﻿168 
  Mr. 
  D. 
  E. 
  Roberts 
  on 
  the 
  Effect 
  of 
  Temperature 
  and 
  

  

  Table 
  I. 
  

  

  Transverse 
  magnetization. 
  Cleavage 
  plane 
  normal 
  

  

  to 
  the 
  field. 
  

  

  Isotherinals 
  at 
  18° 
  C. 
  

  

  Specimen. 
  

  

  E 
  . 
  

  

  R7H 
  =E/R 
  4-A§ 
  m 
  . 
  

  

  a 
  i. 
  4 
  

  

  0-0430 
  ohm 
  

   0-0792 
  „ 
  

   0-0162 
  „ 
  

   0-0430 
  „ 
  

   00323 
  „ 
  

   00316 
  „ 
  

  

  1*745 
  

  

  1-01 
  4- 
  0-0171. 
  ■§ 
  

   1-01 
  4- 
  .0-0205 
  . 
  & 
  1 
  ' 
  745 
  

   1-008 
  4- 
  0-0162 
  . 
  £ 
  1,745 
  

   1-014 
  4- 
  0-0188 
  . 
  § 
  1745 
  

   1-01 
  + 
  0-0198 
  .& 
  1 
  ' 
  745 
  

   1-02 
  + 
  p-0214.^ 
  1 
  ' 
  745 
  

  

  GI. 
  10 
  

  

  G-I.ll 
  

  

  GI.12 
  

  

  GI.12a 
  

  

  GI. 
  15 
  

  

  

  The 
  results 
  of 
  the 
  tests, 
  which 
  were 
  made 
  on 
  the 
  other 
  

   kinds 
  of 
  graphite 
  (see 
  p. 
  163), 
  which 
  all 
  showed 
  the 
  effect 
  

   in 
  a 
  lesser 
  degree 
  or 
  not 
  at 
  all, 
  were 
  as 
  follows 
  : 
  — 
  

  

  G 
  II. 
  The 
  best 
  piece 
  I 
  could 
  prepare 
  gave 
  an 
  increase 
  of 
  

   resistance 
  of 
  only 
  182 
  per 
  cent, 
  in 
  a 
  field 
  of 
  20 
  kilogauss, 
  

   the 
  resistance 
  out 
  of 
  the 
  field 
  being 
  0*0427 
  ohm. 
  

  

  GUI. 
  Different 
  pieces 
  of 
  this 
  graphite 
  gave 
  quite 
  dif- 
  

   ferent 
  results. 
  A 
  thin 
  strip 
  obtained 
  from 
  the 
  upper 
  smooth 
  

   and 
  highly 
  polished 
  surface 
  by 
  cleavage, 
  appeared 
  on 
  its 
  

   underside 
  of 
  a 
  fine 
  granular 
  structure. 
  When 
  transversely 
  

   magnetized 
  in 
  a 
  field 
  of 
  20 
  kilogauss 
  it 
  showed 
  an 
  increase 
  

   of 
  resistance 
  of 
  220 
  per 
  cent., 
  the 
  resistance 
  outside 
  the 
  field 
  

   being 
  0*0786 
  ohm. 
  A 
  thin 
  strip 
  obtained 
  from 
  the 
  under- 
  

   side 
  of 
  the 
  same 
  material, 
  and 
  having 
  a 
  high 
  natural 
  polish 
  

   on 
  both 
  of 
  its 
  surfaces, 
  gave 
  the 
  anomalous 
  results. 
  Its 
  

   resistance 
  outside 
  the 
  field 
  was 
  several 
  hundred 
  ohms, 
  and 
  

   diminished 
  very 
  rapidly 
  with 
  increase 
  of 
  temperature. 
  In 
  a 
  

   magnetic 
  field, 
  however, 
  no 
  change 
  in 
  its 
  resistance 
  could 
  be 
  

   detected, 
  while 
  rough 
  experiments 
  indicated 
  that 
  it 
  was 
  

   paramagnetic. 
  Three 
  pieces 
  similar 
  to 
  the 
  latter 
  were 
  tested 
  

   and 
  agreed 
  in 
  giving 
  these 
  anomalous 
  results. 
  

  

  G 
  IV. 
  The 
  piece 
  tested 
  possessed 
  a 
  specific 
  resistance 
  of 
  

   about 
  15 
  . 
  10~ 
  4 
  ohm 
  per 
  cm. 
  3 
  , 
  i. 
  e. 
  of 
  the 
  same 
  order 
  as 
  the 
  

   average 
  of 
  G 
  I. 
  When 
  transversely 
  magnetized 
  it 
  showed 
  

   an 
  increase 
  of 
  resistance 
  of 
  440 
  per 
  cent, 
  in 
  a 
  field 
  of 
  26 
  

   kilogauss. 
  Its 
  initial 
  resistance 
  was 
  0*009 
  ohm. 
  It 
  appeared 
  

   to 
  be 
  strongly 
  diamagnetic. 
  

  

  