produced in a gas hy 7 rays. 177 



the effect of the secondary radiation from the walls of the 

 chamber is eliminated, a measure of the energy from the 7 ray 

 beam converted directly into h rays. The energy converted into 

 penetrating cathode rays may however be (in the case of 7 rays) 

 comparatively large, even if a comparatively small number of 

 8 rays are produced, for the energy of one of the most penetrating 

 rays is about 2000 times that of a 8 ray. 



The coefficient of absorption of a plate of material placed in 

 the path of a beam of 7 rays is a measure of the energy converted 

 into energy of 8 rays, penetrating cathode rays, and other forms 

 of radiation. The ionisation values for different gases, since they 

 are only a measure of the energy converted into energy of 8 rays, 

 cannot therefore be compared with the coefficient of absorption 

 of materials without any knowledge of the comparative magnitude 

 of the energies of these radiations. Some information on the 

 subject could be obtained by comparing the coefficients of 

 absorption of liquids with the ionisations of their vapours. 



It is not improbable that the ejection of penetrating cathode 

 rays by 7 rays and X rays is accompanied by the production of 

 secondary 7 and X rays, and it would be interesting therefore, 

 when sufficient data are available, to compare the relative 

 secondary 7 and X radiations from different materials with the 

 relative penetrating cathode radiations produced, in order to see 

 how much of the secondary 7 and X radiation is accounted for 

 in the above way. 



