﻿212 
  Mr. 
  P. 
  J. 
  Kirkby 
  on 
  the 
  Electrical 
  Conductivities 
  

  

  7 
  8 
  

  

  Schoenflies 
  does 
  not 
  appear 
  to 
  give 
  his 
  groups 
  V 
  rf 
  and 
  V 
  d 
  

   quite 
  correctly*; 
  he 
  puts 
  the 
  plane 
  of 
  the 
  operations 
  S 
  d 
  (r 
  rf 
  ), 
  

   Si(xd 
  + 
  Tj 
  in 
  the 
  same 
  position 
  as 
  the 
  operations 
  S<* 
  and 
  

   S 
  rf 
  (t 
  ) 
  of 
  Y 
  d 
  and 
  V 
  d 
  ; 
  but 
  in 
  that 
  case 
  the 
  operations 
  referred 
  

   to 
  would 
  not 
  bring 
  the 
  axes 
  of 
  V 
  6 
  into 
  self-coincidence, 
  as 
  is 
  

   necessary. 
  Barlow 
  gives 
  the 
  position 
  of 
  the 
  plane 
  quite 
  

   correctly 
  on 
  p. 
  54, 
  Zeitschr. 
  Kryst. 
  a. 
  Min. 
  xxiii. 
  ; 
  and 
  this 
  

   remark 
  agrees 
  with 
  Schoenflies' 
  own 
  treatment 
  of 
  these 
  

   groups 
  in 
  the 
  Math. 
  Annalen, 
  xxxiv. 
  

  

  Fedorow's 
  comparison 
  of 
  his 
  groups 
  36 
  h, 
  37 
  h. 
  55 
  a, 
  57 
  a, 
  

   60 
  a, 
  61 
  a, 
  65 
  a, 
  66 
  a 
  with 
  Barlow's 
  types 
  seems 
  to 
  be 
  in- 
  

   correct, 
  judging 
  by 
  the 
  Tables 
  V. 
  and 
  VI. 
  given 
  at 
  the 
  end 
  

   of 
  the 
  24th 
  volume 
  of 
  the 
  Zeitschr./. 
  Kryst, 
  u. 
  Min. 
  ; 
  as 
  is 
  

   also 
  his 
  comparison 
  of 
  36 
  a, 
  37 
  a, 
  38 
  a, 
  64 
  a, 
  65 
  a, 
  66 
  a 
  with 
  

   the 
  corresponding 
  groups 
  of 
  Schoenflies. 
  

  

  Fedorow 
  compares 
  72 
  s. 
  73 
  5 
  with 
  O 
  9 
  and 
  O 
  5 
  ; 
  an 
  obvious 
  

  

  9 
  5 
  

  

  misprint 
  for 
  and 
  . 
  

  

  Fedorow's 
  remark 
  on 
  Barlow's 
  type 
  9 
  a 
  1 
  (Zeitschr. 
  Kryst. 
  u. 
  

   Min. 
  xxiv. 
  p. 
  244) 
  seems 
  not 
  to 
  be 
  accurate. 
  The 
  position 
  of 
  

   the 
  inversion 
  centre 
  given 
  by 
  Barlow 
  agrees 
  entirely 
  with 
  

   that 
  given 
  by 
  Schoenflies, 
  and 
  involves 
  symmetry 
  planes 
  

   parallel, 
  not 
  to 
  the 
  surface 
  planes, 
  but 
  to 
  the 
  diagonal 
  planes 
  

   of 
  the 
  cube. 
  

  

  XXII. 
  On 
  the 
  Electrical 
  Conductivities 
  produced 
  in 
  Air 
  by 
  

   the 
  Motion, 
  of 
  Negative 
  Ions. 
  By 
  P. 
  J. 
  Kirkby, 
  M.A., 
  

   Fellow 
  of 
  New 
  College, 
  Oxford^. 
  

  

  IN" 
  the 
  February 
  number 
  of 
  the 
  Philosophical 
  Magazine 
  for 
  

   1901 
  Prof. 
  Townsend 
  described 
  in 
  detail 
  a 
  series 
  of 
  expe- 
  

   riments 
  by 
  which 
  he 
  demonstrated 
  the 
  remarkable 
  fact 
  that 
  

   negative 
  ions 
  produced 
  in 
  a 
  gas 
  are 
  capable 
  of 
  disintegrating 
  

   other 
  molecules 
  with 
  which 
  they 
  collide, 
  and 
  thus 
  generate 
  

   other 
  ions 
  by 
  collision. 
  As 
  this 
  adds 
  one 
  more 
  to 
  the 
  few 
  

   known 
  methods 
  by 
  which 
  ions 
  are 
  produced, 
  the 
  discovery 
  

   opens 
  up 
  a 
  new 
  field 
  of 
  research. 
  A 
  series 
  of 
  experiments 
  

   were 
  given 
  (J. 
  S. 
  Townsend 
  and 
  P. 
  J. 
  Kirkby) 
  in 
  the 
  June 
  

   number 
  of 
  the 
  Phil. 
  Mag. 
  1901, 
  which 
  proved 
  that 
  the 
  same 
  

   results 
  which 
  apply 
  to 
  air 
  apply 
  also 
  to 
  hydrogen 
  and 
  carbonic 
  

   acid 
  gas. 
  These 
  researches 
  exhibited 
  the 
  extraordinary 
  differ- 
  

   ence 
  in 
  the 
  behaviour 
  of 
  positive 
  and 
  negative 
  ions. 
  It 
  

   seemed 
  therefore 
  desirable 
  further 
  to 
  emphasize 
  this 
  difference, 
  

  

  * 
  Krystallsysteme 
  und 
  Krystallstructur, 
  p. 
  497. 
  

   t 
  Communicated 
  by 
  Prof. 
  J. 
  S. 
  Townsend. 
  

  

  