204 
Tra/nsactions of the Royal Society of South Africa. 
These results seem to indicate that there is a marked difference between 
the elastic constants of the two crystals. 
The analysis of these radial lines is of great importance in determining 
the mechanical properties not only of crystals but also of raw materials for 
engineering. 
X Rat Laboratory, 
S.A. College ; 
August 14th, 1916. 
