﻿of 
  Films 
  of 
  Cobalt 
  §c. 
  in 
  Magnetic 
  Fields. 
  

   JSickel 
  Films. 
  

  

  249 
  

  

  The 
  results 
  obtained 
  with 
  nickel 
  differed 
  very 
  much 
  for 
  

   different 
  plates 
  both 
  qualitatively 
  and 
  quantitatively. 
  The 
  

   results 
  were 
  also 
  much 
  complicated 
  by 
  a 
  very 
  great 
  hysteresis 
  

   effect 
  in 
  the 
  variation 
  of 
  resistance 
  ; 
  this 
  caused 
  a 
  greater 
  

   variation 
  in 
  the 
  film's 
  resistance 
  after 
  it 
  had 
  been 
  magnetized 
  

   and 
  demagnetized 
  several 
  times. 
  

  

  For 
  example, 
  with 
  film 
  XXVII. 
  the 
  following 
  results 
  were 
  

   obtained. 
  

  

  No. 
  XXVII. 
  First 
  time 
  used. 
  (13| 
  x 
  8f 
  mm.) 
  

  

  Field. 
  

  

  Hall 
  effect 
  

   in 
  mill 
  i 
  in. 
  

  

  Variation 
  of 
  

   resistance 
  in 
  

   ruillim. 
  

  

  Hall 
  effect 
  

  

  V 
  variation 
  

  

  2,620 
  

  

  4,370 
  

  

  5,590 
  

  

  8,560 
  

  

  11,360 
  

  

  14,070 
  

  

  16,000 
  

  

  152-25 
  

  

  2160 
  

  

  228-1 
  

  

  234-5 
  

  

  24125 
  

  

  242-75 
  

  

  2455 
  

  

  - 
  50-0 
  

  

  - 
  90-0 
  

   -1045 
  

   -116-7 
  

   - 
  1230 
  

   -125 
  

   -1340 
  

  

  21-4 
  

   227 
  

   223 
  

  

  21-7 
  

   21-7 
  

   21-6 
  

   21-2 
  

  

  21-8 
  

  

  Second 
  time 
  used. 
  

  

  2,000 
  

  

  2,620 
  

  

  4,370 
  

  

  5,590 
  

  

  8,560 
  

  

  11,360 
  

  

  14,070 
  

  

  16,000 
  

  

  111-0 
  

  

  152-25 
  

  

  216-0 
  

  

  228-4 
  

  

  234-5 
  

  

  241-25 
  

  

  242-75 
  

  

  2455 
  

  

  — 
  455 
  

  

  - 
  86-0 
  

   -192-2 
  

   -2530 
  

   -316-0 
  

   -347-0 
  

   -3700 
  

   -388-5 
  

  

  16-4 
  

   16-4 
  

   15-5 
  

   14-4 
  

   131 
  

   129 
  

   126 
  

   12-4 
  

  

  A 
  great 
  number 
  of 
  other 
  films 
  behaved 
  in 
  the 
  same 
  manner 
  

   as 
  XXVII. 
  The 
  results 
  for 
  some 
  of 
  them 
  are 
  given 
  in 
  the 
  

   curves 
  on 
  page 
  250. 
  

  

  It 
  will 
  be 
  noticed 
  that 
  the 
  form 
  of 
  the 
  curve 
  is 
  first 
  para- 
  

   bolic, 
  with 
  the 
  convex 
  side 
  towards 
  the 
  horizontal 
  axis 
  ; 
  that 
  

   there 
  is 
  a 
  point 
  of 
  inflexion 
  usually 
  between 
  a 
  field-strength 
  

   of 
  5000 
  and 
  6000 
  C.G.S. 
  units 
  ; 
  and 
  that 
  after 
  that 
  strength 
  

   the 
  concave 
  part 
  of 
  the 
  curve 
  is 
  turned 
  towards 
  the 
  horizontal 
  

   axis. 
  Roughly 
  this 
  is 
  the 
  same 
  thing 
  that 
  we 
  had 
  with 
  

   cobalt 
  ; 
  but 
  here 
  we 
  have 
  not 
  usually 
  a 
  constant 
  quantity 
  

   when 
  the 
  Hall 
  effect 
  is 
  divided 
  by 
  the 
  square 
  root 
  of 
  the 
  

   resistance 
  variation. 
  The 
  difference 
  between 
  the 
  resistance 
  

   variation 
  and 
  the 
  Hall 
  effect 
  squared 
  is 
  shown 
  for 
  film 
  XIV. 
  

   in 
  the 
  graph 
  on 
  page 
  251. 
  

  

  