﻿H. 
  A. 
  Bumstead 
  — 
  Velocities 
  of 
  Delta 
  Hays. 
  97 
  

  

  It 
  was 
  for 
  the 
  purpose 
  of 
  eliminating, 
  if 
  possible, 
  this 
  com- 
  

   plication 
  that 
  the 
  wire-gauze 
  cage 
  was 
  introduced 
  as 
  a 
  substi- 
  

   tute 
  for 
  the 
  magnetic 
  field 
  mentioned 
  in 
  § 
  2. 
  Retarding 
  fields 
  

   may 
  be 
  set 
  up 
  by 
  putting 
  negative 
  potentials 
  on 
  the 
  gauze 
  

   while 
  the 
  case 
  is 
  kept 
  grounded. 
  As 
  the 
  tertiary 
  electrons 
  

   have 
  small 
  velocities, 
  those 
  which 
  are 
  set 
  up 
  at 
  the 
  surface 
  of 
  

   the 
  case, 
  by 
  the 
  S-electrons 
  which 
  have 
  surmounted 
  the 
  field 
  

   and 
  passed 
  through 
  the 
  meshes 
  of. 
  the 
  gauze, 
  will 
  not 
  get 
  back 
  

   to 
  the 
  source 
  on 
  account 
  of 
  the 
  field 
  between 
  the 
  gauze 
  and 
  

   the 
  case.* 
  The 
  electric 
  force 
  is 
  much 
  greater 
  between 
  gauze 
  

   and 
  case 
  than 
  between 
  gauze 
  and 
  source, 
  (though 
  the 
  potential 
  

   difference 
  is 
  the 
  same) 
  because 
  of 
  the 
  smaller 
  distance 
  ; 
  thus 
  a 
  

   considerable 
  fraction 
  of 
  the 
  ternary 
  electrons 
  which 
  originate 
  

   on 
  the 
  wires 
  of 
  the 
  gauze 
  itself 
  will 
  be 
  captured 
  by 
  this 
  field 
  

   and 
  will 
  not 
  get 
  to 
  the 
  source 
  of 
  S-rays. 
  As 
  the 
  case 
  and 
  

   source 
  are 
  always 
  kept 
  at 
  zero 
  while 
  the 
  potential 
  of 
  the 
  gauze 
  

   is 
  changed, 
  the 
  shape 
  of 
  the 
  lines 
  of 
  force, 
  in 
  the 
  neighbor- 
  

   hood 
  of 
  the 
  wires 
  of 
  the 
  gauze 
  and 
  within 
  its 
  meshes 
  will 
  not 
  

   change, 
  and 
  it 
  seems 
  reasonable 
  to 
  assume 
  that 
  a 
  nearly 
  con- 
  

   stant 
  fraction 
  of 
  the 
  tertiary 
  rays 
  originating 
  upon 
  the 
  gauze 
  

   will 
  be 
  captured 
  in 
  this 
  way, 
  and 
  that 
  the 
  number 
  which 
  get 
  

   back 
  to 
  the 
  source 
  in 
  any 
  case 
  will 
  be 
  a 
  small 
  part 
  of 
  the 
  total 
  

   set 
  up 
  by 
  the 
  S-rays 
  on 
  case 
  and 
  gauze 
  together. 
  

  

  With 
  the 
  case 
  grounded 
  and 
  with 
  various 
  negative 
  potentials 
  

   on 
  the 
  gauze 
  cage, 
  readings 
  of 
  the 
  electroscope 
  gave 
  the 
  

   charge 
  acquired 
  by 
  the 
  source 
  in 
  a 
  given 
  time, 
  usually 
  one 
  

   minute. 
  It 
  was 
  soon 
  evident 
  that 
  the 
  readings 
  thus 
  obtained 
  

   varied 
  greatly 
  with 
  the 
  time 
  which 
  had 
  elapsed 
  since 
  the 
  pro- 
  

   duction 
  of 
  the 
  vacuum. 
  Three 
  hours 
  after 
  the 
  liquid 
  air 
  had 
  

   been 
  applied 
  to 
  the 
  charcoal 
  bulb, 
  a 
  negative 
  potential 
  of 
  40 
  

   volts 
  on 
  the 
  gauze 
  was 
  sufficient 
  to 
  give 
  a 
  slight 
  negative 
  

   charge 
  to 
  the 
  electrode 
  (the 
  source 
  of 
  S-rays, 
  B, 
  fig. 
  2) 
  ; 
  and 
  

   larger 
  negative 
  potentials 
  caused 
  a 
  marked 
  increase 
  in 
  this 
  

   negative 
  current. 
  (See 
  Curve 
  I, 
  fig. 
  3). 
  As 
  time 
  went 
  on, 
  

   however, 
  these 
  effects 
  were 
  much 
  altered 
  ; 
  positive 
  currents 
  

   were 
  observed 
  with 
  negative 
  potentials 
  on 
  the 
  gauze 
  greater 
  

   than 
  300 
  volts, 
  and 
  the 
  negative 
  currents 
  at 
  -the 
  higher 
  poten- 
  

   tial 
  were 
  much 
  diminished 
  in 
  magnitude. 
  The 
  results 
  of 
  four 
  

   series 
  of 
  observations 
  are 
  given 
  in 
  Table 
  I 
  and 
  shown 
  graphi- 
  

   cally 
  in 
  fig. 
  3. 
  

  

  * 
  This 
  method 
  has 
  been 
  several 
  times 
  used 
  to 
  prevent 
  the 
  reflection 
  of 
  slow 
  

   electrons 
  in 
  experiments 
  upon 
  cathode 
  rays 
  and 
  on 
  the 
  photo-electric 
  effect. 
  

   v. 
  Baeyer, 
  Phys. 
  Zeitschr., 
  x, 
  174, 
  1909. 
  

  

  