364 
MR. R. T. GLAZEBROOK OR PLARE WAVES IR A BIAXAL CRYSTAL. 
we may therefore obtain corrections to /y /x :2 independently, to fi 1 by supposing an 
increase in the value of L P, to /x 3 by supposing the planes P It. P Q to turn through 
a small anode about some line in them. 
Moreover, we shall consider that line to be in each case the line of intersection with 
the plane A 0 C, and treat this line as the same for both planes, the two lines thus 
considered as coincident are really inclined at an angle of 3'. 
To find then the variation which we must assume in L P to bring the results of 
theory and experiment into closer agreement for the inner sheet, we proceed as follows— 
If in the equation 
9 
( 0 + 0 ') 
we substitute an experimental value for /x l3 we can determine a value of (6+6'). 
Subtracting this from the calculated value, we get 8(9+6'). 
But for the displacement considered $6=89'. 
Hence we have found 86 ; but cos (LN — \)= - -- )S A cos 6. 0 L and X are unaltered 
v ’ cos OL 
by the displacement supposed; therefore we get S(L N), and LP = LN+</>'. <j 7 is 
constant, therefore we have found 8 L P. 
To put this plan into execution, I chose as the experimental value for /x 2 the 21st 
in Table VI. 
^=1-62807 
the differences between theory and experiment having at that point a maximum value 
and being fairly regular. 
The resulting value for (6+6') is 
70° 57' 20" 
The calculated value is 
70° 16' 40" 
The difference is 
0° 40' 40" 
.-. 86 = 0 ° 20 ' 20 " 
This gives for S(L P) 
S(LP) = 0° 21' 20" 
Thus at this point the result of theory and experiment could be brought into 
coincidence by supposing the line O P normal to the face P to turn through an angle of 
0° 21' 20” in the plane L P away from L. 
Before discussing the effect of this change on the values of /x, in other directions, 
let us consider the variation it will be necessary to make in the angle A L N to bring 
the theoretical results for the outer sheet into accordance wdth experiment. Taking 
