﻿212 
  Prof. 
  H. 
  A. 
  Bumstead 
  on 
  the 
  

  

  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 
  0'2 
  mm. 
  from 
  what 
  they 
  were 
  

   after 
  a 
  prolonged 
  exposure 
  to 
  atmospheric 
  pressure. 
  In 
  

   another 
  experiment, 
  air 
  at 
  atmospheric 
  pressure 
  was 
  allowed 
  

   to 
  stand 
  in 
  the 
  chamber 
  for 
  two 
  days 
  ; 
  upon 
  re-exhaustion, 
  

   the 
  same 
  behaviour 
  was 
  observed 
  as 
  that 
  shown 
  in 
  fig. 
  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 
  

   cl 
  large 
  upon 
  the 
  electrode 
  was 
  due 
  to 
  electrons 
  coming 
  to 
  it 
  

   from 
  the 
  gas 
  film 
  on 
  the 
  cnse 
  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 
  

   three 
  sides 
  of 
  a 
  rectangle. 
  One 
  side 
  of 
  this 
  rectangle, 
  21 
  cm. 
  

   long, 
  was 
  surrounded 
  by 
  the 
  magnetizing 
  coil 
  ; 
  the 
  other 
  two 
  

   sides, 
  18 
  cm. 
  long, 
  embraced 
  the 
  case, 
  as 
  shown 
  in 
  fig. 
  2, 
  and 
  

   formed 
  long, 
  narrow 
  pole-pieces. 
  Along 
  these 
  pole-pieces, 
  

   from 
  their 
  ends 
  nearly 
  to 
  the 
  magnetizing 
  coil, 
  the 
  field 
  was 
  

   fairly 
  uniform, 
  not 
  varying 
  more 
  than 
  10 
  per 
  cent., 
  when 
  

   measured 
  by 
  a 
  fluxmeter. 
  In 
  the 
  other 
  two 
  directions 
  at 
  

   right 
  angles 
  to 
  this, 
  the 
  variation 
  of 
  the 
  field 
  was 
  rapid 
  on 
  

   account 
  of 
  the 
  spreading 
  out 
  of 
  the 
  lines 
  of 
  force 
  in 
  the 
  large 
  

   air-gap. 
  With 
  a 
  current 
  of 
  5 
  amperes, 
  for 
  example, 
  the 
  field 
  

   near 
  either 
  pole-piece 
  was 
  530 
  gausses, 
  while 
  half-way 
  between 
  

   them, 
  and 
  in 
  their 
  plane, 
  it 
  was 
  250. 
  The 
  field 
  at 
  any 
  one 
  

   point 
  was 
  nearly 
  proportional 
  to 
  the 
  current 
  in 
  the 
  coil 
  from 
  

   1 
  to 
  8 
  amperes. 
  Before 
  using 
  the 
  magnetic 
  field, 
  the 
  brass 
  

   box 
  which 
  served 
  as 
  the 
  electrode 
  and 
  the 
  source 
  of 
  S-rays 
  

   was 
  provided 
  with 
  the 
  brass 
  ring 
  shown 
  in 
  fig. 
  2 
  (forming 
  

   the 
  brim 
  of 
  the 
  " 
  hat 
  "), 
  wdnch 
  had 
  not 
  been 
  present 
  in 
  

   the 
  preceding 
  experiments. 
  Its 
  purpose 
  was 
  to 
  catch 
  the 
  

   ^-electrons 
  originating 
  near 
  one 
  side 
  of 
  the 
  box 
  when 
  they 
  

   were 
  bent 
  by 
  the 
  magnetic 
  field 
  toward 
  that 
  side. 
  The 
  

   addition 
  of 
  this 
  ring, 
  by 
  increasing 
  the 
  capacity 
  of 
  the 
  elec- 
  

   trode, 
  decreased 
  somewhat 
  the 
  readings 
  of 
  the 
  electroscope. 
  

  

  With 
  the 
  magnetic 
  field, 
  the 
  electrode 
  charged 
  up 
  nega- 
  

   tively, 
  the 
  rate 
  reaching 
  a 
  maximum 
  value 
  with 
  a 
  current 
  of 
  

   3 
  amperes 
  on 
  the 
  magnet 
  and 
  not 
  changing 
  when 
  the 
  current 
  

  

  