﻿422 
  Heating 
  Effects 
  at 
  the 
  Cathode 
  in 
  Vacuum 
  Tubes, 
  

  

  The 
  value 
  o£ 
  the 
  ratio 
  diminishes 
  as 
  the 
  tube 
  becomes 
  old, 
  

   and 
  also 
  the 
  use 
  of 
  nascent 
  sodium* 
  to 
  absorb 
  oxygen 
  

   appears 
  to 
  have 
  the 
  same 
  effect. 
  

  

  § 
  10. 
  These 
  experiments 
  seemed 
  to 
  point 
  to 
  the 
  fact 
  that 
  

   the 
  ratio 
  a.//3 
  would 
  invariably 
  be 
  1*0 
  if 
  the 
  correct 
  value 
  of 
  

   the 
  cathode 
  fall 
  were 
  used. 
  The 
  apparatus 
  was 
  then 
  modified 
  

   so 
  that 
  a 
  sound 
  could 
  be 
  moved 
  into 
  the 
  negative 
  glow, 
  and 
  

   the 
  potential 
  difference 
  between 
  the 
  sound 
  and 
  the 
  cathode 
  

   measured. 
  The 
  following 
  results 
  were 
  obtained 
  : 
  — 
  

  

  Table 
  VIII. 
  

   Cathode 
  — 
  Lead. 
  

  

  Gas. 
  

  

  V" 
  measured. 
  

  

  V 
  book 
  value. 
  

  

  

  

  350 
  

  

  260 
  

   350 
  

   290 
  

  

  373 
  

  

  276 
  

   210 
  

   207 
  

  

  H 
  

  

  N 
  

  

  Air 
  

  

  

  The 
  table 
  shows 
  clearly 
  the 
  reason 
  for 
  the 
  deviation 
  from 
  

   1*0 
  of 
  the 
  ratio 
  a//3. 
  For 
  oxygen 
  and 
  hydrogen 
  the 
  values 
  

   are 
  approximately 
  those 
  given 
  by 
  Rottgardt 
  and 
  Thomson, 
  

   but 
  in 
  air 
  and 
  nitrogen 
  the 
  values 
  are 
  quite 
  different. 
  

  

  Experiments 
  are 
  being 
  performed 
  using 
  the 
  sound 
  to 
  

  

  measure 
  the 
  cathode 
  fall 
  simultaneously 
  with 
  M 
  . 
  -r- 
  , 
  to 
  deter- 
  

   mine 
  more 
  accurately 
  the 
  ratio 
  u//3 
  and 
  to 
  fix 
  its 
  deviation 
  

   from 
  the 
  value 
  1'0. 
  

  

  Summary. 
  

  

  1. 
  With 
  normal 
  glow 
  the 
  heat 
  energy 
  communicated 
  to 
  

   the 
  cathode 
  is 
  proportional 
  to 
  the 
  current. 
  

  

  2. 
  When 
  the 
  abnormal 
  glow 
  sets 
  in 
  the 
  heat 
  given 
  to 
  the 
  

   cathode 
  increases 
  more 
  rapidly 
  as 
  the 
  current 
  increases. 
  

  

  3. 
  The 
  ratio 
  a) 
  ft 
  is 
  approximately 
  1'0, 
  showing 
  that 
  at 
  the 
  

   cathode 
  surface 
  only 
  a 
  few 
  corpuscles 
  are 
  engaged 
  in 
  carrying 
  

   the 
  current. 
  

  

  The 
  above 
  work 
  was 
  done 
  in 
  the 
  physical 
  laboratory 
  of 
  

   the 
  University 
  of 
  Bristol, 
  and 
  the 
  authors' 
  thanks 
  are 
  due 
  to 
  

   Dr. 
  A. 
  M. 
  Tvndall 
  for 
  placing 
  at 
  their 
  disposal 
  the 
  apparatus 
  

   necessary 
  for 
  carrying 
  out 
  the 
  work. 
  

  

  * 
  Warburg, 
  Ann. 
  d. 
  Phys. 
  xl. 
  p. 
  2 
  (1890). 
  

  

  