50 Mr Bragg, The Diffraction of 
corresponding to a value of = between 6 and 9 are represented by 
the most intense spots. 
Every spot in the photograph is accounted for in the following 
So ee 
Tables. J think it is evident that the sets of planes which actually — 
reflect spots can be arranged in a very complete series with few 
or no gaps. Though at first sight it may appear that in the 
TABLE I, 
Planes for which p=1, r=1, l= 2a, X= 4an?. 
p q T s " Intensity hy hg hg 
1 1 1 3 2°8 % 1 3 1 
1 1 1 5 6°8 M% 1 5 1 
1 1 1 7 12°8 % 1 7 1 
1] 1 1 9 20:8 Invisible 1 9 1 
] 3 1 1 2°8 % 3 ih 1 
1 3 1 3 4°8 % 3 3 1 
1 3 1 5) 8:8 DG 3 5 1 
1 3 1 if 14:8 + 3 7 1 
1 3 1 9 22°8 Invisible 3 9 1 
1 5 1 1 6°8 a 5 1 1 
1 5 l 3 8:8 Me 5 3 1 
1 5 1 5 128} * 5 5 1 
1 5 1 7 18°8 Invisible 5 ii 1 
1 7 1 1 12°8 * a ] 1 
1 7 1 3 14:8 + i 3 i 
1 7 1 5 18°8 Invisible 7 5 1 
il 9 1 1 20°8 | Invisible | 9 1 1 
Range of values of , all possible up to 15. 
tables the parameters are selected in a somewhat arbitrary way, 
they are in reality the simplest possible. For instance, in Table — 
III the first values for p, g, 7, s considered are 1, 1,3, 5. This 
is so because ‘r+s’ must be positive. If 7=1, s must be odd. 
