1295 



These characteristics are similar to lliose of fig. 2 ; as a rule however 



they are steeper. Figs. 2 and 

 3 give I he essential features 

 of the audion-characteristics ; 

 (he different forms of andions 

 show more or less important 

 deviations. 



Though the character of the 

 gas and the degree of its 

 rarefaction aie very important 

 in the determination of the 

 individual |)roperties of the 

 J, and ion, they are problablj 

 not of essential signification. 

 At any late Langmuir ^) has 



-B 



-b -^ -Z 

 Fig. 3. 



succeeded in constructing a normally functioning three-electrode- 

 relais, which he calls pliotron, from which every trace of gas seems 

 to have been removed. In the following discussion we may therefore 

 assume that the electric conduction in the audion is exclusively 

 performed by the thermoions. 



For the number ]Sf of electrons, which in the unit of time enter 

 the vacuum from the hot wnre, Richardson found the well-known 

 formula : 



N = aT^ 



(1) 



here 7' is the absolute temperature of- the hot wire, a and h are 

 constants, A is a quantity which differs but little from unity. The 

 emei'ging electrons may be caught on an anode opposite the kathode ; 

 N is then determined by a current-measurement. When 7^is constant, 

 the current increases at first with increasing potential-difference. It 

 is only the maximum current, "the saturation current", which in 

 its dependence on the temperature follows Richardson's formula. 



To explain this initial increase of the curreni with the impressed 

 voltage Langmuik ') gave his theory of the space-charge. The elec- 

 trons in the field between the kathode and the anode diminish the 

 potential-gradient in the neighbourhood of the kathode. When this 



') Langmuir: General Electr. Rev. (1915) p. 327. 



See also Hund : Jahrb. f. Drahtl. Tel. (1916) 10 p. 521. 

 2) Phys. Rev. (1918i p. 457. 



B4* 



