206 



EXPERIMENTS ON DOUBLE VISION. 



till they begin or fifteen inches. 2. In this apparent progress of the bodiei 

 to overlap ; and toward each other, they approach with a pretty regular 

 then blend at motion, till they partly cover each other ; when we see 

 once - them suddenly confounded together, as at one leap ; and 



then the compound sensation is changed into a simple per- 

 ception, and only one single object is discerned, the colour 

 of which is the result of the combination of the colours .of 

 the two pieces of pasteboard. All the primary colours, 

 subjected to the same trial, afforded me analogous results, 

 indicated in the following table, a few modifications except- 

 ed, which I shall notice. 



Red and yellow produced orange. 



Results of the 

 combined per- 

 ceptioi. of dif- 

 ferent colours 

 by reflection. 



Red and orange 

 Red and blue 

 Red and green 

 Red and violet 

 Red and indigo 

 Orange and yellow 

 Orange and blue 

 Orange and green 

 Orange and violet 

 Orange and indigo 

 Yellow and blue 

 Yellow and green 

 Yellow and violet 

 Yellow and indigo 

 Blue and green 



Blue and violet 

 Blue and indigo 

 Green and violet 

 Green and indigo 



a bright aurora. 



violet. 



a rosy green. 



a rosy violet. 



a dingy violet. 



light yellow. 



muddy green. 



reddish green. 



light violet. 



harsh violet. 



faint, indeterminate green. 



light green. 



muddy green. 



a dingy green. 



deep or light green, accord. 



ing to the shade of blue, 

 deep violet, 

 deep blue, 

 a dingy violet, 

 a very deep blue. 



The experi- These experiments, though not difficult to execute, re- 



pract'ice and^ o^nre a certain practice, and steady attention, without 



attention, which they will not succeed. The strong convergence ne- 



and arefatigu- cessary to be given to the optic axes renders them fatiguing, 

 ing to the eyes. * . J .u , , f. . 



I have met with several persons, who, not being able to 



keep up their attention, and view the two objects steadily 



at one time, did not experience the compound sensation, 



