IN CRYSTALLIZED MEDIA. . 303 



In fact, if we substitute these values in the function (4), 

 there will result 



dvY fdw 



dv\* , fdw' 



) + 



fdu dv dw\ z 



U + ^ + &J 



dv dw^ . dv dw\ 

 Tz + dy) ' 4 ^&J 



tt dw\> dudw 



pr \ fdu dv\ 2 dudv\ 

 ~\\dy dxl dy dx} ' 



which, when = A, = J9, = (7, reduces to the last four lines. 



Making the same substitution in the equation (7), we get 



1 = //, (ax + ly + czf - } 



+ (Aa* + M*+Cc*) (x 2 + y* + z*) [ ...... (8). 



+ L(cy- fa)* + M(az- ca) 2 + N(bx- ay? J 



Let us in the first place suppose the system free from all 

 extraneous pressure. 



Then -4 = 0, 5 = 0, (7=0, 



and the above equation, combined with that of a plane parallel 

 to the wave's front, will give 



Q = ax + by+cz ... ................... (9), 



l = L(cy- Izf + M(az- ex)* + N(bx - ay)' 2 , 



