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  XXVII. 
  On 
  the 
  Electric 
  Resistance 
  of 
  Cobalt, 
  Iron, 
  and 
  

   Nickel 
  Films 
  in 
  Magnetic 
  Fields 
  of 
  various 
  strengths. 
  

   By 
  J. 
  C. 
  Bbattie, 
  U.Sc, 
  F.R.S.E* 
  

  

  THE 
  fact 
  that 
  the 
  paramagnetic 
  metals 
  iron, 
  cobalt, 
  and 
  

   nickel 
  have 
  a 
  different 
  electric 
  resistance 
  according 
  as 
  

   the 
  specimens 
  examined 
  are 
  magnetized 
  or 
  not 
  was 
  first 
  

   observed 
  by 
  Lord 
  Kelvin. 
  Attempts 
  have 
  be;n 
  made 
  to 
  

   determine 
  how 
  the 
  change 
  in 
  resistance 
  is 
  related 
  to 
  the 
  

   magnetic 
  properties 
  of 
  the 
  specimen. 
  Some 
  have 
  found 
  that 
  

   the 
  variation 
  is 
  proportional 
  to 
  the 
  magnetic 
  moment 
  ; 
  others, 
  

   again, 
  have 
  found 
  other 
  relations. 
  Certain 
  it 
  is 
  that, 
  in 
  these 
  

   three 
  metals, 
  the 
  variation 
  is 
  an 
  increase 
  when 
  the 
  resistance 
  

   is 
  measured 
  parallel 
  to 
  the 
  lines 
  of 
  magnetic 
  force, 
  a 
  decrease 
  

   when 
  perpendicular 
  to 
  them. 
  In 
  the 
  following 
  pages 
  experi- 
  

   ments 
  will 
  be 
  described 
  which 
  had 
  for 
  their 
  object 
  the 
  

   investigation 
  of 
  the 
  relation 
  of 
  the 
  resistance 
  variation 
  to 
  the 
  

   magnetization 
  in 
  hlms 
  of 
  cobalt, 
  nickel, 
  and 
  iron 
  transversely 
  

   magnetized. 
  For 
  such 
  films, 
  Kundt 
  f 
  has 
  shown 
  that 
  the 
  

   Hall 
  effect 
  is 
  proportional 
  to 
  the 
  magnetization. 
  The 
  method 
  

   employed 
  in 
  the 
  experiments 
  to 
  be 
  described 
  in 
  this 
  paper, 
  

   was 
  to 
  measure 
  for 
  any 
  one 
  film 
  the 
  Hall 
  effect 
  and 
  the 
  

   resistance 
  perpendicular 
  to 
  the 
  lines 
  of 
  magnetic 
  force 
  ; 
  then 
  

   to 
  compare 
  these 
  two 
  effects 
  at 
  different 
  field-strengths 
  ; 
  and 
  

   see 
  whether 
  or 
  not 
  any 
  simple 
  relation 
  between 
  the 
  two 
  

   existed. 
  Did 
  such 
  a 
  relation 
  exist, 
  we 
  could 
  then 
  say 
  in 
  

   what 
  manner 
  the 
  variation 
  of 
  resistance 
  depended 
  on 
  the 
  

   magnetization. 
  

  

  The 
  films 
  were 
  deposited 
  on 
  platinized 
  glass 
  by 
  electrolysis. 
  

   Nickel 
  was 
  obtained 
  from 
  a 
  solution 
  of 
  the 
  double 
  sulphate 
  

   of 
  nickel 
  and 
  ammonium 
  ; 
  cobalt 
  from 
  the 
  double 
  sulphate 
  

   of 
  cobalt 
  and 
  ammonium 
  ; 
  and 
  iron 
  from 
  a 
  solution 
  of 
  four 
  

   parts 
  of 
  iron 
  vitriol 
  and 
  three 
  parts 
  sal 
  ammoniac 
  in 
  thirty 
  

   parts 
  water. 
  

  

  The 
  specimens 
  used 
  were 
  cut 
  in 
  the 
  form 
  of 
  a 
  rectangle 
  

   usually 
  9 
  mm. 
  long 
  by 
  7 
  or 
  8 
  mm. 
  broad; 
  the 
  thickness 
  of 
  

   the 
  films 
  varied 
  from 
  ^-^- 
  of 
  a 
  mm. 
  to 
  -r^ 
  of 
  a 
  mm. 
  Care 
  

   was 
  taken 
  to 
  have 
  the 
  thickness 
  of 
  each 
  film 
  as 
  uniform 
  as 
  

   possible. 
  

  

  To 
  measure 
  the 
  Hall 
  effect 
  the 
  film 
  had 
  the 
  usual 
  two 
  

   primary 
  electrodes 
  soldered 
  along 
  the 
  whole 
  extent 
  of 
  the 
  

   ends, 
  wires 
  from 
  a 
  secondary 
  battery 
  of 
  two 
  cells 
  were 
  soldered 
  

  

  * 
  Communicated 
  by 
  the 
  Author, 
  having 
  been 
  read 
  before 
  the 
  Philo- 
  

   sophical 
  Society 
  of 
  South 
  Africa, 
  Nov. 
  24th, 
  1897. 
  

   t 
  Kundt, 
  Wiedemann's 
  Annalen, 
  1893. 
  

  

  