THE 

 LONDON, KDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 



. 



MARCH 1921. 



XXIX. The Intensity of Reflexion of X- Rays by Rock-Salt. 

 By W. Lawkence Bragg, M.A., Langivorthy Professor of 

 Physics, The University of Manchester ; R. W. James, 

 M.A., Senior Lecturer in Physics, The University of 

 Manchester; and C. H. Bosanqtjet, Balliol College, 

 Oxford*. 



Introduction. 



1. 4 GCU RATE comparisons of the intensity of reflexion 

 u\. of X-rays by crystal-faces were first made by 

 W. H. Bragg f , who measured by the ionization method the 

 energy of the X-rays reflected by various faces of rock-salt. 

 He showed that if X-rays of definite wave-length are 

 reflected at a glancing-angle by a face with one or more 

 even crystallographic indices (e. g. (100) (110)), the in- 

 tensity of the reflected beam can be expressed approximately 

 by the formula 



sm 2 



where A and B are constants and 1$ measures the intensity 

 of the reflected beam of rays. In the case of even orders of 

 reflexion from faces with odd indices, the intensities of 

 reflexion may be expressed by the same formula. When the 

 observed intensities for various faces and orders are plotted 



* Communicated by the Authors. 



t W. H. Bragg, Phil. Mag. vol. xxvii. p. 881 (May 1914). 



Phil. Mag. S. 6. Vol. 41. No. 243. March 1921. Y 



