﻿RATE 
  OF 
  PROPAGATION. 
  53 
  

  

  Chapter 
  IV.— 
  THE 
  RATE 
  OF 
  PROPAGATION, 
  AND 
  TIME 
  

   OF 
  THE 
  COMMENCEMENT 
  OF 
  THE 
  SHOCK. 
  

  

  Of 
  all 
  the 
  data 
  required 
  in 
  seismological 
  investigations 
  none 
  are 
  

   so 
  important 
  and 
  none 
  so 
  difficult 
  to 
  obtain 
  as 
  the 
  exact 
  times 
  at 
  

   which 
  the 
  various 
  phases 
  of 
  an 
  eathquake 
  were 
  felt. 
  This 
  is 
  partly 
  

   due 
  to 
  habitual 
  inaccuracy 
  in 
  timekeeping, 
  accuracy 
  to 
  a 
  second 
  

   or 
  even 
  to 
  a 
  minute 
  of 
  time 
  being 
  seldom 
  required 
  in 
  ordinary 
  life, 
  

   but 
  also 
  to 
  the 
  nature 
  of 
  the 
  eathquake 
  wave 
  or 
  series 
  of 
  waves. 
  

   They 
  do 
  not 
  commence 
  abruptly 
  and 
  cease 
  absolutely 
  at 
  determin- 
  

   able 
  moments, 
  but 
  the 
  sensible 
  shock 
  is 
  preceded 
  by 
  minute 
  tremors 
  

   and 
  followed 
  by 
  longer 
  and 
  slower 
  undulations, 
  both 
  of 
  which 
  are 
  

   insensible, 
  but 
  in 
  different 
  degrees 
  to 
  different 
  people. 
  The 
  time, 
  for 
  

   which 
  the 
  preliminary 
  and 
  terminal 
  stages 
  of 
  the 
  disturbance 
  last, 
  

   increases 
  with 
  the 
  distance 
  from 
  the 
  centre, 
  and 
  it 
  would 
  be 
  possible 
  

   for 
  two 
  careful 
  observers, 
  side 
  by 
  side, 
  to 
  record 
  materially 
  different 
  

   observations 
  of 
  the 
  time 
  of 
  commencement 
  and 
  cessation 
  of 
  the 
  

   shock, 
  as 
  the 
  movements 
  felt 
  by 
  one 
  might 
  be 
  quite 
  insensible 
  to 
  the 
  

   other. 
  

  

  In 
  the 
  case 
  of 
  this 
  earthquake 
  I 
  have 
  received 
  a 
  large 
  number 
  

   of 
  time 
  records 
  from 
  various 
  sources, 
  which 
  may 
  be 
  classified 
  as 
  

   follows 
  : 
  — 
  

  

  (1) 
  The 
  automatic 
  records 
  at 
  Calcutta 
  and 
  Bombay. 
  

  

  (2) 
  Reports 
  from 
  the 
  Telegraph 
  Department. 
  

  

  (3) 
  Reports 
  from 
  Station 
  Masters. 
  

  

  (4) 
  Accounts 
  of 
  private 
  individuals. 
  

  

  The 
  second 
  of 
  these 
  categories 
  comprises 
  the 
  reports 
  which 
  all 
  

   telegraph 
  offices 
  in 
  India 
  and 
  Burma 
  were 
  ordered 
  to 
  submit. 
  It 
  

   might 
  be 
  supposed 
  that 
  the 
  time 
  records 
  from 
  these 
  would 
  show 
  a 
  

   high 
  degree 
  of 
  accuracy, 
  seeing 
  that 
  a 
  time 
  signal 
  is 
  transmitted 
  

   daily 
  to 
  every 
  office. 
  The 
  result 
  has 
  not, 
  however, 
  fulfilled 
  this 
  

   anticipation. 
  It 
  is 
  not 
  in 
  human 
  nature 
  to 
  take 
  more 
  trouble 
  than 
  

   is 
  necessary 
  to 
  attain 
  the 
  purpose 
  desired, 
  and 
  in 
  small 
  offices 
  where 
  

  

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  53 
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