﻿Magnetization 
  on 
  the 
  Resistance 
  of 
  Graphite. 
  169 
  

  

  G 
  V. 
  The 
  best 
  piece 
  of 
  this 
  kind 
  which 
  I 
  could 
  prepare 
  

   gave 
  a 
  specific 
  resistance 
  of 
  about 
  15*6 
  . 
  10 
  ~ 
  4 
  ohm 
  per 
  cm. 
  3 
  , 
  

   and 
  in 
  a 
  transverse 
  field 
  of 
  26 
  kilogauss 
  it 
  showed 
  an 
  

   increase 
  of 
  resistance 
  o£ 
  163 
  per 
  cent. 
  It 
  appeared 
  to 
  be 
  

   diamagnetic. 
  

  

  GVI. 
  Three 
  pieces 
  of 
  this 
  kind 
  were 
  tested, 
  and 
  these 
  

   behaved 
  similarly 
  to 
  graphite 
  III. 
  They 
  possessed 
  a 
  very 
  

   high 
  specific 
  resistance 
  (2*14 
  ohm 
  per 
  cm. 
  3 
  ), 
  and 
  showed 
  

   very 
  marked 
  decrease 
  of 
  resistance 
  with 
  increase 
  of 
  tempe- 
  

   rature 
  (about 
  6 
  per 
  cent, 
  per 
  degree). 
  In 
  a 
  magnetic 
  field 
  

   of 
  26 
  kilogauss 
  no 
  change 
  of 
  resistance 
  could 
  be 
  observed, 
  

   although 
  a 
  change 
  of 
  0*001 
  per 
  cent, 
  could 
  have 
  been 
  de- 
  

   tected. 
  The 
  material 
  appeared 
  to 
  be 
  strongly 
  paramagnetic, 
  

   which 
  may 
  be 
  due 
  to 
  ferruginous 
  impurities. 
  

  

  III. 
  Orientation 
  of 
  the 
  Graphite 
  in 
  the 
  Magnetic 
  Field 
  

   (19°-22°C). 
  

  

  Preliminary 
  observations 
  with 
  G 
  I. 
  12 
  showed 
  that 
  in 
  

   transverse 
  fields 
  the 
  change 
  of 
  resistance 
  of 
  the 
  graphite 
  

   depended 
  greatly 
  on 
  the 
  angle 
  <f> 
  between 
  the 
  crystalline 
  

   axis 
  51 
  and 
  the 
  magnetic 
  field 
  .jj. 
  Thus 
  the 
  effect 
  of 
  a 
  trans- 
  

   verse 
  field 
  of 
  26 
  kilogauss, 
  as 
  expressed 
  by 
  the 
  value 
  of 
  

   (R/ 
  — 
  R)/R, 
  was 
  rather 
  more 
  than 
  5 
  when 
  the 
  crystalline 
  

   axis 
  was 
  parallel 
  to 
  the 
  field, 
  and 
  only 
  0'15 
  when 
  the 
  axis 
  

   was 
  normal 
  to 
  the 
  field. 
  To 
  investigate 
  in 
  detail 
  the 
  varia- 
  

   tion 
  of 
  the 
  change 
  of 
  resistance 
  with 
  the 
  angle 
  between 
  the 
  

   crystalline 
  and 
  field 
  axes, 
  G 
  I. 
  12 
  a 
  (G 
  I. 
  12 
  shortened 
  and 
  

   re-coppered) 
  was 
  used. 
  It 
  was 
  remounted 
  and 
  supported 
  in 
  

   the 
  magnetic 
  field 
  as 
  described 
  above, 
  so 
  that 
  it 
  could 
  be 
  

   rotated 
  about 
  an 
  axis 
  normal 
  to 
  the 
  field 
  (a) 
  with 
  its 
  length 
  

   along 
  the 
  axis 
  of 
  rotation, 
  the 
  graphite 
  in 
  this 
  case 
  being 
  

   always 
  magnetized 
  transversely 
  to 
  its 
  length 
  and 
  the 
  direction 
  

   of 
  the 
  measuring 
  current, 
  and 
  (b) 
  with 
  its 
  length 
  normal 
  to 
  

   the 
  axis 
  of 
  rotation. 
  

  

  In 
  the 
  latter 
  case 
  the 
  graphite 
  became 
  successively 
  trans- 
  

   versely 
  (cleavage 
  plane 
  normal 
  to 
  the 
  field) 
  and 
  longitu- 
  

   dinally 
  magnetized 
  as 
  rotated 
  through 
  90°. 
  

  

  In 
  such 
  investigations 
  as 
  this 
  it 
  is 
  essential 
  to 
  have 
  the 
  

   magnetic 
  fields 
  as 
  uniform 
  as 
  possible, 
  and 
  this 
  condition 
  

   was 
  attained 
  by 
  determining 
  the 
  topography 
  of 
  the 
  field 
  for 
  

   different 
  distances 
  between 
  the 
  pole 
  end-pieces 
  and 
  adjusting 
  

   this 
  distance 
  until 
  uniformity 
  was 
  secured 
  *. 
  

  

  * 
  This 
  problem 
  was 
  mathematical] 
  v 
  discussed 
  by 
  Prof, 
  du 
  ]?ois, 
  

   Versl.Kon. 
  Akad. 
  Wet. 
  Atnst. 
  xxi. 
  p. 
  355 
  (1912) 
  ; 
  Verh. 
  d. 
  D. 
  Phys. 
  Oes. 
  

   xiv. 
  p. 
  758 
  (1912). 
  

  

  