[ 269 ] • '^ 



XXXVII. Ofi some phenomena of Binocular Visio7i, 

 By MM. L. FoucAULT and J. Regnault*. 



IN a beautiful investigation on the vision of objects of three 

 dimensions, Mr. Wheatstonef states that when two visual 

 fields, or the corresponding elements of the two retinae, simul- 

 taneously receive impressions from rays of different refrangi- 

 bility, no perception of mixed colours is produced. The as- 

 sertion of this able philosopher being opposed to the opinion 

 of the majority of those who have attended to the same sub- 

 ject, we have thought it useful to repeat, modify, and extend 

 these experiments. The stereoscope of Mr. Wheatstone 

 offered a simple means of disentangling these delicate obser- 

 vations of all complication capable of injuriously affecting the 

 accuracy of the physiological results. 



The recomposition of mixed tints by means of vibrations 

 produced on the retinae by different coloured rays is beyond 

 doubt. But the aptness varies in a remarkable manner in 

 different individuals; it is possible that it may be exceedingly 

 weak in some persons, and exceptionally null in others. 



The tendency of one of the eyes to become inattentive in this 

 kind of experiment is very remarkable when the whole extent 

 of the visual fields is uniformly lighted up by different coloured 

 rays. If we cause an impression to be made on limited and 

 corresponding parts of the retinse, the power of the attention 

 constantly favours the recomposition. If two coloured rays 

 susceptible, on reaching a white screen, of producing a mixed 

 tint produce the same sensation when acting separately on the 

 corresponding portions of the retinae, it seems probable that 

 two complementary rays will produce the sensation of white 

 by affecting the corresponding elements of the sensitive mem- 

 brane. 



To prove this recomposition with respect to a great number 

 of complementary tints, and present the phaenomenon in all its 

 clearness, we arranged the following experiment : — We affixed 

 to the stereoscope two plane mirrors, forming a variable dihe- 

 dral angle, the vertical edge of which is placed symmetrically 

 in relation to that of the two glasses of the stereoscope. The 

 vertical uprights bearing the grooves for the purpose of intro- 

 ducing the images are perforated by two large circular aper- 

 tures. In the grooves are placed two glasses, on which are 

 pasted two circular screens of white paper of the same size, 

 and of a diameter less than that of the apertures. Two large 

 luminous rays of complementary tints, obtained by chromatic 

 polarization, are directed horizontally upon the plane mirrors 



* From the Comptes Rendus for Jan. 15, 1849. 

 t Philosophical Transactions, part 2, 1838. 



