MR. R. T. GLAZEBROOK OR PLANE WAVES IN A BIAXAL CRYSTAL. 
341 
Let 
MQ'=0 3 
WQ'=e 3 ' 
then 
6' + 0, d'-6, 
COS — 9 — cos -- - 9 
cos Bo = - --— 
COS [l 
6o' + do . do — 6., 
sin — -—- sin 1 
cos a d=- --— 
COS jl 
But 0 3 , 6o are the angles between the faces Q and m, Q and m respectively. 
And observation shows that 
03=19° O' 15"! 
6 3 64° 37' 0"J.^ 
Whence 
/3 3 =35° 58' 41".(4) 
a 3 =60° 42' 56".(5) 
cos Q'BA= 
sm/3 3 
Q / BA=33° 37' 51" 
cos CQ'= sin BQ' sin Q'BA 
•'•73=CQ'=71° o' 44".(6) 
To corroborate these values let us find P Q' and compare with experiment 
A -r, COS /3o 
cos Q AB= . 
Sill « 3 
.•,Q'AB=21° 54' 12" 
But we know from the previous work (Section II.) that 
PAB= 90°—PAC= 58° 42' 42" 
.\PAQ'=36° 48' 30" 
cos PQ'= cos AP cos AQ'-fi sin AP sin AQ' cos PAQ 
Whence 
PQ'=35° 18' 35" 
The mean of a large series of experiments gave 
PQ'=35° 18' 50" 
and again we have strong evidence in favour of the correctness of the work. 
