Physio- 



' Outlines of Human Physiology,' I logische Optik ' (1896), p. 840. 



but neither its theoretical nor its j The invention of photography about 



practical importance was recognised ' the same time (1835, by Daguerre, 



till Wheatstone published his paper 

 in the 'Phil. Trans.' in 1838. He 

 there refers to Leonardo da Vinci as 



after extensive and prolonged ex- 

 periments by himself and Niepce, 

 published in 1839 by Arago), which 



having been the only one before him i was of great importance to optical 

 to notice the difference of binocular ! theory, was also for some time 



singularly little appreciated by 



and monocular vision. Since 

 Wheatstone's invention became 

 known and was perfected by 

 Brews ter, Moser, and others, and 

 especially since Helmholtz entered 

 the field with his extensive and 



theorists. See Rosenberger, ' Gesch. 

 d. Physik,' vol. Hi. p. 316. See also 

 Helmholtz's lecture "Ueber das 

 Sehen des Menschen" (1855). 



