394 Prof. J. J. Thomson and Mr. Rutherford on the Passage 



to pass through the tubes instead of the gas ; then if enough 

 electricity passed through the solution to decompose all the 

 electrolyte the solution when it emerged would be a noncon- 

 ductor ; and this is precisely what happens in the case of the 

 gas. We shall find that the analogy between a dilute solution 

 of an electrolyte and gas exposed to the Rontgen rays holds 

 through a wide range of phenomena, and we have found it of 

 great use in explaining many of the characteristic properties 

 of conduction through gases. 



Thus Rontgen rays supply a means of communicating a 

 charge of electricity to a gas. To do this, take an insulated 

 wire charged up to a high potential and surrounded by a tube 

 made of a non-conducting substance : let this tube lead into 

 a large insulated metallic vessel connected with an electro- 

 meter. If now air which has been exposed to Rontgen rays 

 is blown through the tube into this vessel the electrometer 

 will be deflected. This proves that the gas inside the vessel 

 is charged with electricity. If the Rontgen rays are stopped 

 and the gas blown out of the vessel the charge disappears. 

 In these experiments we took precautions against dust. 



The fact that the passage of a current of electricity through 

 a gas destroys its conductivity explains a very characteristic 

 property of the leakage of electricity through gases exposed 

 to Rontgen rays ; that is, for a given intensity of radiation 

 the current through the gas does not exceed a certain maxi- 

 mum value whatever the electromotive force may be, the 

 current gets, as it were, " saturated." The relation between 

 the electromotive force and the current is shown in the fol- 

 lowing curve, where the ordi nates represent the current and 



Fm. 1. 















■■■ 





the abscissas the electromotive force. It is evident that this 

 saturation must occur if the current destroys the conducting 

 power of the gas, and that the maximum current will be the 

 current which destroys the conductivity at the same rate as 



