﻿Relations 
  between 
  Milier, 
  Matter, 
  and 
  Electricity. 
  367 
  

  

  apparently 
  fail, 
  since 
  no 
  known 
  substance 
  can 
  retain 
  its 
  

   magnetism 
  at 
  the 
  high 
  temperatures 
  which 
  exist 
  in 
  the 
  

   interior. 
  In 
  1879 
  Ayrton 
  and 
  Perry 
  * 
  advanced 
  a 
  theory 
  

   which 
  depends 
  upon 
  Rowland's 
  experimental 
  proof 
  that 
  a 
  

   moving 
  electric 
  charge 
  acts 
  magnetically 
  like 
  a 
  current. 
  

   This 
  theory 
  assumes 
  the 
  presence 
  o£ 
  a 
  large 
  negative 
  charge 
  

   of 
  static 
  electricity 
  placed 
  upon 
  the 
  surface 
  of 
  the 
  earth 
  

   and 
  rotating 
  with 
  it. 
  Rowland 
  f 
  disproved 
  this 
  theory, 
  by 
  

   showing 
  that 
  a 
  surface-density 
  great 
  enough 
  to 
  account 
  for 
  

   terrestrial 
  magnetism 
  would 
  involve 
  a 
  repulsive 
  force 
  sufficient 
  

   to 
  tear 
  away 
  articles 
  on 
  the 
  earth's 
  surface. 
  To 
  overcome 
  

   this 
  difficulty 
  Sutherland 
  J 
  has 
  assumed 
  that 
  an 
  equal 
  positive 
  

   charge 
  is 
  concentrated 
  at 
  the 
  centre 
  which 
  will 
  confine 
  the 
  

   field 
  to 
  the 
  interior 
  of 
  the 
  earth. 
  To 
  keep 
  these 
  charges 
  

   apart 
  an 
  insulation 
  resistance 
  is 
  necessary 
  which 
  will 
  stand 
  a 
  

   fall 
  of 
  potential 
  of 
  2 
  x 
  10 
  8 
  volts 
  per 
  centimetre. 
  The 
  high 
  

   temperature 
  within 
  the 
  earth 
  would 
  destroy 
  the 
  insulating 
  

   power 
  of 
  most 
  substances 
  which 
  are 
  known 
  at 
  the 
  surface, 
  so 
  

   that 
  Mr. 
  Sutherland 
  is 
  forced 
  to 
  assume 
  that 
  pressure 
  will 
  

   counteract 
  this 
  effect 
  and 
  restore 
  the 
  insulating 
  power. 
  Until 
  

   we 
  have 
  more 
  evidence 
  on 
  this 
  point 
  it 
  seems 
  that 
  this 
  

   assumption 
  is 
  hardly 
  warranted. 
  As 
  far 
  back 
  as 
  1825 
  Barlow 
  

   suggested 
  that 
  magnetic 
  polarity 
  might 
  be 
  induced 
  by 
  mere 
  

   rotation 
  of 
  matter, 
  and 
  tried 
  the 
  experiment 
  with 
  iron 
  spheres, 
  

   but 
  found 
  no 
  effect 
  except 
  that 
  due 
  to 
  hysteresis. 
  In 
  recent 
  

   years, 
  however, 
  the 
  belief 
  has 
  been 
  gaining 
  ground 
  that 
  

   terrestial 
  magnetism 
  is 
  due 
  to 
  the 
  rotation 
  of 
  the 
  earth. 
  

   Schuster 
  §, 
  in 
  his 
  presidential 
  address 
  before 
  Section 
  A 
  of 
  the 
  

   British 
  Association, 
  1892, 
  asks 
  the 
  question 
  : 
  u 
  Is 
  every 
  large 
  

   rotating 
  ma«s 
  a 
  magnet?"; 
  while 
  Lord 
  Kelvin 
  || 
  "finds 
  it 
  

   unimaginable 
  but 
  that 
  terrestial 
  magnetism 
  is 
  due 
  to 
  the 
  

   greatness 
  and 
  the 
  rotation 
  of 
  the 
  earth 
  ; 
  " 
  and 
  Professor 
  

   Rowland 
  has 
  frequently 
  suggested 
  such 
  a 
  cause 
  in 
  his 
  lectures. 
  

   If 
  now 
  we 
  may 
  assume 
  that 
  matter, 
  by 
  virtue 
  of 
  its 
  motion, 
  

   has 
  induced 
  in 
  it 
  an 
  electromotive 
  force 
  in 
  the 
  direction 
  

   opposite 
  to 
  that 
  of 
  its 
  motion, 
  currents 
  will 
  be 
  set 
  up 
  within 
  

   the 
  volume 
  of 
  the 
  earth, 
  flowing 
  in 
  cylindrical 
  sheets 
  about 
  

   the 
  axis 
  of 
  the 
  earth, 
  and 
  producing 
  a 
  magnetic 
  field 
  at 
  any 
  

   point 
  on 
  the 
  surface. 
  Assuming 
  the 
  electromotive 
  force 
  in 
  

  

  * 
  Phil. 
  Mag. 
  vii. 
  p. 
  401 
  (1879) 
  ; 
  Proc. 
  Phys. 
  Soc. 
  of 
  London, 
  iii. 
  p. 
  57 
  

   (1880). 
  

  

  t 
  Phil. 
  Mag. 
  viii. 
  p. 
  102 
  (1879) 
  ; 
  Proc. 
  Phvs. 
  Soc. 
  of 
  London, 
  iii. 
  

   p. 
  93 
  (1880). 
  

  

  % 
  ' 
  Terrestial 
  Magnetism 
  and 
  Atmospheric 
  Electricity,' 
  June 
  1900. 
  

  

  § 
  British 
  Association 
  Eeports, 
  1892, 
  p. 
  634. 
  

  

  || 
  Popular 
  Addresses, 
  vol. 
  ii. 
  p. 
  511. 
  

  

  