﻿Effects 
  at 
  the 
  Cathode 
  in 
  Vacuum 
  Tubes, 
  

  

  415 
  

  

  increased 
  with 
  pressure 
  in 
  hydrogen 
  and 
  helium 
  with 
  cathodes 
  

   of 
  aluminium, 
  zinc, 
  magnesium, 
  and 
  platinum. 
  Warburg*, 
  

  

  on 
  the 
  other 
  hand, 
  found 
  it 
  increasing 
  with 
  some 
  electrodes 
  

   and 
  decreasing 
  with 
  others. 
  In 
  order 
  to 
  be 
  certain 
  that 
  the 
  

   effect 
  was 
  not 
  due 
  to 
  difference 
  in 
  the 
  rate 
  of 
  cooling, 
  the 
  

   energy 
  communicated 
  to 
  the 
  cathode 
  was 
  determined 
  as 
  in 
  § 
  3. 
  

   The 
  following 
  results 
  were 
  obtained 
  : 
  — 
  

  

  Table 
  I. 
  

   Copper 
  in 
  Oxygen. 
  (Normal 
  glow.) 
  

  

  Pressure 
  

   (mm. 
  Hg.) 
  

   3'09 
  

  

  Energy 
  (mean 
  of 
  I 
  

   Units 
  arbitrary. 
  

   146 
  

  

  2-64 
  

  

  146 
  

  

  2-12 
  

  

  142 
  

  

  1-63 
  

  

  141 
  

  

  1-34 
  

  

  139 
  

  

  1-04 
  

  

  128 
  

  

  0-83 
  

  

  126 
  

  

  O60 
  

  

  120 
  

  

  * 
  Warburg, 
  Ann. 
  d. 
  Phys. 
  xxxi. 
  p. 
  11 
  (1887) 
  ; 
  xl. 
  p. 
  570 
  (18<JG\ 
  

  

  2 
  F 
  2 
  

  

  