﻿380 
  Mr. 
  J. 
  B. 
  N. 
  Hennessey 
  on 
  the 
  [Apr. 
  29. 
  

  

  mined. 
  Proceeding 
  in 
  this 
  manner, 
  and 
  tabulating 
  the 
  mean 
  of 
  the 
  results 
  

   by 
  the 
  three 
  fixed 
  chronometers, 
  it 
  was 
  determined 
  :— 
  

  

  Mean 
  Results. 
  

  

  Astronomical 
  

   date. 
  

  

  Dec. 
  4. 
  

   „ 
  5. 
  

   „ 
  6. 
  

   „ 
  7. 
  

  

  Chronometer- 
  

   reading, 
  

   h 
  m 
  s 
  

   6 
  47 
  18-5 
  

   6 
  48 
  40-6 
  

   6 
  37 
  19-1 
  

   Cloudy 
  

   6 
  42 
  12-1 
  

   18 
  56 
  17-4 
  

   23 
  17 
  19-4 
  

   6 
  37 
  52-6 
  

  

  Fast 
  on 
  local 
  

   mean 
  time. 
  

  

  31-3 
  

   37-7 
  

   45-1 
  

  

  58-6 
  

  

  2- 
  2 
  

  

  3- 
  5 
  

   5-8 
  

  

  Daily 
  

   rate. 
  

  

  + 
  6-5 
  ^ 
  

  

  + 
  7-5 
  

   + 
  6-7 
  

  

  + 
  7-3 
  

  

  >...(!) 
  

  

  4. 
  On 
  the 
  day 
  of 
  transit 
  the 
  journeyman 
  was 
  compared 
  with 
  the 
  three 
  

   fixed 
  chronometers 
  before 
  and 
  after 
  ingress, 
  and 
  also 
  before 
  and 
  after 
  

   egress 
  ; 
  and 
  by 
  employing 
  the 
  daily 
  rate 
  of 
  -f- 
  7 
  S, 
  3, 
  and 
  correcting 
  the 
  times 
  

   of 
  contact 
  determined 
  by 
  the 
  journeyman 
  chronometer, 
  we 
  obtain 
  : 
  — 
  

  

  Local 
  mean 
  time. 
  

   1874, 
  Dec. 
  8. 
  h 
  m 
  s 
  

  

  1st 
  internal 
  contact 
  occurred 
  19 
  29 
  19*3 
  

  

  2nd 
  „ 
  „ 
  „ 
  23 
  17 
  42-9 
  

  

  2nd 
  external 
  „ 
  „ 
  23 
  44 
  59*9 
  

  

  • 
  (2) 
  

  

  where 
  the 
  tenths 
  of 
  seconds 
  come 
  into 
  existence 
  through 
  the 
  arithmetical 
  

   processes 
  involved. 
  The 
  original 
  times 
  were 
  recorded 
  merely 
  to 
  the 
  

   nearest 
  second, 
  and 
  I 
  have 
  no 
  doubt 
  that 
  the 
  latter 
  degree 
  of 
  rigour 
  was 
  

   much 
  in 
  excess 
  of 
  what 
  the 
  phenomena 
  were 
  susceptible 
  ; 
  so 
  that 
  the 
  pro- 
  

   cedure 
  adopted 
  for 
  determining 
  time 
  appears 
  amply 
  rigorous.' 
  Speaking 
  

   roughly, 
  1" 
  of 
  Venus's 
  diameter 
  took 
  26 
  s 
  to 
  transit 
  ; 
  and 
  supposing 
  that 
  

   I 
  could 
  see 
  0"*1 
  of 
  the 
  former 
  (which 
  I 
  doubt), 
  each 
  contact 
  should 
  have 
  

   lasted, 
  visibly, 
  for 
  say 
  3 
  s 
  . 
  But 
  as 
  regards 
  the 
  estimates 
  of 
  accuracy 
  I 
  

   actually 
  made 
  immediately 
  after 
  the 
  events, 
  I 
  find 
  it 
  recorded 
  that 
  I 
  

   thought 
  my 
  times 
  may 
  be 
  true 
  within 
  the 
  following 
  limits 
  : 
  — 
  

  

  Time 
  of 
  1st 
  internal 
  contact 
  +3 
  S 
  to 
  4 
  s 
  

  

  „ 
  2nd 
  „ 
  „ 
  ± 
  2 
  s 
  

  

  2nd 
  external 
  „ 
  ...... 
  4- 
  1* 
  

  

  . 
  . 
  . 
  (3) 
  

  

  I 
  am 
  now, 
  however, 
  of 
  opinion 
  that 
  these 
  estimates 
  (3) 
  should 
  be 
  

   increased 
  by 
  one 
  half. 
  

  

  5. 
  Erom 
  what 
  has 
  preceded, 
  the 
  Greenwich 
  mean 
  times 
  of 
  contact 
  

   are 
  : 
  — 
  

  

  h 
  m 
  s 
  

  

  1st 
  internal 
  contact 
  14 
  17 
  7*1 
  

  

  2nd 
  „ 
  „ 
  18 
  5 
  30-7 
  y 
  ... 
  (4) 
  

  

  2nd 
  external 
  

  

  18 
  32 
  47-7 
  

  

  