366 MR. R. T. GLAZEBROOK OR PLANE WAVES IN A BTAXAL CRYSTAL. 
while 
for the prism P Q 
log 
cos OL 
cos A 
= 1-9945594 
( 3 ) 
rasOT ,_ 1 . 9970825 
cos A 
(4) 
A, = 5° 10' 20".(5) 
A =3° 54'.(6) 
bg^-^ = P 9 946764 .(7) 
& cos \ x ' 
log C0S ^ ^ = 1-9969629 .(8) 
COS A>. 
The ensuing Table gives the values of /p, /x :3 for nine different incident waves taken 
from the previous work, calculated on the supposition that both these changes have 
been made in the position of the plane P It. 
The column headed Difference gives the excess of theory over experiment ; that 
headed a gives the excess of the theory before it was modified; /3 gives the change in 
the theoretical value of fi 1 due to this displacement. 
