540 Intelligence and Miscellaneous Articles. 



tensities of two complementary colours, we know the ratio of their 

 intensities. From this ratio we deduce the angles of the sectors 

 which ought to reproduce the sensation of white — a condition 

 easily verified by direct experiment. The following Table contains 

 the result of this measurement for ten padre of complementary 

 colours copied upon the chromolithographed circle by M. Digeon, 

 from the chromatic circle of M. Chevreul, whose nomenclature I 

 have retained. 



Eatio of the coloration-intensities, given 



by the construction. by direct experiment. 



3rd yellow-green and violet 1-17 1*25 



4th green and red 3-72 3-73 



Blue-green and orange 6'80 6-70 



1st blue-green and orange- vellow . . 6-28 6-20 



Blue and vellow ." 3"74 3-80 



2nd blue and 1st yellow 3-13 3-18 



3rd blue and complementary yellow 3*07 3-00 



4th blue and 2nd vellow . . . '. 2T6 2-21 



Violet-blue and 4t*h yellow 2-16 2-13 



2nd violet-blue and yellow-green . . 2-18 2 - 00 



The accordance between experiment and construction is one of 

 the most complete, so that the latter can be regarded as summing 

 up exactly the state of our knowledge respecting the mixing of 

 colours. It gives for each the proportion of the primary sensations 

 CB : BB, the coloration-intensity OB, the complementary V, the 



OB 



ratio of the sectors of a pair of complementary colours -— . ne- 



OV 



cessary to produce the sensation of white, the intensity of that 

 sensation, the total luminous intensity, the triads, &c. 



Having obtained all these concordant numerical results, I could 

 not resist the desire to advance a step further and examine if it 

 was possible to express the intensity of a colour by its ratio to 

 that of white, and thereby to learn what is the distance which still 

 separates the finest colours obtained with colouring-matters from 

 those which the eye is susceptible of perceiving. 



In regard to the total luminous intensity that ratio has been 

 exactly determined. The finest aniline-blue represents only one 

 fifteenth, and the chromates of lead one seventh, of the intensity of 

 the white obtained, for one and the same illumination, with 

 barium sulphate. For the coloration-intensity the difference 

 would be still greater ; and hence it is evident that the chemistry 

 of colouring-matters owes us yet much progress before it can 

 realize what light can give us and what the eye is capable of 

 perceiving. — Comptes Rendus de VAcademie des Sciences, May 22, 

 1882, t. xciv. pp. 1411-1414. 



