﻿236 
  Prof. 
  H. 
  A. 
  Bumstead 
  on 
  the 
  

  

  enough 
  to 
  do 
  more 
  than 
  indicate 
  the 
  presence 
  of 
  the 
  swifter 
  

   rays, 
  certainly 
  not 
  to 
  measure 
  them. 
  Only 
  a 
  small 
  fraction 
  

   of 
  the 
  8- 
  rays 
  generated 
  in 
  the 
  chamber 
  escaped 
  through 
  

   the 
  hole, 
  and, 
  even 
  so, 
  the 
  beam 
  was 
  so 
  divergent 
  that 
  the 
  

   Faraday 
  cylinder 
  had 
  to 
  be 
  rather 
  large 
  (5'5 
  X 
  4 
  cm.) 
  ; 
  thus 
  

   its 
  electrostatic 
  capacity 
  was 
  considerable, 
  and 
  one 
  could 
  not 
  

   gain 
  any 
  advantage 
  by 
  substituting 
  a 
  sensitive 
  electroscope 
  

   for 
  the 
  quadrant 
  electrometer. 
  

  

  The 
  next 
  attempt 
  was 
  by 
  insulating 
  the 
  source 
  (either 
  A 
  

   or 
  B) 
  from 
  the 
  case 
  and 
  connecting 
  it 
  to 
  the 
  measuring- 
  

   instrument 
  ; 
  as 
  its 
  capacity 
  was 
  small, 
  an 
  electroscope 
  could 
  

   now 
  be 
  used 
  to 
  advantage. 
  A 
  negative 
  potential 
  applied 
  to 
  

   the 
  case 
  would 
  send 
  back 
  to 
  the 
  source 
  all 
  the 
  electrons 
  whose 
  

   kinetic 
  energy 
  was 
  not 
  sufficient 
  to 
  overcome 
  the 
  opposing 
  

   potential 
  difference. 
  Here 
  the 
  difficulty 
  was 
  to 
  prevent 
  the 
  

   tertiary 
  electrons, 
  set 
  up 
  by 
  the 
  impact 
  of 
  the 
  6-rays 
  upon 
  

   the 
  case, 
  from 
  being 
  carried 
  to 
  the 
  source 
  by 
  the 
  electric 
  

   field. 
  I 
  first 
  tried 
  to 
  obviate 
  this 
  by 
  means 
  of 
  a 
  magnetic 
  

   field. 
  A 
  long 
  cylindrical 
  case 
  was 
  used 
  (the 
  one 
  shown 
  in 
  

   fig. 
  2), 
  with 
  the 
  source 
  of 
  S-rays 
  near 
  the 
  top 
  and 
  the 
  rays 
  

   striking 
  the 
  bottom 
  and 
  the 
  lower 
  part 
  of 
  the 
  sides 
  of 
  the 
  

   case. 
  A 
  magnetic 
  field 
  of 
  about 
  50 
  gausses 
  was 
  applied 
  to 
  

   this 
  part 
  of 
  the 
  case. 
  To 
  prevent 
  this 
  field 
  as 
  much 
  as 
  

   possible 
  from 
  having 
  an 
  effect 
  upon 
  the 
  emission 
  of 
  the 
  

   S-rays 
  themselves, 
  the 
  source 
  was 
  enclosed 
  in 
  a 
  sort 
  of 
  upper 
  

   chamber 
  made 
  of 
  a 
  plate 
  and 
  a 
  ring 
  of 
  soft 
  Norway 
  iron, 
  

   1*5 
  cm. 
  thick 
  (this 
  is 
  not 
  shown 
  in 
  fig. 
  2). 
  A 
  tapered 
  hole 
  

   in 
  the 
  plate 
  allowed 
  the 
  beam 
  of 
  S-rays 
  to 
  pass 
  into 
  the 
  lower 
  

   chamber; 
  both 
  chambers 
  were 
  coated 
  with 
  soot. 
  Preliminary 
  

   measurements 
  of 
  the 
  magnetic 
  field 
  in 
  the 
  upper 
  chamber 
  by 
  

   means 
  of 
  a 
  swinging 
  needle 
  showed 
  that, 
  with 
  a 
  field 
  of 
  

   50 
  gausses 
  near 
  the 
  bottom 
  of 
  the 
  case, 
  the 
  field 
  near 
  the 
  

   source 
  was 
  not 
  more 
  than 
  0*5 
  gauss. 
  

  

  This 
  method 
  was 
  not 
  wholly 
  unsuccessful. 
  In 
  a 
  charcoal 
  

   vacuum 
  which 
  had 
  been 
  maintained 
  for 
  several 
  days, 
  the 
  

   source 
  lost 
  negative 
  electricity 
  in 
  the 
  face 
  of 
  an 
  opposing 
  

   potential 
  of 
  300 
  volts, 
  but 
  beyond 
  that 
  it 
  acquired 
  a 
  negative 
  

   charge. 
  The 
  form 
  of 
  the 
  relation 
  between 
  current 
  and 
  

   potential 
  for 
  the 
  lower 
  voltages 
  was 
  quite 
  similar 
  to 
  those 
  

   obtained 
  later 
  with 
  the 
  final 
  form 
  of 
  apparatus; 
  with 
  potentials 
  

   over 
  250 
  volts, 
  however, 
  the 
  effects 
  of 
  the 
  tertiary 
  electrons 
  

   began 
  to 
  be 
  conspicuous. 
  Moreover, 
  on 
  account 
  of 
  the 
  limited 
  

   beam 
  of 
  S-rays 
  the 
  values 
  of 
  the 
  currents 
  were 
  small 
  and 
  

   necessitated 
  the 
  use 
  of 
  a 
  very 
  sensitive, 
  and 
  consequently 
  

   troublesome, 
  electroscope. 
  

  

  