﻿of 
  Films 
  of 
  Cobalt 
  §c. 
  in 
  Magnetic 
  Fields. 
  247 
  

  

  The 
  films 
  XXIII. 
  and 
  XXY1. 
  were 
  deposited 
  from 
  a 
  

   solution 
  of 
  the 
  double 
  salt 
  of 
  cobalt 
  and 
  ammonium; 
  another 
  

   film 
  was 
  then 
  made 
  from 
  a 
  roseo-cobalt 
  chloride 
  solution. 
  

   With 
  it 
  the 
  following 
  results 
  were 
  obtained. 
  

  

  No. 
  XXXI. 
  — 
  Resistance 
  between 
  primary 
  electrodes 
  4 
  12. 
  

   Primary 
  current 
  ^q 
  amp. 
  (Size 
  10 
  x 
  7 
  mm.) 
  

  

  ! 
  

  

  Field. 
  

  

  Hall 
  effect. 
  

  

  Variation 
  of 
  

   resistance. 
  

  

  Hall 
  effect 
  

  

  I 
  

  

  Rj^ 
  — 
  R 
  

   R 
  

  

  

  V 
  variation 
  

  

  2,500 
  

  

  4,370 
  

  

  5,590 
  

  

  8,560 
  

  

  11,360 
  

  

  14,070 
  

  

  16..275 
  

  

  i 
  

  

  300 
  

   535 
  

   69-5 
  

   1050 
  

   129-5 
  

   145-0 
  

   152-0 
  

  

  2625 
  

  

  43-60 
  

  

  950 
  

  

  1370 
  

  

  1550 
  

  

  1710 
  

  

  103 
  

   106 
  

   105 
  

   110 
  

   11-6 
  

   11-6 
  

  

  109 
  

  

  -0-000355 
  

   -00UO592 
  

   -0001287 
  

   -0 
  001856 
  

   -0 
  002100 
  

   -0 
  002317 
  

  

  Other 
  mirrors 
  were 
  used 
  ; 
  some 
  of 
  the 
  results 
  are 
  given 
  in 
  

   the 
  appended 
  graph. 
  The 
  form 
  of 
  the 
  curve 
  is 
  the 
  same 
  in 
  all. 
  

   We 
  have 
  first 
  a 
  parabolic 
  part 
  starting 
  at 
  the 
  origin 
  and 
  con- 
  

   tinuing 
  up 
  to 
  a 
  field-strength 
  of 
  about 
  9000 
  units 
  ; 
  the 
  form 
  

   then 
  undergoes 
  a 
  change, 
  and 
  finally 
  the 
  concave 
  part 
  is 
  

   turned 
  towards 
  the 
  axis. 
  This 
  form 
  and 
  the 
  fact 
  that 
  the 
  Hall 
  

   effect 
  divided 
  by 
  the 
  square 
  root 
  of 
  the 
  change 
  of 
  resistance 
  

   is 
  constant 
  justifies 
  the 
  conclusion 
  that 
  in 
  cobalt 
  the 
  differ- 
  

   ence 
  in 
  the 
  resistance 
  of 
  a 
  thin 
  film 
  of 
  it 
  when 
  transversely 
  

   magnetized 
  from 
  its 
  resistance 
  when 
  unmagnetized 
  is 
  

   proportional 
  to 
  the 
  magnetization 
  squared. 
  

  

  The 
  value 
  of 
  this 
  variation 
  differs 
  verv 
  much 
  in 
  different 
  

   mirrors. 
  This 
  can 
  best 
  be 
  seen 
  from 
  the 
  curves, 
  which 
  are 
  

   drawn 
  to 
  the 
  same 
  scale. 
  No 
  hysteresis 
  effect 
  was 
  observed, 
  

   although 
  in 
  the 
  Hall 
  effect 
  a 
  slight 
  effect 
  was 
  obtained. 
  

  

  