Notes on Radiation Patterns. 63 
more or less similarly orieiitated, each of which tends to produce its 
individual pattern. 
The effect produced by these elements is augmented by rotating the 
crystal through a small an^le, because the spots which recede from the 
centre become elongated, and hence show their component parts. In a 
perfect diamond the receding spot would be a uniformly drawn-out ellipse, 
whereas in the Rejection Stone it becomes a group of irregular spots 
(PL V, Fig. 10). 
4. Inferior Brown Block with black spot in it. 
This stone was also irradiated normally to an octahedral face. After 
an exposure of three hours the pattern showed that the crystal as a wdiole 
has less discontinuities in its lattice than the Rejection Stone. The pattern, 
however, shows that the distribution of the intensity in the spots is not 
uniform, and in addition there are several markings which are not caused 
by the regular lattice (PI. VI, Fig. 11). 
At this instance we wish to express our thanks to Dr. Percy A. Wagner 
for kindly lending us the above-mentioned stones. 
(e) Diffraction from the Edges of a Square Plate of Iodine. 
A 4 mm. square plate of iodine was placed normal to the diaphragm in 
order to obtain its interference pattern. After an exposure of about one 
hour the experiment w^as discontinued, and the plate developed. This plate 
showed the unexpected phenomenon of diffraction from the edges of the 
crystal (PI. VI, Fig. 12). 
In some respects it is similar to the phenomenon described by Prof. 
Laub of Buenos Ay res. 
These investigations were carried out by means of the grant in aid of 
Research, for which we wish to express our sincere thanks to the 
Grovernment. 
X-E.AT Room, 
South Afkican College, 
Cape Town. 
