﻿678 
  

  

  Prof. 
  J. 
  J. 
  Thomson 
  

  

  on 
  

  

  •72 
  _j_ 
  2 
  

  

  the 
  radius 
  of 
  the 
  critical 
  circle 
  — 
  r 
  ='725 
  mm., 
  we 
  see 
  by 
  

  

  Let 
  

  

  the 
  application 
  of 
  equation 
  (2) 
  that 
  if 
  e/??i 
  = 
  10 
  4 
  , 
  the 
  potential- 
  

   difference 
  V 
  required 
  to 
  reduce 
  the 
  radius 
  of 
  the 
  orbit 
  to 
  the 
  

   critical 
  value 
  would, 
  when 
  the 
  currents 
  through 
  the 
  electro- 
  

   magnets 
  were 
  1, 
  2, 
  3, 
  4 
  amperes, 
  be 
  respectively 
  170, 
  620, 
  

   900, 
  1100 
  volts. 
  These 
  are 
  the 
  potential-differences 
  between 
  

   the 
  gauze 
  and 
  the 
  top 
  of 
  the 
  cylinder 
  N 
  required 
  to 
  send 
  the 
  

   ions 
  to 
  the 
  plate. 
  The 
  following 
  table 
  gives 
  the 
  charge 
  ac- 
  

   quired 
  by 
  the 
  disk 
  when 
  the 
  sum 
  of 
  the 
  charges 
  on 
  the 
  disk 
  

   and 
  Faraday 
  cylinder 
  was 
  100 
  for 
  different 
  strengths 
  of 
  

   magnetic 
  fields 
  ; 
  assuming 
  that 
  all 
  the 
  ions 
  carry 
  the 
  same 
  

   charge, 
  these 
  numbers 
  represent 
  the 
  percentage 
  of 
  the 
  ions 
  

   passing 
  through 
  the 
  hole 
  which 
  reach 
  the 
  disk. 
  In 
  the 
  table 
  

   V 
  is 
  the 
  potential-difference 
  between 
  the 
  gauze 
  and 
  N 
  in 
  

   volts, 
  i 
  the 
  current 
  through 
  the 
  electromagnet 
  in 
  amperes, 
  

   and 
  n 
  the 
  percentage 
  of 
  ions 
  which 
  reach 
  the 
  disk. 
  The 
  gas 
  

   in 
  the 
  tube 
  was 
  hydrogen. 
  

  

  

  V=10. 
  

  

  V=20. 
  

  

  V=30. 
  

  

  V=40. 
  

  

  V 
  = 
  50. 
  

  

  V=60. 
  

  

  V 
  = 
  80. 
  

  

  1 
  

  

  1 
  

  

  2 
  

  

  3 
  

  

  4 
  

  

  n 
  

  

  17 
  

  

  18 
  

  

  11 
  

  

  8 
  

  

  n 
  

  

  18-4 
  

  

  23 
  

  

  16 
  

  

  • 
  

  

  n 
  

  

  18 
  

   23 
  

   22 
  

   20 
  

  

  11 
  

   18 
  

   22 
  

   23 
  

   22-5 
  

  

  11 
  

   18 
  

   22 
  

   25 
  

   25 
  

  

  11 
  

   19 
  

   20 
  

   26 
  

  

  27 
  

  

  ii 
  

   22-8 
  

   19 
  

   21 
  

   26 
  

  

  

  1 
  

  

  o 
  

  

  3 
  

  

  4 
  

  

  V=100. 
  

  

  V=120. 
  

  

  V=140. 
  V=160. 
  

  

  V-180. 
  

  

  V=420. 
  

  

  

  23 
  

   16 
  

   21 
  

   25 
  

  

  25 
  

   17 
  

   19 
  

   23 
  

  

  24 
  

   22 
  

   19 
  

   21 
  

  

  28 
  

   14 
  

   16 
  

  

  18 
  

  

  31 
  

   12 
  

  

  9 
  

  

  15 
  

  

  505 
  

  

  12 
  

  

  9 
  

  

  8 
  

  

  On 
  looking 
  at 
  the 
  numbers 
  we 
  see 
  that 
  until 
  the 
  voltage 
  

   exceeds 
  160 
  volts 
  there 
  is 
  no 
  appreciable 
  difference 
  between 
  

   the 
  number 
  of 
  ions 
  going 
  to 
  the 
  disk 
  when 
  the 
  magnetic 
  

   field 
  is 
  due 
  to 
  a 
  current 
  of 
  1 
  ampere, 
  and 
  when 
  it 
  is 
  due 
  to 
  

   2 
  amperes. 
  We 
  saw, 
  from 
  the 
  preceding 
  calculation, 
  that 
  a 
  

   voltage 
  of 
  170 
  volts 
  would 
  carry 
  ions 
  for 
  which 
  e/m 
  = 
  10 
  4: 
  to 
  

   the 
  disk 
  against 
  the 
  electric 
  current, 
  while 
  it 
  would 
  require 
  

   about 
  700 
  volts 
  to 
  drive 
  them 
  across 
  when 
  the 
  current 
  was 
  

  

  