﻿the 
  Thermo 
  electromotive 
  Force 
  of 
  Nickel 
  and 
  Iron. 
  191 
  

  

  Section 
  II. 
  

  

  Resistance 
  Experiments. 
  

  

  A 
  potentiometer 
  method 
  was 
  used 
  and 
  the 
  general 
  arrange- 
  

   ment 
  of 
  the 
  apparatus 
  is 
  shown 
  in 
  fig. 
  7. 
  

  

  The 
  wire 
  the 
  resistance 
  of 
  which 
  was 
  to 
  be 
  measured 
  was 
  

   wound 
  into 
  a 
  spiral, 
  and 
  the 
  main 
  current 
  leads 
  and 
  

   potential 
  leads 
  of 
  No. 
  28 
  b.w.g. 
  copper 
  were 
  silver-soldered 
  to 
  

   the 
  ends 
  of 
  the 
  spiral 
  ; 
  the 
  other 
  extremities 
  of 
  these 
  four 
  

   leads 
  being 
  soldered 
  to 
  four 
  No. 
  18 
  copper 
  leads 
  which 
  

   projected 
  through 
  the 
  cork 
  of 
  the 
  porcelain 
  tube. 
  The 
  thin 
  

   copper 
  was 
  used 
  in 
  order 
  to 
  minimise 
  conduction 
  of 
  heat 
  

   from 
  the 
  spiral. 
  The 
  standard 
  coil 
  for 
  comparison 
  was 
  of 
  

   manganin 
  and, 
  with 
  its 
  potential 
  leads, 
  was 
  immersed 
  in 
  

   paraffin 
  oil. 
  It 
  was 
  not 
  found 
  necessary 
  to 
  apply 
  any 
  

   correction 
  for 
  temperature 
  changes 
  in 
  the 
  standard. 
  

  

  The 
  porcelain 
  tube 
  containing 
  the 
  spiral 
  was 
  placed 
  in 
  the 
  

   heater 
  as 
  before, 
  with 
  a 
  pyrometer. 
  Care 
  was 
  taken 
  that 
  

   the 
  temperature 
  was 
  steady 
  before 
  making 
  an 
  observation 
  

   of 
  resistance, 
  and 
  in 
  every 
  case 
  a 
  reading 
  of 
  the 
  standard 
  

   resistance 
  w 
  T 
  as 
  taken 
  before 
  and 
  after 
  each 
  reading 
  of 
  the 
  

   resistance 
  (Ni 
  or 
  Fe) 
  required. 
  

  

  Discussion 
  of 
  Results. 
  

  

  The 
  resistance 
  of 
  nickel 
  increases 
  with 
  temperature 
  almost 
  

   parabolically 
  up 
  to 
  370°, 
  when 
  a 
  change 
  of 
  slope 
  occurs, 
  and 
  

   the 
  resistance 
  increases 
  much 
  less 
  rapidly 
  and 
  almost 
  as 
  a 
  

   linear 
  function 
  of 
  the 
  temperature 
  up 
  to 
  1050° 
  (fig. 
  8). 
  

  

  A 
  parabola 
  which 
  fitted 
  the 
  resistance 
  observations 
  very 
  

  

  