﻿COUNTING 
  THE 
  STAES 
  SEARES 
  203 
  

  

  casual 
  inspection 
  of 
  Plate 
  4 
  a, 
  b, 
  c, 
  reveals 
  the 
  dark 
  broken 
  band 
  extend- 
  

   ing 
  the 
  length 
  of 
  the 
  images 
  which 
  is 
  a 
  conspicuous 
  feature 
  of 
  almost 
  

   every 
  edge-on 
  spiral 
  that 
  we 
  know. 
  This 
  band 
  consists 
  of 
  obscuring 
  

   clouds 
  of 
  nebulous 
  material, 
  dark 
  ordinarily, 
  unless 
  illuminated 
  or 
  

   stimulated 
  to 
  shuie 
  by 
  some 
  external 
  source, 
  and 
  invisible, 
  unless 
  

   outlined 
  by 
  projection 
  on 
  a 
  background 
  of 
  stars 
  or 
  luminous 
  cloud. 
  

   Photographs 
  of 
  spirals 
  inclined 
  to 
  the 
  line 
  of 
  sight 
  suggest 
  that 
  these 
  

   dark 
  clouds 
  extend 
  well 
  in 
  toward 
  the 
  central 
  condensation, 
  and 
  would 
  

   blot 
  out, 
  in 
  part 
  at 
  least, 
  the 
  bright 
  central 
  region 
  from 
  our 
  imagined 
  

   point 
  of 
  observation. 
  The 
  chances 
  are, 
  too, 
  that 
  above 
  and 
  below 
  

   the 
  dark 
  clouds, 
  in 
  the 
  general 
  direction 
  of 
  the 
  center, 
  we 
  might 
  see 
  

   outlying 
  aggregations 
  of 
  stars, 
  strewn 
  nearly 
  parallel 
  to 
  the 
  plane 
  of 
  

   the 
  nebula. 
  The 
  Milky 
  Way 
  of 
  the 
  nebula 
  would 
  then 
  appear 
  split 
  

   for 
  part 
  of 
  its 
  length 
  into 
  two 
  branches 
  by 
  a 
  great 
  rift, 
  like 
  that 
  which 
  

   in 
  our 
  own 
  system 
  extends 
  from 
  Cygnus 
  in 
  the 
  north 
  to 
  Circinus 
  far 
  

   down 
  in 
  the 
  southern 
  heavens. 
  We 
  know 
  that 
  much 
  obscuring 
  

   material 
  is 
  scattered 
  over 
  the 
  galactic 
  plane 
  among 
  our 
  own 
  stars, 
  

   and 
  that 
  the 
  dark, 
  almost 
  starless 
  region 
  between 
  the 
  two 
  branches 
  of 
  

   ttie 
  Milky 
  Way 
  is 
  probably 
  a 
  thick 
  pall 
  of 
  cloud. 
  The 
  direction 
  of 
  the 
  

   center 
  of 
  the 
  system 
  cuts 
  into 
  this 
  cloud, 
  and 
  it 
  has 
  been 
  suggested 
  

   that 
  but 
  for 
  the 
  cloud 
  we 
  should 
  see 
  something 
  comparable 
  with 
  the 
  

   central 
  condensation 
  of 
  the 
  spirals. 
  The 
  off-sided 
  concentration 
  of 
  

   stars 
  which, 
  as 
  a 
  central 
  nucleus, 
  seemed 
  so 
  out 
  of 
  harmony 
  with 
  the 
  

   vastness 
  and 
  grandeur 
  of 
  the 
  system, 
  would 
  then 
  represent 
  the 
  crowd- 
  

   ing 
  of 
  the 
  stars 
  naturally 
  to 
  be 
  expected 
  toward 
  the 
  center, 
  modified 
  

   and 
  ultimately 
  suppressed 
  by 
  the 
  obscuring 
  clouds, 
  long 
  before 
  the 
  

   center 
  is 
  reached. 
  

  

  The 
  asymmetry 
  of 
  distribution 
  is 
  further 
  accentuated 
  by 
  the 
  fact 
  

   that 
  the 
  curve 
  for 
  the 
  larger 
  system 
  shown 
  in 
  Figure 
  3 
  has 
  been 
  derived 
  

   from 
  counts 
  made, 
  not 
  in 
  the 
  exact 
  direction 
  of 
  the 
  center, 
  but 
  in 
  the 
  

   branches 
  of 
  the 
  Milky 
  Way 
  immediately 
  above 
  and 
  below 
  the 
  central 
  

   point. 
  For 
  a 
  system 
  perfectly 
  symmetrical 
  about 
  its 
  center, 
  the 
  

   distribution 
  of 
  density 
  along 
  lines 
  thus 
  inclined 
  to 
  the 
  principal 
  plane 
  

   would 
  necessarily 
  be 
  unsymmetrical 
  ; 
  the 
  maximum 
  density 
  would 
  be 
  

   less 
  than 
  at 
  the 
  center, 
  and 
  less 
  distant 
  than 
  the 
  central 
  point. 
  

   Finally, 
  the 
  position 
  of 
  the 
  maximum 
  may 
  also 
  be 
  influenced 
  by 
  one 
  

   of 
  the 
  local 
  aggregations 
  of 
  stars 
  which 
  the 
  Milky 
  Way 
  structure, 
  as 
  

   well 
  as 
  the 
  appearance 
  of 
  the 
  spirals, 
  suggests 
  as 
  lying 
  scattered 
  over 
  

   the 
  galactic 
  plane. 
  

  

  When 
  invoked 
  to 
  explain 
  the 
  peculiarities 
  of 
  stellar 
  distribution, 
  

   the 
  well-known 
  analogies 
  between 
  spirals 
  and 
  our 
  own 
  system 
  answer 
  

   very 
  well; 
  but, 
  unfortunately, 
  they 
  leave 
  us 
  still 
  in 
  doubt 
  as 
  to 
  our 
  

   exact 
  location 
  within 
  the 
  larger 
  system. 
  The 
  presence 
  of 
  obscuring 
  

   material 
  means 
  that 
  star 
  counts 
  probably 
  can 
  never 
  remove 
  that 
  

   doubt. 
  For 
  the 
  present 
  we 
  can 
  only 
  accept 
  Shapley's 
  estimate 
  

  

  