118 P. C on the Colours, ^c. [Aug. 



previous action of two of these colours, they would have 

 been seen in the colour of the third. 



In the exhibition of fire-works, for instance, when intense 

 red light, or any other coloured light, is displayed, surround- 

 ing objects immediately afterwards, if illuminated with 

 white light, appear of a colour in which the light previously 

 exhibited is deficient ; white objects of course assume its 

 complementary colour. 



In order then to account for the phenomena of ocular 

 spectra, we have only to transfer the case of a general im- 

 pression, to an impression upon that part of the retina only 

 which has been subjected to the action of light, of any 

 particular colour or colours for a sufficient time to impair 

 its sensibility. 



Every ray of light makes an impression upon the retina 

 independently of every other ray : a correct image of objects 

 could not be delineated upon any other principle : and 

 although rays of different colours, when within a certain 

 distance of each other, produce a sensation compounded of 

 the whole, and not a distinct sensation for each particular 

 colour, this sensation is produced by their independent 

 action ; it is not a mixture of the light, but a mixture of the 

 sensations, which produces, what appears to be, a simple 

 impression. 



One part of the retina may therefore have its sensibility 

 impaired without its affecting any other part : and any 

 part or the whole may be rendered insensible to one colour, 

 and retain its full power as it relates to others."^ 



If you think your readers will not be tired of the subject, 

 I propose to give in another paper, a class of proofs drawn 

 from quite a different source, which I think will be found 

 to be of some little importance, independent of their prin- 

 cipal object. P. C. 



To the Editor of the Records of General Science. 

 June 22nd, 1835. 



I inadvertently stated in my former paper that a larger 

 proportion of red than what is required to form crimson 

 produces pink, but this is incorrect, pink being a crimson 



* I am here speaking of light of ordinary intensity, very strong light, by dis- 

 organizing the general functions of the eye, would no doubt produce a more 

 extended influence. 



