264 0. JV. Rood— Color System. 



dard to which a great number of reds and blue-greens, more or 

 less pale or intense, could be quantitatively referred. But it 

 might be possible to go farther, and to be able to say that our 

 standard vermilion disc reflected the same amount of red light 

 that is furnished by white card-board under the same illumina- 

 tion, or that at all events it reflected a known fractional part 

 of it. All the colors just spoken of would then be virtually 

 referred to white card- board, or to some other white reflecting 

 surface as might be determined on, and the standard red disc 

 could at will be reproduced at any time or in any part of the 

 world. To the reproduction of standard red discs I have not 

 devoted much time, as before they can be made valuable a 

 much more difficult problem must be solved. 



For if we undertake to go farther than the proceeding just 

 indicated, and build up a whole system of colors we are imme- 

 diately confronted by the fact that we are quite unable to leave 

 our line ; or for example, to express the amount of orange 

 colored light or of green light reflected by other discs in the 

 same terms, or to bring them all into one system. As Helm- 

 holtz has remarked,* masses of colored light which when 

 mixed with their complements furnish in pairs the same white, 

 may be said to belong to the same system and may be located 

 at equal distances from the same center. A set of ideal discs 

 which w T hen combined pair-wise all furnished the same white, 

 would in this system find their positions on the circumference 

 of a circle with white at the center. But it is not practicable 

 to experiment directly in this way, as it is nearly impossible to 

 measure directly the amounts of white light mingled with the 

 colored in the case of painted surfaces. 



I have employed a different proceeding and built up with it 

 a reproducible system, which, as far as I can ascertain, is the 

 one above indicated. Let us suppose that the positions of our 

 standard red and its complement have been laid down at the 

 extremities of a line with white at its center : we then combine 

 with the red disc a green which is a little too blue to be 

 strictly complementary, and obtain the best neutralization, the 

 gray furnished having the least perceptible color, and we will 

 suppose that this takes place when the areas of the two colored 

 surfaces on the composite disc are equal ; we shall then know 

 that the new color also belongs on the circle not far from the 

 complement of vermilion. One step has thus been taken, 

 we have been able to leave our first line of mixtures. We can 

 then with ease and certainty locate the complement of this new 

 hue, which will be a little more orange than the vermilion ; or 

 better still, we may combine the new color with one that is 



* Handbuch der Physiologischen Optik, p. 287. 



