﻿284 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  which 
  would 
  produce 
  a 
  corresponding 
  modification 
  of 
  the 
  earth's 
  

   climates. 
  This 
  purely 
  fanciful 
  conception 
  need 
  not 
  detain 
  us, 
  for 
  

   space 
  can 
  have 
  no 
  temperature, 
  which 
  is 
  a 
  property 
  of 
  matter. 
  That 
  

   the 
  earth 
  could 
  have 
  received 
  an 
  appreciable 
  amount 
  of 
  heat 
  from 
  

   some 
  luminary 
  other 
  than 
  the 
  sun 
  would 
  involve 
  so 
  near 
  an 
  ap- 
  

   proach 
  to 
  another 
  star 
  as 
  to 
  upset 
  the 
  equilibrium 
  of 
  the 
  solar 
  

   system. 
  

  

  B. 
  By 
  a 
  process 
  of 
  elimination 
  we 
  seem 
  to 
  be 
  shut 
  up 
  to 
  the 
  con- 
  

   clusion 
  that 
  Ave 
  must 
  look 
  for 
  the 
  primary 
  causes 
  of 
  changes 
  in 
  the 
  

   earth's 
  climates 
  in 
  the 
  sun 
  itself, 
  as 
  originally 
  suggested 
  by 
  Lord 
  

   Kehdn. 
  As 
  we 
  have 
  just 
  seen, 
  the 
  various 
  terrestrial 
  agencies 
  

   which 
  have 
  been 
  called 
  on 
  to 
  explain 
  these 
  changes 
  are 
  inadequate 
  

   of 
  themselves, 
  while 
  changes 
  in 
  the 
  sun 
  would 
  have 
  universal 
  effects. 
  

   The 
  connection 
  between 
  the 
  sun-spot 
  cycles 
  and 
  terrestrial 
  weather 
  

   has 
  long 
  been 
  recognized, 
  and 
  the 
  Smithsonian 
  observatory, 
  under 
  

   the 
  direction 
  of 
  Doctor 
  Abbot, 
  has 
  shown 
  that 
  variations 
  in 
  solar 
  

   radiation 
  do 
  actually 
  occur, 
  and 
  to 
  a 
  surprising 
  amount, 
  from 
  day 
  

   to 
  day, 
  as 
  well 
  as 
  through 
  longer 
  periods. 
  The 
  observing 
  stations 
  

   have 
  been 
  operated 
  in 
  regions 
  of 
  different 
  climates 
  and 
  altitudes, 
  

   so 
  as 
  to 
  do 
  away 
  with 
  the 
  confusing 
  effects 
  of 
  the 
  earth's 
  atmosphere. 
  

   The 
  work 
  is 
  still 
  in 
  progress, 
  and 
  Doctor 
  Abbot 
  has 
  lately 
  been 
  

   in 
  Africa 
  searching 
  for 
  a 
  satisfactory 
  site 
  on 
  which 
  to 
  place 
  another 
  

   control 
  station, 
  and 
  we 
  may 
  hope 
  soon 
  to 
  have 
  a 
  body 
  of 
  established 
  

   facts 
  concerning 
  solar 
  activity 
  which 
  will 
  be 
  most 
  useful 
  in 
  the 
  so- 
  

   lution 
  of 
  our 
  problem. 
  The 
  manner 
  in 
  which 
  solar 
  changes 
  operate 
  

   on 
  the 
  earth 
  is 
  a 
  very 
  complicated 
  one, 
  and 
  if 
  these 
  changes 
  are 
  of 
  no 
  

   very 
  great 
  amount 
  they 
  would 
  produce 
  different 
  effects 
  in 
  the 
  various 
  

   climxatic 
  zones. 
  This 
  has 
  been 
  well 
  brought 
  out 
  by 
  Mr. 
  Clayton 
  in 
  

   a 
  paper 
  read 
  last 
  April 
  before 
  the 
  National 
  Academy 
  of 
  Sciences. 
  

  

  As 
  Jeffreys 
  has 
  j^ointed 
  out, 
  any 
  hypothesis 
  of 
  this 
  type 
  is 
  very 
  

   difficult 
  either 
  to 
  prove 
  or 
  to 
  disprove 
  ; 
  but 
  we 
  do 
  know 
  that 
  the 
  earth's 
  

   temperature 
  depends 
  on 
  the 
  sun, 
  and 
  that 
  the 
  sun's 
  activity 
  is 
  vari- 
  

   able 
  — 
  not 
  a 
  long, 
  slow 
  decline. 
  Hence 
  arises 
  the 
  probability 
  that 
  

   solar 
  changes 
  are 
  the 
  principal 
  cause 
  of 
  the 
  earth's 
  variations 
  of 
  

   clj-mate. 
  This 
  conclusion 
  does 
  not 
  preclude 
  the 
  acceptance 
  of 
  the 
  ter- 
  

   restrial 
  agencies 
  as 
  modifying 
  the 
  effects 
  of 
  solar 
  change. 
  Assum- 
  

   ing 
  the 
  effectiveness 
  of 
  the 
  latter, 
  the 
  Pleistocene 
  history 
  of 
  the 
  South- 
  

   ern 
  Hemisphere 
  well 
  illustrates 
  such 
  modifying 
  effect. 
  The 
  vast 
  area 
  

   of 
  the 
  seas 
  and 
  the 
  relatively 
  small 
  land 
  surfaces 
  produce 
  an 
  oceanic 
  

   climate 
  in 
  which 
  extremes 
  of 
  heat 
  and 
  cold 
  are 
  rare. 
  All 
  down 
  the 
  

   west 
  coast 
  of 
  southern 
  Chile 
  and 
  Tierra 
  del 
  Fuego, 
  almost 
  to 
  Cape 
  

   Horn, 
  we 
  find 
  an 
  evergreen 
  rain 
  forest 
  of 
  deciduous 
  trees, 
  most 
  of 
  

   which 
  belong 
  to 
  a 
  single 
  species 
  of 
  the 
  southern 
  beech 
  {Nothofagus). 
  

   In 
  this 
  region 
  there 
  is 
  little 
  difference 
  between 
  winter 
  and 
  sununer; 
  

  

  