﻿Motion 
  of 
  Electrons 
  in 
  Solids, 
  217 
  

  

  35. 
  Equation 
  {'o^) 
  shows 
  further 
  that 
  if 
  Ep 
  has 
  not 
  the 
  

   value 
  required 
  for 
  equipartition 
  of 
  energy, 
  it 
  will 
  always 
  

   move 
  towards 
  that 
  value. 
  The 
  total 
  energy, 
  if 
  not 
  equally 
  

   distributed 
  between 
  the 
  different 
  vibrational 
  degrees 
  of 
  

   freedom, 
  must 
  pass 
  towards 
  this 
  state. 
  The 
  " 
  time 
  of 
  re- 
  

   laxation 
  " 
  for 
  radiation 
  of 
  frequency 
  p 
  is 
  

  

  ^TrVVV 
  NV 
  / 
  

   For 
  long 
  waves 
  this 
  becomes 
  K/^ttC^a:, 
  which 
  is 
  equal 
  to 
  the 
  

   *' 
  time 
  of 
  relaxation 
  " 
  for 
  the 
  dissipation 
  of 
  irregularities 
  of 
  

   electric 
  charge 
  inside 
  the 
  same 
  conductor 
  *. 
  

  

  In 
  other 
  words, 
  the 
  energy 
  of 
  great 
  wave-length 
  adjusts 
  

   itself 
  to 
  equipartition 
  exactly 
  as 
  rapidly 
  as 
  electric 
  charges 
  

   adjust 
  themselves 
  to 
  the 
  equalization 
  of 
  potential 
  : 
  the 
  

   radiation 
  of 
  shorter 
  wave-length 
  adjusts 
  itself 
  at 
  a 
  slower, 
  

   but 
  still 
  comparable, 
  rate. 
  

  

  There 
  is 
  one 
  reservation, 
  a 
  very 
  important 
  one, 
  to 
  be 
  made 
  

   to 
  all 
  this. 
  Equation 
  (^QQ) 
  assumes 
  the 
  sether 
  to 
  be 
  already 
  

   tilled 
  with 
  an 
  adequate 
  number 
  of 
  "pulses'^ 
  and 
  waves 
  of 
  

   short 
  wave-length. 
  If 
  this 
  condition 
  is 
  not 
  at 
  first 
  satisfied, 
  

   progress 
  towards 
  a 
  state 
  of 
  equipartition 
  of 
  energy 
  of 
  short 
  

   wave-length 
  will 
  begin 
  slowly, 
  for 
  the 
  creation 
  of 
  pulses 
  and 
  

   short 
  waves 
  is 
  known 
  to 
  be 
  a 
  very 
  slow 
  process 
  (§21). 
  The 
  

   theorem 
  of 
  equipartition 
  shows, 
  however, 
  that 
  the 
  final 
  state 
  

   must 
  be 
  one 
  of 
  equipartition. 
  

  

  Natural 
  Radiation, 
  

  

  36. 
  If 
  the 
  reflecting 
  powers 
  of 
  the 
  walls 
  of 
  the 
  enclosure 
  

   fall 
  short 
  of 
  perfection 
  in 
  any 
  degree, 
  the 
  system 
  may 
  no 
  

   longer 
  be 
  treated 
  as 
  conservative, 
  and 
  there 
  is 
  no 
  justification 
  

   for 
  expecting 
  equipartition 
  of 
  energy 
  [cf. 
  § 
  21). 
  To 
  find 
  the 
  

   partition 
  of 
  radiant 
  energy 
  we 
  fall 
  back 
  on 
  our 
  detailed 
  

   analysis 
  of 
  § 
  2%, 
  

  

  Natural 
  radiation, 
  whether 
  examined 
  when 
  streaming 
  

   freely 
  from 
  a 
  hot 
  body 
  or 
  when 
  taken 
  from 
  an 
  enclosure 
  

   with 
  the 
  most 
  perfectly 
  reflecting 
  walls 
  obtainable, 
  is 
  found, 
  

   as 
  a 
  matter 
  of 
  observation, 
  to 
  be 
  almost 
  totally 
  devoid 
  of 
  

   waves 
  of 
  the 
  shortest 
  wave-lengths. 
  This 
  is 
  what 
  we 
  should 
  

   in 
  any 
  case 
  expect 
  from 
  our 
  knowledge 
  of 
  the 
  slowness 
  with 
  

   which 
  energy 
  of 
  short 
  wave-length 
  is 
  generated, 
  and 
  of 
  the 
  

   imperfect 
  retaining 
  power 
  for 
  such 
  waves 
  of 
  all 
  actual 
  sub- 
  

   .stances. 
  The 
  analysis 
  of 
  §§ 
  30-33 
  assumed 
  the 
  presence 
  in 
  

   abundant 
  quantity 
  of 
  waves 
  of 
  short 
  wave-length 
  : 
  this 
  

   analysis 
  must 
  now 
  be 
  modified 
  to 
  suit 
  natural 
  conditions. 
  

   * 
  Jeans, 
  * 
  Electricity 
  and 
  Magnetism,' 
  § 
  396. 
  

  

  