﻿478 
  Mr. 
  F. 
  W. 
  Very 
  on 
  the 
  Greenhouse 
  

  

  the 
  spectrum, 
  but 
  diminish 
  in 
  width 
  and 
  blackness 
  towards 
  

   the 
  shorter 
  waves, 
  and 
  die 
  out 
  near 
  the 
  middle 
  of 
  the 
  visible 
  

   spectrum. 
  This 
  suggests 
  that 
  there 
  may 
  be 
  present 
  in 
  the 
  

   atmospheres 
  of 
  these 
  planets 
  substances 
  having 
  very 
  numerous 
  

   and 
  intense 
  absorption 
  bands 
  in 
  the 
  infra-red 
  ; 
  and 
  if 
  these 
  

   bands 
  are 
  so 
  strong 
  that 
  they 
  give 
  metallic 
  reflexion 
  for 
  

   surface 
  radiation, 
  even 
  the 
  small 
  amount 
  of 
  energy 
  in 
  the 
  

   solar 
  radiation 
  on 
  Neptune 
  can 
  be 
  so 
  largely 
  stored 
  up 
  that 
  

   a 
  high 
  surface 
  temperature 
  is 
  maintained 
  by 
  the 
  accumulated 
  

   heat. 
  The 
  great 
  inclination 
  of 
  the 
  axes 
  of 
  the 
  two 
  outer 
  

   planets, 
  w 
  r 
  hereby 
  large 
  parts 
  of 
  their 
  surfaces 
  remain 
  for 
  long- 
  

   years 
  in 
  a 
  state 
  of 
  arctic 
  night, 
  may 
  serve 
  in 
  this 
  case 
  as 
  a 
  

   safety-valve 
  by 
  the 
  .transferring 
  of 
  heat 
  to 
  cold 
  regions 
  by 
  

   atmospheric 
  circulation, 
  thus 
  preventing 
  too 
  great 
  an 
  accu- 
  

   mulation 
  in 
  the 
  sunward 
  zones. 
  I 
  believe 
  that 
  this, 
  though 
  

   problematical, 
  is 
  a 
  plausible 
  explanation 
  of 
  the 
  high 
  tempe- 
  

   ratures 
  which 
  exist 
  on 
  the 
  major 
  planets, 
  as 
  evidenced 
  by 
  the 
  

   vigour 
  of 
  their 
  atmospheric 
  circulation, 
  the 
  formation 
  of 
  

   cloud-belts, 
  &c, 
  which 
  has 
  driven 
  some 
  astronomers 
  to 
  

   maintain 
  that 
  these 
  planets 
  are 
  much 
  younger 
  than 
  the 
  earth, 
  

   although 
  there 
  is 
  no 
  reason 
  for 
  such 
  a 
  supposition, 
  and 
  much 
  

   weighty 
  evidence 
  to 
  the 
  contrary. 
  

  

  If 
  in 
  equation 
  (1), 
  distinguishing 
  between 
  relative 
  losses 
  

   by 
  reflexion 
  and 
  absorption, 
  so 
  that 
  the 
  completed 
  equation 
  

   (vide 
  Poynting) 
  is 
  

  

  E 
  = 
  ^S+r 
  1 
  R 
  + 
  |(«S 
  + 
  a 
  1 
  R), 
  .... 
  (1') 
  

  

  we 
  put 
  t 
  = 
  0-1, 
  r 
  = 
  0*7, 
  a 
  = 
  02, 
  a^O'01, 
  r 
  1 
  = 
  0-99, 
  * 
  1= 
  =0, 
  we 
  

   find 
  for 
  ?i==2, 
  

  

  R 
  = 
  40S. 
  

  

  I 
  will 
  take 
  for 
  the 
  maximum 
  or 
  steady 
  temperature 
  in 
  

   sunshine 
  at 
  the 
  earth's 
  distance 
  a 
  mean 
  of 
  my 
  three 
  values, 
  

   1/3(468 
  + 
  463 
  + 
  454) 
  = 
  462° 
  A. 
  Then, 
  since 
  the 
  inverse 
  square 
  

   root 
  of 
  Neptune's 
  distance 
  from 
  the 
  sun 
  is 
  0*18, 
  the 
  sun 
  

   temperature 
  at 
  Neptune 
  is 
  462 
  x 
  018 
  = 
  83° 
  A. 
  = 
  S 
  , 
  and 
  

  

  6x= 
  ^40x(^) 
  4 
  = 
  323°A.= 
  +50°C.; 
  

  

  that 
  is, 
  it 
  is 
  possible 
  for 
  Neptune 
  to 
  have 
  a 
  torrid 
  climate 
  

   from 
  the 
  solar 
  rays 
  alone 
  without 
  owing 
  anything 
  to 
  its 
  own 
  

   internal 
  heat, 
  and 
  this 
  without 
  requiring 
  any 
  exceptional 
  

   action 
  of 
  its 
  atmosphere 
  on 
  luminous 
  rays, 
  or 
  such 
  as 
  would 
  

   be 
  noticed 
  in 
  telescopic 
  examination. 
  

  

  After 
  what 
  precedes, 
  it 
  will 
  be 
  seen 
  that 
  we 
  cannot 
  com- 
  

   pare 
  the 
  heat-retaining 
  powers 
  of 
  the 
  two 
  planets, 
  unless 
  we 
  

   have 
  reason 
  to 
  believe 
  that 
  the 
  heat-retaining 
  process 
  is 
  similar 
  

  

  