﻿320 Prof. Barkla and Mr. Simons on Ionization 



but had latterly been received with some scepticism. Indeed, 

 the experiments had been made with little knowledge of thn 

 laws of secondary radiation. It was important that the 

 question should be conclusively settled. To thoroughly test 

 the relative ionizations in SH 2 and S0 2 , experiments were 

 made by us with X-radiations varying enormously in pene- 

 trating power from that characteristic of Or (series K) to 

 that characteristic of Sb (series K) and many intermediate 

 penetrating powers. Various ionization-chambers of three 

 entirely different types were used, the lengths varying from 

 1 cm/ to 1'2 cm. ; the windows and ends of these were of 

 carbon, paraffin-wax 3 and aluminium ; the terminals were of 

 various forms — some exposed to the X-radiation, others not 

 exposed. Both gases SH 2 and S0 2 were prepared in different 

 ways, in some cases containing a large quantity of aqueous 

 vapour, in others exceedingly dry. Large variations were 

 also made in the intensity of the radiations to which the 

 gases were exposed until the limits of accurate measurement 

 were reached, but no variation of relative ionization was 

 observed ; so that there appears no possibility of the satura- 

 tion-current not having been reached. Only in the case of 

 the short ionization-chamber in which the end-effects were 

 large and unknown did accurate experiments show variations 



Table I. 

 Ionizing radiation : the fluorescent X-radiation (series X) from Ag. 



Length of 

 Ionization- 

 chamber. 



n Observed 



bras -r, , • 



T • , Relative 

 Ionized. T • 



Ionization. 



Corrected 

 Ionization. 



Rc-latire 

 Ionization. 



3-5 cm Air LOO 7 



SH 2 106 107 

 S0 2 8-5 8-6 



1 

 15 - 3 1 ratio 

 12-3 j 124 



ILocm Air 117 



Sff 2 164 

 S0 2 135 



LOO 1 

 17 15'6 I ratio 

 147 12' ( JJ 1-21 



ILocm Air 1 89 1 , . 



SH., + 2 7 5, 74 77,7-6 8'65, 8o5 / ™™ 

 S0 2 "+H 2 G-46. 63 G-0, o"45 7 4, 725' j^ 



Note.- — In the first set of three experiments the air-icnization -was corrected 

 for end corpuscular radiations [from Sadler's results], and the Sjll 2 and 

 S0 2 ionization corrected for absorption. The boundary corpuscular 

 radiation effect in these was negligible. Window and end were of Ah 



In the second set of three experiments a correction for corpuscular 

 radiation from the end was not made, as it was cf paraffin. 



In the third set of three experiments corrections were made for 

 corpuscular radiation from the ends when air was ionized, and for 

 absorption in the gaseous mixtures. 



