(59) 
NOTES ON 
(a) EADIATION PATTERNS OF THE TEANSFORMATION OF 
MAaNESIUM HYDROXIDE TO MAaNESIUM OXIDE. 
' (6) SERPENTINE, MALACHITE, AND PSEUDOMORPH QUARTZ. 
(c) BIJLTFONTEIN APOPHYLLITE. 
(d) DIAMOND TESTS BY RADIATION PATTERNS. 
(e) DIFFRACTION FROM THE EDOES OF A SQUARE PLATE 
OF IODINE. 
By J. Steph. v. d. Lingen. 
(With Plates I-YI.) 
(a) Radiation Patterns of the Transformation of Magnesium 
Hydroxide to Magnesium Oxide. 
In his lecture before the eighty-fifth Naturforscherversammlung in 
Vienna, Frederich described the appearance of certain Rontgen interference 
phenomena in the pattern of certain crystals.* 
These phenomena consist of the usual pattern of points lying on conic 
sections, and in addition the phenomenon of radial lines emanating from 
these points towards the central point. 
This latter phenomenon he ascribed to a two-dimensional grating effect 
of the crystal, co-existent with the usual three-dimensional grating. 
Subsequently von Lane and the author contended that this phenomenon 
was not due principally to the space-lattice of the crystal, but rather to 
cleavage planes, which disturb the regularity of the three-dimensional 
grating, t 
If the regularity is disturbed in one direction, only two of the thi-ee 
factors which determine the maximum intensity remain ; hence the lattice 
of the crystal as a whole tends to become a two-dimensional one. 
This latter contention is supported by the observations on the change 
of magnesium hydroxide to magnesium oxide. 
On transmitting Rontgen rays parallel to the trigonal axis of a micro- 
scopically perfect piece of Brucite it showed the usual interference pattern 
of points without radial lines. 
* 'Phys. Zeit.; 14, 1079, 1913. 
t ' Nat. Wissenschaft,' 13, 319, 1914. 
