﻿1875.] 
  On 
  the 
  Electrical 
  Resistance 
  of 
  Iron 
  and 
  Steel. 
  533 
  

  

  XI. 
  " 
  On 
  the 
  Change 
  produced 
  by 
  Magnetization 
  in 
  the 
  Electrical 
  

   Resistance 
  of 
  Iron 
  and 
  Steel. 
  — 
  -Preliminary 
  Notice." 
  By 
  

   Professor 
  W. 
  G-. 
  Adams, 
  E.R.S. 
  Received 
  June 
  1, 
  1875. 
  

  

  Por 
  some 
  time 
  past 
  Mr. 
  Herbert 
  TomUnson, 
  Demonstrator 
  in 
  the 
  Phy- 
  

   sical 
  Laboratory 
  of 
  King's 
  College, 
  has 
  been 
  engaged 
  in 
  carrying 
  out 
  a 
  

   series 
  of 
  experiments 
  on 
  this 
  subject, 
  and 
  also 
  on 
  the 
  effect 
  of 
  change 
  of 
  

   tension 
  on 
  the 
  electrical 
  resistance 
  of 
  steel 
  and 
  iron 
  wires. 
  

  

  In 
  measuring 
  the 
  resistances 
  of 
  the 
  short 
  lengths 
  of 
  the 
  wires 
  or 
  rods 
  

   which 
  were 
  employed, 
  a 
  unit 
  was 
  chosen 
  which 
  was 
  a 
  small 
  fraction 
  of 
  

   the 
  British-Association 
  unit. 
  

  

  Experiments 
  were 
  made 
  with 
  rods 
  of 
  soft 
  iron 
  about 
  one 
  eighth 
  of 
  an 
  

   inch 
  thick, 
  with 
  soft 
  steel, 
  and 
  also 
  with 
  steel 
  of 
  different 
  degrees 
  of 
  

   hardness. 
  

  

  "With 
  a 
  rod 
  of 
  soft 
  iron 
  about 
  3 
  feet 
  long 
  there 
  was 
  an 
  increase 
  of 
  re- 
  

   sistance 
  of 
  about 
  1 
  per 
  cent, 
  on 
  magnetizing 
  with 
  two 
  Grove's 
  cells. 
  The 
  

   whole 
  resistance 
  of 
  this 
  rod 
  was 
  32 
  units. 
  

  

  The 
  experiments 
  were 
  repeated 
  with 
  the 
  rod 
  placed 
  in 
  ice 
  and 
  also 
  in 
  

   water 
  at 
  the 
  ordinary 
  temperature 
  (about 
  15° 
  C), 
  and 
  with 
  nearly 
  the 
  

   same 
  change 
  in 
  the 
  resistance 
  of 
  the 
  rod. 
  The 
  change 
  in 
  the 
  tempera- 
  

   ture 
  of 
  the 
  water 
  was 
  found 
  to 
  be 
  about 
  1° 
  C. 
  during 
  the 
  experiment. 
  

  

  Another 
  rod 
  of 
  soft 
  iron 
  was 
  employed 
  whose 
  resistance 
  was 
  50 
  units. 
  

   The 
  magnetizing 
  current 
  was 
  measured 
  by 
  means 
  of 
  a 
  tangent-galvano- 
  

   meter, 
  and 
  the 
  resistance 
  was 
  measured 
  by 
  means 
  of 
  Wheatstone's 
  bridge. 
  

   There 
  was 
  found 
  to 
  be 
  an 
  increase 
  in 
  the 
  resistance 
  of 
  the 
  rod 
  when 
  it 
  

   was 
  converted 
  into 
  a 
  magnet 
  by 
  sending 
  the 
  magnetizing 
  current 
  through 
  

   a 
  wire 
  which 
  was 
  coiled 
  round 
  it 
  in 
  the 
  form 
  of 
  a 
  spiral. 
  

  

  It 
  was 
  found 
  that 
  the 
  electrical 
  resistance 
  was 
  increased 
  when 
  any 
  ad- 
  

   dition 
  was 
  made 
  to 
  the 
  strength 
  of 
  the 
  magnetizing 
  current. 
  When 
  the 
  

   increase 
  in 
  the 
  electrical 
  resistance 
  was 
  divided 
  by 
  the 
  square 
  of 
  the 
  

   strength 
  of 
  the 
  magnetizing 
  current, 
  a 
  series 
  of 
  numbers 
  was 
  obtained 
  

   which 
  did 
  not 
  differ 
  much 
  from 
  one 
  another 
  ; 
  the 
  values 
  of 
  these 
  num- 
  

   bers 
  -mostly 
  lie 
  between 
  3 
  and 
  4. 
  

  

  When 
  the 
  magnetizing 
  current 
  is 
  considerably 
  increased, 
  the 
  ratio 
  of 
  

   the 
  increase 
  in 
  the 
  resistance 
  to 
  the 
  square 
  of 
  the 
  magnetizing 
  current 
  

   diminishes 
  rather 
  rapidly. 
  

  

  A 
  similar 
  series 
  of 
  experiments 
  was 
  made 
  with 
  a 
  thick 
  knitting-needle 
  

   made 
  of 
  soft 
  steel. 
  The 
  resistance 
  of 
  the 
  needle 
  was 
  29 
  units. 
  In 
  this 
  

   case 
  also 
  the 
  resistance 
  was 
  found 
  to 
  increase 
  when 
  the 
  strength 
  of 
  the 
  

   magnetizing 
  current 
  was 
  increased. 
  On 
  dividing 
  the 
  increase 
  of 
  resist- 
  

   ance 
  by 
  the 
  square 
  of 
  the 
  magnetizing 
  current, 
  the 
  numbers 
  obtained 
  

   from 
  a 
  considerable 
  number 
  of 
  experiments 
  lie 
  between 
  4-7 
  and 
  5*6, 
  

   showing 
  that 
  the 
  ratio 
  of 
  the 
  increase 
  of 
  resistance 
  to 
  the 
  square 
  of 
  

   the 
  magnetizing 
  current 
  is 
  very 
  nearly 
  constant. 
  

  

  