﻿610 
  F. 
  W. 
  Very 
  — 
  Solar 
  Radiation. 
  

  

  than 
  a 
  moderately 
  close 
  estimate 
  at 
  the 
  best, 
  or 
  than 
  a 
  very 
  

   unfortunate 
  guess 
  at 
  the 
  worst. 
  The 
  ablest 
  investigators, 
  and 
  

   those 
  whose 
  opinions 
  on 
  the 
  subject 
  deserve 
  the 
  greatest 
  

   weight, 
  have 
  said 
  either 
  that 
  the 
  solar 
  constant 
  can 
  never 
  be 
  

   found 
  in 
  any 
  exactly 
  mathematical 
  sense, 
  or 
  that 
  its 
  value 
  is 
  

   best 
  stated 
  with 
  a 
  very 
  wide 
  margin 
  of 
  probable 
  error. 
  

  

  Of 
  the 
  two 
  methods 
  named, 
  the 
  second 
  is 
  least 
  encumbered 
  

   by 
  difficulties 
  from 
  transmissive 
  theory, 
  and 
  thougii 
  circumlo- 
  

   cutory, 
  it 
  is 
  in 
  many 
  respects 
  to 
  be 
  preferred. 
  The 
  radiant 
  

   losses 
  which 
  are 
  most 
  difficult 
  to 
  estimate 
  are 
  those 
  which 
  

   affect 
  all 
  wave-lengths 
  equally, 
  or 
  nearly 
  so. 
  But 
  these 
  losses 
  

   make 
  very 
  little 
  change 
  in 
  the 
  form 
  of 
  the 
  spectral 
  energy- 
  

   curve, 
  and 
  the 
  position 
  of 
  the 
  maximum 
  energy 
  (X 
  max 
  ) 
  will 
  

   scarcely 
  be 
  altered 
  by 
  their 
  neglect. 
  In 
  fact, 
  the 
  chief 
  source 
  

   of 
  uneasiness 
  to 
  the 
  investigator 
  of 
  the 
  spectrum 
  lies 
  in 
  the 
  

   possible 
  existence 
  of 
  a 
  diffuse 
  atmospheric 
  absorption 
  band 
  

   very 
  near 
  to 
  this 
  maximum 
  ordinate 
  of 
  the 
  spectral 
  energy- 
  

   curve. 
  There 
  is 
  considerable 
  evidence 
  of 
  just 
  such 
  a 
  band, 
  

   and 
  a 
  variable 
  one 
  at 
  that 
  ; 
  but 
  conceding 
  that 
  some, 
  at 
  any 
  

   rate, 
  of 
  the 
  observations 
  may 
  have 
  escaped 
  fatal 
  infection 
  from 
  

   this 
  source, 
  and 
  admitting 
  that 
  there 
  are 
  probably 
  no 
  better 
  

   curves 
  than 
  those 
  which 
  have 
  been 
  published 
  by 
  Abbot 
  and 
  

   Fowle, 
  of 
  which 
  a 
  sample 
  is 
  given 
  in 
  figure 
  26 
  of 
  Abbot's 
  

   work 
  on 
  " 
  The 
  Sun," 
  we 
  may 
  push 
  this 
  method 
  for 
  all 
  it 
  is 
  

   worth. 
  I 
  can 
  not 
  do 
  better 
  than 
  to 
  quote 
  from 
  the 
  last- 
  

   mentioned 
  work 
  ; 
  but 
  first 
  let 
  me 
  call 
  attention 
  to 
  the 
  follow- 
  

   ing 
  point. 
  

  

  In 
  a 
  publication 
  on 
  " 
  The 
  Solar 
  Constant 
  "* 
  I 
  noted 
  that 
  the 
  

   extreme 
  infra-red 
  spectrum 
  is 
  much 
  more 
  intense 
  than 
  would 
  

   be 
  expected 
  from 
  a 
  theoretical 
  spectral 
  energy-curve, 
  for 
  such 
  

   temperatures 
  as 
  are 
  indicated 
  by 
  the 
  position 
  of 
  maximum 
  

   energy 
  in 
  the 
  spectrum, 
  and 
  I 
  attributed 
  this 
  divergence 
  to 
  the 
  

   fact 
  that 
  the 
  solar 
  radiation 
  is 
  the 
  sum 
  of 
  emissions 
  from 
  layers 
  

   at 
  various 
  depths 
  and 
  having 
  a 
  wide 
  range 
  of 
  temperature. 
  

   Thus 
  the 
  very 
  intense 
  radiations 
  of 
  short 
  wave-length 
  from 
  the 
  

   deeper 
  layers 
  are 
  greatly 
  absorbed 
  by 
  more 
  elevated 
  layers 
  of 
  

   the 
  solar 
  atmosphere, 
  which 
  are 
  heated 
  thereby 
  and 
  radiate 
  in 
  

   turn, 
  but 
  at 
  a 
  lower 
  temperature 
  and 
  longer 
  wave-length, 
  

   besides 
  transmitting 
  the 
  long-waved 
  emissions 
  from 
  the 
  deeper 
  

   layers 
  more 
  freely, 
  so 
  that 
  the 
  long 
  waves 
  escape 
  more 
  readily 
  

   than 
  the 
  short 
  ones. 
  This 
  peculiarity 
  may 
  also 
  be 
  due 
  in 
  part 
  

   to 
  the 
  predominance 
  in 
  the 
  sun 
  of 
  metals 
  having 
  positive 
  

   coefficients 
  of 
  resistance 
  which 
  radiate 
  long 
  infra-red 
  waves 
  at 
  

   high 
  temperatures 
  with 
  greater 
  intensity 
  than 
  black 
  substances 
  

   do, 
  or 
  which 
  more 
  nearly 
  approach 
  the 
  ideal 
  " 
  black 
  " 
  radiator 
  

  

  * 
  U. 
  S. 
  Weather 
  Bureau 
  Publication, 
  No. 
  254, 
  pp. 
  22-23, 
  1901. 
  

  

  