I. On the Laws of the Reflexion and Refraction of Light at the common 

 Surface of two non-crystallhed Media. By George Green, Esq., 

 B.A., Caius College. 



[Read December 11, 1837-] 



M. Cauchy seems to have been the first who saw fully the 

 utility of applying to the Theory of Light those formulae which re- 

 present the motions of a system of molecules acting on each other by 

 mutually attractive and repulsive forces ; supposing always that in the 

 mutual action of any two particles, the particles may be regarded as 

 points animated by forces directed along the right line which joins 

 them. This last supposition, if applied to those compound particles, at 

 least, which are separable by mechanical division, seems rather restrict- 

 ive ; as many phenomena, those of crystallization for instance, seem 

 to indicate certain polarities in these particles. If, however, this were 

 not the case, we are so perfectly ignorant of the mode of action of 

 the elements of the luminiferous ether on each other, that it would 

 seem a safer method to take some general physical principle as the 

 basis of our reasoning, rather than assume certain modes of action, 

 which, after all, may be widely different from the mechanism employed 

 by nature; more especially if this principle include in itself, as a par- 

 ticular case, those before used by M. Cauchy and others, and also 

 lead to a much more simple process of calculation. The principle 

 selected as the basis of the reasoning contained in the following paper 

 is this: In whatever way the elements of any material system may 

 act upon each other, if all the internal forces exerted be multiplied 

 by the elements of their respective directions, the total sum for any 

 Vol. VII. Part I. A . 



