96 THE VISUAL PROCESS 



whole sensation aroused by X600m|i — that is, a certain amount of yellow- 

 ness. An equal amount of uncancelled redness still remains — the chroma 

 ordinate above the green curve, taken once as to weight in the equation. 

 At X600m|l, then, the interaction of the three processes produces a large 

 amount of whiteness and equal amounts of yellowness and redness. Such 

 a blend, we see as orange. 



Before we leave Figure 32 its representation of relative brightness and 

 saturation need brief consideration. Brightness is most easily disposed 

 of — as the reader has already gathered, it is represented by the total 

 height of the variously-weighted portions of the ordinate. If each ordin- 

 ate were drawn upward like an unfolding telescope to its 'true' height, 

 the overall profile of the graph would represent exactly the curve of 

 brightness of the photopic spectrum. 



Saturation is maximal (100%!) at the ends of the spectrum — a fact 

 which often goes unappreciated because of the low brightness of those 

 regions and the confusion of brightness and saturation in the mind of 

 the student. Saturation is always the degree of freedom from admixture 

 with white, whether white external to the source of color is objectively 

 added to the latter or not; for, the color itself, even if generated by a 

 single wavelength, contains unsaturating whiteness as long as the wave- 

 length in question sets off all three components of the central synthetic 

 mechanism to any extents whatever. Under all ordinary circumstances 

 we cannot have 'pure' colors, even in the spectroscope, without accepting 

 an adulteration thereof by whiteness which arises from causes entirely 

 within the central mechanism. In Figure 32, the intrinsic degree of satur- 

 ation of any wavelength can be seen as the ratio of total chroma to white- 

 ness, remembering to take singly the part of the ordinate from the top- 

 most curve to the next one down, doubly the portion from that curve 

 to the lowest, and triply the heavy line representing whiteness. It is 

 obvious, however, that by fatiguing with the complement of a color we 

 will so greatly reduce the height of the whiteness-ordinate that the satur- 

 ation of the color will be correspondingly increased. Fatiguing with 

 violet, for example, makes the yellow of the spectroscope — ordinarily 

 the least saturated of all its hues — become amazingly rich in chroma; 

 an experience never to be had otherwise, and never to be forgotten. 



Color Blindness — 'Color blindness' is an unfortunate term which in- 

 cludes at least five, perhaps six, kinds of departure from the normal 

 trichromatic system. Total color blindness is the only type in which no 



