﻿Resistance 
  of 
  Metals 
  when 
  placed 
  in 
  a 
  Magnetic 
  Field. 
  649 
  

  

  effect 
  on 
  the 
  result. 
  Moreover, 
  had 
  it 
  been 
  due 
  to 
  the 
  above 
  

   cause, 
  the 
  resistance 
  should 
  have 
  been 
  greater 
  after 
  the 
  field 
  

   was 
  put 
  off, 
  owing 
  to 
  the 
  induced 
  current 
  at 
  break. 
  

  

  As 
  a 
  final 
  test 
  a 
  series 
  of 
  observations 
  were 
  made 
  with 
  the 
  

   poles 
  of 
  the 
  magnet 
  at 
  different 
  distances 
  apart, 
  so 
  that 
  

   different 
  fields 
  were 
  obtained 
  with 
  the 
  same 
  current 
  in 
  the 
  

   magnetizing 
  circuit. 
  The 
  values 
  obtained 
  are 
  given 
  in 
  Table 
  II. 
  

  

  These 
  results 
  show 
  that 
  when 
  the 
  field 
  is 
  constant 
  the 
  

   change 
  of 
  resistance 
  for 
  this 
  field 
  is 
  independent 
  of 
  the 
  

   current 
  in 
  the 
  magnetizing 
  circuit. 
  There 
  are 
  considerable 
  

   differences, 
  it 
  is 
  true, 
  in 
  the 
  magnitude 
  of 
  the 
  change 
  of 
  

   resistance 
  for 
  the 
  same 
  field. 
  It 
  will 
  be 
  seen, 
  however, 
  in 
  

   the 
  column 
  giving 
  the 
  increase 
  of 
  resistance 
  due 
  to 
  the 
  field, 
  

   that 
  these 
  differences 
  occur 
  in 
  the 
  fourth 
  place 
  of 
  decimals 
  

   and 
  this 
  figure 
  is 
  only 
  approximate. 
  

  

  These 
  results 
  confirm 
  those 
  obtained 
  by 
  Lenard 
  * 
  for 
  

   copper. 
  He, 
  however, 
  does 
  not 
  give 
  the 
  magnitude 
  of 
  the 
  

   change 
  which 
  he 
  obtained, 
  except 
  stating 
  that 
  it 
  was 
  very 
  small. 
  

  

  It 
  was 
  hoped 
  that 
  by 
  surrounding 
  the 
  poles 
  of 
  the 
  magnet 
  

   with 
  a 
  water-jacket 
  through 
  which 
  the 
  water 
  could 
  be 
  kept 
  

   flowing, 
  the 
  resistance 
  would 
  be 
  more 
  constant. 
  It 
  was 
  found, 
  

   however, 
  that 
  much 
  more 
  satisfactory 
  results 
  were 
  obtained 
  

   when 
  the 
  water, 
  instead 
  of 
  circulating, 
  was 
  allowed 
  to 
  stand 
  in 
  

   the 
  jacket. 
  

  

  Another 
  spiral 
  of 
  the 
  same 
  copper 
  wire 
  was 
  made 
  with 
  a 
  

   resistance 
  of 
  58' 
  68 
  ohms. 
  The 
  other 
  three 
  resistances 
  were 
  

   made 
  of 
  " 
  Eureka 
  " 
  wire, 
  and 
  had 
  59*6, 
  58*2, 
  58'18 
  ohms 
  

   respectively. 
  With 
  this 
  spiral 
  another 
  series 
  of 
  observations 
  

   were 
  made, 
  the 
  results 
  of 
  which 
  are 
  given 
  in 
  Table 
  III. 
  

  

  Table 
  III. 
  — 
  Copper 
  Wire. 
  

  

  H 
  = 
  

  

  Magnetic 
  

   field. 
  

  

  R 
  = 
  Resistance 
  in 
  

   multiple 
  arc 
  to 
  

   balance 
  bridge. 
  

  

  59.6xR 
  

   59.6+R 
  

  

  increase 
  of 
  

  

  resist, 
  due 
  

  

  to 
  field. 
  

  

  ^10* 
  

  

  Mean 
  

   value 
  of 
  

  

  ^10 
  4 
  . 
  

  

  d"H) 
  13 
  . 
  

   a 
  H 
  a 
  

  

  Field 
  off. 
  

  

  Field 
  on. 
  

  

  Field 
  off. 
  

  

  Field 
  on. 
  

  

  27650 
  

  

  2090 
  

  

  2076 
  

  

  57-9475 
  

  

  579367 
  

  

  •0108 
  

  

  1-86 
  

  

  

  

  27650 
  

  

  2080 
  

  

  2065 
  

  

  579398 
  

  

  57-9281 
  

  

  •0117 
  

  

  202 
  

  

  196 
  

  

  26 
  

  

  27650 
  

  

  2090 
  

  

  2075 
  

  

  57*9475 
  

  

  57 
  9339 
  

  

  •0116 
  

  

  200 
  

  

  

  

  25850 
  

   25850 
  

  

  2072-5 
  

   2062 
  

  

  2060 
  

   2050 
  

  

  57-9340 
  

   57-9257 
  

  

  57-9241 
  

   579162 
  

  

  •0099 
  

   •0095 
  

  

  170 
  

   1-64 
  

  

  167 
  

  

  25 
  

  

  * 
  Wied.-^Lww. 
  vol. 
  xxxix. 
  p. 
  619 
  (1890). 
  

  

  