﻿170 
  Mr. 
  D. 
  E. 
  Roberts 
  on 
  the 
  Effect 
  of 
  Temperature 
  and 
  

  

  In 
  case 
  (a) 
  pole 
  end-pieces 
  (VIII.) 
  of 
  frontal 
  diameter 
  

   12 
  mm. 
  were 
  used, 
  and 
  the 
  distance 
  between 
  them 
  found 
  to 
  

   be 
  very 
  nearly 
  2 
  mm. 
  for 
  most 
  uniform 
  field 
  when 
  the 
  

   current 
  through 
  the 
  magnet 
  was 
  sufficient 
  to 
  saturate 
  the 
  

   iron. 
  This 
  is 
  in 
  good 
  agreement 
  with 
  the 
  theory 
  referred 
  to 
  

   in 
  the 
  footnote 
  (p. 
  169). 
  The 
  adjustment 
  can 
  be 
  very 
  exactly 
  

  

  uniform 
  to 
  within 
  less 
  than 
  1 
  per 
  

   a 
  transverse 
  range 
  of 
  8 
  mm. 
  The 
  

   Fig. 
  2. 
  

  

  made, 
  and 
  finally 
  a 
  field 
  

   cent, 
  was 
  obtained 
  over 
  

  

  Orientation 
  Curves. 
  

  

  resistance 
  of 
  specimen 
  G 
  I. 
  12 
  a 
  was 
  determined 
  potentio- 
  

   metrically 
  as 
  before 
  for 
  different 
  inclinations 
  of 
  its 
  crystalline 
  

   axis 
  to 
  the 
  field 
  as 
  it 
  was 
  rotated 
  through 
  360° 
  in 
  uniform 
  

   transverse 
  fields 
  of 
  21*8 
  and 
  35*2 
  kgss. 
  respectively. 
  The 
  

   increase 
  of 
  resistance 
  was 
  always 
  positive, 
  being 
  a 
  maximum 
  

   or 
  a 
  minimum 
  when 
  the 
  cleavage 
  plane 
  was 
  normal 
  or 
  parallel 
  

   to 
  the 
  field 
  respectively. 
  The 
  results 
  obtained 
  are 
  shown 
  in 
  

   fig. 
  2. 
  Curves 
  I. 
  and 
  III. 
  are 
  for 
  a 
  rotation 
  through 
  180° 
  ; 
  

  

  