VII. On the Propagation of Light in Crystallized Media. 

 By G. Green, B.A. Fellow of Caius College. 



[Read May 20, 1839.] 



In a former paper I endeavoured to determine in what way a plane 

 wave would be modified when transmitted from one non-crystallized 

 medium to another ; founding the investigation on this principle : In 

 whatever manner the elements of any material system may act upon 

 each other, if all the internal forces be multiplied by the elements of 

 their respective directions, the total sum for any assigned portion of the 

 mass will always be the exact differential of some function. This principle 

 requires a slight limitation, and when the necessary limitation is intro- 

 duced, appears to possess very great generality. I shall here endeavour 

 to apply the same principle to crystallized bodies, and shall likewise 

 introduce the consideration of the effects of extraneous pressures, which 

 had been omitted in the former communication. Our problem thus 

 becomes very complicated, as the function due to the internal forces, 

 even when there are no extraneous pressures, contains twenty-one 

 coefficients. But with these pressures we are obliged to introduce six 

 additional coefficients ; so that without some limitation, it appears quite 

 hopeless thence to deduce any consequences which could have the least 

 chance of a physical application. The absolute necessity of introducing 

 some arbitrary restrictions, and the desire that their number should be as 

 small as possible, induced me to examine how far our function would be 

 limited by confining ourselves to the consideration of those media only in 

 which the directions of the transverse vibrations shall always be accurately 

 Vol. VII. Part II. Q 



