BY ELIZABETH J. ARMSTRONG
The reflection of X-rays from crystalline material depends very precisely on the orientation of the crystal structure with respect to the X-ray beam: the intensity of the reflection is related to the structural perfection of the crystal. Based on these fundamental principles various techniques have been and are being devised for the X-ray study of structural disturbances in artificially prepared crystal surfaces and natural faces. These techniques are reviewed, and their potentialities and limitations are noted, with special reference to their use in the study of ground and lapped quartz surfaces.
BY RALPH J. BERNHAGEN
Earth-resistivity surveys operate on the fundamental premise that earth materials of different character react differently to the passage of an electric current. Average . . .