﻿634 
  F. 
  W. 
  Very—Solar 
  Radiation. 
  

  

  incomplete 
  observations 
  are 
  incapable 
  of 
  elucidating 
  the 
  laws 
  

   of 
  atmospheric 
  absorption 
  except 
  through 
  the 
  aid 
  of 
  more 
  per- 
  

   fect 
  measures. 
  By 
  supplying 
  deficiencies 
  under 
  guidance 
  of 
  a 
  

   criterion 
  we 
  may 
  in 
  some 
  cases 
  rescue 
  observations 
  which 
  are 
  

   otherwise 
  useless. 
  

  

  It 
  will 
  sometimes 
  be 
  necessary 
  to 
  discard 
  imperfect 
  or 
  dis- 
  

   crepant 
  observations 
  on 
  good 
  and 
  sufficient 
  grounds, 
  and 
  to 
  

   select 
  the 
  most 
  suitable 
  material 
  for 
  discussion, 
  but 
  the 
  prin- 
  

   ciple 
  of 
  selection 
  must 
  be 
  a 
  rational 
  one, 
  capable 
  of 
  concate- 
  

   nation 
  with 
  known 
  facts 
  in 
  other 
  departments 
  of 
  scientific 
  

   investigation 
  and, 
  if 
  possible, 
  one 
  which 
  can 
  be 
  subjected 
  to 
  

   some 
  critical 
  check. 
  The 
  new 
  thermodynamics 
  of 
  the 
  atmos- 
  

   phere 
  promises 
  to 
  provide 
  such 
  a 
  check 
  on 
  the 
  problems 
  of 
  

   solar 
  radiation. 
  

  

  The 
  conclusion 
  that 
  the 
  equivalent 
  of 
  the 
  solar 
  constant 
  of 
  

   radiation 
  can 
  not 
  be 
  less 
  than 
  three, 
  though 
  it 
  may 
  be 
  as 
  much 
  

   as 
  four 
  gram-calories 
  per 
  sq. 
  cm. 
  per 
  minute, 
  has 
  now 
  been 
  

   forced 
  upon 
  us 
  in 
  many 
  ways. 
  It 
  is 
  of 
  prime 
  importance 
  that 
  

   we 
  recognize 
  the 
  existence 
  of 
  a 
  special 
  region 
  of 
  peculiarly 
  

   potent 
  incipient 
  absorption 
  of 
  solar 
  radiation 
  in 
  the 
  upper 
  air, 
  

   whereby 
  the 
  upper 
  fourth 
  of 
  the 
  atmosphere 
  of 
  oxygen 
  and 
  

   nitrogen 
  with 
  its 
  contained 
  aqueous 
  vapor 
  becomes 
  a 
  reservoir 
  

   of 
  thermal 
  energy 
  and 
  a 
  protective 
  covering 
  for 
  the 
  deeper 
  

   layers.* 
  This 
  great 
  upper 
  nonadiabatic 
  layer 
  of 
  permanent 
  

   temperature-inversion 
  is 
  comparatively 
  quiet 
  as 
  to 
  air 
  move- 
  

   ment, 
  is 
  free 
  from 
  storms, 
  and 
  maintains 
  an 
  almost 
  constant 
  

   average 
  temperature 
  in 
  summer 
  and 
  winter 
  irrespectively 
  ; 
  but 
  

   thermally 
  this 
  region 
  is 
  the 
  most 
  actively 
  changing 
  in 
  the 
  

   entire 
  atmosphere. 
  Here 
  occur 
  the 
  widest 
  fluctuations 
  of 
  

   temperature 
  to 
  be 
  found 
  at 
  any 
  level 
  in 
  the 
  free 
  air 
  within 
  

   intervals 
  of 
  a 
  few 
  days.f 
  It 
  is 
  here 
  that 
  a 
  very 
  large 
  fraction 
  

   of 
  the 
  solar 
  radiation 
  disappears, 
  so 
  that 
  a 
  radiant 
  equivalent 
  

   which 
  may 
  be 
  3*5 
  cal. 
  / 
  sq. 
  cm. 
  min. 
  at 
  the 
  atmospheric 
  limit 
  (or 
  

   possibly 
  even 
  4) 
  is 
  reduced 
  to 
  less 
  than 
  2 
  by 
  the 
  time 
  that 
  

   the 
  rays 
  strike 
  the 
  tops 
  of 
  some 
  of 
  our 
  highest 
  mountains. 
  In 
  

   this 
  great 
  isothermal 
  layer 
  also 
  resides 
  the 
  radiant 
  power 
  of 
  the 
  

   atmosphere. 
  The 
  heat 
  absorbed 
  here 
  from 
  the 
  sun's 
  rays 
  is 
  

   again 
  lost 
  by 
  radiation 
  to 
  space, 
  and 
  does 
  not 
  appear 
  in 
  our 
  

   sea-level 
  observations 
  of 
  solar 
  radiation, 
  nor 
  even 
  in 
  those 
  made 
  

   on 
  mountains. 
  Abbot's 
  hypothetical 
  radiant 
  layer 
  at 
  4000 
  

   meters 
  simply 
  does 
  not 
  exist, 
  but 
  a 
  value 
  of 
  the 
  solar 
  constant 
  

  

  *See 
  Frank 
  W. 
  Very, 
  "Sky 
  Kadiation 
  and 
  the 
  Isothermal 
  Layer," 
  this 
  

   Journal 
  (4), 
  vol. 
  xxxv, 
  p. 
  369, 
  April, 
  1913. 
  

  

  fOn 
  account 
  of 
  this 
  peculiarity 
  it 
  has 
  been 
  proposed 
  to 
  abandon 
  the 
  

   earlier 
  name 
  — 
  "isothermal 
  layer" 
  — 
  in 
  favor 
  of 
  the 
  rather 
  meaningless 
  term, 
  

   "Stratosphere"; 
  but 
  the 
  absence 
  of 
  & 
  seasonal 
  fluctuation 
  of 
  temperature 
  

   still 
  makes 
  the 
  older 
  name 
  appropriate. 
  

  

  