﻿246 
  Prof. 
  H. 
  A. 
  Bumstead 
  on 
  the 
  

  

  Their 
  number 
  decreases, 
  however, 
  as 
  higher 
  negative 
  poten- 
  

   tials 
  are 
  applied, 
  owing 
  to 
  the 
  decreased 
  number 
  of 
  S-eleetrons 
  

   which 
  reach 
  the 
  case. 
  Their 
  presence 
  can 
  still 
  be 
  detected, 
  

   however, 
  at 
  2000 
  volts. 
  The 
  course 
  of 
  II 
  shows 
  that 
  the 
  

   gauze 
  cage 
  acts 
  as 
  an 
  entanglement 
  to 
  the 
  tertiary 
  electrons 
  

   even 
  when 
  there 
  is 
  no 
  field 
  between 
  it 
  and 
  the 
  case; 
  for 
  when 
  

   the 
  cage 
  is 
  absent 
  the 
  tertiary 
  current 
  reaches 
  a 
  maximum 
  at 
  

   40 
  volts, 
  while 
  with 
  the 
  cage 
  (as 
  shown 
  in 
  II) 
  the 
  maximum 
  

   occurs 
  at 
  150 
  volts. 
  

  

  On 
  the 
  view 
  advanced 
  in 
  the 
  preceding 
  section, 
  the 
  negative 
  

   ordinates 
  of 
  I' 
  and 
  II' 
  represent 
  the 
  current 
  carried 
  by 
  

   positive 
  ions 
  generated 
  by 
  the 
  a-rays 
  in 
  the 
  gas 
  film 
  upon 
  

   the 
  electrode. 
  I 
  have 
  b^en 
  unable 
  to 
  find 
  an 
  explanation 
  for 
  

   the 
  difference 
  between 
  the 
  two 
  curves. 
  

  

  Considered 
  as 
  representing 
  the 
  distribution 
  in 
  velocity 
  of 
  

   the 
  swifter 
  fir-rays, 
  the 
  measurements 
  represented 
  by 
  Curve 
  I 
  

   (or 
  by 
  the 
  curves 
  of 
  fig. 
  3) 
  are 
  subject 
  to 
  certain 
  sources 
  of 
  

   error, 
  of 
  which 
  the 
  following 
  appear 
  to 
  be 
  most 
  important. 
  

  

  1. 
  Some 
  of 
  the 
  S-electrons, 
  whose 
  velocity 
  is 
  nearly 
  but 
  

   not 
  quite 
  great 
  enough 
  to 
  get 
  through 
  the 
  electric 
  field, 
  may 
  

   approach 
  near 
  enough 
  to 
  the 
  gauze 
  to 
  be 
  captured 
  by 
  the 
  

   auxiliary 
  field 
  between 
  it 
  and 
  the 
  case. 
  A 
  consideration 
  of 
  

   the 
  electric 
  field 
  in 
  the 
  neighbourhood 
  of 
  the 
  gauze 
  shows, 
  

   however, 
  that 
  to 
  be 
  so 
  captured, 
  an 
  electron 
  must 
  approach 
  

   fairly 
  near 
  to 
  the 
  gauze 
  ; 
  thus 
  at 
  any 
  given 
  voltage, 
  the 
  

   electrons 
  improperly 
  captured 
  must 
  lie 
  between 
  narrow 
  limits 
  

   of 
  velocity 
  and 
  would 
  form 
  a 
  small 
  fraction 
  of 
  the 
  total 
  not 
  

   returned 
  to 
  the 
  electrode. 
  Moreover, 
  since 
  the 
  shape 
  of 
  the 
  

   lines 
  of 
  force 
  near 
  the 
  gauze 
  remains 
  the 
  same, 
  this 
  fraction 
  

   would 
  not 
  vary 
  very 
  much 
  for 
  different 
  potentials. 
  The 
  

   principal 
  effect, 
  therefore, 
  of 
  this 
  error 
  would 
  be 
  to 
  increase 
  

   each 
  ordinate 
  of 
  the 
  curve 
  in 
  nearly 
  the 
  same 
  proportion, 
  

   which 
  would 
  not 
  seriously 
  affect 
  its 
  accuracy. 
  

  

  2. 
  Some 
  of 
  the 
  tertiary 
  electrons, 
  set 
  free 
  by 
  the 
  S-rays 
  

   which 
  strike 
  the 
  gauze, 
  may 
  be 
  returned 
  to 
  the 
  electrode. 
  

   In 
  a 
  preceding 
  section 
  reasons 
  have 
  been 
  given 
  for 
  supposing 
  

   that 
  these 
  will 
  form 
  a 
  nearly 
  constant 
  fraction 
  of 
  all 
  the 
  

   tertiary 
  electrons 
  from 
  both 
  gauze 
  and 
  case, 
  If 
  this 
  be 
  so, 
  

   Curve 
  I 
  lies 
  below 
  its 
  true 
  position, 
  each 
  ordinate 
  having 
  

   subtracted 
  from 
  it 
  a 
  fraction 
  of 
  the 
  corresponding 
  ordinate 
  

   of 
  II. 
  This 
  would 
  alter 
  the 
  course 
  of 
  I, 
  depressing 
  it 
  most 
  

   between 
  100 
  and 
  200 
  volts, 
  and 
  less 
  at 
  higher 
  potentials. 
  

   This 
  correction, 
  however, 
  cannot 
  be 
  large. 
  The 
  wires 
  of 
  the 
  

   gauze 
  occupy 
  only 
  17 
  per 
  cent, 
  of 
  its 
  total 
  area, 
  and 
  certainly 
  

   most 
  of 
  the 
  tertiary 
  electrons 
  which 
  originate 
  upon 
  it 
  must 
  

  

  