﻿H. 
  A. 
  Bumstead 
  — 
  Velocities 
  of 
  Delta 
  Rays. 
  103 
  

  

  of 
  which 
  were 
  made 
  on 
  the 
  same 
  day, 
  after 
  the 
  vacuum 
  had 
  

   been 
  maintained 
  for 
  eight 
  days. 
  Curve 
  I 
  shows 
  the 
  currents 
  

   received 
  by 
  the 
  electrode, 
  with 
  the 
  case 
  grounded 
  and 
  with 
  

   negative 
  potentials 
  between 
  20 
  and 
  1200 
  volts 
  on 
  the 
  gauze 
  

   cage. 
  Curve 
  II 
  represents 
  the 
  currents 
  when 
  both 
  case 
  and 
  

   gauze 
  are 
  charged 
  alike. 
  Curves 
  F 
  and 
  IF 
  give 
  the 
  currents 
  

   observed 
  under 
  similar 
  electrical 
  conditions 
  as 
  in 
  I 
  and 
  II 
  

   respectively, 
  but 
  with 
  a 
  magnetic 
  field 
  sufficient 
  to 
  give 
  its 
  

   maximum 
  effect. 
  Curve 
  I 
  is 
  similar 
  to 
  those 
  plotted 
  in 
  fig. 
  3 
  

   except 
  for 
  the 
  change 
  in 
  scale 
  due 
  to 
  the 
  altered 
  capacity, 
  and 
  

   for 
  the 
  fact 
  that 
  it 
  begins 
  at 
  20 
  volts 
  instead 
  of 
  40. 
  Accord- 
  

   ing 
  to 
  the 
  views 
  advanced 
  in 
  § 
  4, 
  an 
  ordinate 
  of 
  this 
  curve 
  

   represents 
  (with 
  more 
  or 
  less 
  accuracy) 
  the 
  number 
  of 
  elec- 
  

   trons 
  whose 
  energies 
  are 
  greater 
  than 
  that 
  represented 
  by 
  the 
  

   abscissa; 
  these 
  ordinates, 
  however, 
  are 
  to 
  be 
  measured, 
  not 
  

   from 
  the 
  axis, 
  but 
  from 
  a 
  line 
  below 
  it 
  representing 
  the 
  con- 
  

   stant 
  negative 
  current 
  received 
  by 
  the 
  electrode. 
  This 
  cor- 
  

   rected 
  zero 
  line 
  may 
  coincide 
  with 
  F, 
  or 
  it 
  may 
  fall 
  below 
  it, 
  

   since 
  it 
  is 
  not 
  certain 
  that 
  all 
  the 
  carriers 
  of 
  this 
  current 
  get 
  

   through 
  the 
  magnetic 
  field. 
  Curve 
  II 
  represents 
  the 
  resultant 
  

   of 
  the 
  current 
  of 
  S-electrons 
  from 
  the 
  source, 
  and 
  the 
  current 
  

   of 
  tertiary 
  electrons 
  from 
  the 
  case 
  : 
  at 
  20 
  volts 
  the 
  8-ray 
  current 
  

   predominates, 
  but 
  at 
  higher 
  potentials 
  the 
  tertiary 
  electrons 
  

   are 
  in 
  the 
  majority. 
  Their 
  number 
  decreases, 
  however, 
  as 
  

   higher 
  negative 
  potentials 
  are 
  applied, 
  owing 
  to 
  the 
  decreased 
  

   number 
  of 
  S-electrons 
  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 
  F 
  and 
  IF 
  represent 
  the 
  current 
  carried 
  by 
  positive 
  

   ions 
  generated 
  by 
  the 
  a-rays 
  in 
  the 
  gas 
  film 
  upon 
  the 
  electrode. 
  

   I 
  have 
  been 
  unable 
  to 
  find 
  an 
  explanation 
  for 
  the 
  difference 
  

   between 
  the 
  two 
  curves. 
  

  

  Considered 
  as 
  representing 
  the 
  distribution 
  in 
  velocity 
  of 
  

   the 
  swifter 
  S-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 
  neighborhood 
  of 
  the 
  gauze 
  shows, 
  how- 
  

   ever, 
  that 
  to 
  be 
  so 
  captured, 
  an 
  electron 
  must 
  approach 
  fairly 
  

  

  