XIV. On the Transmission of Light in Crystulli%ed Media. By Philip 

 Kelland, B. a. Felloiv and Tutor of Queens' College, Cambridge. 



[Read Feb. 13, 183?.] 



INTRODUCTION. 



The object which I have principally had in view in the Memoirs 

 which I have hitherto laid before this Society, has been the develop- 

 ment of the equations for the motion of a series of particles in a 

 form calculated to lead to a simple and tangible interpretation. 



The point of greatest interest connected with the subject, is the 

 determination of the laiv of force by which the particles act on each 

 other. The data for the investigation of this law are neither numerous 

 nor Avell defined, and one difficulty in particular attaches itself to every 

 part of it, arising from our uncertainty respecting the number and 

 nature of the causes which may conspire to the production of any 

 particular phenomenon. 



In my first Memoir I discarded all complexity from my investiga- 

 tions, and conceived the whole effect to be due to the action of par- 

 ticles of the same kind: from a comparison of my results with those 

 of observation, I was led to the conclusion that the law of force is 

 that of the inverse square of the distance, and by means of that law 

 was enabled to shew that the vibrations are necessarily transversal. 



In my second Memoir I treated the subject in a more general 



manner, attributing the phenomena to the action not of one system 



of particles, but of two, which act mutually on each other. Tliere 



appeared numerous coincidences, which, if they did not suffice perfectly 



Vol. VI. Part II. T t 



