294 Dr. Beatty and Mr. Gilmour on Measurement of 



by inserting a battery in the grid circuit so as to keep the 

 grid at a negative potential, —Vg, with regard to R 

 [curve (c)]. Fig. 4 (h) also shows the effect of negative 

 potential on the grid. 



Fisr. 4. 



10X1CH 



2UX10 4 



X)xlO J 



Increase in C has but little influence on I\. As C in- 

 creases, 1\ and T 2 approach each other and finally coincide. 

 For values o£ C greater than this critical one no silent region 

 exists \cf. fig. 2, curve (c)j. 



Measurement of the second transition point T 2 . 



When C = 0, oscillations do not restart after the silent 

 region is reached. As C increases, T 2 appears at a high 

 value of R and travels to the left [fig. 3, curve (?)], finally 

 coinciding with 1\ [curve (d)~\. 



Thus a finite value of C is necessary for restarting. 

 When, by using some value of C, T 2 is located anywhere 

 on the diagram, it can be displaced by altering K or Yg. 

 Fig. 3, curve (/), shows the effect of altering K, when 

 C = l-9xl0- 4 mi. [cf fig. 5]. 



Fur. 5. 



40xl0 4 t 



(cf) K=0 



C - 0-0\0O4m.f: 



(g) K=0-0&026 m.f: 

 C = 0-OQ04 m. 



fffJ 



IOxio 4 



20XI0 4 

 Resistance in ohms. 



30X.I0 4 



Examples of the application of the method. 



(1) A selenium cell of the d'Albe pattern, of resistance 

 2 x 10 5 ohms, was used as the grid resistance. With 

 0=1-8x10-' 



m. 



f. the circuit functioned at the transition 

 point T 2 , and the light from a candle twenty feet distant was 

 sufficient to cause a note in the previously silent telephone. 



