378 Electrical Coyiduciivity in Gases traversed hy Catliode Rays. 



strength pass through a gas, the number of ions produced per second 

 in 1 c.c. depends only upon the density of the gas, and is independent 

 of its chemical composition. 



From the results thus obtained, the conclusion is drawn that, when 

 cathode rays are absorbed to any extent, the positive and negative 

 ions produced by these absorbed rays are of a definite amount, which 

 bears a constant ratio to the quantity of the rays absorbed ; that is to 

 say, in order to ascertain the relative ionisations produced in any tvv^o 

 gases by cathode rays of the same intensity, it is sufficient to determine 

 the absorbing powers of the two gases for the same rays. In other 

 words, the coefficients of ionisation are determined when the coeffi- 

 cients of absorption for the same gases are known. 



The paper then deals with the ionisation in any particular gas under 

 varying pressures. The inference is drawn that, under rays of con- 

 stant intensity, the ionisation in a particular gas varies directly with 

 the pressure. The very great absorption of the rays by gases at 

 ordinary pressures prevented a direct verification of this relation ; but, 

 as Lenard has shown, the coefficients of absorption for any particular 

 gas to vary directly with the pressure, the conclusion seems quite 

 justifiable in the light of the connection established between ionisation 

 and absorption. 



Assuming this relation to be true, it follows at once that, if rays of 

 constant intensity are allowed to traverse difierent gases at the same 

 pressure, the ionisations produced would be directly proportional to 

 the densities of these gases. 



These numbers for the gases examined are given in column 1 of the 

 appended table, while in column 2 are given the values found by 

 Professor J. J. Thomson for the relative ionisation produced in these 

 same gases by Rontgen rays of constant intensity. 



Grases examined. 



Column I. 

 Ionisation by 

 catliode rays 

 (calculated). 



Column II. 

 Ionization by 

 Kontgen rays 



(observed). 





1-00 



1-00 





1-106 



1-10 





0-97 



0-89 





1-53 



1 -40 





069 



0-33 





1-52 



1 -47 



The numbers, with the exception of those for hydrogen, present a 

 fair agreement, and they show that although the two forms of radia- 

 tion are so very dilferent in many respects, still the products of their 

 actions on the gases examined are practically the same. 



