of Recombination of the Ions of Gases. 429 



the radiation to | of its former value, the value of T rose to 

 •6 second. 



For weak radiation the values of T are much greater than 

 for strong radiation. 



Time in seconds. 



Deflexions, 



•004 



174 



•45 



139 



2 



107 



4 



54 



8 



30 



16 



16 



The above table shows the variation of the after-conduc- 

 tivity with time for very weak radiation. The value of T is 

 about 3 seconds, and even after 16 seconds ^j of the original 

 number of ions are still uncombined. 



Air distant about a metre from an ordinary Crookes* tube 

 possesses quite a measurable proportion of its conductivity 

 for over a minute after the rays have ceased. 



Effect of finely suspended Particles in a Gas on its Rate of 

 Loss of Conductivity. 



It was found that the value of T varied greatly for the 

 same gas for the same intensity of radiation. When, for 

 example, chlorine was first passed into the testing-vessel the 

 value of T was '19 sec. ; after standing for an hour the value 

 of T rose to '3 sec, although the conductivity of the gas as 

 tested by the usual method was found to be unaltered. 

 Freshly made gases were found, in all cases, to lose their 

 conductivity more rapidly than when they had stood undis- 

 turbed for some time. 



The cause of this effect was not at first clear, but later 

 experiments on the influence of dust in the air led to the con- 

 clusion that it was due to the presence of finely divided 

 matter, liquid or solid, in the freshly prepared gas. The 

 value of T was found to be greater for a gas that passed 

 through a long tube filled with cotton- wool than if the cotton- 

 wool were removed. This is probably due to the fact that 

 the cotton-wool would not allow the small particles to pass 

 through its pores. 



The presence of dust in air was found to very greatly 

 affect the duration of the after-conductivity. As an example 

 of the effect of dust we may give the following experiment: — 



The cylinder was filled with air which had passed through 

 a plug of glass-wool, and then allowed to stand all night, and 



