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XL. On the Passage of Electricity through Gases exposed 

 to Rdntgen Rays. By J. J. Thomson, M.A., F.R.S., 

 Cavendish Professor of Experimental Physics, Cambridge, 

 and E. Rutherford, M.A., Trinity College, Cambridge, 

 1851 Exhibition Scholar, New Zealand University* . 



THE facility with which a gas, by the application and 

 removal of Rontgen rays, can be changed from a con- 

 ductor to an insulator makes the use of these rays a valuable 

 means of studying the conduction of electricity through gases, 

 and the study of the properties of gases when in the state into 

 which they are thrown by the rays promises to lead to results 

 of value in connexion with this subject. We have during 

 the past few months made a series of experiments on the 

 passage of electricity through gases exposed to the rays, the 

 results of these experiments are contained in the following 

 paper. 



A gas retains its conducting property for a short time after 

 the rays have ceased to pass through it. This can readily be 

 shown by having a charged electrode shielded from the direct 

 influence of these rays, which pass from the vacuum-tube 

 through an aluminium window in a box covered with sheet 

 lead; then, though there is no leak w T hen the air in the neigh- 

 bourhood of the electrode is still, yet on blowing across the 

 space over the aluminium window on to the electrode the 

 latter immediately begins to leak. 



To make a more detailed examination of this point w r e used 

 the following apparatus. 



A closed aluminium vessel is placed in front of the wdndow 

 through which the rays pass. A tube through which air can 

 be blown by a pair of bellows leads into this vessel : the rate 

 at which the air passed through this tube was measured by a 

 gas-meter placed in series with the tube; a plug of glass wool 

 was placed in the tube leading to the vessel to keep out the 

 dust. The air left the aluminium vessel through another 

 tube, at the end of which was placed the arrangement for 

 measuring the rate of leakage of electricity (usually a wire 

 charged to a high potential placed in the axis of an earth- 

 connected metal tube through which the stream of gas passed, 

 the wire being connected with one pair of quadrants of an 

 electrometer). This arrangement was carefully shielded from 

 the direct effect of the rays, and there was no leak unless a 

 current of air was passing through the apparatus ; when, 



* Communicated by the Authors, having been read before Section A of 

 the British Association, 1896. 



