﻿Energy 
  of 
  Negative 
  Electrons 
  emitted 
  by 
  Hot 
  Bodies. 
  365 
  

  

  ionization, 
  the 
  emitted 
  ions 
  being 
  capable 
  of 
  going 
  against 
  a 
  

   much 
  higher 
  potential 
  than 
  formerly. 
  A 
  detailed 
  investiga- 
  

   tion 
  of 
  this 
  interesting 
  effect 
  has 
  been 
  carried 
  out 
  by 
  Mr, 
  

   Brown, 
  and 
  will 
  shortly 
  be 
  published, 
  so 
  that 
  it 
  is 
  not 
  

   necessary 
  to 
  say 
  much 
  about 
  it 
  here. 
  It 
  is 
  evident 
  that 
  after 
  

   such 
  treatment 
  the 
  hot 
  metal 
  is 
  in 
  a 
  peculiar 
  state. 
  In 
  order 
  

   to 
  ensure 
  that 
  the 
  metal 
  was 
  in 
  a 
  normal 
  state 
  we 
  were 
  

   careful 
  to 
  always 
  keep 
  the 
  potential 
  of 
  the 
  upper 
  plate 
  in 
  the 
  

   neighbourhood 
  of 
  zero 
  so 
  as 
  to 
  make 
  sure 
  that 
  the 
  hot 
  metal 
  

   strip 
  was 
  never 
  placed 
  in 
  a 
  strong 
  electrostatic 
  field. 
  Inci- 
  

   dentally 
  it 
  may 
  be 
  mentioned 
  that 
  it 
  was 
  found 
  that 
  the 
  

   abnormal 
  state 
  induced 
  in 
  this 
  way 
  could 
  be 
  got 
  rid 
  of 
  by 
  

   heating 
  the 
  strip 
  for 
  a 
  short 
  time 
  to 
  a 
  very 
  high 
  temperature. 
  

   This 
  property 
  was 
  made 
  use 
  of 
  in 
  some 
  of 
  the 
  experiments 
  

   which 
  follow. 
  

  

  The 
  pressure 
  of 
  the 
  gas 
  (air) 
  in 
  the 
  different 
  experiments 
  

   varied 
  considerably 
  from 
  '001 
  to 
  as 
  much 
  as 
  % 
  06 
  mm. 
  So 
  

   far 
  as 
  the 
  authors 
  were 
  able 
  to 
  judge, 
  the 
  actual 
  value 
  of 
  the 
  

   pressure 
  had 
  no 
  effect 
  on 
  the 
  phenomena 
  investigated, 
  pro- 
  

   vided 
  it 
  was 
  as 
  low 
  as 
  the 
  above 
  limits 
  indicate. 
  

  

  The 
  chief 
  experimental 
  problem 
  in 
  hand 
  was 
  the 
  determi- 
  

   nation 
  of 
  the 
  current 
  to 
  the 
  upper 
  plate, 
  when 
  this 
  was 
  

   allowed 
  to 
  charge 
  up, 
  as 
  a 
  function 
  of 
  the 
  potential-difference 
  

   between 
  the 
  two 
  plates. 
  This 
  relation 
  when 
  obtained 
  enables 
  

   the 
  applicability 
  of 
  the 
  formulae 
  (10) 
  and 
  (11) 
  to 
  be 
  tested. 
  

   The 
  platinum 
  strip 
  and 
  the 
  lower 
  plate 
  were 
  always 
  main- 
  

   tained 
  at 
  zero 
  potential. 
  The 
  potential 
  of 
  the 
  upper 
  plate 
  

   at 
  any 
  instant 
  was 
  determined 
  by 
  the 
  reading 
  of 
  the 
  electro- 
  

   meter 
  to 
  which 
  it 
  was 
  connected. 
  The 
  electrometer 
  was 
  

   arranged 
  to 
  give 
  115 
  divisions 
  deflexion 
  for 
  a 
  volt, 
  as 
  this 
  

   degree 
  of 
  sensitiveness 
  was 
  found 
  to 
  be 
  most 
  convenient 
  for 
  

   these 
  experiments. 
  The 
  deflexions 
  could 
  be 
  estimated 
  to 
  

   one-tenth 
  of 
  a 
  division. 
  In 
  measuring 
  the 
  currents 
  a 
  suitable 
  

   capacity 
  was 
  connected 
  to 
  the 
  quadrants 
  of 
  the 
  electrometer. 
  

   The 
  readings 
  of 
  the 
  latter, 
  which 
  was 
  nearly 
  dead 
  beat, 
  were 
  

   recorded 
  at 
  definite 
  intervals 
  of 
  time, 
  and 
  the 
  current 
  was 
  

  

  AV 
  

  

  obtained 
  from 
  the 
  formula 
  i=c— 
  r— 
  , 
  where 
  c 
  is 
  the 
  capacity 
  

  

  of 
  the 
  electrometer 
  and 
  its 
  connexions, 
  including 
  the 
  con- 
  

   denser, 
  At 
  is 
  the 
  interval 
  of 
  time 
  between 
  two 
  readings, 
  and 
  

   AY 
  is 
  the 
  corresponding 
  increment 
  of 
  potential. 
  Strictly, 
  

   of 
  course, 
  this 
  formula 
  is 
  only 
  true 
  for 
  infinitesimal 
  intervals, 
  

   but 
  by 
  inserting 
  a 
  sufficiently 
  large 
  capacity 
  in 
  the 
  system 
  it 
  

   was 
  found 
  in 
  practice 
  that 
  the 
  rate 
  of 
  increase 
  of 
  potential 
  

   with 
  the 
  intervals 
  used 
  did 
  not 
  diminish 
  very 
  much 
  during 
  

   any 
  one 
  interval. 
  The 
  error 
  thus 
  introduced 
  was 
  also 
  averaged 
  

  

  