﻿166 
  Mr. 
  D. 
  E. 
  Roberts 
  on 
  the 
  Effect 
  of 
  Temperature 
  and 
  

  

  by 
  analogy 
  with 
  the 
  well-known 
  behaviour 
  of 
  more 
  or 
  less 
  

   pure 
  bismuth*, 
  the 
  assumption 
  appeared 
  justifiable 
  that 
  these 
  

   were 
  more 
  likely 
  to 
  be 
  pure 
  and 
  perhaps 
  of 
  more 
  uniform 
  

   crystalline 
  structure. 
  Some 
  of 
  the 
  specimens 
  were 
  sup- 
  

   ported 
  free 
  between 
  thin 
  mica 
  or 
  glass 
  plates; 
  when 
  imbedded 
  

   in 
  sodium 
  silicate, 
  collodion, 
  or 
  Canada 
  balsam 
  allowed 
  

   afterwards 
  to 
  solidify, 
  they 
  did 
  not 
  experience 
  any 
  change 
  

   in 
  the 
  magnitude 
  of 
  their 
  increase 
  of 
  resistance 
  in 
  the 
  mag- 
  

   netic 
  field, 
  thus 
  eliminating 
  any 
  doubts 
  that 
  the 
  effects 
  were 
  

   due 
  to 
  bodily 
  strains 
  in 
  the 
  graphite. 
  In 
  the 
  final 
  experi- 
  

   ments 
  at 
  different 
  temperatures 
  the 
  graphite 
  pieces 
  were 
  

   supported 
  by 
  thin 
  flexible 
  wires 
  between 
  thin 
  mica 
  plates, 
  so 
  

   as 
  to 
  avoid 
  any 
  strain 
  due 
  to 
  possible 
  expansion 
  or 
  contrac- 
  

   tion. 
  The 
  specimens 
  could 
  be 
  mounted 
  with 
  their 
  con- 
  

   nexions 
  so 
  that 
  the 
  total 
  thickness 
  amounted 
  to 
  less 
  than 
  

   0*7 
  mm., 
  thus 
  enabling 
  them 
  to 
  be 
  examined 
  in 
  fields 
  up 
  to 
  

   50 
  kilogauss. 
  Some 
  of 
  the 
  isothermal 
  carves 
  obtained 
  for 
  

   different 
  specimens, 
  transversely 
  magnetized, 
  at 
  18° 
  C, 
  with 
  

   the 
  cleavage 
  plane 
  normal 
  to 
  the 
  field, 
  are 
  shown 
  in 
  fig. 
  1. 
  

   The 
  curves 
  are 
  for 
  the 
  specimens: 
  — 
  

  

  Specimen. 
  

  

  Resistance 
  R 
  . 
  

  

  GI. 
  4 
  

  

  0043 
  ohm 
  

   0080 
  „ 
  

   0016 
  „ 
  

   0043 
  ., 
  

   0032 
  „ 
  

  

  G-1. 
  10 
  

  

  GI. 
  11 
  

  

  GI 
  12 
  

  

  GI 
  15 
  

  

  

  Attempts 
  to 
  identify 
  the 
  curves 
  with 
  such 
  equations 
  as 
  

  

  §V| 
  +b$ 
  + 
  cff+... 
  

   sx 
  Ho 
  

  

  failed; 
  it 
  was 
  found, 
  however, 
  that 
  all 
  the 
  curves 
  obtained 
  

   at 
  ordinary 
  temperatures 
  could, 
  well 
  within 
  experimental 
  

   errors, 
  be 
  represented 
  by 
  the 
  formula 
  

  

  — 
  = 
  — 
  + 
  A.fi 
  OT 
  . 
  

   Ro 
  Ro 
  

  

  (i) 
  

  

  Owing 
  to 
  the 
  difficulty 
  of 
  determining 
  the 
  dimensions 
  o£ 
  

   * 
  F. 
  C. 
  Blake, 
  Ann. 
  der 
  Physik, 
  xxviii. 
  p. 
  449 
  (1909). 
  

  

  