358 Prof. J. J. Thomson: Experiments on 



saturation, indeed in many such cases the tendency is for 

 the current to increase more rapidly than the electromotive 

 force. In the gas in which continuous ionization is taking 

 place the current gets saturated, the maximum current being 

 the one which takes out of the gas in one second all the ions 

 which are produced in the gas in that time ; the current will 

 not increase beyond this, however much the electromotive 

 force is increased, provided that the electric field does not 

 become so strong that it gives rise to spark or brush discharge. 



Air which has been modified by passing through water 

 shows all the peculiarities of a gas in which continuous 

 ionization is taking place ; the current gets saturated ; 

 although, as is natural, from the much greater conductivity 

 of the gas the electromotive force required to saturate it is 

 much greater than when the gas is in the normal state. 



Many experiments on the relation between the current 

 through the modified gas and the electromotive force acting 

 upon it were made. The following tables embody the results 

 of two such experiments. 



Potential-difference in volts 



n 





between the central wire 



Or 







and the cylinder. 



wire +. 





wire — . 



40 



40 





30 



80 



6Q 





45 



120 



80 





70 



160 



107 





80 



200 



122 





97 



400 



150 





126 



600 



200 





139 



800 



220 





138 



1000 



230 





150 



These results are represented graphically 



in the curves 



in fig. 1. These curves 



clearly show the 



approach to satura- 



tion. The following observations were 



taken with air of 



considerably smaller conductivity than 



that 



used in the 



preceding experiments :- 









Potential-difference in volts 

 between the central wire 



Current. 





and the cylinder. 



wire +• 





wire — . 



40 



18 





17 



80 



2y 





2S 



120 



36 





36 



200 



58 





55 



400 



80 





78 



600 



92 





85 



800 



105 





95 



1000 



110 





95 



