XXII. On the Propagation of Luminous Waves in the interior of 

 Transparent Bodies. By the Rev. M. O'Brien, M.A., late 

 Fellow of Caius College, Cambridge. 



[Read April 25, 1842.] 



§ 1. The chief object of the following Paper is to investigate what 

 effects may be due to the action of the material particles upon the 

 etherial, in the case of light transmitted through a transparent body; 

 and among other things to shew that the dispersion of light in passing 

 through a prism may be acounted for without having recourse to the 

 Hypothesis of Finite intervals*. 



The following is a brief statement of the results arrived at, some of 

 which, if true, must be of considerable importance in the Undulatory 

 Theory of Light. 



§ 2. I have endeavoured to prove : — 



(1°) That the action of the material particles upon the etherial is very 

 nearly the same as if the former particles were absolutely fixed. (See § 14.) 



(2°) That this action introduces certain simple terms, viz. : — 



mC mC n m C 



-— a, -'— /3, - '— y, 

 m m m 



into the equations of motion of the etherial particles. (See § 15.) 



* By the Hypothesis of Finite intervals, I mean the hypothesis that the particles of ether 

 are placed at intervals which are finite compared with A, the length of a luminous wave; 

 or, what amounts to the same thing, that the intensity of the molecular force exercised by 

 one particle upon another is not very small at the distance A. 



I may here observe, however, that the present paper does not in any way assume that 

 this hypothesis is not true, as will appear in Art. 12; it only attempts to shew that the 

 undulatory theory can do without it. In one place, indeed, I have endeavoured to shew 

 that the Hypothesis of Finite intervals is very improbable. 



Vol. VII. Paet III. Yy 



