Thermionic Currents with Potentials. 



551 



from the experiments that it is not a necessary cause of the 

 increase, and that it cannot have caused any considerable 

 fraction of the increase observed in the present experiments. 

 A number of other points connected with initial thermionic 

 emissions have been examined in the course of the in- 



vestigation. 



The experimental investigation involved observations of 

 thermionic currents in good vacua for various temperatures 

 and potentials, and with various other conditions to be de- 

 scribed below. The currents were obtained from platinum 

 wires mounted axiallyin cylindrical vessels, which contained 

 the receiving electrodes. Figs. 1 and 2 show two types of 



Fig-. 2. 



v Sealing wax 



Class 



Class ring ^p, 



L = Filament. H= Brass Electrode . 



vessel used. The currents were measured by an electrometer 

 in the ordinary way. For large currents the electrometer 

 was shunted across a resistance, and in some cases a micro- 

 ammeter was u*ed. Generally speaking, the currents were 

 chosen so as to be as large as possible subject to the decay 

 being negligible during the course of the observations. The 

 vacua were produced by a rotary mercury-pump, and were 

 usually about 3xl0" 5 mm. of mercury on the McLeod 

 gauge. 



