﻿Resistance 
  of 
  Metals 
  when 
  placed 
  in 
  a 
  Magnetic 
  Field. 
  6 
  17 
  

  

  here 
  

  

  a 
  = 
  

  

  CR 
  

  

  U-r-K' 
  

  

  If, 
  now, 
  when 
  the 
  magnetic 
  field 
  is 
  put 
  on, 
  A 
  is 
  increased 
  by 
  

   dA, 
  and 
  consequently 
  a 
  by 
  ~d<r 
  in 
  order 
  that 
  equilibrium 
  may 
  

   be 
  preserved, 
  then 
  

  

  A 
  + 
  dA 
  D 
  A 
  

  

  o- 
  + 
  do- 
  B 
  

  

  or 
  

  

  A 
  a' 
  

  

  Hence 
  the 
  value 
  of 
  the 
  change 
  of 
  resistance 
  due 
  to 
  the 
  

   magnetic 
  field 
  is 
  given 
  by 
  — 
  . 
  

  

  Table 
  I. 
  gives 
  the 
  results 
  obtained 
  for 
  the 
  first 
  set 
  of 
  

   observations. 
  

  

  

  

  Table 
  I. 
  

  

  — 
  Copper 
  Wire. 
  

  

  

  

  

  Magnetic 
  

   field. 
  

  

  R 
  = 
  Resistance 
  in 
  

   multiple 
  arc 
  to 
  

   balance 
  bridge. 
  

  

  ff 
  _24.12xK 
  

   24 
  . 
  12+R" 
  

  

  increase 
  of 
  

  

  resist, 
  due 
  

  

  to 
  field. 
  

  

  ^104 
  

  

  Mean 
  

   value 
  of 
  

  

  ^10*. 
  

   a 
  

  

  d<r 
  10 
  13 
  . 
  

   a 
  IP 
  

  

  Field 
  off. 
  

  

  Field 
  on. 
  

  

  Field 
  off. 
  

  

  Field 
  on. 
  

  

  26500 
  

  

  2175 
  

  

  2215 
  

  

  23-8555 
  

  

  238602 
  

  

  •0047 
  

  

  1-97 
  

  

  

  

  26500 
  

  

  2240 
  

  

  2285 
  

  

  23 
  8631 
  

  

  23-8681 
  

  

  •0050 
  

  

  209 
  

  

  201 
  

  

  29 
  

  

  26500 
  

  

  2300 
  

  

  2345 
  

  

  238697 
  

  

  23-8744 
  

  

  •0047 
  

  

  1-97 
  

  

  

  

  21300 
  

  

  2210 
  

  

  2240 
  

  

  23-8596 
  

  

  238631 
  

  

  •0035 
  

  

  1-46 
  

  

  

  

  21300 
  

  

  2370 
  

  

  2405 
  

  

  23-8770 
  

  

  23-8806 
  

  

  •0036 
  

  

  1-50 
  

  

  150 
  

  

  33 
  

  

  21300 
  

  

  2300 
  

  

  2335 
  

  

  23-8697 
  

  

  23-8734 
  

  

  •0037 
  

  

  1-55 
  

  

  

  

  To 
  test 
  whether 
  the 
  apparent 
  change 
  in 
  the 
  resistance 
  was 
  

   real 
  or 
  due 
  to 
  induction 
  effects 
  or 
  the 
  magnetizing 
  current, 
  the 
  

   galvanometer- 
  circuit 
  was 
  closed, 
  while 
  the 
  battery-circuit 
  

   remained 
  open, 
  but 
  in 
  this 
  case 
  the 
  deflexion 
  of 
  the 
  galva- 
  

   nometer, 
  if 
  any, 
  was 
  the 
  same 
  whether 
  the 
  field 
  was 
  on 
  or 
  

   oft". 
  Reversing 
  the 
  current 
  in 
  the 
  magnet 
  did 
  not 
  affect 
  the 
  

   result. 
  As 
  the 
  four 
  resistances 
  of 
  the 
  Wheatstone 
  bridge 
  

   formed 
  a 
  closed 
  "circuit, 
  the 
  change 
  might 
  be 
  due 
  to 
  a 
  sudden 
  

   heating 
  of 
  the 
  resistances 
  by 
  any 
  induced 
  currents 
  at 
  the 
  

   make 
  or 
  break 
  of 
  the 
  magnetizing 
  circuit. 
  To 
  prevent 
  this, 
  

   the 
  bridge 
  was 
  arranged 
  so 
  that 
  the 
  circuit 
  could 
  be 
  left 
  

   open 
  when 
  the 
  field 
  was 
  put 
  on 
  or 
  off. 
  This 
  also 
  had 
  no 
  

  

  