The Intensity of Reflexion of X-Rays by Rock-Salt. I'd 



grinding the crystal plate on coarse emery-paper, plates 

 prepared in this way giving a 'reflexion over a long range, 

 and abnormally high values for the intensity. 



Fig. 7 will illustrate this effect. A single crystal plate 

 was cut across in two equal portions, and from these 

 two plates of the same thickness (0*78 mm.) were prepared. 



Fig-. 7. 



Crystal Setting. 



&° 7° 



Crystal Setting. 



A. Intensity of reflexion 093. 



B. „ „ „ 1-20. 



The first plate was rubbed down on ground glass with water 

 so as to avoid all mechanical strain. The second was 

 ground down on coarse emery-paper. The curves of fig. 7 

 show the amount of radiation reflected by the plates over a 

 range of a few degrees. The first gives a narrow maximum, 

 showing that the structure is regular ; the second, an irre- 

 gular curve over a much larger angle. The intensities of 

 reflexion in terms of that of the standard plate were 0'93 and 

 1'20 respectively for the (100) reflexion, showing how much 

 greater the intensity is for the irregular than for the regular 

 crystal. In fig. 4, the points corresponding to these two 

 crystals are denoted by " A " and " B ." The irregularity 

 of the points in fig. 4: is therefore to be ascribed to slight 

 differences in the perfection of structure of the crystal 

 plates, and the fact that they can be made to fit with 

 a fair approximation to a te~> xt curve shows that all the 

 plates have much the same degree of irregularity of 

 structure. As stated above, the few abnormal points 

 were all found to correspond to crystals which for some 

 reason had an exceedingly irregular structure. 



