﻿SOME 
  BIOLOGICAL 
  EFFECTS 
  OF 
  SOLAK 
  KADIATION 
  

  

  By 
  Brian 
  O'Brien 
  

  

  Institute 
  of 
  Optics 
  

   The 
  University 
  of 
  Rochester 
  

  

  [With 
  1 
  plate] 
  

  

  Man 
  and 
  the 
  higher 
  animals 
  depend 
  for 
  their 
  very 
  existence 
  upon 
  

   sunlight. 
  The 
  temperature 
  of 
  the 
  earth's 
  surface 
  and 
  of 
  the 
  earth's 
  

   atmosphere 
  is 
  maintained 
  within 
  limits 
  which 
  can 
  support 
  life 
  only 
  

   by 
  the 
  flood 
  of 
  radiation 
  which 
  comes 
  to 
  us 
  from 
  the 
  sun. 
  The 
  power 
  

   supply 
  for 
  all 
  air 
  movement, 
  all 
  winds, 
  everything 
  that 
  goes 
  to 
  make 
  

   up 
  weather, 
  is 
  this 
  same 
  solar 
  radiation. 
  Most 
  of 
  the 
  higher 
  animals 
  

   and 
  land 
  plants 
  can 
  survive 
  only 
  with 
  a 
  supply 
  of 
  fresh 
  water, 
  a 
  

   supply 
  which 
  exists 
  simply 
  because 
  of 
  sunlight. 
  Without 
  the 
  constant 
  

   working 
  of 
  the 
  distillation 
  plant 
  which 
  evaporates 
  water 
  from 
  the 
  

   sea 
  and 
  condenses 
  it 
  as 
  rain 
  and 
  snow 
  there 
  would 
  be 
  nothing 
  but 
  salt 
  

   water 
  on 
  the 
  face 
  of 
  the 
  earth. 
  This 
  distillation 
  plant 
  runs 
  purely 
  

   by 
  solar 
  heat. 
  

  

  But 
  our 
  dependence 
  upon 
  the 
  sun 
  goes 
  far 
  beyond 
  this. 
  Animals 
  

   cannot 
  by 
  themselves 
  synthesize 
  food 
  and 
  fuel. 
  Even 
  man 
  with 
  all 
  

   his 
  ingenuity 
  has 
  not 
  yet 
  learned 
  to 
  do 
  this. 
  He 
  can 
  convert 
  food 
  

   from 
  one 
  kind 
  to 
  another, 
  as 
  he 
  can 
  convert 
  fuel 
  into 
  altered 
  and 
  

   more 
  convenient 
  forms, 
  but 
  he 
  cannot 
  yet 
  create 
  either. 
  This 
  job 
  

   is 
  reserved 
  for 
  the 
  green 
  plants. 
  The 
  green 
  coloring 
  matter, 
  chlo- 
  

   rophyll, 
  permits 
  a 
  plant 
  to 
  utilize 
  sunlight 
  in 
  converting 
  carbon 
  

   dioxide 
  and 
  water 
  vapor 
  into 
  sugars, 
  starches, 
  and 
  cellulose. 
  This 
  

   process, 
  which 
  literally 
  unburns 
  our 
  coal 
  as 
  rapidly 
  as 
  an 
  active 
  

   human 
  race 
  can 
  burn 
  it, 
  supplies, 
  directly 
  or 
  indirectly, 
  all 
  the 
  food 
  

   and 
  fuel 
  available 
  on 
  the 
  earth. 
  Here 
  again, 
  through 
  the 
  medium 
  

   of 
  plant 
  life, 
  man 
  and 
  the 
  higher 
  animals 
  are 
  dependent 
  upon 
  radia- 
  

   tion 
  from 
  the 
  sun. 
  

  

  These 
  relations 
  of 
  sunlight 
  to 
  man 
  have 
  been 
  discussed 
  in 
  previous 
  

   Arthur 
  lectures. 
  Tonight 
  I 
  would 
  like 
  to 
  discuss 
  some 
  less 
  evident 
  

   effects 
  of 
  sunlight, 
  which, 
  though 
  subtler, 
  are 
  important 
  too. 
  These 
  

  

  1 
  The 
  tenth 
  Arthur 
  lecture, 
  given 
  under 
  the 
  auspices 
  of 
  the 
  Smithsonian 
  Institution, 
  

   February 
  25, 
  1941. 
  

  

  109 
  

  

  