The Intensity of Reflexion of X-Rays by Rock-Salt. 325 



At a glancing-angle (0 + e) the amplitude of the reflected 

 beam will be 



. / 2d cos ^ 



smj p.TT.e. — - 



>y_ -V x < 



* 2d cos 

 p.ir.e. — 



T0 ... , 2d cos 6 

 it we put <p =p . 7r . e . , 



Amplitude = D'p . , 



9 



and the energy of the reflected beam is proportional to 



If, now, the crystal is rotated with constant angular 

 velocity &>, the total amount of radiation reflected is pro- 

 portional to 



J-oo </>" 2 P 7rdcos0' a>' 



Since f +co sin 2 <£ 7JL 



this becomes 



CD'fp.X = D , _ nV j, 2 _*_ 4 _ j,X 

 2d cos 6. f» *sin 2 #' ?n 2 c 4 * 2&>d cos ' 



If N = number of atoms per unit volume, 



t = thickness of crystal slip, 



we have n = N.d, t=pd. 



The energy in both the reflected and incident beams is 

 proportional to the square of the amplitude of the electric 

 vector. If the energy of the incident beam falling on the 



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



