﻿244 
  Prof. 
  H. 
  A. 
  Bumstead 
  on 
  the 
  

  

  this 
  question 
  for 
  the 
  following 
  reasons. 
  The 
  magnetic 
  field 
  

   is 
  by 
  no 
  means 
  parallel 
  to 
  the 
  electrode, 
  and 
  some 
  of 
  the 
  

   lines 
  of 
  force 
  meet 
  the 
  surface 
  of 
  the 
  electrode, 
  though 
  not 
  

   at 
  very 
  large 
  angles. 
  A 
  small 
  proportion 
  of 
  the 
  S-electrons 
  

   from 
  any 
  point 
  of 
  the 
  electrode 
  will 
  leave 
  in 
  paths 
  making 
  

   only 
  a 
  small 
  angle 
  with 
  the 
  magnetic 
  field, 
  and 
  will 
  hence 
  

   escape. 
  Now 
  when 
  a 
  positive 
  potential 
  is 
  applied 
  to 
  the 
  

   gauze, 
  the 
  current 
  of 
  electrons 
  leaving 
  the 
  source 
  without 
  a 
  

   magnetic 
  field 
  is 
  more 
  than 
  500 
  times 
  the 
  ionic 
  current 
  

   under 
  consideration. 
  If 
  a 
  fraction 
  of 
  one 
  per 
  cent, 
  of 
  these 
  

   escape 
  along 
  the 
  lines 
  of 
  force, 
  it 
  will 
  be 
  sufficient 
  to 
  cover 
  

   up 
  the 
  possible 
  small 
  current 
  due 
  to 
  negative 
  ions. 
  That 
  

   this 
  is 
  the 
  case 
  will 
  be 
  seen 
  in 
  the 
  following 
  section. 
  

  

  Effects 
  have 
  been 
  observed 
  by 
  other 
  investigators 
  which, 
  I 
  

   believe, 
  indicate 
  the 
  presence 
  of 
  ions 
  from 
  gaseous 
  surface 
  

   films. 
  Thus 
  in 
  the 
  recent, 
  very 
  careful 
  determination 
  by 
  

   Danysz 
  and 
  Duane* 
  of 
  the 
  charge 
  carried 
  by 
  a-rays, 
  the 
  

   screen 
  which 
  limits 
  the 
  beam 
  of 
  a-rays 
  and 
  the 
  opening 
  of 
  

   the 
  Faraday 
  cylinder 
  which 
  receives 
  them 
  are 
  both 
  covered 
  

   with 
  thin 
  aluminium 
  foil, 
  the 
  two 
  foils 
  being 
  parallel 
  and 
  

   0*8 
  cm. 
  apart. 
  A 
  magnetic 
  field 
  of 
  8000 
  units 
  parallel 
  to 
  

   these 
  foils 
  is 
  used 
  to 
  curl 
  up 
  the 
  /3- 
  and 
  8-ra} 
  r 
  s. 
  Even 
  with 
  

   this 
  field, 
  the 
  authors 
  found 
  f 
  that 
  a 
  difference 
  of 
  potential 
  

   of 
  only 
  2 
  volts 
  between 
  the 
  foils 
  increased 
  the 
  charge 
  re- 
  

   ceived 
  by 
  the 
  Faraday 
  cylinder 
  by 
  2*5 
  per 
  cent, 
  or 
  diminished 
  

   it 
  by 
  0*8 
  per 
  cent., 
  according 
  to 
  the 
  direction 
  of 
  the 
  electric 
  

   field; 
  a 
  potential 
  difference 
  of 
  1800 
  volts, 
  they 
  find, 
  may 
  

   affect 
  the 
  current 
  as 
  much 
  as 
  8 
  per 
  cent. 
  It 
  is 
  very 
  difficult 
  

   to 
  believe 
  that 
  these 
  results 
  can 
  be 
  due 
  to 
  a 
  " 
  drift 
  " 
  of 
  the 
  

   S-electrons 
  as 
  the 
  authors 
  suppose 
  ; 
  in 
  their 
  magnetic 
  field, 
  

   the 
  radius 
  of 
  curvature 
  of 
  the 
  path 
  of 
  an 
  electron, 
  moving 
  

   with 
  a 
  velocity 
  corresponding 
  to 
  2 
  volts, 
  would 
  be 
  about 
  

   •0005 
  cm.; 
  with 
  a 
  velocity 
  corresponding 
  to 
  1800 
  volts 
  about 
  

   •02 
  cm. 
  In 
  neither 
  case 
  does 
  it 
  seem 
  possible 
  that 
  an 
  

   electron 
  would 
  be 
  able 
  to 
  traverse 
  the 
  0'8 
  cm. 
  between 
  the 
  

   two 
  foils. 
  In 
  fact, 
  with 
  2 
  volts, 
  it 
  appears 
  that 
  it 
  would 
  

   require 
  a 
  very 
  heavy 
  ion 
  to 
  get 
  through 
  the 
  magnetic 
  field 
  ; 
  

   with 
  1800 
  volts, 
  an 
  oxygen 
  ion 
  should 
  get 
  through. 
  

  

  §5. 
  

   An 
  estimate 
  of 
  the 
  reliability 
  of 
  the 
  present 
  measurements 
  

   of 
  the 
  distribution 
  in 
  velocity 
  of 
  the 
  swifter 
  S-rays 
  will 
  be 
  

   facilitated 
  by 
  a 
  consideration 
  of 
  fig. 
  4, 
  which 
  will 
  also 
  serve 
  

   to 
  give 
  a 
  clearer 
  idea 
  of 
  the 
  somewhat 
  complicated 
  pheno- 
  

   mena 
  which 
  appear 
  when 
  a- 
  rays 
  fall 
  upon 
  a 
  metal 
  in 
  a 
  high 
  

  

  * 
  Am. 
  Journ. 
  Sci. 
  xxxv. 
  p. 
  295 
  (1913). 
  t 
  L. 
  c. 
  p. 
  303. 
  

  

  