﻿G. 
  E. 
  Hale 
  — 
  The 
  Ultra- 
  Violet 
  Spectrum, 
  etc. 
  459 
  

  

  the 
  last 
  degree 
  when 
  large 
  amounts 
  of 
  potassium 
  are 
  to 
  be 
  

   estimated, 
  the 
  method, 
  we 
  think, 
  offers 
  some 
  advantage 
  with- 
  

   out 
  too 
  great 
  sacrifice 
  of 
  exactness 
  in 
  the 
  determination 
  of 
  

   small 
  amounts. 
  In 
  qualitative 
  work 
  the 
  mode 
  of 
  manipula- 
  

   ting 
  described 
  is 
  exceedingly 
  satisfactory. 
  Aside 
  from 
  the 
  

   practical 
  application 
  of 
  the 
  method 
  the 
  point 
  which 
  has 
  been 
  

   of 
  greatest 
  interest 
  to 
  us 
  is 
  the 
  development 
  of 
  the 
  fact 
  that 
  

   the 
  presence 
  of 
  sodium 
  salts 
  in 
  the 
  flame 
  is 
  of 
  direct 
  influence 
  

   in 
  strengthening 
  the 
  spectrum 
  of 
  potassium. 
  

  

  Art. 
  XLIX. 
  — 
  The 
  Ultra- 
  Violet 
  Spectrum 
  of 
  the 
  Solar 
  Prom- 
  

   inences 
  ; 
  by 
  George 
  E. 
  Hale.* 
  

  

  In 
  various 
  papers 
  published 
  during 
  the 
  past 
  year, 
  I 
  have 
  

   called 
  attention 
  to 
  some 
  of. 
  the 
  advances 
  in 
  our 
  knowledge 
  of 
  

   the 
  Solar 
  Prominences 
  which 
  might 
  be 
  expected 
  to 
  follow 
  the 
  

   application 
  of 
  photographic 
  methods 
  to 
  a 
  study 
  of 
  their 
  forms 
  

   and 
  spectra. 
  A 
  recent 
  number 
  of 
  this 
  Journal, 
  August, 
  1891, 
  

   p. 
  160, 
  contains 
  reproductions 
  of 
  some 
  photographs 
  ' 
  obtained 
  

   in 
  the 
  course 
  of 
  my 
  investigations 
  on 
  this 
  subject 
  at 
  the 
  

   Kenwood 
  Physical 
  Observatory. 
  I 
  am 
  indebted 
  to 
  Professor 
  

   Lockyer 
  for 
  the 
  use 
  of 
  a 
  measuring 
  machine 
  during 
  a 
  recent 
  

   visit 
  to 
  London, 
  and 
  I 
  am 
  now 
  able 
  to 
  give 
  my 
  determinations 
  

   of 
  wave-length 
  for 
  the 
  new 
  prominence 
  lines, 
  and 
  some 
  con- 
  

   clusions 
  to 
  be 
  drawn 
  from 
  them. 
  But 
  perhaps 
  it 
  will 
  first 
  be 
  

   well 
  to 
  consider 
  for 
  a 
  moment 
  the 
  apparatus 
  and 
  methods 
  at 
  

   present 
  employed 
  in 
  the 
  work. 
  

  

  To 
  the 
  eye 
  end 
  of 
  the 
  12*2 
  inch 
  equatorial 
  refractor 
  of 
  the 
  

   Kenwood 
  Observatory 
  a 
  large 
  solar 
  spectroscope 
  is 
  rigidly 
  

   attached 
  by 
  three 
  steel 
  tubes, 
  and 
  as 
  the 
  spectroscope 
  extends 
  

   about 
  five 
  feet 
  beyond 
  the 
  focus 
  of 
  the 
  telescope, 
  the 
  declina- 
  

   tion 
  axis 
  is 
  placed 
  at 
  the 
  center 
  of 
  the 
  combined 
  lengths 
  of 
  

   the 
  two 
  instruments, 
  in 
  order 
  to 
  reduce 
  the 
  amount 
  of 
  counter- 
  

   balance 
  required 
  at 
  the 
  object-glass 
  end. 
  The 
  result 
  is 
  very 
  

   satisfactory, 
  and 
  there 
  can 
  certainly 
  be 
  little 
  fear 
  of 
  flexure 
  in 
  

   the 
  combination. 
  The 
  whole 
  spectroscope 
  may 
  be 
  rotated 
  by 
  

   a 
  rack 
  and 
  pinion, 
  so 
  as 
  to 
  make 
  the 
  slit 
  tangential 
  or 
  radial 
  at 
  

   any 
  point 
  on 
  the 
  sun's 
  limb. 
  The 
  object-glasses 
  of 
  the 
  col- 
  

   limator 
  and 
  observing 
  telescope 
  have 
  3J- 
  inches 
  clear 
  aperture, 
  

   and 
  42J 
  inches 
  focal 
  length. 
  The 
  4-inch 
  Rowland 
  grating 
  is 
  

   ruled 
  with 
  14,438 
  Knes 
  to 
  the 
  inch, 
  and 
  as 
  the 
  telescopes 
  make 
  

   with 
  each 
  other 
  a 
  constant 
  angle 
  of 
  25°, 
  different 
  orders 
  of 
  

  

  * 
  Read 
  at 
  the 
  Cardiff 
  Meeting 
  of 
  the 
  British 
  Association 
  for 
  the 
  Advance- 
  

   ment 
  of 
  Science, 
  August, 
  1891. 
  

  

  