﻿BicKEKTDN. 
  — 
  On 
  Temporary 
  and 
  Yariahle 
  Stars, 
  119 
  

  

  radiated 
  from 
  each 
  square 
  yard 
  of 
  our 
  sun's 
  surface 
  is 
  estimated 
  to 
  be 
  equal 
  

   to 
  the 
  combustion 
  of 
  ten 
  cubic 
  yards 
  of 
  coal 
  in 
  every 
  hour, 
  while 
  the 
  sun's 
  

   disc 
  has 
  four 
  times 
  the 
  area 
  enclosed 
  by 
  the 
  orbit 
  of 
  the 
  moon. 
  The 
  star 
  of 
  

   1866 
  \^heu 
  first 
  seen 
  was 
  of 
  the 
  second 
  magnitude, 
  and 
  its 
  spectrum 
  shows 
  

   that 
  it 
  consisted 
  of 
  a 
  nucleus 
  oi 
  compressed 
  gas, 
  or 
  of 
  liquid 
  or 
  of 
  solid 
  matter. 
  

   This 
  was 
  surrounded 
  by 
  an 
  atmosphere 
  of 
  heated 
  gas, 
  having 
  a 
  greater 
  

   monochromatic 
  light 
  than 
  the 
  nucleus 
  ; 
  or 
  it 
  might 
  have 
  been 
  simply 
  a 
  

   small 
  permanent 
  star 
  in 
  the 
  same 
  line 
  of 
  vision 
  as 
  the 
  gaseous 
  temporary 
  

   star. 
  I 
  cannot 
  say 
  if 
  this 
  suggestion 
  agrees 
  with 
  the 
  x^i'esent 
  condition 
  of 
  

   the 
  star. 
  This 
  star 
  diminished 
  from 
  a 
  star 
  of 
  the 
  second 
  magnitude 
  to 
  the 
  

   tenth 
  in 
  about 
  a 
  fortnight. 
  The 
  spectroscope 
  showed 
  the 
  star 
  of 
  1877 
  to 
  be 
  

   io-nited 
  gas 
  only, 
  and 
  from 
  the 
  number 
  of 
  the 
  lines 
  diminishing 
  the 
  tempera- 
  

   ture 
  and 
  pressure 
  probably 
  did 
  so 
  likewise. 
  The 
  intensity 
  diminished 
  in 
  

   four 
  months 
  from 
  the 
  third 
  magnitude 
  to 
  the 
  ninth. 
  

  

  Many 
  hypotheses 
  have 
  been 
  formed 
  to 
  account 
  for 
  the 
  nature 
  of 
  these 
  

   stars, 
  of 
  which 
  the 
  following 
  appear 
  to 
  be 
  the 
  most 
  noteworthy 
  : 
  — 
  

  

  1. 
  Zoolner 
  imagines 
  a 
  sun 
  in 
  which 
  spots 
  have 
  covered 
  the 
  whole 
  

   surface, 
  the 
  temporary 
  stars 
  being 
  produced 
  by 
  the 
  breaking 
  of 
  such 
  a 
  

   surface. 
  

  

  2. 
  Vogel 
  assumes 
  a 
  volcanic 
  bursting-out 
  on 
  a 
  dead 
  sun. 
  

  

  In 
  both 
  of 
  these 
  hypotheses 
  a 
  decomposition 
  and 
  combustion 
  of 
  hydrogen 
  

   and 
  other 
  elements 
  is 
  also 
  assumed 
  to 
  account 
  for 
  the 
  great 
  intensity. 
  

  

  3. 
  Meyer 
  and 
  Klein 
  suppose 
  that 
  a 
  similar 
  dark 
  body 
  is 
  suddenly 
  raised 
  

   to 
  incandescence 
  by 
  the 
  projection 
  of 
  a 
  planet 
  or 
  other 
  body 
  upon 
  its 
  

   surface. 
  

  

  4. 
  Proctor 
  supposes 
  that 
  the 
  atmosphere 
  of 
  a 
  dead 
  sun 
  is 
  suddenly 
  

   brought 
  to 
  a 
  high 
  degree 
  of 
  luminosity 
  by 
  the 
  passage 
  of 
  a 
  meteoric 
  train 
  

   through 
  it. 
  

  

  In 
  examining 
  these 
  hypotheses, 
  we 
  find 
  that 
  there 
  is 
  one 
  thing 
  in 
  

   common, 
  namely, 
  the 
  assumption 
  of 
  the 
  existence 
  of 
  large 
  dark 
  bodies 
  in 
  

   space. 
  The 
  first 
  two 
  of 
  them 
  also 
  depend 
  on 
  the 
  existence 
  of 
  internal 
  com= 
  

   motion, 
  attended 
  with 
  combustion. 
  The 
  last 
  two 
  depend 
  upon 
  the 
  energy 
  

   developed 
  by 
  gravitation. 
  

  

  A 
  little 
  consideration 
  will 
  be 
  suificient 
  to 
  show 
  that, 
  on 
  grounds 
  of 
  

   intensity 
  alone, 
  Zoolner's 
  and 
  Vogel's 
  — 
  in 
  fact, 
  any 
  hypothesis 
  not 
  

   dependent 
  upon 
  gravitation 
  — 
  is 
  improbable. 
  Is 
  it 
  conceivable 
  that 
  a 
  

   dark 
  body 
  should 
  suddenly 
  change 
  its 
  surface 
  by 
  volcanic 
  or 
  other 
  internal 
  

   action 
  in 
  such 
  a 
  manner 
  as 
  to 
  heat 
  gases 
  to 
  a 
  pitch 
  of 
  luminosity 
  as 
  high 
  

   as 
  our 
  sun's, 
  especially 
  when 
  it 
  is 
  considered 
  that 
  if 
  a 
  gas 
  and 
  solid 
  be 
  at 
  

   the 
  same 
  temperature, 
  the 
  solid 
  is 
  much 
  the 
  more 
  luminous 
  of 
  the 
  two 
  ; 
  mat 
  

   would 
  combustion 
  or 
  decomposition 
  help 
  it 
  ; 
  generally 
  the 
  latter 
  would 
  take 
  

  

  