270 On some yhcenomena of Binocular Vision. 



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 which reflect them ; they traverse the glasses of the grooves 

 which remain dark ; but when reflected irregularly on the cir- 

 cular screens they give two coloured discs, exactly identical as 

 to form and extent, which become the images conveyed by the 

 stereoscope to the corresponding elements of the retinae. We 

 might, by means of an appropriate disposition of the polarizing 

 apparatus, successively present numerous complementary tints, 

 vary at the same time the intensity of the two coloured images, 

 and modify the intensity of one or other of the images separately. 



The following are the physiological results we have ob- 

 served. When the corresponding elements of the retinae re- 

 ceive an impression at the same time, the alternations of acti- 

 vity or inertness of one of the eyes is generally manifested at 

 the commencement of the experiment, and sometimes one of 

 the tints is perceived, and at other times its complementary 

 one ; but after a duration of observation, varying considerably 

 according to the individuals, only a single white circle is seen. 



When the eyes are in some degree accustomed to this un- 

 usual mode of impression, the tendency to recomposition be- 

 comes so energetic in some persons, that the screens might 

 present successively all the complementary tints which the ap- 

 paratus furnishes without there being any sensation corre- 

 sponding to the colours; only white light is seen. 



On diminishing the intensity of one of the colours, the other 

 remaining constant, recomposition still takes place; but the 

 white disc appears to become covered more or less strongly 

 with the predominant tint. 



If the intensity of the complementary rays is varied in the 

 same manner for the two collections of rays, the recomposi- 

 tion is made with greater facility at the commencement of the 

 observation, as their intensity is more moderated. 



Of the complementary rays which we have examined, the 

 sensible blue and the yellow tints are best adapted for the ex- 

 periment, and immediately furnish the sensation of white. 



We believe that this phsenomenon is owing to the circum- 

 stance, that the accommodation of the eyes being the same for 

 these groups of rays, according to the portions of the spectrum 

 which they occupy, the efforts necessary to produce recom- 

 position are on that account considerably less. 



We find that, saving exceptional cases, the sensation of 

 white light may be produced by any two complementary chro- 

 matic impressions in ench of the eyes ; that the sensation solely 

 of white arising from two complementary rays is independent 

 of any mutual action of these rays externally to the visual 

 apparatus; that the luminous impressions produced on the 

 retinae retain their properties even to the innermost recesses 

 of the brain. 



