130 Prof. Thomson & Mr M e Glelland, On the Leakage of [Mar. 9, 



Rate of leak through coal-gas at different pressures. 



769 58 1606 



579 70 1680 



374 81 1563 



Rate of leak through hydriodic acid gas at different pressures. 



769 7 194 



489 8-5 189 



289 10-5 178 



89 20-5 193 



These numbers show that over a considerable range of pressures 

 the rate of leakage through the gas, i.e. the electrical conductivity 

 of the gas, is approximately proportional to the square root of the 

 pressure. Now we know from the theory of the dissociation of 

 gases that in cases where the dissociation is small, i.e. where the 

 number of ions is small compared with the number of the un- 

 dissociated molecules, the number of ions is proportional to the 

 square root of the pressure. Hence the results of our experiments 

 indicate that the electrical conductivity of gases traversed by 

 the Rontgen rays is proportional to the number of ions, and as 

 long as the gas and the number of ions is the same is independent 

 of the number of undissociated molecules, or in other words, the 

 electrical conductivity is a function of the number of ions and not 

 of their mean free path. 



Effect of temperature upon the conductivity of a gas at con- 

 stant pressure. A few experiments were made to determine the 

 effect of temperature upon the conductivity of air at constant 

 pressure. It was found that the conductivity at high tem- 

 peratures was slightly less than that at the temperature of the 

 room. 



Further experiments showed that as the gas was heated up 

 the conductivity attained a maximum value, after which it began 

 to diminish. 



As an instrument for measuring high temperatures was not 

 available at the time of making these experiments, further 

 consideration of these effects must be reserved for a future 

 paper. 



Effect of Variation in the Potential Difference on the rate of 

 leak under the influence of the Rontgen rays. A very remarkable 

 and characteristic property of the conductivity produced by these 

 rays in a gas, is that the rate of leak as the potential difference 

 increases soon reaches a maximum value and becomes almost 

 independent of the potential difference. Many experiments were 

 made to investigate this point, using both methods A, B. The 



