﻿1875.] 
  On 
  White 
  Lines 
  in 
  the 
  Solar 
  Spectrum. 
  259 
  

  

  (1) 
  In 
  view 
  of 
  the 
  light-ring 
  L 
  k 
  , 
  and 
  of 
  the 
  peculiar 
  boiling 
  annulus 
  

   around 
  V 
  n 
  , 
  which 
  may 
  be 
  called 
  L 
  n 
  , 
  I 
  have 
  no 
  doubt 
  that 
  L 
  n 
  was, 
  in 
  fact, 
  

   a 
  continuation 
  of 
  the 
  light-ring 
  L 
  k 
  , 
  ivhich 
  latter, 
  beyond 
  all 
  question, 
  was 
  

   plainly 
  visible; 
  and 
  under 
  these 
  circumstances 
  it 
  may 
  be 
  urged 
  that 
  

   Venus 
  is 
  surrounded 
  by 
  an 
  atmosphere 
  which 
  at 
  the 
  time 
  was 
  made 
  visible 
  

   to 
  the 
  extent 
  of 
  2" 
  to 
  under 
  4" 
  in 
  breadth. 
  

  

  (2) 
  As 
  a 
  matter 
  of 
  fact, 
  the 
  pear-drop 
  and 
  the 
  ligament 
  were 
  visible 
  at 
  a 
  

   height 
  of 
  2200 
  feet, 
  but 
  at 
  6500 
  feet 
  the 
  ligament 
  was 
  invisible. 
  The 
  

   influence 
  generally 
  of 
  height 
  of 
  statiou, 
  from 
  this 
  evidence, 
  appears 
  unde- 
  

   niable 
  ; 
  but 
  the 
  phenomenon 
  still 
  remains 
  to 
  be 
  accounted 
  for 
  definitely. 
  

   If, 
  however, 
  an 
  effective 
  atmosphere 
  of 
  x 
  breadth 
  around 
  Venus 
  be 
  con- 
  

   ceded, 
  this 
  atmosphere 
  may 
  be 
  supposed 
  to 
  stop 
  a 
  certain 
  amount 
  of 
  

   direct 
  light 
  from 
  the 
  sun, 
  producing 
  a 
  slight 
  shade 
  around 
  Venus 
  corre- 
  

   sponding 
  to 
  the 
  breadth 
  x. 
  This 
  shade 
  would, 
  I 
  conceive, 
  be 
  quite 
  invi- 
  

   sible 
  when 
  its 
  outer 
  edge 
  is 
  backed 
  by 
  the 
  sun's 
  bright 
  light; 
  but 
  could 
  

   we 
  contract 
  the 
  sun 
  to 
  a 
  diameter 
  equal 
  to 
  that 
  of 
  Venus 
  plus 
  twice 
  x, 
  

   and 
  make 
  Venus 
  and 
  the 
  sun 
  concentric, 
  it 
  appears 
  likely 
  that 
  we 
  should 
  

   see 
  a 
  shaded 
  annulus 
  right 
  round 
  Venus 
  between 
  her 
  limb 
  and 
  that 
  of 
  the 
  

   sun 
  ; 
  further, 
  that 
  the 
  annulus 
  would 
  appear 
  darker 
  at 
  low 
  than 
  at 
  

   higher 
  altitudes, 
  and 
  would 
  become 
  invisible 
  when 
  the 
  observer 
  was 
  

   raised 
  above 
  a 
  sufficiency 
  of 
  the 
  earth's 
  atmosphere. 
  Should 
  these 
  

   suggestions 
  prove 
  tenable, 
  the 
  ligament 
  seen 
  would 
  break 
  when 
  the 
  

   outer 
  edge 
  of 
  the 
  shade, 
  corresponding 
  to 
  x, 
  transited 
  across 
  the 
  sun's 
  

   limb. 
  

  

  (3) 
  Solar 
  light 
  shining 
  through 
  Venus's 
  atmosphere, 
  if 
  any, 
  produces 
  

   no 
  alteration 
  in 
  the 
  lines 
  of 
  the 
  solar 
  spectrum, 
  so 
  far 
  as 
  the 
  dispersion 
  

   of 
  a 
  single 
  simple 
  prism 
  can 
  show. 
  Also 
  Venus's 
  face, 
  turned 
  towards 
  

   us, 
  reflects 
  no 
  light 
  during 
  transit, 
  subject 
  to 
  the 
  same 
  instrumental 
  test. 
  

  

  Night 
  of 
  10th 
  Dec, 
  1874. 
  

  

  III. 
  " 
  Appendix 
  to 
  Note, 
  dated 
  November 
  1873, 
  on 
  White 
  Lines 
  in 
  

   the 
  Solar 
  Spectrum." 
  By 
  J. 
  B. 
  N. 
  Hennessey, 
  F.R.A.S. 
  

   Communicated 
  by 
  Professor 
  Stokes, 
  Sec.E.S. 
  Received 
  

   January 
  11, 
  1875. 
  

  

  After 
  detection 
  of 
  the 
  white 
  lines 
  1650 
  and 
  1658 
  (Kirchhoffs 
  scale) 
  at 
  

   Mussoorie 
  in 
  November 
  1873, 
  I 
  discovered 
  two 
  other 
  such 
  lines 
  before 
  

   leaving 
  that 
  station 
  of 
  observation, 
  viz. 
  2009 
  and 
  2068 
  (about). 
  On 
  

   20th 
  November, 
  1873, 
  I 
  packed 
  up 
  the 
  spectroscope, 
  taking 
  particular 
  

   care 
  that 
  the 
  prisms 
  should 
  not 
  shift 
  from 
  the 
  position 
  they 
  then 
  

   occupied. 
  

  

  On 
  28th 
  November, 
  1873, 
  I 
  set 
  up 
  the 
  spectroscope 
  in 
  the 
  Dome 
  

   Observatory 
  at 
  Dehra, 
  in 
  the 
  valley 
  below, 
  the 
  prisms 
  retaining 
  their 
  

   former 
  position, 
  and 
  my 
  recollection 
  of 
  the 
  white 
  lines 
  seen 
  at 
  Mussoorie 
  

  

  