﻿Resistance 
  of 
  Metals 
  when 
  placed 
  in 
  a 
  Magnetic 
  Field. 
  651 
  

  

  where 
  

  

  A 
  = 
  BG{a 
  + 
  b 
  + 
  * 
  + 
  /3)+B(b 
  + 
  *)(a 
  + 
  !3) 
  + 
  G{a 
  + 
  b){* 
  + 
  /3) 
  

   + 
  aba, 
  -f 
  ab/3 
  + 
  aafi 
  4- 
  bx(3> 
  

  

  where 
  z 
  is 
  the 
  current 
  through 
  the 
  galvanometer, 
  E 
  the 
  

   E.M.F. 
  of 
  the 
  battery 
  : 
  B 
  the 
  resistance 
  of 
  the 
  battery 
  

   circuit 
  and 
  Gr 
  that 
  of 
  the 
  galvanometer 
  ; 
  a, 
  b, 
  a, 
  j3 
  the 
  

   resistances 
  of 
  the 
  arms 
  of 
  the 
  bridge. 
  The 
  results 
  obtained 
  

   are 
  given 
  in 
  Table 
  IV. 
  

  

  Table 
  IV. 
  — 
  Mercury. 
  

  

  Magnetic 
  

   field. 
  

  

  (? 
  = 
  resistance 
  

   of 
  spiral. 
  

   No 
  field. 
  

  

  Den. 
  of 
  

  

  Galvanometer. 
  

  

  Field 
  on. 
  

  

  ^rr 
  = 
  increase 
  

   of 
  resistance 
  

   due 
  to 
  field. 
  

  

  d* 
  10 
  i 
  

  

  24900 
  

  

  2 
  3990 
  

  

  4-1 
  ram. 
  

  

  •00076 
  

  

  318 
  

  

  22600 
  

  

  2-3990 
  

  

  36 
  „ 
  

  

  •00067 
  

  

  2-80 
  

  

  22300 
  

  

  2-3990 
  

  

  3-3 
  „ 
  

  

  •00070 
  

  

  2 
  92 
  

  

  18100 
  

  

  2-3774 
  

  

  29 
  „ 
  

  

  •00054 
  

  

  2-27 
  

  

  14400 
  

  

  23990 
  

  

  20 
  „ 
  

  

  •00037 
  

  

  1-54 
  

  

  For 
  the 
  remainder 
  of 
  the 
  experiments, 
  the 
  sensitiveness 
  

   of 
  the 
  galvanometer 
  was 
  changed 
  from 
  2*4 
  x 
  10~ 
  8 
  to 
  1*9 
  X 
  10 
  -9 
  

   ampere 
  per 
  scale-division. 
  This 
  made 
  the 
  period 
  of 
  the 
  

   galvanometer 
  much 
  longer, 
  but 
  it 
  allowed 
  the 
  current 
  in 
  the 
  

   bridge 
  to 
  be 
  decreased 
  very 
  much. 
  Usually 
  500 
  ohms 
  were 
  

   inserted 
  in 
  the 
  battery 
  circuit. 
  

  

  Instead 
  of 
  winding 
  the 
  wire 
  to 
  be 
  tested 
  in 
  a 
  spiral, 
  it 
  was 
  

   found 
  much 
  better 
  and 
  more 
  convenient 
  to 
  wind 
  it 
  on 
  strips 
  

   of 
  mica 
  about 
  r 
  ^ 
  mm. 
  thick, 
  13 
  mm. 
  wide, 
  and 
  14 
  mm. 
  long 
  

  

  Fisr. 
  4. 
  

  

  The 
  small 
  fraction 
  of 
  the 
  wire 
  that 
  was 
  parallel 
  to 
  the 
  

   direction 
  of 
  the 
  lines 
  of 
  force 
  would 
  not 
  amount 
  to 
  1 
  per 
  

   cent, 
  of 
  the 
  total, 
  and 
  in 
  these 
  experiments 
  was 
  negligible. 
  

   No 
  water-bath 
  was 
  required 
  with 
  this 
  arrangement. 
  

  

  Experiments 
  were 
  made 
  with 
  gold, 
  platinum, 
  silver, 
  zinc, 
  

   tin, 
  cadmium, 
  and 
  carbon. 
  The 
  gold, 
  platinum, 
  and 
  silver 
  

  

  