﻿of 
  the 
  Solar 
  Prominences. 
  467 
  

  

  very 
  much 
  brighter 
  than 
  any 
  other 
  of 
  the 
  seven 
  ghosts 
  of 
  H 
  

   and 
  K, 
  and 
  its 
  position 
  with 
  respect 
  to 
  H 
  is 
  not 
  symmetrical 
  

   with 
  that 
  of 
  the 
  first 
  ghost 
  on 
  the 
  opposite 
  side 
  of 
  this 
  line, 
  

   while 
  in 
  the 
  case 
  of 
  K 
  the 
  ghosts 
  are 
  very 
  regularly 
  spaced. 
  

   My 
  assistants 
  report 
  that 
  they 
  were 
  able 
  to 
  see 
  H 
  very 
  plainly 
  

   double 
  in 
  a 
  bi'illiant 
  metallic 
  prominence 
  observed 
  July 
  27, 
  

   and 
  on 
  one 
  or 
  two 
  occasions 
  Professor 
  Young 
  has 
  made 
  out 
  the 
  

   same 
  thing. 
  The 
  agreement 
  in 
  wave-length 
  with 
  Ames's 
  

   hydrogen 
  line 
  at 
  3970*25 
  is 
  by 
  no 
  means 
  satisfactory, 
  and 
  more 
  

   observations 
  and 
  measures 
  are 
  required 
  before 
  a 
  conclusion 
  can 
  

   be 
  reached. 
  

  

  ~No 
  one 
  can 
  doubt 
  that 
  the 
  next 
  four 
  prominence 
  lines 
  are 
  

   members 
  of 
  the 
  well-known 
  hydrogen 
  series, 
  for 
  their 
  agree- 
  

   ment 
  in 
  wave-length 
  with 
  the 
  values 
  given 
  by 
  Ames 
  is 
  cer- 
  

   tainly 
  very 
  striking. 
  Cornu's 
  measures 
  show 
  considerable 
  

   differences, 
  as 
  do 
  also 
  those 
  of 
  Dr. 
  Huggins, 
  but 
  the 
  small 
  dis- 
  

   persion 
  employed 
  by 
  the 
  latter 
  in 
  this 
  investigation 
  must 
  be 
  

   borne 
  in 
  mind. 
  There 
  can 
  be 
  little 
  question 
  that 
  Ames' 
  wave- 
  

   lengths 
  are 
  very 
  near 
  the 
  truth, 
  for 
  they 
  almost 
  exactly 
  corre- 
  

   spond 
  with 
  those 
  calculated 
  by 
  Balmer's 
  formula. 
  The 
  meas- 
  

   ures 
  of 
  the 
  jDi'ominence 
  lines 
  also 
  serve 
  to 
  confirm 
  them.. 
  

  

  The 
  remaining 
  prominence 
  line 
  at 
  / 
  3888*73 
  has 
  not 
  been 
  

   accounted 
  for. 
  It 
  forms 
  a 
  close 
  double 
  with 
  the 
  hydrogen 
  

   line 
  at 
  / 
  3889*14, 
  and 
  with 
  it 
  attains 
  as 
  great 
  elevations 
  above 
  

   the 
  limb 
  as 
  those 
  reached 
  by 
  H 
  and 
  K. 
  The 
  character 
  of 
  the 
  

   lines, 
  however, 
  is 
  quite 
  different, 
  for 
  while 
  the 
  hydrogen 
  line 
  

   is 
  wider, 
  and 
  slightly 
  diffuse, 
  the 
  line 
  at 
  / 
  3888*73 
  is 
  very 
  

   narrow 
  and 
  sharp. 
  I 
  have 
  seen 
  no 
  statement 
  that 
  the 
  hydrogen 
  

   line 
  has 
  shown 
  any 
  signs 
  of 
  duplicity, 
  and, 
  as 
  Mrs. 
  Huggins 
  

   has 
  had 
  the 
  kindness 
  to 
  examine 
  the 
  corresponding 
  line 
  in 
  

   some 
  very 
  sharp 
  photographs 
  of 
  steller 
  spectra 
  with 
  the 
  same 
  

   result, 
  we 
  have 
  reason 
  to 
  consider 
  an 
  independent 
  origin 
  prob- 
  

   able. 
  

  

  The 
  results 
  so 
  far 
  obtained 
  can 
  only 
  be 
  regarded 
  as 
  prelim- 
  

   inary, 
  for 
  with 
  the 
  improvements 
  now 
  being 
  carried 
  out 
  in 
  the 
  

   telescope 
  and 
  spectroscope, 
  and 
  the 
  much 
  greater 
  frequency 
  

   of 
  metallic 
  eruptions 
  as 
  the 
  maximum 
  sun-spot 
  period 
  is 
  

   approached, 
  it 
  is 
  certainly 
  to 
  be 
  hoped 
  that 
  many 
  more 
  lines 
  

   will 
  be 
  photographed. 
  The 
  ultra-violet 
  spectra 
  of 
  sun-spots 
  

   have 
  also 
  been 
  worked 
  upon 
  with 
  some 
  indications 
  of 
  success, 
  

   and 
  there 
  will 
  evidently 
  be 
  no 
  lack 
  of 
  opportunity 
  in 
  the 
  new 
  

   and 
  interesting 
  fields 
  thus 
  opened 
  to 
  investigation. 
  

  

  London, 
  August 
  13 
  r 
  1891. 
  

  

  