EXPERIMENTS ON DOUBLE VISION. 209 



I shall not enlarge on this article, as theory' alone is suf- In all cases one 



ficient to determine all the cases of alteration of figure by °^' ectseet " s 



» J placed on the 



double vision ; for it is sufficient to imagine the two objects other. 

 placed one upon the other, the effect which double vision 

 produces. 



I was not satisfied with thus combining the primary co- More than tw 

 lours by pairs only, but extended my researches to more cooul:> ' 

 numerous and complicated associations, which led me to 

 some remarkable results, that could not have been deduced Four cotours 

 by analogy alone from the simple association. The first of ? ive tWo ob " 

 these results is, that it is possible to receive at one time two 

 distinct and comparable sensations by the simultaneous im- 

 pression of several objects on our eyes. Little parallel- 

 ograms of red, blue, yellow, and green, placed parallel to 

 each other, and on opposite sides of the vertical plane of 

 the apparatus, in the order I have mentioned, and subject- 

 ed to double vision, give the perception of orange, produc- 

 ed by the association of red and yellow, and of sea green, 

 produced by the green and the light blue. 



The second remarkable result is, that the colours, is They hare a 

 their apparent associations or combinations, seem obedient? 01 ' 1 of affinity, 



} ^ , , ■ ' by which they 



to a kind of affinity, by virtue of which those that have seek on- those 



most analogy to each other combine in preference, be the most co; ' s , ema * 

 ° J r ' to each other. 



disposition of the parallelograms what they may. Thus 



the yellow combines with the red, and the blue with the 

 green, let them be disposed in either of the following modes t 

 yellow, blue, red, green; or yellow, blue, green, red; 

 or blue, yellowy red, green ; arrangements in which the 

 colours are obliged to jump over one another, if I may use 

 the expression, to seek out and combiue with those analo- 

 gous to themselves. This tendency of certain colours to This perhaps 

 combine together in preference to others appears to me toP revcnIstlle 



k 4.x. • • i a * 4.x. '4i combination of 



be the principal cause, that opposes the recomposition of all into white 

 light by placing all the primary colours on Gach side of the !l S !u - 

 vertical plane, which I at first hoped to have effected. 



The experiments on double vision by means of reflected The effects of 

 and refracted light suppose a third class, composed of a ref ? ectcd and 



, . . * i /. . i retracted ravs 



combination of the processes of the other two; but, as together are 

 there is no essential difference in the resultSj I proceed to sliml,u- 

 explain, these phenomena^ 



The 



