﻿462 
  Mr. 
  F. 
  W. 
  Very 
  on 
  the 
  Greenhouse 
  

  

  good 
  a 
  conducting 
  material 
  as 
  carbon 
  in 
  the 
  spark-gap 
  could 
  

   be 
  entirely 
  without 
  effect 
  upon 
  the 
  discharge. 
  Rather, 
  it 
  

   seems 
  likely 
  that 
  the 
  particles 
  present 
  before 
  the 
  first 
  spark 
  

   were 
  as 
  effective 
  as 
  carbon 
  particles. 
  The 
  writer* 
  has 
  shown 
  

   clearly 
  that 
  the 
  passage 
  of 
  a 
  spark 
  through 
  an 
  oil 
  does 
  very 
  

   materially 
  affect 
  the 
  potential 
  required 
  to 
  produce 
  the 
  dis- 
  

   charge. 
  So 
  that, 
  valuable 
  as 
  the 
  results 
  of 
  Earhart 
  and 
  

   Shaw 
  are 
  as 
  representing 
  the 
  actual 
  working 
  conditions 
  which 
  

   usually 
  obtain, 
  they 
  may 
  not 
  be 
  taken 
  to 
  represent 
  the 
  

   potentials 
  necessary 
  to 
  produce 
  spark 
  discharges 
  through 
  the 
  

   distances 
  given, 
  in 
  the 
  pure 
  liquid. 
  

  

  The 
  Brace 
  Laboratory, 
  

  

  Lincoln, 
  Nebr., 
  U.S.A. 
  

  

  XLI. 
  The 
  Greenhouse 
  Theory 
  and 
  Planetary 
  Temperatures. 
  

   By 
  Frank 
  W. 
  Very|. 
  

  

  WHEN 
  Tyndall, 
  as 
  the 
  result 
  of 
  his 
  measures 
  of 
  the 
  

   absorption 
  of 
  terrestrial 
  radiation 
  by 
  water-vapour, 
  

   assured 
  us 
  that 
  the 
  removal 
  of 
  moisture 
  from 
  its 
  atmospheric 
  

   covering 
  would 
  plunge 
  the 
  British 
  Isles 
  into 
  a 
  more 
  than 
  

   Arctic 
  winter, 
  he 
  directed 
  attention 
  to 
  that 
  which, 
  next 
  to 
  the 
  

   solar 
  radiation 
  itself, 
  is 
  the 
  most 
  potent 
  factor 
  in 
  terrestrial 
  

   climate. 
  In 
  a 
  general 
  way 
  this 
  is 
  now 
  universally 
  recognized 
  ; 
  

   but 
  we 
  have 
  not 
  yet 
  arrived 
  at 
  unanimity 
  as 
  to 
  the 
  details 
  of 
  

   the 
  process 
  by 
  which 
  this 
  protective 
  agency 
  works, 
  or 
  of 
  

   their 
  applicability 
  to 
  other 
  worlds 
  than 
  ours. 
  

  

  Never 
  having 
  had 
  any 
  experience 
  with 
  gases 
  devoid 
  of 
  

   convection, 
  nor 
  with 
  solids 
  lacking 
  thermal 
  conductivity, 
  it 
  is 
  

   perhaps 
  hardly 
  safe 
  to 
  speculate 
  as 
  to 
  how 
  such 
  substances 
  

   would 
  or 
  would 
  not 
  behave 
  ; 
  but 
  if 
  a 
  guess 
  may 
  be 
  hazarded 
  

   on 
  the 
  subject 
  of 
  Professor 
  Poynting's 
  ideal 
  greenhouse 
  J, 
  

   one 
  would 
  suppose 
  that 
  if 
  the 
  background 
  were 
  absolutely 
  

   nonconducting, 
  unless 
  it 
  were 
  a 
  perfect 
  reflector, 
  in 
  which 
  

   case 
  it 
  would 
  not 
  be 
  heated 
  at 
  all, 
  the 
  heating 
  effect 
  of 
  solar 
  

   rays 
  would 
  be 
  increased 
  in 
  something 
  like 
  the 
  proportion 
  of 
  

   six 
  to 
  one 
  even 
  without 
  any 
  glass. 
  For 
  if 
  we 
  suppose 
  cubical 
  

   particles, 
  each 
  containing 
  a 
  cubic 
  centimetre 
  of 
  perfectly 
  

   absorbing 
  and 
  conducting 
  substance, 
  to 
  be 
  maintained 
  in 
  the 
  

   sun's 
  rays 
  at 
  an 
  excess 
  of 
  10° 
  above 
  an 
  initial 
  temperature 
  of 
  

   300° 
  A., 
  and 
  then 
  reduce 
  the 
  thickness 
  of 
  the 
  normal 
  absorbing 
  

  

  * 
  Almy, 
  Ann. 
  der 
  Phys. 
  [4] 
  i. 
  p. 
  508 
  (1900). 
  

  

  f 
  Communicated 
  by 
  the 
  Author. 
  

  

  X 
  J. 
  H. 
  Poynting, 
  " 
  On 
  Prof. 
  Lowell's 
  Method 
  for 
  Evaluating 
  the 
  

   Surface 
  Temperatures 
  of 
  the 
  Planets," 
  Phil. 
  Mag. 
  [6] 
  vol. 
  xiv. 
  p. 
  749, 
  

   December 
  1907. 
  

  

  