188 DK. JAMES BOTTOMLEY ON THE ABSORPTION 



object seen through the liquid seems of diminished dis- 

 tinctness. 



As a typical case take carbon diffused through water. In 

 a paper which I read at the last Meeting of the Physical 

 and Mathematical Section I alluded to some attempts to 

 obtain a soluble black in order to make some experiments 

 on the absorption of light. To assist my judgment as to 

 the appearance which such a liquid should present, I had 

 a cylinder containing a little carbon diffused through water. 

 Weak diffusions of carbon in the colorimeter gave the same 

 appearance when I looked at external white surfaces as I 

 should have expected a liquid containing a soluble black in 

 solution to give under the same conditions. A diffusion 

 of carbon both disperses light and absorbs light. The 

 dispersion gives rise to a greyish tint, due to the light 

 coming from the innumerable particles of carbon. Owing 

 to the absorption a white surface seen through the column 

 of liquid seems of diminished whiteness. Hence, under 

 ordinary circumstances the light which comes to the eye 

 has a twofold origin, part being transmitted light and part 

 dispersed light. My first object was to dissociate these 

 two phenomena. I therefore used cylinders which were 

 covered with black cloth, admitting light by circular aper- 

 tures at the bottom, 8 millim. in diameter. In this way 

 the dispersed light was almost wholly cut off. In some 

 cases a feebly nebulous light could be seen around the 

 apertures ; but it was very slight and did not interfere with 

 experiments to determine the absorptive properties. With 

 any attempt to explain by physical optics the analogy of 

 the absorption of light by solutions and diffusions I have 

 nothing to do ; but, on the supposition that there was con- 

 tinuity, I was led to expect that a function of the same 

 form would express the intensity of the transmitted light in 

 both cases. Also, independently of such considerations, it 



