﻿of 
  the 
  Solar 
  Prominences. 
  4(53 
  

  

  a 
  fine, 
  sharp 
  line. 
  Other 
  stars 
  give 
  intermediate 
  breadths, 
  and 
  

   in 
  some 
  instances 
  it 
  has 
  entirely 
  disappeared. 
  In 
  the 
  case 
  of 
  

   H 
  the 
  question 
  is 
  complicated 
  by 
  the 
  fact 
  that 
  hydrogen 
  and 
  

   calcium 
  possess 
  lines 
  which 
  form 
  a 
  close 
  double 
  at 
  this 
  point, 
  

   so 
  it 
  is 
  best 
  to 
  consider 
  only 
  K. 
  From 
  the 
  variations 
  of 
  this 
  

   line 
  it 
  will 
  be 
  seen, 
  apart 
  from 
  the 
  interesting 
  subject 
  of 
  stellar 
  

   evolution 
  so 
  evidently 
  suggested, 
  that 
  the 
  narrow 
  dark 
  line 
  at 
  

   the 
  center 
  is 
  very 
  possibly 
  produced 
  by 
  the 
  same 
  substance 
  

   which, 
  vibrating 
  under 
  different 
  conditions, 
  causes 
  by 
  its 
  ab- 
  

   sorption 
  the 
  broad 
  dark 
  band. 
  

  

  As 
  the 
  central 
  dark 
  line 
  is 
  known 
  with 
  a 
  high 
  degree 
  of 
  cer- 
  

   tainty 
  to 
  be 
  due 
  to 
  calcium, 
  it 
  becomes 
  likely 
  that 
  the 
  band 
  is 
  

   due 
  to 
  the 
  same 
  substance, 
  and 
  as 
  the 
  central 
  dark 
  line 
  of 
  H 
  is 
  

   also 
  a 
  calcium 
  line, 
  it 
  might 
  perhaps 
  be 
  safe 
  to 
  attribute 
  the 
  H 
  

   band 
  to 
  the 
  same 
  metal, 
  though 
  in 
  neither 
  case 
  is 
  it 
  well 
  to 
  be 
  

   too 
  positive 
  in 
  the 
  assertion, 
  for 
  it 
  is 
  somewhat 
  peculiar 
  that 
  

   the 
  bands 
  and 
  lines 
  appear 
  together 
  in 
  the 
  solar 
  spectrum. 
  If 
  

   the 
  same 
  substance 
  produces 
  both, 
  and 
  each 
  requires 
  different 
  

   conditions, 
  possibly 
  of 
  temperature 
  or 
  pressure, 
  for 
  its 
  produc- 
  

   tion, 
  these 
  conditions 
  must 
  presumably 
  exist 
  at 
  different 
  eleva- 
  

   tions 
  above 
  the 
  photosphere. 
  

  

  The 
  question 
  now 
  arises 
  whether 
  the 
  bright 
  lines 
  in 
  the 
  

   prominence 
  spectrum 
  agree 
  in 
  position 
  with 
  the 
  dark 
  lines 
  at 
  

   the 
  center 
  of 
  the 
  H 
  and 
  K 
  bands. 
  Only 
  one 
  or 
  two 
  of 
  my 
  

   prominence 
  spectra 
  happened 
  to 
  be 
  given 
  the 
  proper 
  exposure 
  

   to 
  bring 
  out 
  both 
  the 
  bright 
  and 
  dark 
  lines, 
  but 
  in 
  these 
  the 
  

   coincidence 
  is 
  fairly 
  satisfactory. 
  I 
  have 
  not 
  as 
  yet, 
  however, 
  

   been 
  able 
  to 
  obtain 
  the 
  wave-lengths 
  of 
  the 
  dark 
  lines 
  in 
  

   hundredths 
  of 
  a 
  tenth-meter, 
  but 
  Professor 
  Rowland's 
  deter- 
  

   minations 
  of 
  wave-lengths 
  for 
  the 
  corresponding 
  calcium 
  lines 
  

   will 
  answer 
  nearly 
  as 
  well. 
  These 
  have 
  been 
  given 
  in 
  the 
  

   third 
  column 
  of 
  the 
  table 
  of 
  wave-lengths. 
  It 
  will 
  be 
  seen 
  

   that 
  in 
  the 
  case 
  of 
  H 
  the 
  prominence 
  line 
  is 
  O05 
  tenth-meters 
  

   more 
  refrangible, 
  while 
  at 
  K 
  the 
  prominence 
  line 
  is 
  0-06 
  tenth- 
  

   meters 
  less 
  refrangible. 
  Professor 
  Rowland 
  considers 
  his 
  values 
  

   correct 
  within 
  1 
  or 
  2 
  hundredths 
  tenth-meters, 
  while 
  the 
  prob- 
  

   able 
  errors 
  in 
  the 
  position 
  of 
  the 
  prominence 
  lines, 
  deduced 
  on 
  

   the 
  assumption 
  of 
  equal 
  weights 
  for 
  the 
  wave-lengths 
  given 
  by 
  

   each 
  of 
  six 
  plates, 
  are 
  0*021 
  and 
  0*036 
  tenth-meters 
  for 
  H 
  and 
  

   K 
  respectively. 
  On 
  the 
  whole, 
  then, 
  there 
  can 
  be 
  little 
  doubt 
  

   that 
  these 
  prominence 
  lines 
  are 
  due 
  to 
  calcium, 
  and 
  are 
  there- 
  

   fore 
  probably 
  true 
  reversals 
  of 
  the 
  central 
  dark 
  lines 
  of 
  the 
  H 
  

   and 
  K 
  bands. 
  

  

  It 
  will 
  be 
  of 
  interest 
  next 
  to 
  consider 
  briefly 
  the 
  character 
  of 
  

   these 
  two 
  prominence 
  lines. 
  In 
  all 
  cases 
  they 
  are 
  quite 
  narrow 
  

   and 
  sharp, 
  except 
  when 
  motion 
  in 
  the 
  line 
  of 
  sight 
  has 
  pro- 
  

   duced 
  broadening 
  or 
  distortion. 
  In 
  seven 
  photographs 
  made 
  

  

  