178 SATURDAY LECTURES. 



be more in keeping with known facts, and more in accord- 

 ance with operation of analogous functions in the human 

 body. 



The theor}' of Prof. Hering, of Prague, has received most 

 attention from those who have been bold enough to reject 

 the hypothesis of Young. 



This theory presupposes the existence in the retina of 

 three chemical substances, which, on account of their pre- 

 sumed functions, are called the red-green substance, the hlue- 

 yellow substance, and the hlach-wliite substance. 



An action of light on the red-green substance, which tends 

 to decompose it, produces red; wdiile an action which tends 

 to regenerate it produces green. A decomposing action 

 of light on the blue-yellow substance causes a sensation of 

 yellow; a regenerating action, the sensation of blue; while 

 a destruction of the white-black substance produces white, 

 its regeneration black. According to this theory there are 

 three pairs of opposing colors, (including white and black,) 

 and the fundamental colors are four, red, green, blue, and 

 yellow, and the so-called complementary^ colors are in reality 

 antagonistic. Thus you see Hering's theory is more com- 

 plicated than that of Young, likewise demands the accept- 

 ance of unproved and unprovable postulates, and makes 

 even greater draughts upon our scientific faith. It has this 

 advantage over its rival, however, that it explains in a 

 much more satisfactory manner some of the phenomena of 

 color-blindness. 



The fundamental objection to this theory, as to thtt of 

 Young-Helmholtz, is that it presupposes the existence of 

 new tissues, the like of wdiich are not found in any other 

 part of the human body, and novel reactions of these tissues 

 to light. It may be accepted as a law of universal applica- 

 tion that Nature always works in the simplest manner pos- 

 sible, and we have no right to suppose that the function of 

 vision forms any exception to the rule. Is it possible to ac- 

 count for the perception of colors in a simple and direct 

 manner ? I think it is, and that, too, without doing any 

 violence to laws, the existence of w^hicli has been estab- 



