220 ON ACCIDENTAL OR SUBJECTIVE COLOES- 



hair white, the eyes would have the pupils white on a black ground, &c., which 

 would of course produce a hideous representation; but on looking fixedly and 

 sufficiently long at one point in this figure, and then casting the eyes on a white 

 wall, there will be seen the appearance of a head with its natural colors. 



Second class — Simultaneous subjective colors. — All the appearances with which 

 we have been thus far occupied sticceed the contemplation of the colored objects ; 

 but experiment proves that even during this contemplation there is manifested 

 another order of phenomena consisting also in the apparition of complementary 

 colors, and which form the second class of subjective or accidental colors. Thus 

 Buffon remarked that whilst we are looking fixedly at a colored object placed 

 on a black ground, there is perceptible outside of this object and along its con- 

 tour a colored border of a tint similar to that of the subjective image, which is 

 obtained by afterwards casting the eyes on another part of the white ground. 

 Here, then, it is not at a succeeding time, but in the contiguous space that the 

 accidental color arises. Some physicists, however, have assigned this phenome- 

 non to the preceding class of subjective colors, by attributing it to the circum- 

 stance that, during the contemplation of the object, the eye cannot remain com- 

 pletely immovable, whence the image vacillates on the retina, and around this 

 image there are parts of the retina which, after having received the impression 

 of the colored light proceeding from the border of the object, receive the im- 

 pression of the white ground. But without speaking- of this circumstance, there 

 are a multitude of other experiments which evince the production of accidental 

 colors during the contemplation of colored objects. 



Let us refer in the first place to colored shadows. Thus Rumford has shown 

 that when a shadow is produced in a colored light, this shadow is tinged with 

 the complementary color; if, for example, a paper be illuminated with green 

 light, a body illuminated with white light and interposed between the green 

 light and the paper, will cast on the latter a red shadow. 



Thus again, according to the observations of Meusnier, when the interior of 

 an apartment is illuminated only by the light of the sun transmitted through a 

 curtain of colored stuff, and this curtain is pierced with a hole some millimetres 

 in diameter, through which the direct light may penetrate, if this pencil of light 

 be received on white paper, the part of the paper illumined by the white light 

 of the sun appears vividly colored with a tint complementary to that of the cur- 

 tain. 



Prieur, of the Cote d'Or, has shown that if we place between the window and 

 the eye a piece of colored paper possessing a certain transparence, and apply 

 on this paper a small strip of white pasteboard, the strip will appear tinged with 

 the complementary color ; we shall see a rose color on green paper, lilac on yel- 

 low paper, &c. The effect is more decided for certain positions of the colored 

 paper, positions which are readily found on making the experiment ; moreover, 

 if the small strip of pasteboard is itself colored, its own color combines with 

 the complementary of the color of the paper. Thus a blue strip will appear 

 violet On green paper, a yellow strip will appear green on orange colored paper, &c. 



Let us cite further an experiment made by Dr. Smith : it consists in applying 

 to one of the eyes a small tube of transparent colored paper, on which a strong 

 light is thrown sideways. Then if a white surface be looked at, both eyes 

 being open, the portion of that surface seen through the colored tube appears 

 tinged with the complementary color. 



[I have found the following arrangement to afford a very satisfactory means 

 of exhibiting colored shadows : Place before the object-glass of a magic lantern, 

 or before a convex lens through which a beam of light from the sun is passing, 

 a plate of colored glass so as to cast upon a white screen or an opposite wall, in 

 a dark room, a colored circle of, say, six feet in diameter. If on this circle the 

 more feeble light of a candle is thrown, and an object, such as the hand, is in- 



