﻿160 
  G. 
  K 
  Hale 
  — 
  Photographic 
  Investigation 
  of 
  

  

  Art. 
  XI 
  Y. 
  — 
  Photographic 
  Investigation 
  of 
  Solar 
  Promi- 
  

   nences 
  and 
  their 
  Spectra; 
  by 
  George 
  E. 
  Hale. 
  With 
  

   Plate 
  Till. 
  

  

  It 
  is 
  now 
  many 
  years 
  since 
  any 
  important 
  advance 
  has 
  been 
  

   made 
  in 
  our 
  knowledge 
  of 
  the 
  solar 
  prominences. 
  With 
  the 
  

   exception 
  of 
  spectrum 
  photographs 
  made 
  at 
  the 
  Siam 
  and 
  

   Egyptian 
  eclipses, 
  and 
  the 
  momentary 
  glimpses 
  of 
  mysterious 
  

   " 
  white 
  prominences 
  " 
  during 
  totality, 
  almost 
  nothing 
  has 
  been 
  

   added 
  to 
  the 
  collection 
  of 
  facts 
  gathered 
  nearly 
  twenty 
  years 
  

   ago. 
  After 
  Professor 
  Young's 
  vigorous 
  attack 
  upon 
  the 
  chro- 
  

   mosphere 
  and 
  prominence 
  lines 
  at 
  Mount 
  Sherman 
  and 
  else- 
  

   where, 
  other 
  investigators 
  seem 
  to 
  have 
  been 
  impressed 
  with 
  

   the 
  belief 
  that 
  no 
  further 
  additions 
  could 
  be 
  made 
  to 
  the 
  long 
  

   catalogue 
  of 
  lines 
  drawn 
  up 
  by 
  our 
  most 
  skillful 
  solar 
  observer, 
  

   and 
  the 
  spectroscopic 
  side 
  of 
  the 
  matter 
  was 
  allowed 
  to 
  rest, 
  

   though 
  a 
  continuous 
  record 
  has 
  been 
  kept 
  of 
  the 
  forms 
  of 
  

   chromosphere 
  and 
  prominences. 
  While 
  it 
  is 
  probably 
  true 
  

   that 
  the 
  most 
  persistent 
  watching 
  would 
  be 
  required 
  to 
  in- 
  

   crease 
  the 
  number 
  of 
  known 
  lines 
  in 
  the 
  visual 
  spectrum, 
  it 
  is 
  

   rather 
  singular 
  that 
  the 
  importance 
  of 
  photography 
  in 
  a 
  study 
  

   of 
  the 
  ultra-violet 
  has 
  been 
  entirely 
  overlooked. 
  While 
  the 
  

   positions 
  of 
  spots 
  on 
  the 
  sun's 
  disc 
  are 
  daily 
  recorded 
  by 
  pho- 
  

   tography, 
  the 
  same 
  cannot 
  be 
  said 
  of 
  the 
  chromosphere 
  and 
  

   prominences, 
  and 
  even 
  in 
  investigations 
  of 
  the 
  extremely 
  com- 
  

   plicated 
  spot 
  spectra, 
  photography 
  has 
  been 
  but 
  little 
  employed, 
  

   experiments 
  with 
  it 
  not 
  having 
  proved 
  very 
  successful. 
  

  

  It 
  is 
  unnecessary 
  here 
  to 
  urge 
  the 
  importance 
  of 
  using 
  pho- 
  

   tographic 
  processes 
  to 
  assist 
  the 
  eye 
  in 
  nearly 
  all 
  classes 
  of 
  

   solar 
  investigation. 
  What 
  has 
  been 
  said 
  for 
  photography 
  in 
  

   other 
  fields 
  of 
  astronomical 
  or 
  physical 
  research 
  will 
  apply 
  

   with 
  equal 
  force 
  in 
  the 
  present 
  instance, 
  and 
  the 
  results 
  of 
  

   many 
  years 
  speak 
  forcibly 
  for 
  themselves. 
  It 
  is 
  of 
  course 
  very 
  

   desirable 
  that 
  the 
  ultra-violet 
  should 
  be 
  studied, 
  and 
  for 
  this 
  

   purpose 
  visual 
  observations 
  are 
  of 
  no 
  service. 
  Again, 
  promi- 
  

   nence 
  forms 
  as 
  photographed 
  through 
  different 
  lines 
  should 
  be 
  

   compared, 
  and 
  the 
  sequel 
  will 
  show 
  that 
  photography 
  affords 
  

   the 
  only 
  means 
  of 
  investigating 
  the 
  white 
  prominences.* 
  

  

  The 
  history 
  of 
  attempts 
  at 
  solar 
  prominence 
  photography 
  

   extends 
  over 
  twenty 
  years, 
  and 
  it 
  is 
  remarkable 
  that 
  the 
  earliest 
  

   experiments 
  were 
  the 
  only 
  ones 
  which 
  gave 
  any 
  indications 
  of 
  

   possible 
  success. 
  In 
  1870 
  Professor 
  C. 
  A. 
  Young 
  made 
  the 
  

   first 
  prominence 
  photographs 
  taken 
  without 
  an 
  eclipse. 
  Using 
  

   ' 
  the 
  hydrogen 
  7 
  line 
  (G 
  / 
  ), 
  and 
  a 
  wide 
  tangential 
  slit, 
  a 
  magni- 
  

   fied 
  image 
  of 
  the 
  prominence 
  was 
  formed 
  upon 
  an 
  ordinary 
  

   * 
  See 
  also 
  Technology 
  Quarterly, 
  vol. 
  iii, 
  No. 
  4. 
  

  

  