﻿BicKEKTON, 
  — 
  Oil 
  Temporary 
  and 
  Variable 
  Stan, 
  i2B 
  

  

  whilst, 
  on 
  the 
  other 
  hand, 
  we 
  have 
  inertia 
  and 
  gravity 
  tending 
  to 
  keep 
  the 
  

   mass 
  together. 
  The 
  centrifugal 
  force 
  acts 
  only 
  in 
  one 
  plane, 
  whilst 
  the 
  re- 
  

   pellent 
  force 
  of 
  heat 
  acts 
  in 
  every 
  plane 
  ; 
  a 
  bun-shaped 
  mass 
  must 
  result, 
  

   with 
  a 
  number 
  of 
  distinct 
  pieces, 
  which 
  at 
  first 
  at 
  least 
  are 
  in 
  advance 
  of 
  the 
  

   general 
  mass. 
  Follow 
  it 
  on 
  in 
  time 
  and 
  we 
  get 
  the 
  ring 
  nebulEe, 
  with 
  or 
  

   without 
  a 
  luminous 
  centre 
  ; 
  in 
  the 
  latter 
  case, 
  with 
  a 
  dark 
  circle 
  dividing 
  

   those 
  parts 
  whose 
  velocity 
  has 
  carried 
  them 
  beyond 
  the 
  powers 
  of 
  the 
  

   attractive 
  force, 
  from 
  those 
  parts 
  held 
  prisoner 
  by 
  it. 
  These 
  parts, 
  as 
  they 
  

   gradually 
  radiate 
  heat 
  into 
  space, 
  are 
  once 
  more 
  slowly 
  attracted 
  to 
  the 
  

   centre 
  by 
  gravitation. 
  If 
  the 
  piece 
  struck 
  off 
  from 
  each 
  body 
  were 
  very 
  

   small, 
  then 
  complete 
  dissipation 
  of 
  the 
  whole 
  into 
  space 
  would 
  result. 
  

   Clearly 
  such 
  collisions 
  as 
  I 
  have 
  described 
  would 
  be 
  competent 
  to 
  produce 
  

   every 
  variety 
  of 
  temporary 
  stars 
  that 
  has 
  appeared. 
  Applyiiag 
  the 
  spectro- 
  

   scope 
  to 
  such 
  a 
  star, 
  we 
  get 
  at 
  first 
  a 
  continuous 
  spectrum 
  ; 
  then 
  black 
  

   lines, 
  quickly 
  followed 
  by 
  bright 
  lines 
  and 
  spectrum 
  ; 
  then 
  bright 
  lines 
  

   alone. 
  Again, 
  if 
  the 
  colliding 
  bodies 
  were 
  of 
  very 
  different 
  size, 
  or 
  if 
  the 
  

   heat 
  were 
  not 
  great 
  enough 
  to 
  entirely 
  volatilize 
  the 
  star, 
  v/e 
  should 
  have 
  

   lines 
  and 
  spectrum. 
  Lastly, 
  as 
  heat 
  and 
  pressure 
  diminish 
  by 
  the 
  dissipa- 
  

   tion 
  of 
  the 
  body 
  into 
  space, 
  we 
  get 
  fewer 
  and 
  fewer 
  lines, 
  until 
  only 
  those 
  

   substances 
  in 
  greatest 
  quantity, 
  or 
  of 
  greatest 
  power 
  in 
  giving 
  lines 
  at 
  

   lowest 
  temperature 
  and 
  pressure, 
  remain 
  luminous, 
  and 
  we 
  have 
  a 
  nebulae 
  

   left 
  ; 
  or 
  in 
  the 
  case 
  of 
  total 
  dissipation 
  of 
  the 
  gaseous 
  mass 
  all 
  evidence 
  

   of 
  its 
  existence 
  will 
  disappear. 
  It 
  will 
  be 
  seen 
  how 
  exactly 
  the 
  above 
  

   hypothesis 
  agrees 
  with 
  the 
  spectroscopic 
  observation 
  of 
  temporary 
  stars 
  ; 
  

   and 
  I 
  have 
  showa 
  as 
  fully 
  as 
  perhaps 
  it 
  is 
  wise 
  to 
  do 
  in 
  this 
  paper, 
  that 
  the 
  

   hypothesis 
  of 
  partial 
  impact 
  is 
  competent 
  to 
  account 
  for 
  every 
  variety 
  of 
  

   these 
  bodies, 
  and 
  also 
  for 
  their 
  intensity 
  and 
  short 
  duration. 
  

  

  We 
  must 
  now 
  return 
  to 
  the 
  parent 
  bodies 
  which 
  we 
  left 
  travelling 
  on 
  in 
  

   space. 
  A 
  cylindrical 
  or 
  curved 
  slice 
  has 
  been 
  cut 
  out 
  of 
  each 
  ; 
  sometimes 
  

   that 
  is 
  the 
  chief 
  thing 
  that 
  will 
  happen. 
  But 
  on 
  the 
  other 
  hand 
  we 
  may 
  have 
  

   the 
  molten 
  interior 
  of 
  the 
  body 
  exposed 
  to 
  view. 
  If 
  there 
  were 
  atmosphej-es 
  

   on 
  the 
  two 
  colliding 
  bodies, 
  a 
  very 
  great 
  heating 
  of 
  the 
  surface 
  of 
  the 
  section 
  

   would 
  result, 
  and 
  when 
  both 
  causes 
  are 
  acting 
  in 
  unison 
  a 
  stupendous 
  lake 
  

   of 
  fire 
  must 
  be 
  formed. 
  Let 
  such 
  a 
  body 
  rotate 
  on 
  its 
  axis, 
  alternately 
  the 
  

   light 
  and 
  dark 
  sides 
  are 
  shown, 
  and 
  we 
  get 
  a 
  variable 
  star. 
  May 
  not 
  Mira 
  in 
  

   this 
  way 
  be 
  attempting 
  to 
  tell 
  us 
  her 
  autobiography 
  ; 
  how 
  she 
  is 
  a 
  dark 
  body, 
  

   with 
  a 
  molten 
  lake 
  of 
  fire, 
  30 
  degrees 
  of 
  arc, 
  a 
  lake 
  as 
  big 
  as 
  our 
  sun, 
  and 
  

   how 
  she 
  rotates 
  about 
  an 
  axis 
  in 
  a 
  little 
  less 
  than 
  a 
  year 
  ? 
  If 
  it 
  be 
  so, 
  she 
  

   tells 
  us 
  of 
  a 
  dark 
  body 
  almost 
  as 
  large 
  as 
  Sirius, 
  or 
  how 
  would 
  80 
  degrees 
  

   of 
  arc 
  produce 
  a 
  star 
  of 
  the 
  first 
  magnitude 
  ? 
  Algol 
  appears 
  to 
  tell 
  us 
  that 
  

   it 
  is 
  a 
  dark 
  and 
  gloomy 
  parent, 
  with 
  a 
  brilliant 
  son 
  who 
  periodically 
  passes 
  

  

  