﻿Magnetization 
  on 
  the 
  Resistance 
  of 
  Graphite. 
  171 
  

  

  a 
  further 
  rotation 
  gives 
  again 
  equal 
  corresponding 
  values 
  : 
  

   (R' 
  — 
  R)/R 
  is 
  plotted 
  radially, 
  the 
  angles 
  <f> 
  shown 
  being 
  

   those 
  between 
  the 
  field 
  and 
  the 
  crystalline 
  axis, 
  

  

  I. 
  e. 
  (R' 
  — 
  R)/R 
  = 
  the 
  radius 
  vector 
  p 
  = 
  function 
  (</>). 
  

  

  The 
  radius 
  vectors 
  of 
  the 
  curves 
  I. 
  and 
  III. 
  represent 
  the 
  

   effect 
  for 
  the 
  fields 
  21*8 
  and 
  35*2 
  kgss. 
  respectively. 
  

  

  Determinations 
  of 
  the 
  change 
  of 
  resistance 
  with 
  magnetic 
  

   field 
  were 
  also 
  made 
  for 
  the 
  maximum 
  and 
  minimum 
  posi- 
  

   tions, 
  and 
  are 
  given 
  in 
  Table 
  II. 
  in 
  the 
  second 
  and 
  third 
  

   columns. 
  The 
  numbers 
  in 
  the 
  second 
  column 
  correspond, 
  

   mutatis 
  mutandis 
  *, 
  to 
  the 
  curves 
  in 
  fig. 
  1. 
  

  

  In 
  case 
  (b) 
  no 
  end-pieces 
  were 
  used 
  but 
  only 
  pole-shoes 
  

   (VII.) 
  of 
  end 
  diameter 
  43 
  mm., 
  and 
  at 
  a 
  distance 
  apart 
  of 
  

   8 
  5 
  mm. 
  The 
  field 
  was 
  practically 
  uniform 
  at 
  this 
  distance. 
  

   After 
  the 
  graphite 
  had 
  been 
  necessarily 
  differently 
  mounted, 
  

   the 
  (b) 
  position, 
  the 
  variation 
  of 
  the 
  resistance 
  was 
  deter- 
  

   mined 
  for 
  .0 
  = 
  21*9 
  kgss. 
  as 
  the 
  graphite 
  was 
  rotated 
  from 
  

   the 
  longitudinal 
  to 
  the 
  transverse 
  position. 
  As 
  the 
  rotation 
  

   was 
  carried 
  through 
  360° 
  practically 
  equal 
  corresponding- 
  

   values 
  were 
  obtained 
  in 
  each 
  quadrant, 
  showing 
  that 
  the 
  

   increase 
  of 
  resistance 
  is 
  perfectly 
  independent 
  of 
  the 
  direction 
  

   of 
  the 
  current 
  relative 
  to 
  the 
  field 
  and 
  dependent 
  only 
  on 
  the 
  

   acute 
  angle 
  between 
  the 
  crystalline 
  and 
  field 
  axes. 
  The 
  

   results 
  for 
  a 
  rotation 
  of 
  180° 
  are 
  shown 
  in 
  fig. 
  2, 
  curve 
  II. 
  

   It 
  will 
  be 
  noticed 
  that 
  this 
  curve 
  nearly 
  coincides 
  with 
  curve 
  

   No. 
  I. 
  ; 
  and 
  remembering 
  the 
  difference 
  in 
  the 
  field 
  (21*9 
  

   and 
  21*8 
  kilogauss) 
  we 
  may 
  conclude 
  that, 
  within 
  experi- 
  

   mental 
  errors, 
  the 
  value 
  of 
  (R' 
  — 
  R)/R 
  depends 
  only 
  on 
  the 
  

   orientation 
  of 
  the 
  crystalline 
  axis 
  in 
  the 
  field. 
  The 
  variation 
  

   of 
  (R' 
  — 
  R)/R 
  with 
  longitudinal 
  field 
  is 
  given 
  in 
  Table 
  II., 
  

   column 
  four. 
  

  

  The 
  results 
  obtained 
  for 
  G 
  I. 
  12 
  a 
  when 
  transversely 
  mag- 
  

   netized, 
  with 
  the 
  crystalline 
  axis 
  parallel 
  to 
  the 
  field, 
  follow 
  

   the 
  empirical 
  formula 
  (1) 
  well 
  within 
  experimental 
  errors. 
  

   (m=l-74l 
  A 
  = 
  0'0198.) 
  

  

  For 
  the 
  cases 
  when 
  the 
  graphite 
  has 
  its 
  axis 
  normal 
  to 
  the 
  

   field 
  and 
  is 
  transversely 
  or 
  longitudinally 
  magnetized 
  the 
  

   agreement 
  is 
  not 
  so 
  good. 
  The 
  resistances 
  measured 
  and 
  

   the 
  changes 
  involved 
  are, 
  however, 
  always 
  small, 
  and 
  the 
  

   experimental 
  errors 
  of 
  greater 
  influence. 
  At 
  the 
  higher 
  

  

  * 
  As 
  the 
  experiments 
  described 
  in 
  this 
  section 
  were 
  carried 
  out 
  at 
  

   temperatures 
  (19°-22°C), 
  (R'-R)/R 
  has 
  been 
  considered 
  instead 
  of 
  

  

  (R'— 
  R)/R 
  ; 
  the 
  expressions 
  differ 
  only 
  by 
  the 
  constant 
  1 
  — 
  *p 
  which 
  

   differs 
  very 
  little 
  from 
  zero. 
  

  

  