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

 Corrected Values for Fci and F^ a . 



8. From the curve in fig. 3, we can calculate the absolute 

 value of Q ( ioo) and therefore the value of Fci-f-F Na for rays 

 diffracted through an angle of 12° 34' (twice the glancing 

 angle for reflexion from this face). This, as stated above, 

 comes to be 2O10. Since allowance has been made for the 

 extinction-coefficient, this is now an accurate determination. 

 In the previous paper the value of Fci + F^a was obtained by 

 measurements on the intensity of reflexion from a face, taking 

 jju to be 10'7. These measurements give F C i + FN a = 16 68. 

 The difference between the two values shows the effect of 

 allowing for the extinction-coefficient. 



We now have sufficient data to calculate the correct values 

 for Fci and F^a over the whole range of angles which has 

 been examined. When the glancing angle is large, the 

 reflexion is so weak that the extinction-coefficient may 

 be neglected. The values for Fci — F^a, given in the 

 previous paper, therefore hold good, allowance being made 

 for the differences due to the re-determination of the absolute 

 intensity of reflexion mentioned above. On the other hand, 

 the measurements described in paragraph 4 make possible 

 the absolute determination of Fci + F^ a for the angle of 

 most intense reflexion, by a method which is independent 

 of any uncertainty as to the value of yu. We can therefore 

 estimate to what extent the (100) reflexion is diminished by 

 the extinction-coefficient in the case of the measurements 

 with a crystal face, and using the formula ^ = /x -l- H we 

 can raise the values of the (110), (222), (200), and other 

 strong reflexions, so as to bring them into line with the 

 new data. The values for Fci and F Na so obtained are 

 tabulated below, and plotted in fig. 8. 



Values of Fci and F^- a . 



sine. Fd+F^. ( ^f ^ Fci-F Na . F C1 . F Xa . 29. 



•1000 17-12 21-05 4-40 12-72 8-32 11° 24' 



•1305 15-66 18-21 2-98 10*59 761 15° 



•1736 13-86 14-89 2-32 8-60 6-23 20° 



•2164 11-71 12-35 2-53 7*44 491 25° 



•2588 10-19 10-51 2-49 6-50 4'01 30° 



•3007 8-86 9-11 2-46 5-78 3"37 35° 



•3420 7-84 7-90 2-40 5-15 2*75 40° 



•3827 6-83 6-83 2-39 4-61 2-22 45° 



•4226 5-91 591 2'39 415 1-76 50° 



•4617 5-07 507 2-33 3"70 137 55° 



•5000 392 3-92 240 3-16 076 60° 



