Physical Conditions and Absolution of Light. &2.> 



contained helium at a pressure of about 8 millimetres. Such an 

 active plate causes a vigorous recoil o£ the atoms of actinium 

 D. Some throws were observed large compared with those of 

 the a particle ; but the interpretation of the experiments is 

 complicated by the natural disturbances due to the uncovered 

 opening and to the strong ionization produced by the 

 radiating source outside the opening. Further experiments 

 are in progress to test whether this method can be employed 

 to count the recoil atoms with certainty. 



Universit}' of Manchester, 

 August 16, 1912. 



LYIII. On the Influence of the Physical Conditions of a Sub- 

 stance on its Abso?*ption of Light. By G. H. Livens, B.A., 



Fellow of Jesus College, Cambridge* . 



IN a recent communication to this Journal I have given a 

 discussion of the effect of the density of a gas on its 

 line spectrum. The results there obtained have, however, a 

 wider application than appeared at first sight. An expla- 

 nation of several other experimental facts concerning the 

 effect of the physical circumstances of a substance on its 

 absorption of light also appear to be contained in the theory. 

 An interesting account of the phenomena under discussion is 

 given by Prof. Wood in his book on ' Physical Optics.' 



A few of the results here obtained have already been 

 deduced by Dr. Haveloek |, and the reader is referred 

 to that author's papers for a more complete discussion. 

 Dr. Haveloek' s results however, are, owing to their gene- 

 rality, exhibited in rather a complicated form, and it seems 

 as well to present them in the much simpler form in which 

 they are deducible from the present theory. 



1. The influence of the nature of the solvent upon the 

 position of the absorption bands of the dissolved substance. — 

 Wood gives a short account of Kundt's work on this subject, 

 and summarizes the results in the following statement of 

 Kundt's law: — If one transparent medium has a higher 

 refractive index than another, the absorption bands of a 

 dissolved substance lie nearer the red end of the spectrum 

 when it is dissolved in the former than when it is dissolved 

 in the latter. 



I shall now adopt the notation of my previous paper and 



* Communicated by the Author. 

 t Proc. R. S. 1910, 1911. 



