﻿436 Prof. W. L. Bragg and Messrs. James and Bosanquet : 



difficulties o£ estimating intensities in this way, of the few 



points which they obtained on the curve for the ™ x • ratio, 



of the difficulties in interpreting intensities which we have 

 discussed in our papers, and of the large extrapolation 

 which they had to make in order to get the limiting value 



of -j= — j-. , we feel that their results cannot be regarded as 

 r — .Li 



proving that the transference of the valency electron has 



taken place. The fact of the transference is supported by 



much indirect evidence, and their conclusion is probably 



correct. 



Debye and Scherrer also compared the intensities reflected 

 by various planes of the diamond, and concluded that the 

 electrons in the carbon o atoms were contained within a 

 sphere of diameter 043 A, assuming a uniform distribution 

 throughout this sphere. 



In all the above cases, the results were obtained by com- 

 paring the relative intensities of reflexion by various faces. 

 The results which we have obtained, and which will be used 

 to calculate the distribution of electrons in sodium and 

 chlorine, are, on the other hand, absolute determinations. 

 The intensity of reflexion was compared in each case with 

 the strength of the primary beam of X-rays, so that the 

 absolute efficiency of the atom as a scattering agent could 

 be deduced. 



In a paper on "The Reflection Coefficient of Monochro- 

 matic X Rays from Bock Salt and Calcite " *, Compton 

 made comparisons of the incident and reflected beam, for 

 the first order reflexion from cleavage faces of these crystals. 

 He obtained results for rock-salt which were rather less than 

 those which we afterwards obtained for a ground face, but 

 he noted that the effect was increased by grinding the face. 

 In our notation the results were 



Compton ^ - -00044 + '00002 



;XaCl(100). 

 B.J. and B. ^ = v 00055 



As Compton surmised, and as we have found experimentally, 

 this figure for the efficiency of reflexion has to be modified 

 considerably to allow for the extinction factor. The difference 



* A. H. Compton, Phys. Rev. vol. x. p. 95, July 1917. 



