Pressure for Rontgen Rays in different Gases. 



35 



It should, however, be quite perceptible in the ionization 

 pressure curve for ethyl bromide, and on turning to Fig. 1 it will 

 be seen that this is the case. 



The curve for ethyl bromide, unlike those obtained for other 

 gases, has a distinct upward tendency, and from the magnitude of 

 its departure from the tangent through the origin, it is easy to 

 deduce that, at a pressure of 160 mm., the ionization due to the 

 secondary rays is about 16 °/^ of that due to the primary. 



For the other gases tried the curves shew that the effect of 

 the penetrating secondary rays may be neglected. 



'Pressure 



Fig. 1. 



mm. 



2. It was thought possible that in addition to the penetrating 

 secondary rays there might be some soft secondary radiation 

 (possibly soft yS-rays) emitted by the gas under the action of the 

 Rontgen rays. It was with the special object of investigating 

 this point that the present experiments were undertaken. It can 

 easily be seen that if the pressure of the gas is so low that the 

 soft secondary rays from the gas are not completely absorbed in 



3—2 



