﻿160 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1922. 
  

  

  wire 
  will 
  supply 
  the 
  void 
  and 
  take 
  up 
  the 
  excess 
  as 
  long 
  as 
  these 
  

   inequalities 
  remain, 
  just 
  as 
  air 
  molecules 
  rush 
  along 
  to 
  equalize 
  pres- 
  

   sure 
  differences. 
  So 
  it 
  is 
  that 
  as 
  water 
  buckets 
  at 
  a 
  country 
  fire 
  are 
  

   passed 
  from 
  hand 
  to 
  hand, 
  the 
  electric 
  current 
  does 
  not 
  require 
  to 
  

   be 
  conveyed 
  by 
  original 
  electrons 
  all 
  the 
  way 
  through 
  the 
  wire 
  from 
  

   the 
  negative 
  pole 
  to 
  the 
  positive 
  pole. 
  

  

  But 
  some 
  one 
  may 
  ask 
  : 
  " 
  If 
  the 
  solid 
  bar 
  I 
  push 
  my 
  top 
  window 
  

   shut 
  with 
  is 
  no 
  more 
  than 
  a 
  flimsy 
  structure 
  of 
  flying 
  motes, 
  how 
  can 
  

   it 
  transmit 
  pressure 
  ? 
  " 
  The 
  forces 
  of 
  electrical 
  attraction 
  and 
  repul- 
  

   sion 
  retain 
  to 
  the 
  bar 
  its 
  form, 
  and, 
  somewhat 
  as 
  a 
  steam 
  or 
  air 
  

   riveting 
  hammer 
  can 
  be 
  operated 
  by 
  a 
  medium 
  made 
  up 
  of 
  particles 
  

   well 
  separated, 
  so 
  pressure 
  can 
  be 
  transmitted 
  by 
  a 
  bar 
  made 
  up 
  of 
  

   protons 
  and 
  electrons. 
  

  

  Without 
  pursuing 
  this 
  resume 
  of 
  atomic 
  science 
  further 
  at 
  the 
  

   moment, 
  let 
  us 
  turn 
  to 
  some 
  aspects 
  of 
  the 
  stars. 
  

  

  As 
  regards 
  their 
  intrinsic 
  brightness, 
  the 
  stars 
  are 
  now 
  classed 
  

   as 
  the 
  giants 
  and 
  the 
  dwarfs. 
  Giants 
  are 
  stars 
  which 
  are 
  many 
  times, 
  

   even 
  thousands 
  of 
  times, 
  more 
  luminous 
  than 
  the 
  sun. 
  Dwarfs 
  are 
  

   stars 
  which 
  range 
  from 
  near 
  the 
  brightness 
  of 
  the 
  sun 
  to 
  complete 
  

   extinction 
  into 
  cold 
  nonluminosity 
  like 
  that 
  of 
  the 
  earth. 
  As 
  regards 
  

   their 
  color 
  and 
  the 
  details 
  of 
  their 
  spectra, 
  99 
  per 
  cent 
  of 
  the 
  stars 
  

   are 
  assigned 
  according 
  to 
  the 
  universally 
  accepted 
  Harvard 
  classi- 
  

   fication 
  in 
  six 
  principal 
  types, 
  called 
  by 
  the 
  letters 
  B, 
  A, 
  F, 
  G, 
  K, 
  M. 
  

   Originally 
  all 
  the 
  letters 
  of 
  the 
  alphabet 
  from 
  A 
  to 
  M 
  were 
  used, 
  

   but 
  it 
  was 
  found 
  presently 
  that 
  the 
  classes 
  assigned 
  to 
  other 
  letters 
  

   were 
  unnecessary 
  and 
  only 
  those 
  above 
  named 
  were 
  retained. 
  More- 
  

   over, 
  in 
  the 
  rational 
  order 
  of 
  development 
  of 
  spectrum 
  characteristics, 
  

   class 
  B 
  appeared 
  to 
  precede 
  class 
  A, 
  hence 
  the 
  irregular 
  order 
  as 
  

   given 
  above 
  is 
  now 
  always 
  followed. 
  

  

  There 
  is 
  a 
  very 
  extraordinary 
  march 
  of 
  change 
  of 
  density 
  asso- 
  

   ciated 
  with 
  these 
  star 
  classes. 
  The 
  giant 
  red 
  star 
  a 
  Orionis 
  ( 
  Betel 
  - 
  

   geuse), 
  of 
  spectrum 
  type 
  M, 
  recently 
  measured 
  at 
  Mount 
  Wilson, 
  is 
  

   300 
  times 
  the 
  diameter 
  of 
  our 
  sun 
  and 
  not 
  more 
  than 
  a 
  thousandth 
  

   part 
  as 
  dense 
  as 
  the 
  air 
  of 
  the 
  room. 
  Our 
  sun, 
  a 
  dwarf 
  of 
  type 
  G, 
  

   is 
  1.4: 
  times 
  as 
  dense 
  as 
  water. 
  Barnard's 
  " 
  runaway 
  star," 
  a 
  dwarf 
  

   of 
  type 
  M, 
  is 
  probably 
  nearly 
  as 
  dense 
  as 
  the 
  earth. 
  This 
  leads 
  us 
  

   up 
  to 
  the 
  view 
  which 
  astronomers 
  now 
  generally 
  hold 
  as 
  to 
  the 
  evo- 
  

   lution 
  of 
  stars. 
  Beginning 
  to 
  glow 
  as 
  rare 
  gaseous 
  giants 
  of 
  type 
  

   M, 
  showing 
  in 
  their 
  spectra 
  the 
  lines 
  and 
  bands 
  of 
  the 
  metals 
  and 
  

   compounds 
  of 
  them, 
  they 
  grow 
  denser 
  and 
  hotter 
  as 
  time 
  goes 
  on, 
  

   apparently 
  simplifying 
  in 
  spectra. 
  First, 
  the 
  bands 
  due 
  to 
  com- 
  

   pounds 
  fall 
  out, 
  for, 
  as 
  we 
  well 
  know, 
  high 
  temperatures 
  break 
  up 
  

  

  