﻿H. 
  A. 
  Bumstead 
  — 
  Velocities 
  of 
  Delta 
  Bays. 
  99 
  

  

  It 
  will 
  be 
  observed 
  that 
  these 
  differences 
  are 
  constant, 
  and 
  

   that 
  the 
  four 
  curves 
  of 
  ftg. 
  3 
  have 
  the 
  same 
  form 
  and 
  are 
  

   merely 
  shifted 
  vertically 
  on 
  the 
  diagram. 
  It 
  is 
  quite 
  clear 
  that 
  

   we 
  have 
  here 
  the 
  resultant 
  of 
  two 
  effects, 
  the 
  tirst 
  independent 
  

   of 
  the 
  time 
  since 
  the 
  vacuum 
  was 
  made, 
  and 
  depending 
  upon 
  

   the 
  applied 
  potential, 
  while 
  the 
  second 
  is 
  independent 
  of 
  the 
  

   potential, 
  but 
  does 
  vary 
  greatly 
  with 
  the 
  time. 
  The 
  first 
  effect 
  

   is 
  plainly 
  due 
  (at 
  least 
  in 
  great 
  part) 
  to 
  the 
  escape 
  from 
  the 
  

   source, 
  B, 
  of 
  the 
  swifter 
  S-rays, 
  thus 
  giving 
  it 
  a 
  positive 
  

   charge, 
  which 
  is 
  decreased 
  as 
  larger 
  opposing 
  potentials 
  are 
  

   applied 
  to 
  the 
  gauze. 
  The 
  second 
  phenomenon 
  causes 
  the 
  

   source 
  to 
  gain 
  negative, 
  or 
  to 
  lose 
  positive, 
  electricity 
  at 
  a 
  rate 
  

   which 
  is 
  independent 
  of 
  the 
  potential 
  beyond 
  40 
  volts 
  ; 
  and 
  its 
  

   variation 
  with 
  the 
  time 
  shows 
  that 
  it 
  must 
  be 
  due 
  to 
  residual 
  

   gas 
  — 
  either 
  that 
  which 
  occupies 
  the 
  volume 
  of 
  the 
  chamber, 
  or 
  

   that 
  which 
  is 
  condensed 
  upon 
  its 
  walls 
  and 
  on 
  the 
  electrode. 
  

  

  It 
  seemed 
  desirable 
  first 
  to 
  investigate 
  the 
  nature 
  and 
  cause 
  

   of 
  the 
  second 
  effect. 
  When 
  the 
  apparatus 
  was 
  in 
  the 
  condition 
  

   which 
  gave 
  the 
  upper 
  curve 
  (IV) 
  in 
  fig. 
  3, 
  the 
  liquid 
  air 
  was 
  

   removed 
  from 
  the 
  charcoal, 
  and 
  a 
  small 
  quantity 
  of 
  air 
  admit- 
  

   ted 
  to 
  the 
  chamber 
  so 
  that 
  the 
  pressure 
  rose 
  to 
  0'2 
  mm 
  . 
  This 
  

   was 
  allowed 
  to 
  remain 
  for 
  about 
  15 
  minutes, 
  when 
  exhaustion 
  

   was 
  recommenced, 
  while 
  the 
  charcoal 
  bulb 
  was 
  heated 
  in 
  the 
  

   usual 
  manner. 
  When 
  the 
  pressure 
  had 
  fallen 
  to 
  -OOS" 
  1 
  ™, 
  the 
  

   liquid 
  air 
  was 
  again 
  applied. 
  Three 
  hours 
  later 
  a 
  series 
  of 
  

   measurements 
  was 
  taken, 
  the 
  results 
  of 
  which 
  were 
  between 
  

   those 
  represented 
  in 
  Curves 
  II 
  and 
  III, 
  fig. 
  3. 
  This 
  shows 
  

   that 
  the 
  effect 
  in 
  question 
  is 
  not 
  due 
  to 
  a 
  volume 
  ionization 
  of 
  

   the 
  residual 
  gas. 
  For 
  the 
  amount 
  of 
  gas 
  in 
  the 
  chamber 
  three 
  

   hours 
  after 
  the 
  application 
  of 
  the 
  liquid 
  air 
  could 
  not 
  have 
  been 
  

   very 
  different 
  from 
  that 
  which 
  was 
  present 
  when 
  Curve 
  I 
  was 
  

   taken. 
  On 
  the 
  other 
  hand, 
  the 
  surface 
  films 
  on 
  the 
  metals 
  

   might 
  well 
  be 
  different 
  after 
  a 
  brief 
  exposure 
  to 
  a 
  pressure 
  of 
  

   02 
  mm 
  from 
  what 
  they 
  were 
  after 
  a 
  prolonged 
  exposure 
  to 
  

   atmospheric 
  pressure. 
  In 
  another 
  experiment, 
  air 
  at 
  atmos- 
  

   pheric 
  pressure 
  was 
  allowed 
  to 
  stand 
  in 
  the 
  chamber 
  for 
  two 
  

   days 
  ; 
  upon 
  re-exhaustion, 
  the 
  same 
  behavior 
  was 
  observed 
  as 
  

   that 
  shown 
  in 
  Hg. 
  3. 
  It 
  seems 
  clear 
  therefore 
  that 
  the 
  effect 
  

   is 
  due 
  to 
  the 
  presence 
  of 
  surface 
  films 
  which 
  are 
  removed 
  only 
  

   very 
  slowly 
  in 
  a 
  high 
  vacuum 
  and 
  probably 
  not 
  completely 
  

   removed 
  in 
  any 
  case. 
  

  

  The 
  next 
  question 
  to 
  be 
  considered 
  was 
  whether 
  the 
  negative 
  

   charge 
  upon 
  the 
  electrode 
  was 
  due 
  to 
  electrons 
  coming 
  to 
  it 
  

   from 
  the 
  gas 
  film 
  on 
  the 
  case 
  and 
  gauze 
  or 
  to 
  positive 
  ions 
  lost 
  

   by 
  the 
  film 
  on 
  the 
  electrode 
  itself. 
  To 
  determine 
  this 
  a 
  

   magnetic 
  field 
  was 
  employed. 
  The 
  core 
  of 
  the 
  magnet 
  was 
  a 
  

   bar 
  of 
  soft 
  iron 
  2 
  inches 
  square 
  in 
  section, 
  bent 
  so 
  as 
  to 
  form 
  

  

  