76 DR. JAMES BOTTOMLEY ON A 



would have its value ; aud an investigation into the de- 

 partures from the law might lead to interesting results, 

 and give some insight into the operation of those mole- 

 cular forces which separately elude observation, but whose 

 joint effect must necessarily have some influence in deter- 

 mining the intensity of colour. 



Some of the above reasoning applies to the case of 

 turbid liquids ; and I was led to the conclusion that a 

 carbon diffusion would behave with regard to the extinc- 

 tion of light in the same manner that it would do if the 

 carbon were actually in solution. The only difference in 

 the reasoning is, that the different series of carbon points, 

 instead of falling on one section, are distributed through 

 a series of circular sections of the containing cylinder, 

 these sections being parallel to the external white surface. 

 As I have shown in another paper, the results of the ex- 

 periments agree very well with the theory. So far I have 

 considered the intensity of the residual whiteness when we 

 mix black with white. The same course of reasoning 

 might be applied to determine the residual colour when we 

 mix black with any colour. Suppose, for instance, we 

 take a mass M of yellow, and let the initial yellow be Yo. 

 Then, if we mix with it a mass m of black, we shall remove 

 some fraction of the yellow ; let this be denoted by nYo, 

 so that the residual yellow is Yo(i—n), or YoR. After n 

 repetitions according to the proportions laid down in the 

 case of black and white, the intensity of the residual 

 yellow will be YoR w . 



Another problem is the mixture of white with some 

 opaque colour, red for instance. Suppose we start with a 

 white area A, then the quantity of white light given off 

 normally may be denoted by yuA. Suppose now a great 

 number of red points to fall upon this surface and to be 

 equally diffused, so that the eye does not perceive detached 



