SENSE OF VISION COMPLEMENTARY COLORS. 773 



the eye has been for some time contemplating an object in motion, and is 

 then directed towards stationary objects, these appear for a short time to 

 have a like movement. Any railroad traveller may try this simple experi- 

 ment, by first looking at the hedges, etc., which he is rapidly passing, and 

 then at some part of the interior of the carriage itself, especially one which 

 presents a series of parallel lines. But when the impression of movement 

 has been of longer duration, its effects are less transient ; thus a person who 

 has been for some time on board ship, sees the floors, walls, and ceilings of his 

 apartments on shore in a state of continual up and down motion, even for 

 some days after he has lauded. This would seem to be rather a sensorial 

 than a retinal phenomenon. 



629. When the Retina has been exposed for some time to a strong im- 

 pression of some particular kind, it seems less susceptible of feebler impres- 

 sions of the same kind. Thus, if we look at any brightly luminous object, 

 and then turn our eyes on a sheet of white paper, we shall perceive a dark 

 spot upon it ; the portion of the retina which had been affected by the bright 

 image, not being able to receive an impression from the fainter rays reflected 

 by the paper. The dark spectrum does not at once disappear, but assumes 

 different colors in succession, these being expressions of the states through 

 which the retina is passing, in its transition to the natural condition. If the 

 eye has received a strong impression from a colored object, the spectrum 

 exhibits the complementary color; 1 thus, if the eye be fixed for any length of 

 time upon a bright red spot on a white ground, and be then suddenly turned 

 so as to rest upon the Avhite surface, we see a spectrum of a green color. 

 The same explanation applies to the curious phenomenon of " colored shad- 

 ows." It may not unfrequently be observed at sunset, that, when the light 

 of the sun acquires a bright orange color from the clouds through which it 

 passes, the shadows cast by it have a blue tint. Again, in a room with red 

 curtains, the light which passes through these produces green shadows. In 

 both instances, a strong impression of one color is made on the general sur- 

 face of the retina ; and at any particular spots, therefore, at which the light 

 is colorless but very faint, that color is not perceived, its complement only 

 being visible. The correctness of this explanation is proved by the fact, 

 that, if the shadow be viewed through a tube, in such a manner that the 

 colored ground is excluded, it seems like an ordinary shadow. It is not 

 unlikely that, as Miiller suggests, the predominant action of one color on the 

 retina disturbs (as it were) the equilibrium of its condition, and excites in it 

 a tendency to the development of a state corresponding to that which is 

 produced by the impression of the complementary color ; for the latter is 

 perceived, as he remarks, even where it does not exist ; as when the eye, 

 after receiving a strong impression from a colored spot, and being directed 

 upon a completely dark surface or into a dark cavity, still perceives the 

 spectrum. This change, indeed, extends beyond the spot on which the im- 

 pression is made ( 633) ; for, as is well known to Artists, the sensory im- 

 pression produced by any color is greatly affected by neighboring hues. 

 Thus, if four strips of colored paper, or any other fabric, A, B, c, D, two 

 of them, A, B, of one color (e.g., red), and the other two, c, D, of some differ- 

 ent color (e.g., blue), be laid side by side at intervals of about half an inch, 

 the hues of the two central strips B, c, will be decidedly modified by each 



1 By the "complementary" color is meant that which would be required to make 

 white or colorless light, when mixed with the original : thus red is the complement 

 of green (which may be made by mixing yellow and blue) ; blue is the complement 

 of orange (red and yellow) ; and yellow of purple (red and blue.) ; and vice verad in 

 all instances. 



