﻿Commencement. 
  

  

  Close. 
  

  

  . 
  i6h. 
  5m. 
  

  

  i6h. 
  34m. 
  

  

  , 
  i6h. 
  2.5m. 
  

  

  i6h. 
  36m. 
  

  

  . 
  i6h. 
  6.5m. 
  

  

  i6h. 
  14m. 
  

  

  . 
  i6h. 
  5.5m. 
  

  

  i6h. 
  I2'5m. 
  

  

  62 
  OLDHAM 
  : 
  GREAT 
  EARTHQUAKE 
  OF 
  1897. 
  

  

  this 
  is 
  regulated 
  with 
  the 
  same 
  accuracy 
  as 
  those 
  of 
  the 
  magnetic 
  

   instruments, 
  and 
  that 
  the 
  time 
  derived 
  from 
  it 
  may 
  be 
  regarded 
  as 
  

   accurate 
  within 
  one 
  minute 
  at 
  the 
  outside. 
  

  

  Abstracting 
  the 
  results, 
  we 
  have 
  the 
  following 
  times 
  of 
  com- 
  

   mencement 
  and 
  cessation 
  of 
  movement 
  as 
  derived 
  from 
  the 
  records 
  

   of 
  the 
  different 
  instruments: 
  — 
  

  

  Declination 
  ...» 
  

   Horizontal 
  force 
  . 
  

   Vertical 
  force 
  . 
  . 
  . 
  

  

  Barograph 
  . 
  

  

  It 
  will 
  be 
  seen 
  that 
  the 
  disturbance 
  of 
  the 
  horizontal 
  force 
  

   instrument 
  commences 
  2-J- 
  minutes 
  before 
  that 
  of 
  the 
  declination, 
  

   while 
  the 
  vertical 
  force 
  shows 
  no 
  disturbance 
  till 
  i£ 
  minutes 
  

   later. 
  The 
  disturbance 
  of 
  the 
  barograph 
  must 
  necessarily 
  be 
  purely 
  

   mechanical, 
  and 
  the 
  early 
  commencement 
  of 
  the 
  disturbance 
  of 
  the 
  

   horizontal 
  force 
  instrument 
  is 
  probably 
  the 
  same, 
  but 
  it 
  is 
  doubtful 
  

   which 
  of 
  these 
  we 
  should 
  compare 
  with 
  the 
  commencement 
  of 
  the 
  

   sensible 
  earthquake 
  at 
  other 
  places. 
  The 
  movements 
  which 
  affected 
  

   the 
  horizontal 
  force 
  instrument 
  are 
  very 
  likely 
  due 
  to 
  the 
  small 
  

   unfelt 
  tremors 
  which 
  run 
  in 
  advance 
  of 
  the 
  main 
  earthquake 
  wave 
  

   and 
  gain 
  on 
  it 
  as 
  they 
  travel 
  from 
  the 
  origin. 
  This 
  being 
  so, 
  it 
  is 
  the 
  

   barograph 
  and 
  the 
  vertical 
  force 
  instrument 
  that 
  more 
  closely 
  re- 
  

   corded 
  the 
  advent 
  of 
  the 
  phase 
  of 
  the 
  disturbance 
  which 
  corresponds 
  

   to 
  the 
  commencement 
  of 
  the 
  felt 
  earthquake 
  at 
  places 
  further 
  east. 
  

  

  How 
  far 
  the 
  difference 
  in 
  the 
  recorded 
  times, 
  i6h. 
  5'5m. 
  and 
  

   i6h. 
  6'5m. 
  is 
  due 
  to 
  a 
  difference 
  in 
  the 
  sensitiveness 
  of 
  the 
  two 
  

   instruments, 
  and 
  how 
  far 
  to 
  errors 
  of 
  the 
  timepiece, 
  or 
  of 
  reading 
  

   the 
  traces, 
  it 
  is 
  not 
  possible 
  to 
  say. 
  Probably 
  the 
  best 
  result 
  would 
  

   be 
  obtained 
  by 
  taking 
  a 
  mean 
  of 
  the 
  two, 
  or 
  i6h. 
  6m. 
  local 
  time. 
  

   As 
  the 
  difference 
  in 
  longitude 
  between 
  the 
  Madras 
  and 
  Bombay 
  

   Observatories 
  is 
  29m. 
  43*5s., 
  this 
  makes 
  the 
  Madras 
  time 
  i6h. 
  35m. 
  

   43*5s., 
  or 
  say 
  i6h. 
  35*75m. 
  If 
  the 
  time 
  of 
  commencement 
  is 
  taken 
  from 
  

   the 
  horizontal 
  force 
  instrument 
  this 
  would 
  be 
  i6h, 
  32'25m. 
  or 
  3'5m. 
  

   earlier. 
  

  

  ( 
  62 
  ) 
  

  

  