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  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1929 
  

  

  solid, 
  able 
  to 
  bear 
  loads 
  indefinitely? 
  Where 
  is 
  it 
  weak, 
  so 
  weak 
  as 
  

   to 
  permit 
  movements 
  of 
  the 
  material 
  horizontally 
  and 
  vertically, 
  

   under 
  the 
  urge 
  of 
  moderate 
  internal 
  pressures? 
  

  

  These 
  questions 
  represent 
  fundamentals 
  of 
  the 
  new 
  earth-lore, 
  

   already 
  rapidly 
  growing 
  in 
  our 
  own 
  century 
  as 
  investigators 
  continue 
  

   to 
  employ 
  new 
  methods 
  of 
  research. 
  The 
  problems 
  are 
  largely 
  mat- 
  

   ters 
  for 
  the 
  physicist, 
  but 
  an 
  unusual 
  kind 
  of 
  physicist, 
  one 
  who 
  makes 
  

   experiments, 
  like 
  any 
  of 
  his 
  fellows, 
  but 
  keeps 
  thinking 
  of 
  a 
  whole 
  

   planet. 
  He 
  is 
  an 
  earth 
  physicist, 
  a 
  "geophysicist." 
  The 
  jnterpre- 
  

   tation 
  of 
  messages 
  from 
  the 
  earth's 
  interior 
  demands 
  all 
  the 
  resources 
  

   of 
  ordinary 
  physics 
  and 
  of 
  extraordinary 
  mathematics. 
  The 
  geo- 
  

   physicist 
  is 
  of 
  a 
  noble 
  company, 
  all 
  of 
  whom 
  are 
  reading 
  messages 
  

   from 
  the 
  untouchable 
  reality 
  of 
  things. 
  The 
  inwardness 
  of 
  things 
  — 
  

   atoms, 
  crystals, 
  mountains, 
  planets, 
  stars, 
  nebulas, 
  universes 
  — 
  is 
  the 
  

   quarry 
  of 
  these 
  hunters 
  of 
  genius 
  and 
  Promethean 
  boldness. 
  The 
  

   unseen 
  atom 
  has 
  been 
  shown 
  to 
  be 
  no 
  less 
  miraculous 
  than 
  the 
  invisible 
  

   interior 
  of 
  sun 
  or 
  star. 
  And 
  now, 
  lately, 
  the 
  inner 
  earth 
  as 
  a 
  whole 
  is 
  

   the 
  gripping 
  subject 
  of 
  research 
  for 
  some 
  of 
  the 
  intellectual 
  giants 
  of 
  

   our 
  time. 
  To 
  a 
  considerable 
  extent 
  the 
  methods 
  used 
  by 
  all 
  these 
  

   students 
  of 
  the 
  invisible, 
  the 
  essence 
  of 
  each 
  problem, 
  are 
  in 
  principle 
  

   the 
  same. 
  

  

  The 
  feature 
  common 
  to 
  most 
  of 
  the 
  productive 
  methods 
  is 
  the 
  use 
  

   of 
  waves, 
  vibrations, 
  rhythmic 
  motions. 
  From 
  the 
  interior 
  of 
  star 
  

   or 
  nebula 
  come 
  light 
  waves, 
  heat 
  waves, 
  and 
  whole 
  troops 
  of 
  different 
  

   unfelt 
  waves. 
  Each 
  of 
  these 
  waves, 
  whatever 
  its 
  nature, 
  radiates 
  

   through 
  the 
  "ether." 
  With 
  the 
  speed 
  of 
  light, 
  each 
  rushes 
  along 
  

   lines 
  that 
  are 
  always 
  perpendicular 
  to 
  the 
  front 
  of 
  the 
  wave. 
  These 
  

   lines 
  are 
  the 
  wave 
  paths 
  or 
  "rays" 
  of 
  the 
  astrophysicist. 
  In 
  the 
  

   exploration 
  of 
  the 
  universe 
  of 
  stars, 
  he 
  uses 
  light 
  rays, 
  actinic 
  rays, 
  

   heat 
  rays, 
  and 
  cosmic 
  rays 
  of 
  less 
  familiar 
  kinds. 
  The 
  exquisite 
  

   internal 
  architecture 
  of 
  crystals 
  is 
  being 
  rapidly 
  revealed 
  with 
  X 
  rays. 
  

   The 
  atom 
  is 
  becoming 
  understood 
  through 
  its 
  radiant 
  effects 
  and 
  

   through 
  experimenta,! 
  tests 
  with 
  external 
  rays. 
  

  

  So 
  it 
  is 
  with 
  the 
  new 
  study 
  of 
  the 
  earth 
  ; 
  its 
  profounder 
  exploration 
  

   is 
  possible 
  by 
  means 
  of 
  waves, 
  which 
  may 
  be 
  of 
  either 
  natural 
  or 
  arti- 
  

   ficial 
  origin. 
  Waves 
  extremely 
  short, 
  as 
  measured 
  from 
  "crest" 
  to 
  

   "crest," 
  are 
  the 
  X 
  rays, 
  used 
  in 
  learning 
  the 
  atomic 
  architecture 
  of 
  

   crystals. 
  The 
  somewhat 
  longer 
  waves 
  of 
  light 
  tell 
  us 
  about 
  the 
  nature 
  

   of 
  stars. 
  The 
  still 
  longer 
  sound 
  waves 
  are 
  now 
  used 
  to 
  give 
  the 
  depths 
  

   of 
  the 
  invisible 
  ocean 
  floor. 
  "Radio" 
  waves, 
  yet 
  longer, 
  are 
  telling 
  

   the 
  aerologists 
  much 
  about 
  the 
  nature 
  of 
  the 
  inaccessible, 
  upper 
  

   atmosphere. 
  For 
  the 
  study 
  of 
  the 
  earth's 
  skin, 
  to 
  the 
  depth 
  of 
  a 
  

   score 
  of 
  miles 
  or 
  so, 
  the 
  controlled 
  shocks 
  by 
  artificial 
  explosives, 
  

   which 
  give 
  elastic 
  waves 
  longer 
  than 
  even 
  "radio" 
  waves, 
  are 
  used. 
  

   Longest 
  of 
  all 
  are 
  the 
  elastic 
  waves 
  set 
  going 
  when 
  the 
  hammer 
  of 
  

  

  