188 ON THE SENSES. 



Light and color are specific qualities of sensation, tLe result of the activity of 

 the nerves, through whatever means that activity is called forth, whether by 

 ethereal undulations, electricity, or mechanical agency. But as the nerves of 

 touch are destined for excitation by pres.'^ure, heat, and cold, the auditory nerve 

 for excitation by the Avaves of sound, and both are arranged with a view to th^* 

 impression of these agents alone, so the optic nerve is not designed for mechan- ' 

 ical or electrical irritation, but is exclusively destined and contrived for excita- 

 tion by the waves of the luminous ether. Hence that wonderfully perfect opti- 

 cal apparatus before the retina, which conducts the rays of light and disposes 

 them for the formation of exact images ; hence the complicated and as yet im- 

 perfectly understood apparatus of the retina irself, by which the vibrations of 

 the luminous ether are enabled to transmit their specific excitation to the opt"-^ 

 nerve, while for the electric current or far pressure no such enabling apparatus 

 has been provided, but both agents must act immediately on the naked fibres of 

 each nerve in order to set in motion their respective currents. 



So much for the origin of a simple sensation of light in general and of its 

 qualities specifically. In relation to the latter, namely, the colors in which ob- 

 served objects appear to us, we must call attention to some highly interesting 

 but as regards their nature not wholly explained facts, which are known in part 

 to every novice, but often pass without consideration. The same object does 

 not always appear to us of the same color; although the waves of light proceed- 

 ing from it are the same, the quality of the sensation is in some manner changed 

 in conformity with the color of the objects simultaneously perceived in close 

 proximity with it. If a red wafer on white paper be attentively observed for 

 some time, it will be seen that the paper around the wafer appears no longer of 

 a pure white, but assumes a greenish hue and at length a red tint like the wafer 

 itself If we look at a white wall through a hole in a gr^en paper it appears at 

 first of a reddish color, but afterwards of a greenish hue like the paper. These 

 experiments may be varied at pleasure. Eveu black objects, from which no 

 light is emitted into the eye, appear on a colored ground not black, but per- 

 ceptibly tinted — green, for instance, on a red ground, and green also on a green 

 ground. As already intimated, no certain explanation has been given of these 

 foicts.* We know only that the red or green color of the white ground around 

 a green or red wafer is not objective — that is to say, that light-waves of the 

 corresponding velocity do not pass from the paper into our eye, but waves of 

 the same compound (white) light, as when we observe the paper alone. Hence 

 the color of the paper is subjective — that is to say, it depends on a peculiar 

 mode of perception by our own mind. The mind conceives white to be green 

 when it appears beside red, to be red when it appears beside green. Red and 

 green form for our mental perception contrasted (complementary) colors ; so 

 likewise do blue and yellow, &c. In the white light of the paper, as has been 

 shown, all colors are contained ; it may well be, therefore, that when we see red 

 near white we overlook in the compound white the red ingredient and more 

 clearly perceive the complementary color, the green ingredient; single it out in 

 some measure from the mixture and substitute it for the objective white, of 

 which it is a part. This is the commonly received explanation, but it is not 

 full one. It is still more difficult to account for the color:::* which black objects 

 assume on a colored ground, for here the question no longer relates to the dif- 

 ferent interpretation of the quality of a definite sensation, but to the perception 

 of color by the retina, when in fact no light falls on it. Black is no color. 

 When we see therefore black objects colored, our perceptive faculty must coii- 

 ceivo a sensation of definite quality without any apparent objective cause ; how 

 this comes to pass, what, as regards the mind, is the provocative thereto, and 

 why the conceptions of color in this case maintain a constant quality in relation 



See article on Subjective or xVccidental Colors. 



