160 ACCIDENTAL COLORS. SECT. XIX. 



of orange is blue ; that of yellow is indigo ; of green, 

 reddish-white ; of blue, orange-red ; of violet, yellow ; 

 and of white, black ; and vice versa. When the direct 

 and accidental colors are of the same intensity, the acci- 

 dental is then called the complementary color, because 

 any two colors are said to be complementary to one an- 

 other which produce white when combined. 



From recent experiments by M. Plateau of Brussels, 

 it appears that two complementary colors from direct 

 impression, which would produce white when combined, 

 produce black, or extinguish one another by their union, 

 when accidental ; and also that the combination of all the 

 tints of the solar spectrum produces white light if they 

 be from a direct impression on the eye, whereas black- 

 ness results from a union of the same tints if they be 

 accidental ; and in every case where the real colors pro- 

 duce white by their combination, the accidental colors 

 of the same tints produce black. When the image of 

 an object is impressed on the retina only for a few mo- 

 ments, the picture left is exactly of the same color with 

 the object, but in an extremely short time the picture 

 is succeeded by the accidental image. M. Plateau at- 

 tributes this phenomenon to a reaction of the retina after 

 being excited by direct vision, so that the accidental im- 

 pression is of an opposite nature to the corresponding 

 direct impression. He conceives, that when the eye is 

 excited by being fixed for a time on a colored object, and 

 then withdrawn from the excitement, that it endeavors 

 to return to its state of repose, but in so doing that it 

 passes this point and spontaneously assumes an opposite 

 condition, like a spring, which, bent in one direction, in 

 returning to its state of rest bends as much the contrary 

 way. The accidental image thus results from a partic- 

 ular modification of the organ of sight, in virtue of which 

 it spontaneously gives us a new sensation after it has 

 been excited by direct vision. If the prevailing impres- 

 sion be a very strong white light, its accidental image is 

 not black, but, a variety of colors in succession. Accord- 

 ing to M. Plateau, the retina offers a resistance to the 

 action of light, which increases with the duration of this 

 action ; whence, after looking intently at an object for a 

 long time, it appears to decrease in brilliancy. The im- 



