1919 - 20 .] 
The Absorption of X-Kays. 
37 
and that g v the value of g for which k has half its maximum value, is 
given by 
/ - mg 1 2 = ± hg m or m{gj - g *) = ± hg m . 
± — — . . 
Hence 
On substituting for g this equation gives 
N 
i 2 t 'Kinc l K m ( 1 
which becomes 
AA Aj 2 
N = 
mTT_ 4k ot (A 1 - A m ) 
e 2 A A 
( 7 ) 
on changing to electromagnetic units and remembering that A 1 does not 
differ much from \ m . On substituting 
X = 
P 
wm n 
and 
4:7TK 
= — A~ 
in (7), we obtain for the number of electrons per atom 
1 (g,n\ (K - Kn) w 
1*772 x 10 11 \ p ) A m 2 
( 8 ) 
In this formula is the maximum value of the linear absorption 
coefficient, \ m the position of the maximum, and X 1 a wave-length at which 
/ul has half its maximum value. 
On applying (6) and (8) to the experimental data we obtain the results 
given in the following table. The wave-lengths in the case of the K and L 
bands were obtained from Moseley’s paper,* using the values for the K a 
and La radiations, and interpolating and extrapolating when the radiations 
in question were not given in the paper. 
Substance. 
w. 
/im p • 
Am- 
Aj Am- 
No. of ele 
at( 
by (8). 
ctrons per 
Dm 
by (6). 
Fe . 
56 
314 
1-66 
•24 
•798 
1-01 
Ni . 
59 
265 
1-44 
•22 
•935 
•84 
CuK . 
64 
176 
1-20 
•24 
1-06 
•66 
CuL . 
64 
177 
1-316 
•25 
•923 
•70 
Zn 
65 
203 
1-20 
•26 
1-34 
2-01 
Ag . 
108 
56-1 
•462 
•06 
•959 
1-08 
C 2 H 5 Br . 
109 
66*3 
*88 
•15 
•790 
•784 
Ft ' . 
195 
180 
•88 
•18 
4-60 
1*94 
Au 
197 
160 
•88 
•22 
4-01 
1-76 
A1 . 
27 
•853 
•387 
•024 
•00208 
H 2 0 . 
18 
•335 
•376 
•037 
•00089 
* Phil. Mag., xxvii, 1914, p. 703. 
