1915] on Electrons and Heat 453 



currents from tungsten in high vacua are not minute affairs requiring 

 elaborate apparatus for their detection, but, at high temperatures, 

 are of such magnitude as to be worthy of the consideration of the 

 practical electrician. I have here a tungsten lamp, containing a fila- 

 ment 14 mm. long and about 3 mils, in diameter, in series with an 

 ammeter, a resistance, a battery, and a second ammeter. They are 

 arranged in the order named, so that there is an ammeter at each 

 end of the lamp. In addition there is a side line from the cylin- 

 drical electrode of the lamp, which can be switched through either a 

 millammeter or an electric bell to the positive end of the battery. 

 There is no auxiliary voltage in this side line. When I turn the 

 current on, you observe that the ammeters read differently, showing 

 that more current is flowing into the filament at one end than out of 

 it at the other. The difference is, in fact, equal to the electron 

 current which flows into the wire sideways and is registered by the 

 millammeter. Those of you who cannot see the instruments will, at 

 any rate, hear the electric bell Avhen I switch the electron current 

 through it. With a lamp which was somewhat better designed 

 for the purpose than the present one, I have recorded a current of 

 0'7 ampere at one end, 0*45 at the other, and 0*25 in the branch 

 circuit. So far as my experience goes, the only limit to the size of 

 these electron currents is that which is set by the magnitude of the 

 current which fuses the filament, provided the requisite driving 

 voltage is available. 



[0. W. R.] 



