THE 



AMERICAN 



JOURNAL OF SCIENCE AND ARTS. 



[THIRD SERIES.] 



Art. XXVI.— Note on the Sensation of Color; by C. S. Peirce. 



It may, perhaps, be worth while to notice a few consequences 

 of three theories concerning color which are usually regarded 

 with some favor. 



First hypothesis.— The appearance of every mixture of lights 

 depends solely on the appearances of the constituents, without 

 a of their physical constitution. This I believe is 

 established. 



tecond hypothesis. — Every sensation of light is compounded 

 of not more than three independent sensations, which do not 

 influence one another. This is Young's theory. It follows 

 that, if we denote the i 



\ji and k, every sensation of light may be represented by 

 an expression of the form, 



Xi+Yj+Zk. 

 Third hypothesis.— The intensitv of a sensation is propor- 

 tional to the logarithm of the strength of the excitation, the 

 barely perceptible excitation being taken of unit strength, 

 ^egative logarithms are to be taken as zero. This is Fechner's 

 Jaw. It is known to be approximately and only approximately 

 true, for the sensation of light. From this it follows that, if 

 x \ V, 2 be the relative proportions of a mixture of three lights 

 giving the elementary sensations i, j, k, the sensation produced 



I logx.i+J logy J+K log*.*, 

 *here I, J, K , are three constants. 



*rom these principles, it follows that if a light giving any 

 sensation such as that just written have its intensity increased 

 ln m y ratio r, the resulting sensation will be, 

 **- Jodb. 8ci.— Third Sbbies, Vol. XIII, No. 76.— Apbil, 1877. 



