﻿438 Prof. W. L. Bragg and Messrs. James and Bosanquet r • 



inappreciable. We use a large crystal consisting of num- 

 bers of such homogeneous units and deduce, from its 

 reflecting power, the reflecting power Q per unit volume 

 of the units of which it is composed. The assumptions made 

 in doing this are by no means free from objections, and will 

 be discussed later in this paper. Taking this to be justifiable, 

 however, our experimental results yield the value of Q for 

 rock-salt over a wide range of angles, and from them the 

 values of F C i and F Na follow directly. These values are 

 shown in fig. 1. 



Fur. 1. 



18 





1 











\ 

 \ 



\ 

 % 













12 



8 



\ 



\ 

 'I 













\ 

















































4 

























*P) 















'(c) 



0-3 

 S/o A 



(a) F C1 corrected for Debye factor, (c) F Na corrected for Debye factor. 



(b) F cl uncorrected „ „ (d) F Na uncorrected „ ,, 



4. We must now consider more closely the significance of 

 the factor F. The most simple case is that of a crystal con- 

 taining atoms of one kind only. Parallel to any face of the 



