﻿t 
  411 
  ] 
  

  

  XXXI. 
  Heating 
  Effects 
  at 
  the 
  Cathode 
  in 
  Vacuum 
  Tabes. 
  By 
  

   B. 
  Hodgson, 
  M.Sc, 
  Ph.D., 
  Assistant 
  Lecturer 
  in 
  Physics, 
  

   and 
  P. 
  A. 
  Mainstone, 
  B.Sc, 
  The 
  University, 
  Bristol*. 
  

  

  § 
  l.TT 
  was 
  known 
  to 
  the 
  early 
  experimenters 
  in 
  vacuum- 
  

   JL 
  tube 
  work 
  that 
  the 
  electrodes 
  became 
  heated 
  during 
  

   the 
  discharge, 
  and 
  that 
  the 
  cathode 
  became 
  hotter 
  than 
  the 
  

   anode. 
  Pliicker 
  t 
  c 
  Tiled 
  the 
  negative 
  electrode 
  the 
  Warmepol, 
  

   and 
  Hittorf 
  suggested 
  that 
  the 
  big 
  potential 
  gradient 
  near 
  

   the 
  cathode 
  was 
  the 
  cause 
  of 
  the 
  higher 
  temperature. 
  The 
  

   first 
  calorimetric 
  measurements 
  of 
  the 
  heat 
  energy 
  given 
  to 
  

   the 
  cathode 
  appear 
  to 
  have 
  been 
  made 
  by 
  Naccari 
  and 
  

   Bellati 
  $ 
  in 
  1878. 
  They 
  observed 
  the 
  proportionality 
  between 
  

   current 
  and 
  heat 
  energy, 
  and 
  also 
  the 
  fact 
  that 
  the 
  cathode 
  

   received 
  from 
  8 
  to 
  23 
  times 
  as 
  much 
  heat 
  as 
  the 
  anode. 
  

   Granqvist§ 
  later 
  verified 
  the 
  proportionality 
  of 
  current 
  and 
  

   cathode 
  temperature 
  ; 
  and 
  one 
  of 
  the 
  authors 
  || 
  measured 
  in 
  

   absolute 
  units 
  the 
  heat 
  energy 
  communicated 
  with 
  various 
  

   currents 
  and 
  gas 
  pressures. 
  This 
  measurement 
  led 
  to 
  the 
  

   conclusion 
  that 
  only 
  a 
  small 
  number 
  of 
  negative 
  carriers 
  

   took 
  part 
  in 
  the 
  discharge 
  at 
  the 
  cathode 
  surface. 
  

  

  § 
  2. 
  Apparatus. 
  

  

  This 
  work 
  was 
  continued 
  with 
  improved 
  apparatus 
  and 
  

   with 
  electrodes 
  of 
  different 
  metals 
  in 
  the 
  gases 
  oxygen, 
  

   hydrogen, 
  nitrogen, 
  and 
  air. 
  The 
  electrical 
  arrangements 
  

   were 
  those 
  described 
  previously^. 
  Two 
  types 
  of 
  vacuum- 
  

   tubes 
  were 
  used. 
  The 
  first 
  is 
  shown 
  in 
  fig. 
  1. 
  

  

  The 
  tube 
  A 
  was 
  made 
  in 
  two 
  sections, 
  fitting 
  together 
  by 
  

   means 
  of 
  the 
  ground-glass 
  joint 
  J. 
  The 
  cathode 
  K 
  consisted 
  

   of 
  a 
  cylindrical 
  cup, 
  the 
  cavity 
  of 
  which 
  was 
  of 
  such 
  a 
  size 
  

  

  * 
  Communicated 
  by 
  the 
  Authors. 
  

  

  t 
  Pliicker, 
  Ann. 
  dJPfajs. 
  ciii. 
  p. 
  90 
  (1858). 
  

  

  \ 
  Naccari 
  and 
  Bellati, 
  Beibl. 
  d. 
  Ann. 
  vol. 
  ii. 
  p. 
  720 
  (1878). 
  

  

  § 
  Granqvist, 
  Of 
  v. 
  Kon. 
  Vet.-Akad. 
  Stockholm. 
  No. 
  43, 
  p. 
  727 
  (1898). 
  

  

  || 
  Hodgson, 
  Phil 
  Mag-. 
  April 
  1913, 
  p. 
  453. 
  

  

  ^[ 
  Hodgson, 
  loc. 
  cit. 
  

  

  