﻿612 
  

  

  F. 
  W. 
  Very 
  — 
  Solar 
  Radiation. 
  

  

  erly 
  reduced 
  ; 
  but 
  it 
  is 
  impossible 
  to 
  reach 
  even 
  approximations 
  

   to 
  the 
  truth 
  by 
  such 
  methods 
  of 
  reduction 
  as 
  have 
  been 
  used 
  

   by 
  Pouillet, 
  or 
  by 
  Abbot 
  and 
  Fowle. 
  The 
  neglect 
  of 
  the 
  diur- 
  

   nal 
  variation 
  of 
  atmospheric 
  quality, 
  and 
  the 
  erroneous 
  suppo- 
  

   sition 
  that 
  the 
  same 
  coefficient 
  of 
  transmission 
  can 
  be 
  used 
  

   at 
  all 
  hours 
  of 
  the 
  day, 
  completely 
  vitiates 
  these 
  reductions. 
  

   Having 
  obtained 
  in 
  this 
  way 
  a 
  supposed 
  solar 
  constant 
  of 
  1*95 
  

   cal./sq. 
  cm. 
  min., 
  Mr. 
  Abbot 
  says 
  : 
  " 
  From 
  this, 
  T 
  = 
  5860° 
  

   Absolute 
  C. 
  As 
  this 
  value 
  falls 
  below 
  those 
  obtained 
  previ- 
  

   ously 
  [by 
  the 
  bolometric 
  method], 
  we 
  may 
  suppose 
  the 
  sun's 
  

   constant 
  of 
  emission 
  is 
  a 
  little 
  less 
  than 
  that 
  of 
  a 
  perfect 
  radi- 
  

   ator." 
  * 
  This 
  may 
  indeed 
  be 
  the 
  case, 
  and 
  the 
  exponent 
  of 
  T 
  

   in 
  Stefan's 
  law 
  possibly 
  differs 
  somewhat 
  from 
  4 
  for 
  a 
  body 
  of 
  

   solar 
  composition 
  and 
  temperature, 
  but 
  if 
  the 
  hypothesis 
  that 
  

   the 
  sun 
  is 
  a 
  perfect 
  radiator 
  can 
  be 
  tolerated 
  for 
  Mr. 
  Abbot's 
  

   use 
  in 
  the 
  bolometric 
  computation, 
  it 
  ought 
  to 
  be 
  good 
  enough 
  

   for 
  the 
  actinometric 
  one. 
  To 
  use 
  the 
  hypothesis 
  in 
  the 
  one 
  

   case, 
  and 
  reject 
  it 
  in 
  the 
  other, 
  is 
  not 
  admissible 
  ; 
  and 
  the 
  dis- 
  

   crepancy 
  between 
  the 
  temperatures 
  computed 
  on 
  this 
  basis 
  

   remains 
  as 
  a 
  contradiction 
  which 
  overthrows 
  the 
  alleged 
  deter- 
  

   mination 
  of 
  the 
  solar 
  constant 
  to 
  three 
  significant 
  figures. 
  

   "Warned 
  by 
  this 
  example, 
  we 
  shall 
  perhaps 
  do 
  well 
  not 
  to 
  

   attempt 
  the 
  assignment 
  of 
  a 
  definite 
  value 
  to 
  the 
  solar 
  constant 
  

   at 
  the 
  present 
  time 
  further 
  than 
  to 
  say 
  that 
  it 
  probably 
  lies 
  be- 
  

   tween 
  3 
  and 
  4, 
  and 
  apparently 
  not 
  far 
  from 
  3*5 
  or 
  3*6 
  gram 
  

   cal./sq. 
  cm. 
  min. 
  

  

  If 
  we 
  take 
  the 
  spectral 
  energy-curve 
  of 
  the 
  center 
  of 
  the 
  

   solar 
  disk, 
  corrected 
  for 
  instrumental 
  errors 
  and 
  approximately 
  

   for 
  the 
  absorption 
  of 
  the 
  earth's 
  atmosphere, 
  to 
  get 
  relative 
  

   values 
  which 
  are 
  correct 
  as 
  far 
  as 
  the 
  ratios 
  for 
  different 
  wave- 
  

   lengths 
  are 
  concerned, 
  the 
  maximum 
  ordinate 
  according 
  to 
  

   Abbotf 
  is 
  X 
  max 
  . 
  = 
  0'458/u-. 
  Applying 
  to 
  this 
  curve 
  the 
  appro- 
  

   priate 
  coefficients 
  of 
  transmission 
  by 
  the 
  sun's 
  atmosphere,^: 
  we 
  

   get 
  the 
  results 
  given 
  in 
  the 
  following 
  table 
  : 
  

  

  \ 
  

  

  0-3 
  

  

  0-4 
  

  

  0-5 
  

  

  0-6 
  

  

  0-7 
  

  

  0-8 
  

  

  0-9 
  

  

  1-0 
  

  

  1-5 
  

  

  20 
  

  

  a 
  

  

  b 
  

  

  0-008 
  

   0-05 
  

  

  0-372 
  

   0-18 
  

  

  0-490 
  

   0-29 
  

  

  0-405 
  

   0-37 
  

  

  0-308 
  

   0-43 
  

  

  0-226 
  

   0-475 
  

  

  0-157 
  

   0-51 
  

  

  0-120 
  

   0-54 
  

  

  0051 
  

   064 
  

  

  0-018 
  

   0-69 
  

  

  c 
  

  

  0-16 
  

  

  2-07 
  

  

  1-69 
  

  

  1-09 
  

  

  0-72 
  

  

  0-48 
  

  

  0-31 
  

  

  0-22 
  

  

  0-08 
  

  

  0-03 
  

  

  For 
  curve 
  c, 
  X 
  ma 
  x=0-41fJ.. 
  

  

  *Op. 
  cit., 
  p. 
  114. 
  

  

  f 
  The 
  Sun, 
  figure 
  26, 
  page 
  109. 
  

  

  X 
  Frank 
  W. 
  Very 
  : 
  " 
  The 
  Absorptive 
  Power 
  of 
  the 
  Solar 
  Atmosphere 
  " 
  — 
  Mis- 
  

   cellaneous 
  Papers 
  of 
  the 
  Allegheny 
  Observatory, 
  New 
  Series, 
  No. 
  9, 
  Table 
  5, 
  

   p. 
  18. 
  

  

  