﻿158 
  Mr. 
  D. 
  E. 
  Roberts 
  on 
  the 
  Effect 
  of 
  Temperature 
  and 
  

  

  recalls 
  the 
  emission 
  theory 
  developed 
  by 
  Newton, 
  while 
  the 
  

   main 
  features 
  o£ 
  the 
  undnlatory 
  theory 
  are 
  conserved. 
  But 
  

   the 
  emission 
  theory 
  definitely 
  postulates 
  the 
  kinetic 
  nature 
  

   of 
  the 
  whole 
  of 
  the 
  optical 
  energy 
  in 
  a 
  medium 
  — 
  in 
  strict 
  

   accordance 
  with 
  Fermat's 
  law. 
  We 
  conclude, 
  accordingly, 
  

   that 
  either 
  theory 
  leads 
  to 
  the 
  same 
  conclusion. 
  

  

  28. 
  Again, 
  the 
  motion 
  of 
  the 
  Faraday 
  tubes, 
  in 
  a 
  medium, 
  

   which 
  may 
  be 
  taken 
  to 
  be 
  a 
  fluid 
  medium 
  of 
  some 
  kind, 
  

   recalls 
  the 
  " 
  motion 
  of 
  hollow 
  vortex 
  rings 
  in 
  a 
  fluid 
  in 
  

   which 
  portions 
  in 
  rotational 
  and 
  irrotational 
  motion 
  are 
  

   freely 
  mixed 
  together 
  and 
  which 
  Lord 
  Kelvin 
  has 
  called 
  

   vortex 
  sponge." 
  Now 
  it 
  has 
  been 
  shown 
  that 
  the 
  equation 
  

   of 
  propagation 
  of 
  a 
  plane 
  wave 
  in 
  such 
  a 
  medium 
  is 
  the 
  same 
  

   as 
  the 
  equation 
  of 
  propagation 
  of 
  luminous 
  vibrations 
  in 
  the 
  

   sether, 
  and 
  that 
  a 
  spiral 
  vortex 
  in 
  such 
  a 
  medium 
  would 
  behave 
  

   in 
  the 
  same 
  way 
  as 
  a 
  tube 
  of 
  electric 
  force. 
  If 
  this 
  view 
  of 
  

   the 
  electromagnetic 
  field 
  is 
  accepted, 
  the 
  energy 
  of 
  the 
  field 
  

   intrinsic 
  and 
  actual 
  must 
  necessarily 
  be 
  entirely 
  kinetic. 
  

  

  29. 
  Finally, 
  whether 
  we 
  view 
  an 
  atom 
  as 
  a 
  vortex 
  ring 
  or' 
  

   simply 
  regard 
  it 
  as 
  made 
  up 
  of 
  corpuscles 
  and 
  ions 
  in 
  rapid 
  

   rotation, 
  a 
  molecule 
  must 
  be 
  regarded 
  intrinsically 
  as 
  a 
  con- 
  

   servative 
  system, 
  whose 
  energy 
  is 
  entirely 
  kinetic, 
  on 
  any 
  

   theory 
  which 
  at 
  all 
  holds 
  the 
  field. 
  As 
  further, 
  we 
  have 
  

   argued 
  that 
  vibratory 
  energy 
  is 
  also 
  entirely 
  kinetic, 
  we 
  

   reach 
  the 
  broad 
  generalization 
  that 
  every 
  form 
  of 
  energy 
  

   involves 
  motion, 
  sethereal, 
  corpuscular, 
  or 
  molar. 
  

  

  VI. 
  The 
  Effect 
  of 
  Temperature 
  and 
  Magnetization 
  on 
  the 
  

   Resistance 
  of 
  Graphite. 
  By 
  David 
  E. 
  Roberts, 
  B.Sc, 
  

   Research 
  Fellow 
  of 
  the 
  University 
  of 
  Wales 
  *. 
  

  

  Notation. 
  

   9 
  = 
  Temperature. 
  

   $ 
  = 
  Intensity 
  of 
  magnetic 
  field. 
  

   R 
  = 
  Resistance 
  in 
  zero 
  field 
  at 
  0°. 
  

   R 
  = 
  Resistance 
  in 
  zero 
  field 
  at 
  0°. 
  

   R' 
  = 
  Resistance 
  in 
  field 
  $ 
  at 
  0°. 
  

   A, 
  a 
  = 
  Empirical 
  constants. 
  

   m 
  — 
  Exponential 
  constant. 
  

   = 
  Angle 
  between 
  § 
  and 
  crystalline 
  axis 
  (%). 
  

  

  ^l^HE 
  investigations 
  of 
  Grunmach 
  and 
  Weidert*, 
  

   A 
  Patterson 
  f, 
  and 
  others, 
  on 
  the 
  effect 
  of 
  transverse 
  

   magnetization 
  on 
  the 
  electrical 
  resistance 
  of 
  various 
  sub- 
  

   stances, 
  show 
  that 
  paramagnetic 
  and 
  diamagnetic 
  metals 
  

  

  * 
  Communicated 
  by 
  Dr. 
  H. 
  du 
  Bois. 
  A 
  preliminary 
  publication 
  

   appeared 
  in 
  Proc. 
  Roy. 
  Acad. 
  Amst. 
  xxi. 
  p. 
  221 
  (1912). 
  

  

  t 
  L. 
  Grunmach 
  and 
  F. 
  Weidert, 
  Ann. 
  der 
  Phys. 
  xxii. 
  p. 
  141 
  (1907). 
  

   X 
  J. 
  Patterson, 
  Phil. 
  Mag. 
  [6] 
  iii. 
  p. 
  643 
  (1902). 
  

  

  