of Recombination of the Ions of Gases. 



425 



represents very closely the law of the rate of recombination 

 of the ions. This agreement has been tested for a large 



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number of experiments in which the intensity of the radiation 

 varied widely, but in all cases the rate of decay was found to 

 be in close agreement with theory. 



Second Method. 



The method just described of determining the duration of 

 the conductivity by blowing air along a tube, could only be 

 used for air on account of the large volume of gas required 

 for a series of observations. 



The following method could be used for testing the rate of 

 recombination of the ions for different gases, and for widely 

 different values of intensity of radiation. 



A glass bell-jar was taken, the bottom of which was covered 

 with a plate of thin ebonite. A central electrode which 

 reached nearly to the bottom of the bell-jar was insulated by 

 passing through a paraffin stopper in the mouth of the jar. 

 The outside of the bell-jar was coated with tinfoil which had 

 a metallic connexion with the inside. The bell-jar was placed 

 on insulating blocks over a hole in the metal tank, which was 

 covered with aluminium, and the Crookes' tube was placed in 

 position beneath. 



In order to determine the after-conductivity the coil was 

 turned on for a few seconds and then turned off. At definite 



