﻿F. 
  W. 
  Very 
  — 
  Solar 
  JRadiation. 
  631 
  

  

  vapor 
  in 
  the 
  air, 
  ought 
  to 
  appear 
  in 
  the 
  separate 
  values 
  of 
  A 
  

   for 
  a 
  given 
  date, 
  since 
  no 
  attempt 
  has 
  been 
  made 
  to 
  eliminate 
  

   the 
  diurnal 
  change 
  of 
  quality, 
  and 
  the 
  depression 
  does 
  appear 
  

   in 
  the 
  Mt. 
  Wilson 
  reductions 
  ; 
  but 
  there 
  is 
  little 
  evidence 
  of 
  

   this 
  feature 
  in 
  the 
  reductions 
  for 
  Washington, 
  D.G., 
  whence 
  

   we 
  must 
  conclude 
  that 
  the 
  ordinates 
  of 
  the 
  sea-level 
  curves, 
  e 
  = 
  1 
  

   and 
  e 
  = 
  2 
  (full 
  lines), 
  which 
  are 
  most 
  used 
  in 
  the 
  midday 
  reduc- 
  

   tions, 
  are 
  relatively 
  a 
  little 
  too 
  high 
  (i.e. 
  the 
  curves 
  for 
  e 
  = 
  3 
  and 
  4 
  

   should 
  be 
  raised 
  a 
  little), 
  and 
  that 
  the 
  chart 
  automatically, 
  but 
  

   unintentionally 
  and 
  indirectly, 
  obliterates 
  the 
  depression 
  to 
  a 
  

   great 
  extent 
  at 
  sea 
  level. 
  By 
  comparing 
  numerous 
  radiation 
  

   measures 
  for 
  vapor 
  pressures 
  ranging 
  between 
  5 
  and 
  15 
  ram 
  , 
  

   mid4ay 
  radiations 
  of 
  solar 
  radiations 
  covering 
  Q-% 
  cal. 
  in 
  ther- 
  

   mal 
  equivalent 
  may 
  be 
  found, 
  but 
  the 
  most 
  potent 
  influence 
  

   of 
  aqueous 
  vapor 
  does 
  not 
  begin 
  to 
  appear 
  until 
  vapor 
  pres- 
  

   sures 
  much 
  less 
  than 
  l 
  mm 
  are 
  reached. 
  

  

  The 
  need 
  of 
  rational 
  methods 
  and 
  of 
  judicious 
  selection 
  of 
  

   material 
  according 
  to 
  reliable 
  criteria 
  was 
  never 
  more 
  pressing 
  

   than 
  in 
  the 
  reduction 
  of 
  observations 
  of 
  solar 
  radiation. 
  The 
  

   treatment 
  of 
  climatic 
  problems 
  involving 
  radiant 
  functions 
  has 
  

   been 
  vitiated 
  by 
  indiscriminate 
  averaging 
  of 
  statistic 
  in 
  which 
  

   delicate 
  details, 
  whose 
  preservation 
  is 
  important, 
  have 
  been 
  

   swamped. 
  Professor 
  Simon 
  Newcomb, 
  in 
  an 
  elaborate 
  memoir 
  

   of 
  seventy-nine 
  quarto 
  pages, 
  " 
  A 
  Search 
  for 
  Fluctuations 
  in 
  

   the 
  Sun's 
  Thermal 
  Radiation 
  through 
  their 
  Influence 
  on 
  Ter- 
  

   restrial 
  Temperature," 
  * 
  arrived 
  at 
  the 
  result 
  that 
  no 
  solar 
  radi- 
  

   ant 
  variations 
  of 
  sensible 
  amount 
  can 
  be 
  recognized 
  by 
  their 
  

   effect 
  on 
  climate. 
  He 
  concluded 
  that 
  " 
  all 
  the 
  ordinary 
  phe- 
  

   nomena 
  of 
  temperature, 
  rainfall 
  and 
  winds 
  are 
  due 
  to 
  purely 
  

   terrestrial 
  causes 
  and 
  that 
  no 
  changes 
  occur 
  in 
  the 
  sun's 
  radia- 
  

   tion 
  which 
  have 
  any 
  influence 
  upon 
  them" 
  (p. 
  384). 
  

  

  The 
  fundamental 
  principles 
  assumed 
  in 
  Newcotnb's 
  work 
  may 
  

   be 
  seen 
  from 
  the 
  following 
  quotations 
  : 
  " 
  A 
  change 
  in 
  the 
  sun's 
  

   radiation 
  will 
  necessarily 
  affect 
  every 
  part 
  of 
  the 
  earth. 
  If 
  

   therefore 
  a 
  change 
  of 
  temperature 
  in 
  one 
  region 
  has 
  this 
  cause 
  

   as 
  a 
  factor, 
  we 
  may, 
  accidental 
  causes 
  aside, 
  expect 
  a 
  similar 
  

   change 
  in 
  every 
  other 
  region. 
  ... 
  To 
  speak 
  more 
  precisely, 
  

   if, 
  on 
  any 
  one 
  day, 
  it 
  is 
  found 
  that 
  the 
  temperature 
  in 
  every 
  

   part 
  of 
  the 
  earth 
  is 
  in 
  the 
  general 
  average 
  above 
  or 
  below 
  the 
  

   normal, 
  we 
  might 
  rationally 
  attribute 
  this 
  result 
  to 
  the 
  sun. 
  

   We 
  thus 
  see 
  that 
  a 
  very 
  obvious 
  way 
  of 
  testing 
  the 
  constancy 
  

   of 
  the 
  solar 
  radiation 
  is 
  to 
  determine 
  the 
  deviation 
  of 
  the 
  

  

  * 
  Transactions 
  of 
  the 
  American 
  Philosophical 
  Society, 
  N.S., 
  vol. 
  xxi, 
  Part 
  5, 
  

   pp. 
  309-387, 
  1908. 
  The 
  distinction 
  of 
  " 
  thermal 
  " 
  radiation 
  is 
  superfluous, 
  

   since 
  all 
  radiation 
  is 
  capable 
  of 
  producing 
  thermal 
  effects. 
  The 
  word 
  was 
  

   not 
  introduced 
  in 
  the 
  obsolete 
  sense 
  of 
  " 
  infra-red, 
  ' 
  ? 
  but 
  to 
  distinguish 
  

   ordinary 
  radiation 
  from 
  possible 
  " 
  magnetic 
  or 
  radio-active 
  emanations, 
  

   whatever 
  they 
  may 
  be 
  " 
  (p. 
  382). 
  

  

  