1835.] Accidental and Completnentary Colours. 291 



remarked to me that although the fire was certainly red 

 enough, it always left an impression of green. This remark 

 has been elicited from persons of good general perception 

 of colour, and I have endeavoured to ascertain, from, them, 

 whether the green impression has ever been succeeded by 

 red, and I have always received a negative answer. With 

 this view I have repeated the experiment alone, and in 

 company, and the general result of my inquiries has been 

 unfavourable to M. Plateau's system of oscillations. 



9. In considering M. Plateau's next proposition, [3.] we 

 must carefully bear in mind the difference already stated to 

 exist between the two species of colour (5 and 6). As I 

 have already shewn that complementary colours may be 

 seen together with the fundamental colours, they surely do 

 not so much differ in their nature as that accidental colours 

 can onli/ be seen by a previous preparation of the eye. This 

 preparation, however, it is admitted by P. C. (page 179), 

 need only be the act of " less than a second ;" and I have 

 before stated cases (5.) where the accidental tint has been 

 seen immediately on observing the primitive colour, and, it 

 seems to me that '* less than a second," as stated by P. C, 

 and " immediately," as stated by myself, are synonymous 

 terms. The difference, however, between the two colours, 

 as stated by Brewster, is that, " if the primitive colour, or 

 that which impresses the eye, is reduced to the same degree 

 of intensity as the accidental colour, we shall find that the 

 one is the complement of the other, or what the other wants 

 to make it white light ; that is, the primitive and the acci- 

 dental colours will, when reduced to the same degree of 

 intensity which they have in the spectrum, and when mixed 

 together, make white light. On this account accidental 

 colours have been called complementary colours." Optics, 

 page 305, and at pages 308 and 309, he seems to employ 

 both terms somewhat indiscriminately. P.C., also, in his 

 last paper, (page 172, ante.), does not seem to distinguish 

 between the two colours. In his notice at the com- 

 mencement of his paper, of my two papers, he has omitted 

 the word " complementary," although it forms part of the 

 title of my second paper,^ and he does not apply either term 



• See page 21 of this vol. In the 9th line from bottom, for ** the same," read 

 «' an." 



u2 



