﻿164 
  G. 
  E. 
  Hale 
  — 
  Photographic 
  Investigation 
  of 
  

  

  variations, 
  and 
  in 
  several 
  cases 
  I 
  have 
  photographed 
  both 
  H 
  

   and 
  K 
  expanded 
  and 
  reversed 
  over 
  spots 
  in 
  which 
  the 
  C 
  and 
  F 
  

   lines 
  showed 
  no 
  signs 
  of 
  reversal. 
  Some 
  very 
  recent 
  photo- 
  

   graphs 
  suggest 
  the 
  possibility 
  that 
  the 
  substance 
  producing 
  the 
  

   H 
  and 
  K 
  bright 
  lines 
  occasionally 
  ascends 
  in 
  prominences 
  to 
  a 
  

   higher 
  level 
  than 
  that 
  reached 
  by 
  hydrogen 
  itself 
  (observed 
  

   through 
  0) 
  in 
  the 
  same 
  prominences, 
  and 
  the 
  u 
  white 
  prom- 
  

   inences 
  " 
  observed 
  and 
  photographed 
  at 
  several 
  eclipses 
  offer 
  a 
  

   most 
  interesting 
  case 
  in 
  point. 
  At 
  the 
  Grenada 
  eclipse 
  of 
  

   August 
  29, 
  1886, 
  Prof. 
  "W. 
  H. 
  Pickering 
  found 
  in 
  his 
  photo- 
  

   graphs 
  made 
  during 
  totality 
  a 
  spiral 
  prominence 
  150,000 
  miles 
  

   high, 
  which 
  had 
  for 
  the 
  only 
  lines 
  in 
  its 
  spectrum 
  H, 
  K, 
  and 
  a 
  

   faint 
  trace 
  of 
  an 
  ultra-violet 
  line 
  about 
  half-way 
  between 
  K 
  

   and 
  L. 
  There 
  was 
  also 
  a 
  brilliant 
  continuous 
  spectrum 
  in 
  the 
  

   visible 
  region, 
  but 
  as 
  the 
  usual 
  hydrogen 
  lines 
  were 
  absent, 
  

   Prof. 
  Tacchini 
  was 
  unable 
  to 
  see 
  the 
  prominence 
  by 
  the 
  usual 
  

   spectroscopic 
  method, 
  either 
  before 
  or 
  after 
  totality. 
  In 
  his 
  

   report 
  Prof. 
  Pickering 
  adds 
  : 
  " 
  It 
  is 
  highly 
  probable 
  that 
  a 
  

   great 
  number 
  of 
  prominences 
  pass 
  by 
  entirely 
  unnoticed, 
  be- 
  

   cause 
  we 
  rely 
  solely 
  upon 
  visual 
  instead 
  of 
  photographic 
  

   methods 
  of 
  observation."* 
  At 
  the 
  present 
  moment 
  I 
  have 
  not 
  

   the 
  remaining 
  literature 
  of 
  this 
  subject 
  within 
  reach, 
  and 
  must 
  

   trust 
  to 
  memory 
  for 
  a 
  few 
  more 
  references 
  to 
  simular 
  phe- 
  

   nomena. 
  In 
  the 
  report 
  of 
  the 
  eclipse 
  of 
  Jan. 
  1, 
  1889, 
  published 
  

   by 
  the 
  Lick 
  Observatory, 
  Dr. 
  Swift 
  alludes 
  to 
  the 
  peculiar 
  

   white 
  appearance 
  of 
  some 
  of 
  the 
  prominences, 
  and 
  in 
  com- 
  

   paring 
  the 
  prominences 
  photographed 
  at 
  the 
  same 
  eclipse 
  with 
  

   those 
  observed 
  on 
  the 
  same 
  day 
  at 
  Palermo, 
  P. 
  Tacchini 
  notes 
  

   the 
  presence 
  in 
  the 
  photographs 
  of 
  two 
  prominences 
  seen 
  

   neither 
  at 
  Palermo 
  or 
  Rome, 
  and 
  concludes 
  that 
  they 
  are 
  

   white 
  prominences, 
  similar 
  to 
  the 
  great 
  white 
  prominence 
  

   shown 
  in 
  the 
  Grenada 
  photographs. 
  f 
  Capt. 
  Abney's 
  photo- 
  

   graphs 
  of 
  the 
  prominence 
  spectrum 
  at 
  the 
  Egyptian 
  eclipse, 
  

   and 
  a 
  suspicion 
  of 
  Trouvelot's 
  (given 
  in 
  the 
  Comptes 
  Rendus) 
  

   that 
  a 
  certain 
  floating 
  prominence 
  must 
  have 
  some 
  invisible 
  

   connection 
  with 
  the 
  chromosphere, 
  make 
  evident 
  the 
  extreme 
  

   desirability 
  of 
  some 
  means 
  of 
  photographing 
  both 
  visible 
  and 
  

   invisible 
  prominences 
  in 
  full 
  sunshine. 
  The 
  various 
  theories 
  

   connecting 
  sun-spots 
  and 
  prominences 
  are 
  based 
  upon 
  observa- 
  

   tions 
  in 
  the 
  visual 
  region, 
  and 
  the 
  invisible 
  prominences, 
  

   which 
  are 
  shown 
  by 
  the 
  Grenada 
  photographs, 
  to 
  reach 
  at 
  

   times 
  to 
  great 
  elevations, 
  have 
  been 
  left 
  entirely 
  out 
  of 
  account. 
  

   It 
  will 
  be 
  seen 
  shortly 
  that 
  this 
  need 
  no 
  longer 
  be 
  the 
  case, 
  and 
  

   we 
  may 
  hope 
  soon 
  to 
  have 
  a 
  daily 
  record 
  of 
  all 
  classes 
  of 
  prom- 
  

   inences, 
  both 
  visible 
  and 
  invisible. 
  

  

  * 
  Annals 
  of 
  Harvard 
  College 
  Observatory, 
  vol. 
  xviii, 
  No. 
  V, 
  p. 
  99. 
  

   f 
  Atti 
  della 
  R. 
  Accad., 
  dei 
  Lincei, 
  1889. 
  

  

  