MR. R. T. GLAZEBROOK ON PLANE WAVES IN A BIAXAL CRYSTAL. 
331 
PART II. 
Section I .*—Description of a Second Crystal and Residts of Experiments. 
Before asking permission to lay the results obtained in the previous part of the 
paper before the Society, I thought it would be better, if possible, to repeat the inves¬ 
tigation with a second piece of the crystal. With some trouble I obtained a suitable 
piece last February from A. Hilger, of Tottenham Court Road. 
Like the former piece, it was an hexagonal prism in shape, but of considerably 
smaller cross-section. 
Fig. 1. 
The axis of the prism was parallel to the axis of c, the base being perpendicular to 
the axis, while the top was broken off obliquely. 
The planes m / m gave the best reflexions, and were therefore chosen to determine 
the position of artificial faces. 
My chief aim in having the prism cut was to get as long a continuous arc on the 
wave surface as possible. To attain this I had a face R, fig. 2, polished as nearly 
coincident with c as possible. 
Fig. 2. 
The oblique end was cut (P, fig. 2) so as to be inclined at about 37° to R, the edge 
of the prism thus formed between P and R being nearly parallel to the intersection of 
m and c. 
* N.B. The two Parts being quite distinct, the numbering of the Sections and Figures is commenced 
afresh with Part II. 
2 u 2 
