﻿Magnetization 
  on 
  the 
  Resistance 
  of 
  Graphite. 
  173 
  

  

  of 
  <f> 
  were 
  obtained. 
  Now 
  the 
  second 
  term 
  in 
  equation 
  (2) 
  

   is, 
  except 
  when 
  (/> 
  is 
  nearly 
  90°, 
  very 
  small 
  compared 
  with 
  the 
  

   first 
  term. 
  One 
  is 
  therefore 
  led 
  to 
  think 
  that 
  possibly 
  it 
  

   may 
  represent 
  nothing 
  more 
  than 
  a 
  spurious 
  effect 
  due 
  to 
  

   the 
  crystalline 
  non-uniformity 
  of 
  the 
  samples 
  ; 
  in 
  fact, 
  devia- 
  

   tions 
  of 
  the 
  axes 
  at 
  different 
  points 
  of 
  the 
  graphite 
  strip 
  of 
  

   the 
  order 
  of 
  1° 
  would 
  suffice 
  to 
  explain 
  such 
  an 
  apparent 
  

   effect 
  ; 
  the 
  distribution 
  of 
  the 
  current 
  may 
  also 
  be 
  non- 
  

   unidirectional. 
  It 
  is 
  hardly 
  possible 
  with 
  the 
  graphite 
  

   specimens 
  yet 
  available 
  to 
  settle 
  this 
  point. 
  If 
  we 
  may 
  

   neglect 
  the 
  second 
  term, 
  we 
  obtain 
  the 
  equation 
  in 
  polar 
  

   coordinates 
  

  

  ?^^ 
  = 
  p 
  = 
  2acos 
  m 
  (l> 
  (3) 
  

  

  The 
  curves 
  in 
  fig. 
  2 
  are 
  drawn 
  according 
  to 
  this 
  equation, 
  

   a 
  being 
  of 
  course 
  determined 
  by 
  experiment. 
  The 
  points 
  

   indicated 
  were 
  experimentally 
  determined. 
  Curve 
  IV. 
  is 
  

   the 
  circle 
  

  

  p 
  = 
  2a 
  cos 
  cp. 
  

  

  IV. 
  Experiments 
  at 
  Low 
  and 
  High 
  Temperatures. 
  

  

  In 
  these 
  experiments 
  the 
  cleavage 
  plane 
  of 
  the 
  specimen 
  

   investigated 
  was 
  kept 
  normal 
  to 
  the 
  field. 
  Observations 
  were 
  

   taken 
  at 
  temperatures 
  of 
  -179°,0°, 
  +11°, 
  +95°, 
  +179°C, 
  

   the 
  field 
  being 
  varied 
  from 
  to 
  40 
  kgss. 
  The 
  methods 
  of 
  

   measurement 
  were 
  the 
  same 
  as 
  those 
  adopted 
  for 
  the 
  measure- 
  

   ments 
  at 
  ordinary 
  temperatures 
  ; 
  the 
  determinations 
  offered 
  

   no 
  difficulties, 
  the 
  resistances 
  being 
  quite 
  steady. 
  At 
  the 
  

   lower 
  and 
  higher 
  temperatures 
  thermo-electric 
  effects 
  were 
  

   sometimes 
  evident, 
  but 
  by 
  successive 
  reversals 
  these 
  were 
  

   eliminated*. 
  For 
  the 
  specimens 
  Gr 
  I. 
  and 
  IV. 
  investigated 
  

   an 
  increase 
  of 
  resistance 
  with 
  temperature 
  was 
  found, 
  the 
  

   coefficient 
  being 
  of 
  the 
  high 
  order 
  of 
  +O001 
  per 
  degree. 
  

   The 
  temperature 
  curve 
  (.0 
  = 
  0) 
  R/R 
  = 
  Funct 
  (0) 
  is 
  given 
  

   in 
  fig. 
  3 
  for 
  specimen 
  Gr 
  I. 
  15 
  ; 
  a 
  similar 
  curve 
  (also 
  shown) 
  

   was 
  obtained 
  for 
  GI. 
  11. 
  Both 
  show 
  a 
  strongly 
  marked 
  

   inflexion 
  in 
  the 
  region 
  of 
  ordinary 
  temperatures. 
  It 
  is 
  

   interesting 
  to 
  compare 
  these 
  with 
  one 
  obtained 
  by 
  Kamer- 
  

   lingh 
  Onnes 
  and 
  Clay 
  f, 
  which 
  is 
  for 
  a 
  bismuth 
  spiral, 
  

  

  * 
  It 
  was 
  incidentally 
  observed 
  that 
  these 
  thermo-electric 
  effects 
  — 
  

   when 
  occurring 
  at 
  the 
  connexions 
  of 
  the 
  graphite 
  and 
  therefore 
  within 
  

   the 
  magnetic 
  field 
  — 
  were 
  influenced 
  by 
  the 
  field. 
  Thus 
  in 
  one 
  case 
  the 
  

   thermo-electric 
  effect 
  was 
  increased 
  fourfold 
  by 
  a 
  field 
  of 
  26 
  kgss. 
  

  

  t 
  H. 
  Kamerlingh 
  Onnes 
  and 
  J. 
  Clay, 
  Versl. 
  Kon. 
  Akad. 
  Wet. 
  Amst. 
  

   xvi. 
  p. 
  176 
  (1907). 
  Cf. 
  also 
  W. 
  Nernst 
  and 
  F. 
  A. 
  Lindemann, 
  Berl. 
  Ber. 
  

   p. 
  306 
  (1911). 
  

  

  