532 



Mr. N. R. Campbell on Radiation 



of the arrangement shown in fig. 1. The point on the scale 

 of the observing microscope occupied by the leaf was noted 

 the electrode earthed by inserting the wire C in the mercury 



Fig. 1. 



W BATTERY 



SULPHUR 



cup »!, and resistances taken out of the box E until, on 

 depressing the key K, the leaf returned to the position noted 

 from the value ot the resistances and of the B.M.F. of the cell" 

 tr the required potential can be easily calculated 



The time for which the leak was measured was chosen so 

 that the potential acquired was about one volt, giving 55 to 

 60 scale-divisions ; the potential could be read with an 

 accuracy of one per cent. 



The field necessary to send the saturation current throuah 

 the gas was derived from an excellent battery of small cells 

 Care was taken that the current was saturated and that all 

 insulation (sulphur was used throughout) was acting 

 efficiently. _ The direction of the field was occasional^ 

 reversed ; m all cases in which the contrary is not explicitly 

 stated, the magnitude of the leak was independent of its 



The capacity of the insulated electrode system, the product 

 of which with the potential acquired in unit time gives the 



Z 1 ' 1 '^ i i° U fr n; e ,P S ',I aS measured V means of the device 



described by McClelland *. The current is given throughout 



the paper on an arbitrary scale, in which the unit of capacity 



* McClelland, Eoy. Dublin Soc. Proc. 10. 18, p. 167 (Feb. 26, 1904). 



