'60 
Transactions of the Royal Society of South Africa. 
On heating the same crystal over 300 degrees, and obtaining its inter- 
ference pattern at this temperature, tlie plate showed only six radial lines, 
with no trace whatsoever of the usual pattern. 
The same specimen was then examined at room-temperature. In this 
case, ceterihus paribus, the plate showed an increase in the number of radial 
lines, but no interference points. That there are fewer radial lines in the 
former case than in the latter is due to the Debye effect,* 
Tlie intensity curve of the incident Rontgen rays is reflected in these 
radial lines, which now represent the complete reflected spectrum. 
On examining the specimen macroscopically it was found to be now 
perfectly opaque, and so brittle that it crumbled into small flakes upon 
touching it. 
The experiments recently carried out by the author show that the 
displacement of water molecules causes the displacement of the three 
principal points of the usual pattern, so that they become drawn out along 
radial lines, which seems to indicate a uniform displacement of the reflect- 
ing planes (vide PL I, Figs. 1 and 2 and PI. II, Fig. 3). 
Consequently we may conclude that whenever radial lines appear in the 
interference patterns there has been a weakening of the lattice of the original 
homogeneous crystal. 
(6) Serpentine, Malachite, and Pseudomorph Quartz. 
Serpentine. 
Some crystallogra.phers classify Serpentine as triclinic, whereas others 
# simply state that the form of crystallisation is uncertain. Therefore it 
may be interesting to consider what light treatment with X rays may throw 
upon the matter. Moreover, it appears to be physically analogous with 
pseudoisotropic liquids when placed in a magnetic field. 
It seems analogous only in so far as one axial direction is fixed. 
A plate of Carolina (Transvaal) serpentine | mm. thick was placed so 
that the threads were perpendicular to the incident rays. After an exposure 
of four hours the photographic plate showed a pattern symmetrical about 
the direction of the threads. The radial lines parallel to the threads showed 
a greater intensity than the subordinate lines, which are inclined at 30° and 
60° respectively to the threads (vide PI. II, Fig. 4). 
On rotating this crystal round the direction of the threads through an 
angle of 60°, the subordinate lines were hardly discernible after an exposure 
of three hours. 
If this mineral be heated the subordinate lines would probably vanish, 
and the pattern would consist only of a line parallel to the threads — 
phenomenon displayed by pseudoisotropic layers of para-azoxyanisol after 
an exposure of some forty hours. 
* ' Phys. Zeit.' 15, 75, 1914 ; ' Nat. Wissenschaft,' 15, 371, 1914. 
