THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



^. pr 



[SIXTH SERIES,] 



JUL Y 1921. 



I. The Intensity of Reflexion of X-Rays by Rock- Salt. — 

 Part II. By W. L. Bragg, F.R.S., Langwortliy Professor 

 of Physics, Manchester' University, It. W. James, M.A ., 

 Senior Lecturer in Physics, Manchester University, and 

 C. H. Bosanqtjet, Bal'Uol College, Oxford * 



Reflexion Formidoe. 



1. TN a previous. paper in the Philosophical Magazine f, 

 J- we described a series of measurements of the in- 

 tensity of reflexion of X-rays by various planes of the rock- 

 salt crystal structure. In analysing the results obtained, 

 a formula for the intensity of reflexion was assumed which 

 is essentially the same as that obtained by Darwin % and 

 Compton §. 



Let the Intensity I of a beam of homogeneous X-rays, at 

 a given point, be defined as the total amount of radiation 

 falling on an area of one square centimetre at right-angles 

 to the direction of the beam. If a crystal-element of 

 volume dY , supposed to be so small that absorption of the 

 rays by the crystal is inappreciable, be placed so that it is 

 bathed by the X-rays, and if it is turned with angular 



* Communicated by the Authors. 



t Bragg, James, and Bosanquet, Phil. Mag-, vol. xli. p. o09 (March 

 1921). 



t C. G. Darwin, Phil. Mag. vol. xxvii. pp. 315 & 675 (Feb. and 

 April 1914). 



§ A. II. Compton, Phys. Rev. ix. p. 1 (Jan. 1917). 



Phil. Mag. S. 6. Vol". 12, No, 217. July 1921. B 



