﻿Effects 
  at 
  the 
  Cathode 
  in 
  Vacuum 
  Tubes. 
  

  

  413 
  

  

  § 
  3. 
  Relation 
  between 
  current 
  and 
  heat 
  energy 
  given 
  to 
  the 
  

   cathode 
  in 
  the 
  case 
  of 
  the 
  normal 
  cathode 
  glow. 
  

  

  It 
  was 
  shown 
  * 
  that 
  there 
  existed 
  a 
  linear 
  relation 
  between 
  

   current 
  and 
  cathode 
  temperature, 
  and 
  the 
  statement 
  made 
  

   that 
  i£ 
  the 
  rate 
  of 
  cooling 
  of 
  the 
  cathode 
  was 
  proportional 
  

   to 
  its 
  excess 
  temperature, 
  then 
  a 
  linear 
  relation 
  would 
  exist 
  

   between 
  current 
  and 
  cooling-rate, 
  that 
  is, 
  between 
  current 
  

   and 
  heat 
  energy 
  supplied 
  by 
  bombarding 
  ions. 
  That 
  this 
  is 
  

   true 
  was 
  verified 
  in 
  the 
  following 
  way. 
  The 
  current-tempe- 
  

   rature 
  curve 
  was 
  obtained, 
  and 
  also 
  the 
  cooling-rates 
  for 
  

   the 
  whole 
  range 
  of 
  temperature 
  involved. 
  The 
  value 
  of 
  the 
  

  

  cooling-rate 
  -^r 
  was 
  plotted 
  against 
  current, 
  and 
  a 
  straight 
  

  

  line 
  obtained. 
  A 
  few 
  of 
  these 
  are 
  shown 
  in 
  Curves 
  I., 
  II., 
  

   and 
  III. 
  This 
  is 
  to 
  be 
  expected, 
  for 
  with 
  the 
  normal 
  glow 
  

   the 
  only 
  condition 
  changing 
  with 
  an 
  increase 
  of 
  current 
  is 
  

   the 
  area 
  of 
  the 
  cathode 
  covered 
  with 
  glow; 
  the 
  cathode 
  fall 
  

   and 
  the 
  current 
  density 
  both 
  remain 
  constant. 
  

  

  As 
  soon 
  as 
  the 
  cathode 
  is 
  covered 
  with 
  glow 
  then 
  both 
  

   the 
  cathode 
  fall 
  and 
  current 
  density 
  increase. 
  The 
  cathode 
  

   temperature 
  was 
  next 
  investigated 
  under 
  these 
  circumstances. 
  

  

  * 
  Hodgson, 
  Phil. 
  Mag. 
  April 
  1913, 
  p. 
  454. 
  

   Phil. 
  Mag. 
  S. 
  6. 
  Vol. 
  26. 
  No. 
  153. 
  Sept. 
  1913. 
  

  

  2 
  F 
  

  

  