MODERN OPTICS AND PAINTING. 417 



gradually into an orange tint, and, gaining greatly in luminosity, be- 

 comes pure yellow ; passing thence by gradations into green and blue, 

 it gently fades out in a violet 'and faint violet-gray or lavender. Be- 

 yond this point are yet more minute waves, but, in pursuing them, we 

 enter once more what is for us a region of silence and darkness, and 

 we are compelled to feel our way with the help of photographic plates. 



The series of tints just mentioned is now on the screen, and, were 

 it worth while, the existence of systems of invisible waves upon either 

 side could easily be demonstrated. The statements that I have made 

 lead us, however, a little unexpectedly to a remarkable conclusion. 

 They show that the beautiful colors now displayed have no existence 

 outside of ourselves — that, outside of ourselves, there are merely waves, 

 longer or shorter. Color is a sensation existing merely in ourselves. 

 On the other hand, our eyes might have been made quite insensible to 

 color while still preserving the power of vision, and it is not impossi- 

 ble for us to conceive the existence of beings to whom the luminous 

 waves might only be what to us are the breakers on a sea-beach. 



But, to resume : if we allow all these luminous waves to act simul- 

 taneously upon the eye, we obtain, not, as might perhaps be expected, 

 a still richer and more gorgeous tint, but simply the sensation called 

 white — brightness without color. 



Now, it happens somewhat remarkably that all the color sensations 

 I have mentioned, and all intermediate ones, can be approximately re- 

 produced by the mixture in various proportions of merely three pow- 

 ders : when viewed by ordinary daylight one of the powders must be 

 capable of reflecting red light, the others yellow and blue light re- 

 spectively, that is to say, they must reflect abundantly the waves ca- 

 pable of producing these three sensations ; the rest of the waves fall- 

 ing on them they must absorb and destroy, to a greater or less extent ; 

 or, finally, in common language, out of the mixture of red, yellow, and 

 blue pigments, all the colors can be produced. This fact has been 

 known for ages — it was old in the time of the Greeks, and probably 

 dates back to that early period when the first serious attempts at 

 painting were made by the human race. What could be more natural 

 than that it should lead to the theory of the existence of only three 

 primary colors, red, yellow, and blue, out of which all the others could 

 be compounded: thus, orange out of a mixture of red and yellow, 

 green by blue and yellow, and violet from red and blue. This theory 

 was firmly established before Newton's time. During the present cen- 

 tury it was the glory of one of England's greatest physicists that he 

 had strengthened its foundations (it is found in most text-books on 

 physics and art), and is to-day almost universally credited by paint- 

 ers. We have here upon the screen its well-known typical expression: 

 three overlapping circles, the red one producing orange where it crosses 

 vol. iv. — 27 



