﻿MODERN" 
  ASTRONOMY 
  ABBOT 
  159 
  

  

  demands 
  which 
  biologists 
  and 
  geologists 
  may 
  be 
  led 
  to 
  make 
  from 
  

   their 
  studies 
  of 
  existing 
  life 
  and 
  the 
  paleontological 
  records 
  of 
  the 
  

   past. 
  

  

  The 
  surface 
  temperatures 
  of 
  the 
  stars 
  are 
  estimated 
  by 
  measuring 
  

   the 
  distribution 
  of 
  the 
  energy 
  of 
  their 
  radiation 
  in 
  the 
  spectrum. 
  

   As 
  the 
  blacksmith's 
  iron 
  glows 
  with 
  a 
  different 
  color 
  according 
  to 
  

   the 
  degree 
  of 
  its 
  heat, 
  so 
  do 
  the 
  stars. 
  Laboratory 
  experiments 
  have 
  

   developed 
  laws 
  and 
  foirmulae, 
  connecting 
  the 
  temperatures 
  and 
  

   energy 
  spectra 
  of 
  sources, 
  which, 
  like 
  the 
  stars, 
  emit 
  continuous 
  

   spectra. 
  It 
  is 
  by 
  applying 
  these 
  relations 
  that 
  star 
  temperatures 
  are 
  

   determined. 
  

  

  The 
  surface 
  temperatures 
  of 
  the 
  hotter 
  stars 
  exceed 
  any 
  which 
  we 
  

   are 
  able 
  to 
  maintain 
  continuously 
  in 
  the 
  laboratory. 
  Hence 
  it 
  is 
  

   very 
  useful 
  that 
  Anderson 
  has 
  recently 
  invented 
  a 
  method 
  of 
  explod- 
  

   ing 
  wires 
  by 
  tremendous 
  electric 
  discharges, 
  able 
  to 
  yield 
  instan- 
  

   taneous 
  temperatures 
  of 
  20,000° 
  to 
  30,000°. 
  This 
  permits 
  the 
  experi- 
  

   mental 
  study 
  of 
  radiation 
  from 
  such 
  hot 
  sources. 
  

  

  It 
  was 
  a 
  mystery 
  until 
  recently 
  why 
  the 
  profusion 
  of 
  intense 
  

   Fraunhofer 
  lines 
  which 
  exist 
  in 
  the 
  spectra 
  of 
  yellow 
  stars, 
  like 
  

   our 
  sun, 
  should 
  yield 
  to 
  fainter 
  and 
  fewer 
  lines 
  for 
  still 
  hotter 
  

   stars. 
  Indeed, 
  in 
  the 
  blue 
  stars 
  of 
  Type 
  BO 
  the 
  visible 
  and 
  photo- 
  

   graphic 
  spectra 
  are 
  almost 
  devoid 
  of 
  lines. 
  We 
  now 
  understand 
  that 
  

   the 
  absence 
  of 
  lines 
  does 
  not 
  mean 
  the 
  absence 
  of 
  the 
  chemical 
  ele- 
  

   ments 
  which 
  produce 
  them. 
  Rather 
  the 
  elementary 
  atoms, 
  under 
  

   the 
  tremendous 
  excitations 
  prevailing 
  in 
  these 
  very 
  hot 
  star 
  surfaces, 
  

   have 
  lost 
  several 
  of 
  the 
  electrons 
  of 
  their 
  outer 
  orbits. 
  They 
  are 
  

   " 
  stripped," 
  as 
  physicists 
  say, 
  and 
  the 
  residual 
  fragments 
  of 
  such 
  

   stripped 
  atoms 
  give 
  spectra 
  whose 
  lines 
  are 
  beyond 
  the 
  short-wave 
  

   limit 
  of 
  spectra 
  transmissible 
  by 
  our 
  atmosphere. 
  

  

  If 
  it 
  were 
  not 
  for 
  a 
  high-level 
  layer 
  of 
  atmospheric 
  ozone, 
  so 
  

   scanty 
  that 
  if 
  brought 
  to 
  the 
  earth's 
  surface 
  it 
  would 
  make 
  a 
  gaseous 
  

   mantle 
  no 
  thicker 
  than 
  a 
  sheet 
  of 
  cardboard, 
  the 
  sun 
  and 
  stars 
  would 
  

   send 
  us 
  rays 
  of 
  much 
  shorter 
  wave 
  lengths. 
  In 
  these 
  extreme 
  ultra- 
  

   violet 
  regions 
  would 
  be 
  found 
  the 
  rich 
  line 
  spectra 
  of 
  the 
  stripped 
  

   atoms 
  of 
  the 
  hotter 
  stars. 
  

  

  All 
  that 
  we 
  know 
  of 
  astronomy 
  depends 
  on 
  radiation. 
  But 
  the 
  

   nature 
  of 
  radiation 
  itself 
  is 
  more 
  mysterious 
  than 
  was 
  supposed 
  30 
  

   years 
  ago. 
  At 
  the 
  end 
  of 
  the 
  nineteenth 
  century 
  it 
  was 
  agreed 
  that 
  

   radiation 
  is 
  a 
  transverse 
  wave 
  vibration, 
  set 
  up 
  in 
  the 
  luminiferous 
  

   ether 
  by 
  the 
  stimulus 
  of 
  the 
  violent 
  internal 
  motions 
  of 
  the 
  molecules 
  

   of 
  heated 
  substances. 
  All 
  of 
  the 
  phenomena 
  of 
  the 
  propagation 
  of 
  

   light, 
  highly 
  complex 
  and 
  varied 
  though 
  they 
  are, 
  seemed 
  to 
  be 
  

   explained 
  satisfactorily 
  in 
  this 
  way. 
  Yet 
  now 
  the 
  newjy 
  gained 
  

  

  