486 Perkins — Rectification Effect in a Vacuum Tube. 



tion was too small to be observed, however, when the poten- 

 tial of the ring was less than 550 volts, or when the ring was 

 so situated that the glow did not reach to both electrodes. If 

 the ring was moved in successive readings from A to B, a 

 curve of deflections was obtained of the general character of 

 tig. 2. This current was practically zero at A and B, but on 

 moving toward the center it increased very rapidly beyond 

 5 cm from the ends, went through a maximum, then decreased 

 very rapidly and reversed sign when the ring was at the 



Uerat/sd plot of trnJf cf 

 Current- Fbf/tio/1 Curje 



CurM S/low/nf fr/ccr of 

 rbryinf flTitofion of Tf/uo 

 (twrneut c/ionoc cf pcr/ticnj 



Saucst. w.'<'/ ionization Ertf. 



center and went through a similarly situated maximum on the 

 other side, the two halves of the curve being substantially 

 alike. 



The readings between the two maxima were very unsteady, 

 but the maxima themselves and points outside them as steady 

 as could be expected with the somewhat variable nature of 

 the commercial E. M. F. The actual currents indicated by 

 the maxima varied greatly with the exciting E. M. F., but 

 currents of the order 5XlO~ 7 were readily obtained and, with 

 a short thick tube, still larger ones. 



Fig. 3 gives a rough idea of the effect on the current of 

 varying the exciting field, at the maximum points. It shows a 

 sudden appearance of the phenomenon when the pressure 

 exceeds a certain minimum value, and after that a less rapid 

 but fairly steady rate of increase. 



