TRANSACTIONS OP THE SECTIONS. 545 



Newton asserts, in a letter to Oldenburg, that " if any two 

 coloursT)e mixed, which in the series of those generated by the 

 prism are not too far distant from one another, they, by their 

 mutual allay, compound that colour which in the said series 

 appeareth in the mid-way between them*." 



Dr. Young states that " perfect sensations of yellow and of 

 blue are produced respectively by mixtures of red and green, 

 and of green and violet light f." 



According to the theory here proposed, the compound colour 

 is independent of the origins of the component rays, for c and 

 d may be any arbitrary quantities ; and this agrees with ex- 

 perience. 



It follows, too, from this theory that the red and violet can- 

 not be produced by mixing two colours of the spectrum, but 

 every other prismatic colour may. Dr. Young takes red, green, 

 and violet as fundamental colours in his theory of composition. 

 In Mayer's theory, red, yellow, and blue are the fundamental 

 colours, and violet is supposed to be a compound only because 

 it produces, without being mixed with any other colour, a sen- 

 sible impression of redness. See Herschel's Treatise on Lisht, 

 Art. 515. ^ 



The difference between two rays expressed respectively by 



the functions m sin {^ + cj and 2 m cos (^ + cA 



sm y-jj + c), IS exhibited in figures 1 and 2. Since it is 



known by experience that the eye is not sensible to a momen- 

 tary interruption of a ray (as exhibited in fig. 3.), there seems 

 to be no reason to expect that it would perceive any difference 

 between the rays of figures 1 and 2. Nothing in light corre- 

 sponds to discords in sound. 



Fiff.l. 



Fig. 5. ^ 



Sir John Herschel is of opinion that the fact of the complete 

 imitation of the prismatic green by a mixture of adjacent colours 



* Horsley's Edition of Newton's Worlcs, vol. iv. p. 303. 

 + Lectures on Natural Philosophy, vol. i. p. 439. 

 1834. 2 N 



