﻿620 
  

  

  F. 
  W. 
  Very 
  — 
  Solar 
  Radiation. 
  

  

  combinations 
  of 
  atmospheric 
  conditions,* 
  but 
  since 
  actinome- 
  

   tric 
  observations 
  are 
  easily 
  made 
  and 
  have 
  been 
  accumulated 
  

   in 
  great 
  numbers 
  for 
  many 
  years, 
  it 
  is 
  desirable 
  to 
  see 
  whether 
  

   some 
  use, 
  even 
  though 
  an 
  imperfect 
  one, 
  may 
  be 
  made 
  of 
  this 
  

   material, 
  and 
  especially 
  whether 
  a 
  way 
  may 
  be 
  found 
  to 
  elimi- 
  

   nate 
  the 
  depleting 
  action 
  of 
  aqueous 
  vapor. 
  The 
  chart 
  (fig. 
  1) 
  

   has 
  been 
  constructed 
  from 
  the 
  numbers 
  in 
  the 
  following 
  table.f 
  

  

  Air-masses 
  

  

  £ 
  

  

  1 
  

  

  2 
  

  

  3 
  

  

  4 
  

  

  5 
  

  

  6 
  

  

  7 
  

  

  8 
  

  

  9 
  

  

  10 
  

  

  Pressure 
  

  

  of 
  

  

  aqueous 
  

  

  vapor. 
  

  

  Eadiation 
  (gr. 
  

   calories 
  per 
  

   sq. 
  cm. 
  per 
  

   min.) 
  

  

  2-66 
  

   2-40 
  

   1-86 
  

  

  2-22 
  

   1-88 
  

   1-22 
  

  

  1-73 
  

   1-36 
  

   0-97 
  

  

  1-46 
  

   1-13 
  

  

  0-83 
  

  

  1-26 
  

   1-01 
  

   0-73 
  

  

  1-12 
  

   0-89 
  

   0-68 
  

  

  1-02 
  

   0-79 
  

   0-63 
  

  

  0-94 
  

  

  0-72 
  

   0-59 
  

  

  0-87 
  

   0-66 
  

   0*55 
  

  

  0'81 
  

   0-59 
  

   0-51 
  

  

  0-76 
  

   0-53 
  

   0-47 
  

  

  mm. 
  

   0-8 
  

  

  5-0 
  

  

  15-0 
  

  

  Factors 
  reduc- 
  

   ing 
  to 
  Solar 
  

   constant. 
  

  

  1-316 
  

  

  1-46 
  

  

  1-88 
  

  

  1-58 
  

   1-84 
  

  

  2-82 
  

  

  2-01 
  

  

  2-57 
  

   3-61 
  

  

  2-40 
  

   3-05 
  

  

  4-22 
  

  

  2-78 
  

   3-47 
  

   4-70 
  

  

  3-13 
  

  

  3-93 
  

  

  I 
  5-15 
  

  

  3 
  43 
  

   4-43 
  

   5'56 
  

  

  372 
  

  

  4-86 
  

   5-93 
  

  

  4-02 
  

   5-30 
  

   6-36 
  

  

  432 
  

  

  5-85 
  

   1 
  6-60 
  

  

  4-61 
  

   6-42 
  

   695 
  

  

  0-8 
  

  

  5-0 
  

  

  15-0 
  

  

  By 
  the 
  aid 
  of 
  this 
  chart 
  actinometric 
  measures 
  may 
  be 
  cor- 
  

   rected 
  for 
  atmospheric 
  absorption 
  in 
  a 
  somewhat 
  rude 
  but 
  

   fairly 
  satisfactory 
  manner, 
  provided 
  a 
  sufiicient 
  body 
  of 
  data 
  

   exists 
  for 
  the 
  elimination 
  of 
  fluctuations 
  in 
  a 
  final 
  mean 
  value. 
  

   The 
  method 
  requires, 
  in 
  addition 
  to 
  the 
  actinometric 
  readings, 
  

   simultaneous 
  observations 
  of 
  the 
  atmospheric 
  aqueous 
  vapor. 
  

   By 
  rights 
  these 
  should 
  include 
  the 
  distribution 
  of 
  aqueous 
  

   vapor 
  through 
  a 
  considerable 
  part 
  of 
  the 
  air 
  column, 
  which 
  

   can 
  be 
  obtained 
  only 
  by 
  the 
  meteorological 
  records 
  of 
  high 
  

   kite-flights, 
  or 
  of 
  sounding 
  balloons. 
  In 
  the 
  absence 
  of 
  vapor 
  

   records 
  for 
  the 
  upper 
  air, 
  wide 
  fluctuations 
  in 
  the 
  computed 
  

   solar 
  constant 
  must 
  inevitably 
  be 
  found, 
  because 
  the 
  pressure 
  

   of 
  aqueous 
  vapor 
  at 
  the 
  earth's 
  surface 
  is 
  only 
  imperfectly 
  

   related 
  to 
  the 
  quantity 
  of 
  precipitable 
  and 
  absorbent 
  vapor 
  in 
  

   the 
  entire 
  air-column. 
  

  

  As 
  an 
  example 
  of 
  the 
  results 
  to 
  be 
  expected 
  from 
  this 
  chart, 
  

   I 
  take 
  at 
  random 
  from 
  volume 
  2 
  of 
  the 
  Annals 
  of 
  the 
  Smith- 
  

   sonian 
  Astrophysical 
  Observatory, 
  the 
  actinometric 
  observa- 
  

   tions 
  of 
  five 
  days 
  at 
  Washington, 
  merely 
  looking 
  out 
  to 
  get 
  a 
  

   considerable 
  range 
  in 
  the 
  pressure 
  of 
  aqueous 
  vapor 
  so 
  as 
  to 
  

   test 
  the 
  method. 
  The 
  recorded 
  data 
  are 
  insufficient 
  for 
  more 
  

   than 
  rough 
  approximations. 
  Only 
  one, 
  or 
  at 
  most 
  two 
  vapor 
  

   readings 
  (Aq.) 
  are 
  given 
  on 
  each 
  day. 
  In 
  these 
  examples, 
  

  

  * 
  For 
  which 
  see 
  " 
  A 
  Criterion 
  of 
  Accuracy 
  in 
  Measurements 
  of 
  Atmos- 
  

   pheric 
  Transmission 
  of 
  Solar 
  Radiation," 
  Astrophysical 
  Journal, 
  vol. 
  xxxvn, 
  

   p. 
  31, 
  January, 
  1913. 
  , 
  , 
  , 
  . 
  . 
  , 
  , 
  

  

  fEead 
  from 
  fig. 
  4 
  of 
  my 
  " 
  Criterion" 
  paper 
  just 
  cited, 
  and 
  checked 
  by 
  

   numerous 
  examples. 
  

  

  

  