Reflexion of X Rays by Crystals. 



897 



means of the same ionization .chamber, placed in different 

 positions, as shown in the figure. 



Fig. 10. 



too 







• 

 • 



\ 



200 

 100 











/ 



\ 



&°\5' 



35* 



w 



CLbsorpt'Ccm band of 'Kk lint 

 u*. cUavn.on.cl (ill) 



Upper curve chous band 



Lower •> .. Unt 



The I existence of this special reflexion makes it very 

 difficult to interpret the experimental results. The ratio of 

 8'95 to 1 given above may be explained on the supposition 

 that there is no appreciable temperature effect in the diamond, 

 which would be in agreement with DebijVs theory, that the 

 intensity in such case varies as the inverse square of the sine 

 of the glancing angle, and that for the first and third orders 

 the crystal may be treated as infinitely thick. But there 

 may be other explanations. In any case further experiment 

 is needed. 



A useful result of a different nature may be derived from 

 the measurements with the diamond. By averaging the 

 large number ol observations an accurate value can be found 

 for the difference between the glancing angles of reflexion 

 of the first and third order. The means of two different sets 

 of observations gave 17° 59*8' and 18° 00*9' respectively : 

 the figures refer to the larger constituent of the doublet. 

 From this we may. determine the value of the glancing angle 

 for either order. 



When a crystal is mounted on the spectroscope table, it 

 has generally some error of adjustment. This may be cor- 

 rected by swinging the ionization chamber over to the other 



