﻿534 
  On 
  the 
  Electrical 
  Resistance 
  of 
  Iron 
  and 
  Steel, 
  [June 
  17, 
  

  

  When 
  the 
  magnetizing 
  current 
  is 
  considerably 
  increased, 
  this 
  ratio 
  is 
  

   found 
  to 
  diminish, 
  just 
  as 
  in 
  the 
  case 
  of 
  soft 
  iron. 
  

   Different 
  kinds 
  of 
  hard 
  steel 
  were 
  tried. 
  

  

  (1) 
  An 
  ordinary 
  knitting-needle, 
  of 
  which 
  the 
  resistance 
  was 
  66*5 
  

   units. 
  

  

  On 
  magnetizing 
  with 
  currents 
  of 
  different 
  strengths, 
  there 
  was 
  found 
  

   to 
  be 
  a 
  diminution 
  in 
  the 
  resistance; 
  and 
  it 
  was 
  also 
  found 
  that 
  the 
  diminu- 
  

   tion 
  of 
  resistance 
  increased 
  when 
  the 
  strength 
  of 
  the 
  current 
  was 
  increased. 
  

   "With 
  currents 
  varying 
  from 
  tan 
  15° 
  to 
  tan 
  54° 
  30' 
  the 
  diminution 
  

   amounted 
  to 
  4-33, 
  i. 
  e. 
  about 
  6-5 
  per 
  cent, 
  of 
  the 
  whole 
  resistance. 
  The 
  

   temperature 
  increased 
  about 
  2° 
  C. 
  during 
  the 
  experiment. 
  

  

  Dividing 
  the 
  loss 
  of 
  resistance 
  by 
  the 
  square 
  of 
  the 
  magnetizing 
  

   current, 
  the 
  results 
  of 
  four 
  sets 
  of 
  experiments 
  gave 
  the 
  following 
  

   values 
  : 
  — 
  

  

  •165 
  

  

  (tan 
  15°) 
  2 
  

   •7525 
  

  

  (tan 
  30°)* 
  

  

  = 
  2-29, 
  

   =2-26, 
  

  

  2-3225 
  ;2 
  . 
  2 
  . 
  

  

  (tan 
  45° 
  30') 
  2 
  

  

  4-330 
  

   (tan 
  54° 
  30')' 
  

  

  = 
  2-21. 
  

  

  Tour 
  Grove's 
  cells 
  were 
  employed 
  for 
  the 
  strongest 
  current. 
  

  

  Two 
  other 
  experiments 
  which 
  had 
  been 
  -tried 
  previously 
  gave 
  results 
  

   2-30 
  and 
  2-26 
  for 
  the 
  ratio 
  of 
  the 
  diminution 
  of 
  resistance 
  to 
  the 
  square 
  

   of 
  the 
  magnetizing 
  current, 
  thus 
  showing 
  that 
  the 
  diminution 
  in 
  the 
  

   resistance 
  is 
  almost 
  exactly 
  proportional 
  to 
  the 
  square 
  of 
  the 
  current. 
  

  

  The 
  diminution 
  in 
  resistance 
  does 
  not 
  take 
  place 
  all 
  at 
  once, 
  but 
  gra- 
  

   dually, 
  and 
  also 
  ceases 
  gradually 
  when 
  the 
  current 
  is 
  stopped. 
  

  

  (2) 
  A 
  steel 
  needle 
  was 
  also 
  magnetized 
  longitudinally 
  by 
  placing 
  it 
  on 
  

   a 
  copper 
  strip 
  at 
  right 
  angles 
  to 
  the 
  lines 
  of 
  force 
  of 
  a 
  current 
  across 
  the 
  

   strip. 
  

  

  There 
  was 
  found 
  to 
  be 
  diminution 
  of 
  resistance 
  on 
  increasing 
  the 
  cur- 
  

   rent. 
  The 
  values 
  obtained 
  from 
  two 
  series 
  of 
  experiments 
  were 
  : 
  — 
  

  

  •064 
  = 
  2-^8 
  

   (tan8°30') 
  2 
  ' 
  ' 
  

  

  ' 
  192 
  =2-63. 
  

  

  (tan 
  15°) 
  2 
  

  

  With 
  stronger 
  currents 
  this 
  ratio 
  was 
  found 
  to 
  diminish. 
  

  

  On 
  magnetizing 
  the 
  wires 
  transversely 
  by 
  sending 
  a 
  current 
  in 
  the 
  di- 
  

   rection 
  of 
  their 
  length, 
  a 
  diminution 
  of 
  resistance 
  was 
  also 
  observed, 
  which 
  

   diminution 
  also 
  increased 
  when 
  the 
  strength 
  of 
  the 
  current 
  was 
  increased. 
  

  

  When 
  a 
  current 
  was 
  sent 
  along 
  the 
  wire 
  itself, 
  on 
  increasing 
  the 
  

  

  