﻿1875.] 
  

  

  on 
  the 
  Transit 
  of 
  Venus. 
  

  

  315 
  

  

  The 
  time 
  was 
  given 
  by 
  a 
  chronometer 
  marked 
  " 
  Wiren 
  34," 
  which 
  was 
  

   lent 
  to 
  me 
  by 
  the 
  celebrated 
  astronomer, 
  "William 
  Dollen, 
  of 
  Pulkowa. 
  

  

  At 
  18 
  h 
  40 
  m 
  M. 
  T. 
  the 
  sun 
  rose 
  clear 
  and 
  brilliant 
  over 
  the 
  eastern 
  range 
  

   of 
  the 
  Arabian 
  hills 
  on 
  the 
  valley 
  of 
  the 
  Nile 
  under 
  very 
  favourable 
  con- 
  

   ditions 
  of 
  sky 
  and 
  atmosphere, 
  more 
  so 
  on 
  this 
  occasion 
  than 
  on 
  any 
  

   other 
  morning 
  during 
  our 
  stay 
  of 
  20 
  days 
  at 
  Luxor. 
  The 
  first 
  glance 
  

   showed 
  us 
  the 
  image 
  of 
  the 
  planet 
  Yenus 
  on 
  the 
  sun's 
  disk 
  in 
  the 
  pre- 
  

   dicted 
  place, 
  making 
  progress 
  in 
  her 
  path 
  across 
  the 
  sun 
  to 
  the 
  point 
  

   of 
  egress. 
  

  

  At 
  the 
  first 
  observation 
  the 
  borders 
  of 
  the 
  planet 
  appeared 
  jagged 
  and 
  

   ill-defined, 
  but 
  as 
  the 
  altitude 
  increased 
  she 
  presented 
  a 
  dark 
  disk, 
  clearly 
  

   defined 
  on 
  the 
  sun. 
  When 
  the 
  time 
  of 
  internal 
  contact 
  approached, 
  the 
  

   edge 
  of 
  the 
  planet 
  and 
  the 
  limb 
  of 
  the 
  sun 
  were 
  both 
  very 
  distinct, 
  and 
  

   favourable 
  for 
  making 
  accurate 
  observations. 
  

  

  When 
  the 
  moment 
  of 
  internal 
  contact 
  drew 
  near, 
  I 
  gave 
  my 
  utmost 
  

   attention 
  for 
  observing 
  the 
  appearance 
  of 
  the 
  black 
  drop 
  ; 
  but 
  I 
  could 
  not 
  

   detect 
  it, 
  though 
  I 
  could 
  perceive 
  with 
  great 
  nicety 
  the 
  instant 
  of 
  con- 
  

   tact. 
  The 
  margin 
  of 
  the 
  sun's 
  limb 
  and 
  that 
  of 
  Yenus 
  were 
  most 
  clearly 
  

   defined 
  to 
  my 
  vision. 
  

  

  Immediately 
  after 
  internal 
  contact 
  a 
  bright 
  illumination 
  manifested 
  

   itself 
  on 
  the 
  emerged 
  part 
  of 
  Yenus 
  ; 
  this 
  light 
  continued 
  bordering 
  on 
  the 
  

   cusp 
  for 
  about 
  three 
  fourths 
  of 
  the 
  time 
  between 
  internal 
  contact 
  and 
  

   external 
  contact 
  at 
  egress. 
  

  

  The 
  following 
  are 
  the 
  times 
  shown 
  by 
  chronometer 
  for 
  contacts 
  and 
  

  

  phenomena 
  : 
  — 
  

  

  h 
  m 
  s 
  

  

  Time 
  at 
  internal 
  contact 
  20 
  01 
  02-5 
  

  

  Cusp 
  of 
  Yenus 
  illuminated 
  20 
  2 
  00 
  

  

  5 
  Yenus 
  emerged, 
  cusp 
  illuminated 
  20 
  7 
  25 
  

  

  Light 
  on 
  right 
  side 
  of 
  cusp 
  became 
  brighter 
  . 
  . 
  20 
  9 
  00 
  

  

  Light 
  on 
  left 
  side 
  became 
  fainter 
  20 
  15 
  00 
  

  

  Light 
  at 
  time 
  of 
  Yenus's 
  j 
  emergence 
  20 
  15 
  30 
  

  

  Illumination 
  diminishing 
  20 
  17 
  00 
  

  

  Illumination 
  disappeared 
  20 
  20 
  00 
  

  

  | 
  Yenus 
  emerged 
  20 
  24 
  00 
  

  

  Time 
  of 
  external 
  contact 
  at 
  egress 
  20 
  29 
  25 
  

  

  I 
  must 
  remark 
  that 
  I 
  found 
  it 
  a 
  matter 
  of 
  considerable 
  difficulty 
  to 
  

   note 
  the 
  precise 
  instant 
  of 
  the 
  last 
  or 
  external 
  contact 
  at 
  egress, 
  as 
  the 
  in- 
  

   dentation 
  became 
  so 
  extremely 
  slight 
  towards 
  the 
  planet 
  making 
  final 
  egress. 
  

  

  The 
  error 
  of 
  the 
  chronometer 
  was 
  estimated 
  to 
  be 
  very 
  nearly 
  

   + 
  15 
  m 
  02 
  s, 
  by 
  preliminary 
  calculation 
  ; 
  hence 
  the 
  times 
  of 
  contact 
  by 
  

   my 
  observations, 
  corrected 
  for 
  mean 
  time 
  at 
  Luxor, 
  will 
  stand 
  thus 
  :" 
  — 
  

  

  h 
  m 
  s 
  

  

  Internal 
  contact 
  at 
  egress 
  20 
  16 
  04*5 
  

  

  External 
  contact 
  at 
  egress 
  20 
  44 
  27'0 
  

  

  2 
  b 
  2 
  

  

  