﻿Positive 
  Rays. 
  677 
  

  

  on 
  the 
  cylinder. 
  In 
  my 
  experiments 
  the 
  diameter 
  of 
  the 
  

   hole, 
  "9 
  mm., 
  was 
  a 
  considerable 
  fraction 
  of 
  the 
  length 
  

   1*6 
  mm. 
  of 
  the 
  tunnel, 
  so 
  that 
  there 
  was 
  a 
  considerable 
  

   latitude 
  in 
  the 
  direction 
  of 
  propagation 
  of 
  ions 
  through 
  the 
  

   hole. 
  This 
  has 
  the 
  effect 
  of 
  making 
  the 
  ratio 
  of 
  the 
  charges 
  

   on 
  the 
  cylinder 
  and 
  disk 
  change 
  much 
  less 
  abruptly 
  than 
  if 
  

   they 
  were 
  all 
  projected 
  in 
  the 
  same 
  direction, 
  since 
  those 
  

   ions 
  which 
  are 
  projected 
  towards 
  the 
  side 
  of 
  the 
  cylinder 
  to 
  

   which 
  they 
  are 
  bent 
  by 
  the 
  magnetic 
  field, 
  will 
  be 
  carried 
  to 
  

   the 
  side 
  by 
  a 
  smaller 
  magnetic 
  force 
  than 
  those 
  which 
  are 
  

   projected 
  at 
  right 
  angles 
  to 
  the 
  disk. 
  When 
  the 
  hole 
  is 
  very 
  

   small, 
  the 
  charge 
  carried 
  by 
  the 
  ions 
  passing 
  through 
  it 
  in 
  a 
  

   given 
  time 
  is 
  also 
  very 
  small, 
  and 
  the 
  potentials 
  of 
  the 
  disk 
  

   and 
  cylinder 
  change 
  very 
  slowly. 
  The 
  purpose 
  for 
  which 
  

   these 
  experiments 
  were 
  made 
  was 
  not 
  so 
  much 
  to 
  get 
  accurate 
  

   values 
  of 
  e/m 
  for 
  the 
  ions 
  as 
  to 
  find 
  out 
  whether 
  these 
  had 
  

   masses 
  comparable 
  with 
  the 
  mass 
  of 
  an 
  atom 
  of 
  hydrogen, 
  or 
  

   of 
  oxygen, 
  &c. 
  The 
  arrangement 
  used 
  was 
  adequate 
  for 
  

   doing 
  this, 
  and 
  had 
  the 
  advantage 
  of 
  giving 
  a 
  supply 
  of 
  

   ions 
  which 
  could 
  produce 
  measurable 
  effects 
  in 
  a 
  minute 
  or 
  

   so, 
  thus 
  avoiding 
  many 
  difficulties 
  as 
  to 
  insulation 
  which 
  

   crop 
  up 
  when 
  the 
  experiments 
  have 
  to 
  be 
  extended 
  over 
  very 
  

   much 
  longer 
  periods. 
  Experiments 
  with 
  very 
  much 
  smaller 
  

   holes 
  are, 
  however, 
  in 
  progress. 
  

  

  The 
  strength 
  of 
  the 
  magnetic 
  field 
  between 
  the 
  poles 
  was 
  

   determined 
  by 
  comparing 
  the 
  currents 
  induced 
  in 
  a 
  small 
  

   coil 
  when 
  suddenly 
  withdrawn 
  from 
  the 
  magnetic 
  field 
  with 
  

   the 
  current 
  obtained 
  by 
  turning 
  an 
  earth 
  inductor 
  through 
  

   180° 
  in 
  the 
  earth's 
  magnetic 
  field. 
  When 
  the 
  pole-pieces 
  

   were 
  1*15 
  cm. 
  apart, 
  the 
  magnetic 
  forces 
  H 
  for 
  different 
  

   currents 
  through 
  the 
  coils 
  of 
  the 
  electromagnet 
  were 
  as 
  

   follows 
  : 
  — 
  

  

  Current 
  through 
  Electromagnet 
  

  

  in 
  amperes. 
  H. 
  

  

  •5 
  1330 
  

  

  1 
  2570 
  

   2-5 
  4000 
  

  

  2 
  4900 
  

   2-5 
  5600 
  

  

  3 
  6000 
  

   3-5 
  6400 
  

   4-0 
  6660 
  

  

  When, 
  as 
  in 
  our 
  Faraday 
  cylinder, 
  d 
  = 
  o 
  mm. 
  £ 
  = 
  2 
  mm., 
  

  

  