OF THE 



((UJnVEESITT 1 



IN CRYSTALLIZED MEDIA. X^[j ^97 



metry with respect to the plane (yz), will require <f> to remain 

 unchanged, when we change 



x 



x 



But thus a 2 , 6 2 , c 2 and a' evidently remain unaltered; moreover 



become 



7 ' 



Hence we get 



Applying the like reasoning to the other co-ordinate planes, 

 we see that the ultimate result will be 



<t,=f(a*,b\c\a'*,p*,^) ................ (2). 



The foregoing values are perfectly general, whatever the 

 disturbance may be; but if we consider this disturbance as very 

 small, we may make 



x = x + Uj 



z = z + w, 



u, v, and w being very small functions of a?, y, z, and t of the 

 first order. Then by substitution we get 



+ W- 1+ <0 



<y /du\* /dv\ 2 /dwV* _ 

 ~dy \dy) \dy) \dy) ' 



, dv dw du du dv dv dw dw 

 = Tz + ty Jr TyTz*~dyTz~fy~dx 



, du dw du du dv dv dw dw 



