﻿F. 
  W. 
  Very 
  — 
  Solar 
  Radiation. 
  611 
  

  

  in 
  this 
  part 
  of 
  the 
  spectrum 
  than 
  lampblack 
  and 
  similar 
  sub- 
  

   stances, 
  which 
  are 
  reputed 
  black 
  for 
  the 
  shorter 
  waves, 
  but 
  

   become 
  transparent 
  and 
  less 
  perfect 
  radiators 
  in 
  the 
  extreme 
  

   infra-red, 
  whereas 
  metals 
  at 
  high 
  temperatures 
  become 
  trans- 
  

   parent 
  for 
  the 
  short 
  waves 
  of 
  the 
  visible 
  spectrum. 
  Although 
  

   not 
  extending 
  to 
  as 
  great 
  wave-lengths 
  as 
  those 
  on 
  which 
  my 
  

   conclusions 
  were 
  based, 
  these 
  holographs 
  by 
  the 
  Smithsonian 
  

   observers 
  confirm 
  the 
  statement 
  in 
  a 
  general 
  way. 
  The 
  bolo- 
  

   metric 
  method 
  which 
  rests 
  on 
  the 
  shape 
  of 
  the 
  spectral 
  energy- 
  

   curve, 
  obviously 
  tends 
  to 
  underrate 
  the 
  solar 
  temperature 
  by 
  

   overestimating 
  the 
  importance 
  of 
  the 
  longer 
  waves, 
  and 
  shift- 
  

   ing 
  the 
  maximum 
  in 
  their 
  direction. 
  

  

  Referring 
  to 
  the 
  distribution 
  of 
  energy 
  computed 
  by 
  the 
  

   Wien-Planck 
  formula 
  for 
  temperatures 
  7000° 
  and 
  6200° 
  Abs. 
  

   C, 
  Mr. 
  Abbot 
  says 
  of 
  the 
  observed 
  curves 
  : 
  " 
  Their 
  infra-red 
  

   parts 
  correspond 
  to 
  much 
  hotter 
  sources 
  than 
  do 
  their 
  visible 
  

   and 
  ultra-violet 
  parts. 
  It 
  is 
  evident, 
  however, 
  that 
  the 
  7000° 
  

   curve, 
  except 
  in 
  the 
  ultra-violet, 
  is 
  a 
  better 
  match 
  for 
  the 
  

   observations 
  than 
  the 
  6200° 
  curve" 
  (The 
  Sun, 
  p. 
  112). 
  On 
  

   page 
  114 
  {op. 
  cit.), 
  the 
  solar 
  temperature 
  is 
  said 
  to 
  be 
  " 
  cer- 
  

   tainly 
  above 
  6200°, 
  and 
  possibly 
  near 
  7000° 
  " 
  ; 
  and 
  on 
  page 
  

   420, 
  " 
  it 
  seems 
  most 
  probable 
  that 
  the 
  photosptieric* 
  tempera- 
  

   ture 
  should 
  be 
  set 
  not 
  lower 
  than 
  6500° 
  Absolute." 
  

  

  We 
  shall 
  not 
  be 
  far 
  from 
  the 
  truth 
  if 
  we 
  take 
  the 
  effective 
  

   solar 
  temperature 
  as 
  6800° 
  Abs. 
  C, 
  which 
  gives 
  for 
  the 
  solar 
  

   constant 
  at 
  the 
  earth's 
  mean 
  distance 
  by 
  Stefan's 
  law, 
  

  

  A= 
  (6800) 
  4 
  X 
  1-267 
  X 
  (10)~ 
  12 
  X 
  60 
  X 
  sin 
  2 
  15' 
  59".63 
  

  

  = 
  3-518 
  gram 
  cal. 
  /sq. 
  cm. 
  min. 
  

  

  This 
  value 
  is 
  in 
  close 
  agreement 
  with 
  that 
  which 
  I 
  have 
  given 
  

   in 
  my 
  paper, 
  "A 
  High-level 
  Measurement 
  of 
  Solar 
  Radiation, 
  "f 
  

   founded 
  on 
  an 
  observation 
  by 
  Yiolle, 
  and 
  with 
  concordant 
  

   values 
  which 
  are 
  obtained 
  in 
  my 
  paper, 
  "A 
  Criterion 
  of 
  Accu- 
  

   racy 
  in 
  Measurements 
  of 
  Atmospheric 
  Transmission 
  of 
  Solar 
  

   Radiation," 
  $ 
  from 
  observations 
  by 
  Savelief 
  and 
  by 
  Kimball, 
  

   when 
  treated 
  by 
  a 
  modification 
  of 
  Crova's 
  method. 
  The 
  latter 
  

   values 
  have 
  been 
  obtained 
  by 
  actinometric 
  modes 
  which 
  are 
  

   thus 
  shown 
  to 
  be 
  capable 
  of 
  yielding 
  correct 
  results 
  when 
  prop- 
  

  

  * 
  Although 
  continuing 
  to 
  use 
  the 
  word 
  " 
  photospheric," 
  Mr. 
  Abbot 
  rejects 
  

   the 
  usual 
  conception 
  of 
  a 
  layer 
  of 
  opaque, 
  incandescent 
  cloud 
  at 
  a 
  definite 
  

   level, 
  and 
  holds 
  that 
  the 
  solar 
  radiation 
  conies 
  entirely 
  from 
  layers 
  of 
  rela- 
  

   tively, 
  but 
  still 
  imperfectly, 
  transparent 
  gas 
  at 
  various 
  depths 
  ; 
  that 
  is 
  to 
  say, 
  

   he 
  denies 
  that 
  there 
  is 
  any 
  basal 
  layer 
  giving 
  a 
  continuous 
  spectrum, 
  or 
  any 
  

   continuous 
  spectrum 
  other 
  than 
  a 
  virtual 
  one 
  produced 
  by 
  the 
  broadening 
  of 
  

   gaseous 
  emission 
  lines 
  through 
  pressure. 
  This 
  point 
  needs 
  separate 
  discus- 
  

   sion, 
  which 
  can 
  not 
  be 
  attempted 
  here. 
  It 
  is 
  sufficient 
  to 
  note 
  that 
  the 
  " 
  pho- 
  

   tospheric 
  " 
  temperature 
  in 
  the 
  above 
  quotation 
  is 
  not 
  distinguished 
  from 
  

   the 
  effective 
  solar 
  temperature.- 
  

  

  f 
  Astrophysical 
  Journal, 
  vol. 
  xxxvii, 
  p. 
  25, 
  January, 
  1913. 
  

  

  {Ibid., 
  p. 
  31, 
  January, 
  1913. 
  

  

  