﻿840 
  Sir 
  J. 
  J. 
  Thomson 
  on 
  

  

  the 
  heavy 
  negative 
  ions 
  which 
  move 
  on 
  to 
  the 
  disk, 
  and 
  are 
  

   not 
  deflected 
  until 
  the 
  magnetic 
  force 
  is 
  strong 
  enough 
  

   to 
  deflect 
  ions 
  whose 
  mass 
  is 
  comparable 
  with 
  that 
  of 
  

   atoms. 
  

  

  I 
  have 
  occasionally 
  observed 
  a 
  similar 
  eff'ect 
  when 
  the 
  

   positive 
  instead 
  o£ 
  the 
  negative 
  ions 
  were 
  sent 
  through 
  the 
  

   cylinder. 
  

  

  This 
  eff'ect 
  has 
  only 
  been 
  observed 
  when 
  the 
  potential- 
  

   difference 
  between 
  the 
  gauze 
  and 
  the 
  top 
  o£ 
  the 
  plate 
  exceeded 
  

   about 
  120 
  volts, 
  and 
  then 
  only 
  occasionally 
  ; 
  still, 
  on 
  several 
  

   occasions 
  it 
  was 
  found 
  that 
  the 
  amount 
  of 
  positive 
  electricity 
  

   going 
  to 
  the 
  cylinder 
  when 
  there 
  there 
  was 
  no 
  magnetic 
  

   tield 
  on, 
  was 
  a 
  larger 
  multiple 
  of 
  that 
  going 
  to 
  the 
  disk 
  than 
  

   when 
  the 
  magnetic 
  field 
  was 
  increased 
  to 
  about 
  100 
  units 
  : 
  

   this 
  effect 
  is 
  similar 
  to 
  that 
  observed 
  with 
  negative 
  electricity 
  

   and 
  which 
  could 
  be 
  explained, 
  as 
  we 
  saw, 
  by 
  supposing 
  that 
  

   there 
  were 
  particles 
  of 
  exceedingly 
  small 
  mass 
  along 
  with 
  

   the 
  others. 
  Are 
  we 
  to 
  conclude 
  that 
  there 
  are 
  similar 
  small 
  

   positive 
  particles, 
  particles 
  whose 
  mass 
  is 
  very 
  small 
  compared 
  

   with 
  that 
  of 
  the 
  atom 
  ? 
  I 
  do 
  not 
  think 
  that 
  the 
  effect 
  I 
  am 
  

   describing 
  is 
  due 
  to 
  this. 
  In 
  the 
  first 
  place, 
  while 
  the 
  effect 
  

   is 
  invariably 
  observed 
  with 
  negative 
  electricity, 
  it 
  is 
  quite 
  

   exceptional 
  with 
  positive. 
  

  

  I 
  had 
  worked 
  with 
  the 
  apparatus 
  described 
  for 
  months, 
  

   making 
  observations 
  almost 
  daily, 
  before 
  I 
  found 
  an 
  example 
  

   of 
  it. 
  I 
  think 
  that 
  it 
  arises 
  from 
  the 
  presence 
  among 
  the 
  

   stream 
  of 
  positive 
  ions 
  which 
  pass 
  through 
  the 
  hole 
  in 
  the 
  

   plate, 
  of 
  some 
  ions 
  which 
  are 
  moving 
  with 
  much 
  smaller 
  

   velocity 
  than 
  that 
  which 
  they 
  would 
  acquire 
  by 
  a 
  fall 
  

   through 
  a 
  potential-difference 
  equal 
  to 
  that 
  between 
  the 
  

   gauze 
  and 
  the 
  plate. 
  

  

  We 
  have 
  seen 
  that 
  these 
  positive 
  ions 
  are 
  continually 
  

   getting 
  neutralized 
  in 
  their 
  journey 
  through 
  the 
  gas, 
  and 
  

   that 
  some 
  of 
  them 
  are 
  hardly 
  deflected 
  at 
  all, 
  that 
  is, 
  do 
  not 
  

   acquire 
  an 
  appreciable 
  velocity 
  whilst 
  they 
  are 
  passing 
  

   through 
  the 
  electric 
  field. 
  

  

  Thus 
  we 
  might 
  expect 
  that 
  some 
  of 
  the 
  ions 
  would 
  be 
  

   neutralized 
  for 
  part 
  of 
  their 
  journey 
  between 
  the 
  gauze 
  and 
  

   the 
  plate, 
  and 
  would 
  thus 
  only 
  acquire 
  a 
  small 
  fraction 
  of 
  the 
  

   velocity 
  due 
  to 
  a 
  fall 
  through 
  the 
  whole 
  potential- 
  diff'erence 
  

   between 
  the 
  plates. 
  

  

  ; 
  These 
  slowly 
  moving 
  ions 
  would 
  be 
  easily 
  deflected, 
  and 
  a 
  

   comparatively 
  weak 
  magnetic 
  field 
  will 
  be 
  sufficient 
  to 
  

   prevent 
  them 
  entering 
  the 
  Faraday 
  cylinders. 
  If 
  the 
  eff'ect 
  

   I 
  am 
  describing 
  is 
  due 
  to 
  the 
  slowly 
  moving 
  ions, 
  it 
  ought 
  

  

  