'890 



Prof. W. H. Bragg on the Intensity of 



Considering, therefore, all the reflexions in which the 

 effects of the various atoms add together directly, there is 

 Jiot a different law for each face, but one law for all the 





Fig. 4. 







100 



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50 













•\ 











1 1 





•~- — 1 





i /e jd a 



?J£ 5-- P)3 



faces ; and it is of especial interest that those reflexions from 

 the. (Ill) planes, in which the effects of the two kinds of 

 plane add together, fell in with the rest. 



It will be observed that the intensities fall away somewhat 

 more rapidly than the inverse square of the sine of the 

 glancing angle. For convenience of comparison, the upper 

 curve in the figure shows how the observed points would 

 have been placed if the law had been that of the inverse 

 square. 



It will be possible eventually to express each of the 

 intensities in the above table in absolute terms, which are 

 independent of all circumstances of the experiment and 

 depend only on the nature of the crystal, the order of the 

 spectrum, or more generally the glancing angle, the tem- 

 perature, and the wave-length of the rays reflected. This is 

 to be done in the manner explained above (p. 885). I have 

 not attempted to do this so far. It will be necessary to use 

 as primary rays a pencil which has been sorted by reflexion. 

 In these experiments the full stream of rays from a rhodium 

 bulb has been used. Some idea of the efficiency of reflexion 

 may be given by the following experimental results. 



