Results of Crystal Analysis. 417 



differences in the position o£ the hydrogen atoms ; and from 

 these faces we can determine the parameter / with an 

 accuracy which is indeed greater than we might expect, on 

 account of the small reflecting power of the hydrogen 

 atoms. 



If we would try to determine y and a' from the above 

 formula, the best values would probably be 



*> = 34°, \ = 35°, and / = 0\5-0'6 ; 



but we may, in fact, get an equally good agreement if 

 we put 



7 



= a! = <f>, 



and then the expression for the amplitudes takes the 

 following simpler form : 



(100) A n = 74 + 12 cos n<f> + 2 [2 cos n 2f<j> + 2 cos n 2(1 + /)</> 



+ cos7*2(l + 2/')</>] 



(110) A n = 60(-l) n + 28cosn(/> + 8cos<l + 2/)(/>, 

 (001) A„ = (35+(-l) n 53)cos720 + 8cosn(l + 2/)(/), 



(101) A„= (72(-l)»+12cos^)cos»^-<^ 



+ 2(-l)» [cos W (|-0) + cosn(|-(l+/)^) 



+ cosn(|-(l + 3/)*)] +2 cos n(|-^) 

 + 2 cos n (| - (2 + 3/>) + cos n (| + 2#) 



+ cos n(j- 2(1 +./>), 



(111) A n = (53 + ( - 1) B 7 4- 24 cos i,<j>) cos ?i</> + 2 + 4 cos 2rc/0 



+ 4 cos 2n(l+f)<f> + 2 cos 2«(1 + 2/)<£. 



The value of </> can be found with a considerable accuracy. 

 1 have calculated the values of the amplitudes corresponding 

 to various values of <f> and /, and from the results of the*e 



