304 Mr McClelland, On the Action of Incandescent Metals 



6. The numbers given below refer to experiments when the 

 pressure of the air is j 1 ^ mm. 



Wire negative 

 volts 



Current in arbitrary 

 units 



40 



57 



80 



68 



160 



80 



240 



86 



320 



94 



400 



100 



Wire positive 

 volts 



Current in arbitrary 

 units 



40 



7 



80 



13 



160 



20 



240 



32 



320 



54 



400 



100 



As mentioned previously the current is always very much 

 greater when the wire is charged negatively ; the above numbers 

 are not to scale in the two cases. The curves referring to these 

 numbers are given in Fig. 6. The current when the wire is 





















































































































































































































g 



■a 











































3 



















































































































































































































160 200 



Volts. 

 Fig. 6. 



240 



charged negatively does not increase rapidly with the higher 

 potential, which means that at this pressure the velocity of the 

 negative ions even with small voltage is such that ionisation is 



