432 
MR. R. T. GLAZEBROOK ON DOUBLE REFRACTION 
Table VII. gives the results of these calculations. The first column gives the face 
to which the normal considered is drawn and its direction with reference to the 
crystal prism. The next two columns give the values of 0 l 0. 2 , the last two those 
of a (3. 
The values of f3 show that the principal plane of the prism which contains the 
normals to the faces P and Q is nearly coincident with the plane z Ox. 
We proceed to find the position of the line of junction of these planes and the 
angle between them. 
Fig. 3. 
Let P Q (fig. 3) meet z x in M. 
Draw Q K, P L arcs perpendicular to z x. 
Then from triangle P M L 
sin PL = sin PM sin PML 
From triangle Q K M 
Whence 
and we have 
sin QK = sin (PM + PQ) sin PML 
sin (PM + PQ)_sin QK 
sin PM sin PL 
cot PM sin pQ = EL^_cog PQ 
sin LP 
(3) 
If P and Q are on opposite sides of 2 x, we get 
cot PM sin PQ=-r-yrw + cos PQ.(4) 
sm LP v ' 
In these formulas, P Q, P L, Q K being known from Table VII. and the angle of the 
prism, we can find P M. 
