from, an Arc and from Incandescent Metals. 



243 



the tube A and insulated by an ebonite plug. This terminal is 

 connected to a pair of quadrants of an electrometer; both pairs 

 of quadrants are first connected together and to one pole of a 

 battery of storage cells, the other pole of which is to earth; one 

 pair of quadrants is kept joined to the cells, and the pair in 

 connection with B is disconnected and leaks owing to the con- 

 ductivity of the gas passing B. 



C is another similar terminal used in other experiments which 

 can be joined to earth or kept at any required potential by being 

 joined to the storage cells. 



(2) By charging the terminal B to any potential and observing 

 the initial rate of leak we get the current through the gas for that 

 potential difference between the terminal B and the tube A. The 

 following table shows the result of an experiment : 



The curve in Fig. 2 is plotted from these numbers, and shows 

 that as the e.m.f. increases the current approaches a maximum 

 value. 





20 



40 



60 



VOLTS 

 Fig. 2. 



120 



140 



160 



180 200 



At first the current increases rapidly and is approximately 

 proportional to the E.M.F. ; when we reach an E.M.F. sufficient to 

 discharge all the carriers before they pass the terminal the current 

 increases but little, although a further increase of e.m.f. by dis- 

 charging the carriers sooner and thereby diminishing the loss of 



