The Method of Debye-Scherrer and Hull

Continual variation of the angle of incidence p and the corresponding satisfaction of condition (2) may be attained in a different way. If, instead of a single crystal, a powder consisting of very many small crystals is placed in the path of an x-ray beam, it will happen in general that, because of the random orientation of the little crystals, a characteristic lattice plane will always be available for any incident angle whatsoever a multiplicity of (p values is furnished in this case by the proximity of many tiny particles. 

It may be added that the Laue-diagram affords the third possibility, 

It may be mentioned that G. D. Preston, Nature 142, 569 (1938), has recently discovered x-ray reflections of a different type, which are due to the interaction of the x-rays with the heat waVes, which travel through the lattice in all directions. 

The use of such layer line diagrams has frequently proved highly useful in determining complicated structures. 

With regard to reflection from planes which are not parallel to the axis of rotation, there is an important effect observable on irradiating a disoriented crystal powder. If, for example, the small crystals in the irradi- 

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