﻿908 
  Mr. 
  C. 
  D. 
  Child 
  on 
  Line 
  Spectrum 
  

  

  When 
  F 
  is 
  charged 
  negatively 
  to 
  about 
  100 
  volts 
  there 
  is 
  

   a 
  non-luminous 
  layer 
  extending 
  from 
  F 
  for 
  about 
  1 
  mm., 
  

   but 
  the 
  remainder 
  of 
  the 
  region 
  above 
  c 
  is 
  not 
  affected 
  by 
  a 
  

   negative 
  charge 
  on 
  F. 
  It 
  seemed 
  surprising 
  that 
  the 
  dark 
  

   space 
  should 
  extend 
  for 
  so 
  short 
  a 
  distance. 
  An 
  arrange- 
  

   ment 
  was 
  therefore 
  made 
  which 
  was 
  somewhat 
  different 
  from 
  

   that 
  shown 
  in 
  the 
  diagram, 
  so 
  that 
  a 
  movable 
  exploring 
  wire 
  

   could 
  be 
  introduced 
  between 
  F 
  and 
  c. 
  It 
  was 
  then 
  found 
  

   that 
  when 
  F 
  was 
  charged 
  negatively, 
  approximately 
  all 
  of 
  

   the 
  drop 
  in 
  the 
  potential 
  betw 
  r 
  een 
  F 
  and 
  c 
  occurred 
  within 
  a 
  

   millimetre 
  of 
  F. 
  

  

  The 
  large 
  drop 
  near 
  the 
  electrode 
  was 
  undoubtedly 
  due 
  to 
  

   the 
  fact 
  that 
  the 
  current 
  to 
  F 
  was 
  being 
  carried 
  by 
  the 
  com- 
  

   paratively 
  slow-moving 
  positive 
  ions. 
  Such 
  a 
  drop 
  occurs 
  

   when 
  current 
  is 
  carried 
  by 
  one 
  kind 
  of 
  ions 
  only, 
  unless 
  the 
  

   ions 
  move 
  very 
  rapidly 
  or 
  the 
  current 
  is 
  exceedingly 
  small. 
  

   It 
  is, 
  therefore, 
  true 
  that 
  in 
  this 
  case 
  also 
  there 
  is 
  no 
  luminosity 
  

   where 
  there 
  is 
  an 
  electric 
  field. 
  

  

  Light 
  not 
  caused 
  by 
  Chemical 
  Action. 
  — 
  The 
  fact 
  that 
  the 
  

   luminosity 
  in 
  the 
  region 
  above 
  the 
  arc 
  can 
  be 
  destroyed 
  

   under 
  certain 
  conditions 
  by 
  an 
  electric 
  field, 
  shows 
  that 
  it 
  

   cannot 
  be 
  due 
  to 
  chemical 
  action 
  ; 
  for 
  an 
  electric 
  field 
  would 
  

   not 
  stop 
  changes 
  of 
  such 
  a 
  character. 
  Moreover, 
  so 
  far 
  

   as 
  we 
  know, 
  there 
  is 
  no 
  opportunity 
  for 
  chemical 
  action. 
  

   All 
  the 
  gases 
  aside 
  from 
  mercury 
  vapour 
  are 
  carried 
  beyond 
  

   the 
  point 
  where 
  the 
  mercury 
  condenses 
  by 
  the 
  first 
  flow 
  of 
  

   the 
  vapour 
  from 
  the 
  arc, 
  so 
  that 
  nothing 
  is 
  left 
  in 
  the 
  region 
  

   where 
  the 
  light 
  appears 
  except 
  such 
  vapour. 
  

  

  As 
  far 
  as 
  could 
  be 
  discovered 
  the 
  phenomenon 
  did 
  not 
  

   depend 
  in 
  any 
  w 
  7 
  ay 
  on 
  the 
  purity 
  of 
  the 
  mercury 
  ; 
  and 
  the 
  

   spectrum 
  of 
  the 
  light 
  showed 
  no 
  lines 
  except 
  those 
  due 
  to 
  

   the 
  mercury. 
  

  

  Light 
  not 
  caused 
  by 
  Ionization. 
  — 
  The 
  fact 
  that 
  the 
  light 
  ia 
  

   destroyed 
  by 
  an 
  electric 
  field 
  shows 
  that 
  it 
  is 
  caused 
  by 
  the 
  

   presence 
  of 
  ions. 
  The 
  vibrations 
  of 
  molecules 
  which 
  produce 
  

   light 
  are 
  caused 
  by 
  some 
  shock, 
  such 
  as 
  that 
  which 
  occurs 
  

   when 
  the 
  molecules 
  are 
  broken 
  into 
  ions, 
  or 
  when 
  the 
  ions 
  

   recombine 
  into 
  molecules. 
  Let 
  us 
  first 
  consider 
  the 
  possibility 
  

   that 
  the 
  vibrations 
  are 
  started 
  at 
  the 
  time 
  when 
  the 
  ionization 
  

   occurs. 
  The 
  ionization 
  must 
  occur 
  either 
  in 
  the 
  arc 
  or 
  in 
  the 
  

   region 
  above 
  it. 
  If 
  the 
  ions 
  are 
  formed 
  in 
  the 
  arc 
  and 
  the 
  

   vibrations 
  are 
  started 
  at 
  that 
  time, 
  they 
  must 
  continue 
  while 
  

   the 
  ions 
  move 
  through 
  the 
  luminous 
  region. 
  

  

  This 
  region 
  often 
  extends 
  for 
  20 
  or 
  30 
  cm. 
  above 
  the 
  arc. 
  

   From 
  measurements 
  of 
  the 
  Hall 
  effect, 
  Stark* 
  concluded 
  that 
  

   * 
  l 
  J 
  hys. 
  Zeit. 
  iv. 
  p. 
  440 
  (1903). 
  

  

  