﻿RECENT 
  DEVELOPMENTS 
  OF 
  COSMICAL 
  PHYSICS^ 
  

  

  By 
  J. 
  II. 
  .Teians 
  

  

  Until 
  recent 
  years, 
  astronomy 
  was 
  concerned 
  almost 
  entirely 
  with 
  

   the 
  sun, 
  moon, 
  and 
  planets; 
  the 
  stars 
  were 
  mere 
  points 
  of 
  light 
  so 
  

   inconceivably 
  remote 
  as 
  to 
  bo 
  of 
  only 
  minor 
  interest. 
  To-day 
  Urania 
  

   has 
  wearied 
  of 
  the 
  speck 
  of 
  dust 
  we 
  call 
  the 
  solar 
  system, 
  and 
  claims 
  

   the 
  whole 
  universe 
  for 
  her 
  playground; 
  the 
  astronomer's 
  interest 
  

   centers 
  almost 
  exclusively 
  on 
  the 
  stars. 
  The 
  dynamical 
  astronomer, 
  

   for 
  example, 
  having 
  lost 
  interest 
  in 
  the 
  motions 
  of 
  the 
  planets 
  and 
  

   their 
  satellites, 
  studies 
  the 
  arrangement 
  and 
  motions 
  of 
  the 
  stars 
  in 
  

   the 
  hope 
  of 
  discovering 
  the 
  general 
  plan 
  at 
  least 
  of 
  the 
  architecture 
  

   and 
  mechanism 
  of 
  the 
  universe; 
  for 
  him 
  the 
  whole 
  universe 
  is 
  a 
  

   single 
  d3'namical 
  system 
  formed 
  of 
  innumerable 
  particles 
  — 
  the 
  stars 
  — 
  

   each 
  of 
  which 
  attracts 
  each 
  other 
  according 
  to 
  the 
  universal 
  law 
  of 
  

   gravitation. 
  

  

  The 
  physical 
  astronomer 
  finds 
  a 
  different 
  interest 
  in 
  the 
  stars. 
  

   For 
  him 
  each 
  separate 
  star 
  is 
  a 
  complete 
  physical 
  system 
  : 
  it 
  is 
  a 
  

   crucible 
  in 
  which 
  matter 
  is 
  subjected 
  to 
  temperatures 
  and 
  pressures 
  

   far 
  beyond 
  any 
  available 
  to 
  the 
  terrestrial 
  physicist. 
  From 
  a 
  study 
  

   of 
  the 
  radiation 
  emitted 
  by 
  the 
  stars, 
  the 
  ph^^sical 
  astronomer 
  tries 
  to 
  

   unravel 
  their 
  physical 
  structure, 
  to 
  discover 
  how 
  they 
  generate 
  their 
  

   energy, 
  and 
  by 
  what 
  mechanism 
  this 
  energy 
  is 
  transniitted 
  to 
  their 
  

   surfaces 
  and 
  discharged 
  into 
  si)ace 
  as 
  radiation. 
  In 
  this 
  way 
  he 
  may 
  

   perchance 
  happen 
  upon 
  properties 
  of 
  matter 
  which 
  have 
  eluded 
  the 
  

   terrestrial 
  physicist 
  owing 
  to 
  the 
  small 
  range 
  of 
  physical 
  conditions 
  

   at 
  his 
  command. 
  If 
  the 
  simile 
  ma}^ 
  be 
  pardoned, 
  on 
  the 
  plea 
  that 
  

   it 
  is 
  at 
  least 
  true 
  to 
  scale, 
  the 
  animalculse 
  which 
  inhabit 
  a 
  raindrop 
  

   may 
  learn 
  something 
  of 
  the 
  properties 
  of 
  water 
  by 
  manipulating 
  the 
  

   particles 
  of 
  the 
  raindrop 
  with 
  their 
  puny 
  strength, 
  but 
  they 
  may 
  also 
  

   learn 
  something 
  by 
  watching 
  the 
  uncontrollable 
  fall 
  of 
  torrents 
  over 
  

   Niagara. 
  The 
  primary 
  study 
  of 
  the 
  physical 
  astronomer 
  is 
  precisely 
  

   this 
  external 
  fall 
  of 
  torrents 
  over 
  Niagara; 
  his 
  ultimate 
  aim 
  is 
  to 
  

   weld 
  cosmical 
  physics 
  onto 
  terrestrial 
  physics 
  so 
  as 
  to 
  form 
  one 
  all- 
  

   embracing 
  science. 
  Only 
  when 
  this 
  has 
  been 
  done 
  will 
  it 
  be 
  possible 
  

   to 
  understand 
  the 
  main 
  trend 
  of 
  events 
  in 
  the 
  physical 
  universe. 
  

  

  'A 
  lecture 
  delivered 
  at 
  University 
  College, 
  London, 
  on 
  Nov. 
  9, 
  1926. 
  Reprinted 
  by 
  per- 
  

   mission 
  from 
  Supplement 
  to 
  Nature, 
  Dec. 
  4, 
  1926. 
  

  

  167 
  

  

  