The Intensity of Reflexion of X- Rays by Rock-Salt. 327 



By equation (3) the reflecting power of a thickness t o£ 

 the crystal is given by the formula 



I ~ 2 sin 2 6> cos 6> mV " 



The total reflecting power of the crystal face is therefore 

 equal to 



N 2 \ 3 _ e 



l sin^ a cos v m 



2 c 4 1 



v Jo 



IfXZ 



F 2 ^,! e~^dz 



N 2 X^ y sin (9 



2 sin 2 '6* cos 6' mV'" 2^ 



N 2 X 3 _ e A 



~2yasin2(9 ,F2 m 2 c 4 ^ 



Oompton gives his formula in the form 



E r N 2 ^y i_ 



"E, ~ 2/* sin 2(9 '&0' 



which agrees with this, since his factors N 2 </> 2 -^ 2 have the 

 same meaning as N 2 F 2 —^- t t defined as above. Compton 



derives the equation by a more complete mathematical 

 treatment, and has discussed very fully the effect of imper- 

 fection of the crystal and of the length of the wave-train. 

 He arrives at the same formula, whatever assumptions are 

 made. 



This expression must now be multiplied by a " polariza- 

 tion factor" 1 ± c ^ s !^ an d a "Debye factor" r 2 ^ 2 ". 



The complete expression for the reflecting power R is 

 therefore 



I ~ a ~ 2/j,sm20\ mV 2 '* " ' W 



The Debye Factor for Rock-salt. 



14. Debye * gives the formula for the factor which 

 expresses the diminution of the intensity of reflexion with 

 rise of temperature in the form 



/,-B sin- 9 



t ? 



* P. Debve, Ann. der Phys. (4) xliii. p. 49 (1914). 

 Z 2 



