252 ON THE REFLEXION AND REFRACTION OF LIGHT. 



and 



u j ,u + v$0 



v [ becomes J v u&0. 

 w J I w 



Making these substitutions in (^1), we see that the form of 

 will not remain the same for the new axes, unless 



and thus we get 



under which form it may possibly be applied to uniaxal 

 crystals. 



Lastly, if we suppose the function < 2 symmetrical with respect 

 to all three axes, there results 



and consequently, 



aw 



