PROF. C. G. BARKLA ON X-RAYS AND THE THEORY OF RADIATION. 
331 
can be most clearly explained by reference to the results obtained in one particular 
substance, ethyl bromide. 
Experiments were commenced by the writer and Mr. M. Thomas* on the ionization 
produced in ethyl bromide vapour by a number of approximately homogeneous 
X-radiations of various wave-lengths. One series of these experiments was made 
in a very large ionization chamber cylindrical in shape, of length 68 cm., diameter 
44 cm., and with an axial electrode connected through a side tube to an external 
electroscope. Ionization-pressure curves were obtained in the usual way and with 
great care, both with air and with ethyl bromide in the chamber, all other 
conditions being similar. After the usual correction for absorption in the gases 
themselves, the relative ionizations given in Table III. were obtained. Column I. 
Table III. 
I. 
n. 
III. 
IV. 
Source of X-rays. 
Approximate wave-length (K ai ). 
Absorbability ( — j 
m 
W 
o 
• r—i 
-G> 
.3 
*3 
£ 
O 
o 
r*j 
o 
c3 
O 
HH 
Ionization coefficient in air (K, L ...) 
Cu 
cm. 
1•54 xlO- 8 
47-7 
50 
As 
1-17 x10-« 
22-5 
49 
•3 
Se 
1-10 xlO" 8 
18-9 
* 
50 
•5 
Sr 
0-871xlO" 8 
9-40 
165 
Mo 
0-710 x lO" 8 
4-70 
221 
Ag 
0-562 xlO -8 
2-50 
279 
Sn 
0-487 x lO" 8 
1-57 
298 x 
1-32 
Ce 
0-355 xlO" 8 
0-6 
= (393) 
342 x 1-39 
= (475) 
V. 
VI. 
K 
o 
d 
£ 
*3 
£ 
<D 
o 
o 
d 
"3 
c3 
N 
M 
kyT 
i—i 
oS 
'3 
50 
<X> 
o 
o 
115 
171 
229 
343 
W 
>o 
C-J 
Q 
•S 
s 
o 
23 
P. 
s-i 
o 
to 
rP 
o 
<3 
s 
A 
Pt 
u 
O 
to 
rO 
24- 4 
25- 3 
26- 2 
159 
190 
210 
267 
425 ; 321 
VII. 
»o 
o 
d 
+3 
P. 
o 
‘sH' 
A 
A 
t-, 
"cS 
P 
o 
co 
rO 
<1 
133 
164 
184 
241 
295 
VIII. 
O 
S-. 
PQ 
o 
m 
C-J 
o 
P 
c3 
A 
p 
o 
Pi 
rP 
g P 
3 O 
cr'-rs 
u "V 
O eS 
C4-I P-i 
2'05 
1-94 
1-93 
IX. 
cS 
O ^ 
g S 
f- 
O 
M 
c3 
c8 -S 
a*. 2 
- 4-3 
^ "2 
O c8 
M-l s— 
0 • 865 
1-04 
1-255 
1-42 
1-44 
* Shortly after the outbreak of war, Mr. Thomas was given a commission in the army, so was unable 
to complete the work he commenced so successfully. He was killed in action on December 31, 1915. 
VOL, CCXVIL—A. 3 A 
