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  V. 
  Note 
  on 
  the 
  Tlieorii 
  of 
  the 
  Greenhouse. 
  By 
  C. 
  G. 
  Abbot, 
  

   Director^ 
  Astrovhy 
  steal 
  Observatory., 
  Smithsonian 
  Institution 
  *. 
  

  

  IN 
  a 
  paper 
  o£ 
  the 
  above 
  title 
  f 
  Professor 
  R. 
  W. 
  Wood 
  

   states 
  that 
  he 
  has 
  compared 
  two 
  " 
  hot-boxes 
  " 
  one 
  having 
  

   a 
  glass 
  cover, 
  the 
  other 
  a 
  cover 
  of 
  rock 
  salt, 
  but 
  otherwise 
  

   similar. 
  A 
  glass 
  plate 
  was 
  interposed 
  in 
  the 
  path 
  of 
  the 
  

   entering 
  sun 
  rays. 
  He 
  observed 
  a 
  maximum 
  temperature 
  of 
  

   about 
  55° 
  C. 
  within 
  each 
  box 
  when 
  exposed 
  to 
  the 
  sun. 
  He 
  

   concludes 
  that 
  the 
  function 
  of 
  the 
  cover 
  is 
  mainly 
  to 
  prevent 
  

   the 
  loss 
  of 
  heat 
  by 
  convection, 
  rather 
  than 
  the 
  escape 
  of 
  long 
  

   wave 
  rays, 
  and 
  asks 
  : 
  "Is 
  it 
  therefore 
  necessary 
  to 
  pay 
  much 
  

   attention 
  to 
  trapped 
  radiation 
  in 
  deducing 
  the 
  temperature 
  of 
  

   a 
  planet 
  as 
  affected 
  by 
  its 
  atmosphere 
  ? 
  " 
  

  

  It 
  may 
  interest 
  some 
  to 
  know 
  that 
  much 
  higher 
  temperatures 
  

   can 
  be 
  reached 
  within 
  a 
  "hot-box" 
  than 
  that 
  observed 
  by 
  

   Professor 
  Wood, 
  if 
  precautions 
  are 
  taken 
  to 
  diminish 
  the 
  

   loss 
  of 
  heat 
  by 
  convection 
  from 
  the 
  warmed 
  outer 
  surface 
  of 
  

   the 
  cover. 
  On 
  November 
  4, 
  1897, 
  the 
  thermometer 
  recorded 
  

   118° 
  C. 
  within 
  a 
  circular 
  wooden 
  box 
  50 
  centimetres 
  in 
  

   diameter, 
  10 
  centimetres 
  deep^ 
  insulated 
  in 
  feathers, 
  covered 
  

   with 
  three 
  superposed 
  and 
  separated 
  sheets 
  of 
  plate 
  glass 
  and 
  

   exposed 
  normally 
  to 
  the 
  sun 
  rays 
  in 
  the 
  yard 
  of 
  the 
  Astro- 
  

   physical 
  Observatory 
  at 
  Washington. 
  The 
  temperature 
  

   outside 
  was 
  16^ 
  C. 
  

  

  Agreeing 
  with 
  Professor 
  Wood 
  that 
  the 
  main 
  function 
  of 
  

   the 
  cover 
  of 
  a 
  " 
  hot-box 
  " 
  or 
  " 
  hot-house 
  '' 
  is 
  to 
  prevent 
  loss 
  

   of 
  heat 
  by 
  convection, 
  it 
  is 
  interesting 
  to 
  see 
  if 
  this 
  could 
  be 
  

   predicted. 
  Published 
  experiments 
  on 
  the 
  cooling 
  of 
  solids 
  

   in 
  dry 
  air 
  and 
  in 
  vacuum 
  give 
  the 
  relative 
  rates 
  of 
  loss 
  by 
  

   convection 
  and 
  radiation 
  under 
  known 
  circumstances. 
  

   Planck's 
  radiation 
  formula 
  for 
  the 
  " 
  black 
  body 
  " 
  enables 
  

   computations 
  to 
  be 
  made 
  of 
  the 
  losses 
  by 
  radiation 
  for 
  different 
  

   temperatures 
  of 
  source 
  and 
  sink. 
  The 
  transmission 
  of 
  glass, 
  

   salt, 
  and 
  the 
  water 
  vapour 
  of 
  the 
  atmosphere, 
  and 
  the 
  

   effective 
  temperature 
  of 
  the 
  latter 
  are 
  approximately 
  known. 
  

   I 
  have 
  attempted 
  to 
  compute 
  from 
  such 
  data 
  the 
  relative 
  

   hindrance 
  which 
  salt 
  and 
  glass 
  covers 
  would 
  interpose 
  to 
  the 
  

   loss 
  of 
  heat 
  by 
  convection 
  and 
  radiation 
  combined 
  from 
  a 
  

   " 
  black 
  " 
  surface 
  at 
  55° 
  C. 
  For 
  the 
  dependence 
  of 
  the 
  tem- 
  

   perature 
  of 
  the 
  earth's 
  surface 
  on 
  the 
  atmosphere, 
  some 
  

   numerical 
  data 
  can 
  be 
  assigned 
  also, 
  and 
  as 
  shown 
  below 
  

   there 
  is 
  reason 
  to 
  think 
  that 
  " 
  trapping 
  '' 
  is 
  more 
  important 
  

   perhaps 
  than 
  Professor 
  Wood 
  thinks. 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  Published 
  by 
  permission 
  of 
  the 
  

   Secretary 
  of 
  the 
  Smithsonian 
  Institution. 
  

  

  t 
  Phil. 
  Mag. 
  6th 
  series, 
  vol. 
  xvii. 
  p. 
  319 
  (1909). 
  

  

  