﻿EFFECTS 
  OF 
  SOLAR 
  RADIATION 
  — 
  O'BRIEN 
  115 
  

  

  tomic 
  oxygen, 
  located 
  somewhere 
  in 
  the 
  earth's 
  atmosphere. 
  Since 
  

   only 
  traces 
  of 
  ozone 
  could 
  be 
  detected 
  in 
  the 
  atmosphere 
  at 
  the 
  earth's 
  

   surface, 
  Hartley 
  concluded 
  that 
  the 
  ozone 
  must 
  be 
  at 
  a 
  considerable 
  

   elevation. 
  In 
  1920 
  Fabry 
  and 
  Buisson, 
  at 
  the 
  University 
  of 
  Mar- 
  

   seilles, 
  measured 
  the 
  ultraviolet 
  end 
  of 
  the 
  sun's 
  spectrum 
  very 
  care- 
  

   fully, 
  and 
  from 
  these 
  measurements 
  and 
  previous 
  laboratory 
  measure- 
  

   ments 
  which 
  they 
  had 
  made 
  upon 
  known 
  amounts 
  of 
  ozone, 
  concluded 
  

   that 
  the 
  total 
  amount 
  in 
  the 
  earth's 
  atmosphere 
  was 
  equal 
  to 
  a 
  layer 
  of 
  

   the 
  pure 
  gas 
  about 
  3 
  millimeters 
  thick 
  at 
  standard 
  temperature 
  and 
  

   pressure. 
  Subsequent 
  measurements 
  have 
  confirmed 
  this, 
  and 
  we 
  now 
  

   know 
  that 
  ozone 
  is 
  distributed 
  in 
  the 
  earth's 
  atmosphere 
  in 
  amounts 
  

   dependent 
  upon 
  the 
  latitude 
  and 
  the 
  season 
  of 
  the 
  year. 
  This 
  is 
  im- 
  

   portant 
  to 
  us, 
  since 
  fluctuation 
  in 
  this 
  amount 
  of 
  ozone 
  causes 
  a 
  very 
  

   large 
  fluctuation 
  in 
  the 
  amount 
  of 
  ultraviolet 
  light 
  reaching 
  the 
  earth's 
  

   surface 
  at 
  the 
  limit 
  of 
  the 
  sun's 
  spectrum. 
  

  

  The 
  profound 
  effect 
  of 
  ozone 
  is 
  evident 
  from 
  an 
  examination 
  of 
  its 
  

   absorption 
  spectrum. 
  This 
  is 
  shown 
  in 
  figure 
  3 
  in 
  the 
  form 
  of 
  a 
  plot 
  

   of 
  optical 
  density 
  (logarithm 
  to 
  the 
  base 
  10 
  of 
  the 
  reciprocal 
  of 
  the 
  

   transmission) 
  as 
  a 
  function 
  of 
  wave 
  length. 
  The 
  very 
  rapid 
  increase 
  

   in 
  absorption 
  at 
  wave 
  lengths 
  below 
  3200 
  angstroms 
  is 
  evident 
  from 
  an 
  

   inspection 
  of 
  this 
  curve. 
  

  

  Recently 
  automatic 
  instruments 
  have 
  been 
  devised 
  for 
  measuring 
  

   by 
  spectroscopic 
  means 
  the 
  amount 
  of 
  ozone 
  over 
  any 
  given 
  station 
  and 
  

   recording 
  this 
  amount 
  from 
  hour 
  to 
  hour. 
  As 
  might 
  be 
  expected, 
  fluc- 
  

   tuations 
  do 
  occur, 
  although 
  the 
  average 
  amounts 
  for 
  any 
  given 
  week 
  

   or 
  month 
  appear 
  to 
  follow 
  the 
  general 
  seasonal 
  and 
  latitude 
  distri- 
  

   bution. 
  In 
  figure 
  4 
  is 
  shown 
  the 
  day-to-day 
  variation 
  of 
  ozone 
  in 
  a 
  

   zenith 
  atmosphere 
  over 
  Rochester, 
  N. 
  Y. 
  (latitude 
  43° 
  7' 
  N.), 
  for 
  4 
  

   weeks 
  in 
  the 
  summer. 
  The 
  two 
  curves 
  labeled 
  "3050 
  A." 
  and 
  "3110 
  A." 
  

   are 
  simply 
  independent 
  determinations 
  of 
  the 
  same 
  quantity 
  and 
  will 
  

   be 
  seen 
  to 
  be 
  very 
  consistent. 
  

  

  Not 
  only 
  the 
  amount 
  of 
  ozone 
  in 
  a 
  zenith 
  atmosphere 
  but 
  the 
  angle 
  

   at 
  which 
  the 
  sun's 
  rays 
  pass 
  through 
  the 
  atmosphere 
  is 
  of 
  importance 
  

   in 
  determining 
  the 
  ozone 
  absorption. 
  This 
  will 
  be 
  evident 
  from 
  con- 
  

   sidering 
  the 
  path 
  of 
  solar 
  rays 
  through 
  the 
  atmosphere 
  when 
  the 
  sun 
  

   is, 
  say, 
  30° 
  above 
  the 
  horizon. 
  For 
  this 
  condition 
  (a 
  zenith 
  angle 
  of 
  

   60°) 
  the 
  light 
  path 
  will 
  be 
  increased 
  by 
  the 
  secant 
  of 
  60°, 
  or 
  by 
  a 
  

   factor 
  of 
  2. 
  This 
  is 
  referred 
  to 
  as 
  air 
  mass 
  2, 
  air 
  mass 
  1 
  being 
  the 
  

   mass 
  of 
  air 
  through 
  which 
  light 
  must 
  travel 
  in 
  passing 
  through 
  a 
  

   zenith 
  atmosphere. 
  

  

  A 
  striking 
  example 
  of 
  the 
  influence 
  of 
  sunlight 
  upon 
  man 
  is 
  found 
  

   in 
  the 
  disease 
  of 
  rickets. 
  Affecting 
  infants 
  and 
  young 
  children, 
  it 
  

   was 
  long 
  known 
  to 
  be 
  associated 
  with 
  dietary 
  deficiencies 
  and 
  par- 
  

   ticularly 
  with 
  a 
  deficiency 
  of 
  fats. 
  Cod-liver 
  oil 
  was 
  known 
  to 
  be 
  an 
  

  

  