﻿358 
  OLDHAM: 
  GREAT 
  EARTHQUAKE 
  OF 
  1897. 
  

  

  in 
  the 
  direction 
  of 
  overthrow. 
  At 
  a 
  greater 
  distance 
  from 
  the 
  epicentre 
  and 
  

   where 
  it 
  has 
  come 
  to 
  subtend 
  but 
  a 
  small 
  angle, 
  it 
  is 
  to 
  be 
  remarked 
  that 
  the 
  

   directions 
  of 
  overthrow 
  almost 
  all 
  point 
  towards 
  it. 
  

  

  From 
  this 
  it 
  would 
  seem 
  that 
  the 
  method 
  of 
  determining 
  the 
  epicentre 
  by 
  

   means 
  of 
  the 
  direction 
  of 
  overthrow 
  of 
  free-falling 
  objects 
  is 
  one 
  that 
  may 
  be 
  

   depended 
  on, 
  when 
  other 
  means 
  fail. 
  Certain 
  obvious 
  precautions 
  must 
  be 
  taken. 
  

   The 
  objects 
  whose 
  direction 
  of 
  overthrow 
  is 
  taken 
  must 
  be 
  of 
  such 
  a 
  shape 
  that 
  

   they 
  have 
  no 
  greatly 
  prevalent 
  tendency 
  to 
  fall 
  in 
  one 
  direction 
  rather 
  than 
  another 
  

   and 
  they 
  must 
  have 
  been 
  overthrown 
  cleanly. 
  If 
  the 
  surface 
  of 
  fracture 
  shows 
  

   great 
  crushing 
  at 
  the 
  edges, 
  indicating 
  that 
  the 
  pillar 
  has 
  rocked 
  to 
  and 
  fro 
  before 
  

   falling, 
  it 
  should 
  not 
  be 
  utilised, 
  as 
  the 
  final 
  direction 
  of 
  overthrow 
  is 
  almost 
  cer- 
  

   tain 
  not 
  to 
  be 
  that 
  in 
  which 
  it 
  was 
  first 
  set 
  rocking. 
  Another 
  precaution 
  to 
  be 
  

   observed 
  is 
  that 
  the 
  observations 
  must 
  be 
  sufficiently 
  numerous, 
  and 
  the 
  inter- 
  

   sections 
  lie 
  pretty 
  close 
  together. 
  This 
  is 
  necessary 
  for, 
  though 
  it 
  is 
  certain 
  that 
  in 
  

   some 
  earthquakes 
  the 
  greatest 
  and 
  most 
  violent 
  motion 
  is 
  directly 
  in 
  the 
  line 
  of 
  

   propagation 
  of 
  the 
  earthquake 
  wave, 
  it 
  is 
  possible 
  that 
  in 
  others 
  the 
  reverse 
  may 
  

   be 
  the 
  case, 
  and, 
  if 
  so, 
  the 
  directions 
  of 
  overthrow 
  will 
  not, 
  if 
  produced, 
  intersect 
  at 
  

   or 
  near 
  the 
  right 
  point. 
  

  

  Appendix 
  E. 
  

  

  Details 
  of 
  the 
  records 
  of 
  the 
  Seismometers 
  at 
  S 
  hit 
  long 
  and 
  

  

  Silchar. 
  

  

  In 
  1882 
  seismometers 
  of 
  Mallet's 
  cylinder 
  pattern 
  were 
  set 
  up 
  in 
  ShiHong 
  

   and 
  Silchar. 
  Each 
  consists 
  of 
  a 
  set 
  of 
  cylinders 
  12 
  inches 
  in 
  height 
  and 
  of 
  the 
  

   following 
  diameters 
  : 
  — 
  

  

  No.o 
  1" 
  No. 
  3 
  375" 
  No. 
  6 
  7-0" 
  

  

  „ 
  1 
  i'5" 
  n 
  4 
  5'o 
  " 
  » 
  1 
  8-o" 
  

  

  „ 
  2 
  25" 
  „ 
  5 
  6*o" 
  „ 
  8 
  9'o" 
  

  

  The 
  corresponding 
  accelerations 
  in 
  ft. 
  per 
  sec. 
  per 
  sec. 
  required 
  for 
  overthrow 
  

  

  are 
  : 
  — 
  

  

  No. 
  o 
  27 
  No. 
  3 
  io'o 
  No. 
  6 
  188 
  

  

  „ 
  1 
  4'o 
  „ 
  4 
  I 
  3°° 
  » 
  7 
  21*5 
  

  

  „ 
  2 
  67 
  „ 
  5 
  16-1 
  „ 
  8 
  24-2 
  

  

  Besides 
  these 
  there 
  was 
  at 
  Silchar 
  a 
  square 
  wooden 
  post, 
  4*05 
  ft. 
  in 
  height, 
  at 
  

   «ach 
  top 
  corner 
  of 
  which 
  a 
  cubical 
  recess 
  was 
  cut, 
  containing 
  a 
  small 
  bullet 
  

   to 
  be 
  projected 
  by 
  the 
  shock. 
  Full 
  details 
  of 
  these 
  instruments 
  will 
  be 
  found 
  in 
  

   Memoirs 
  Vol. 
  XIX, 
  Pt. 
  1, 
  Appendix, 
  pages 
  93-0,8, 
  and 
  need 
  not 
  be 
  repeated 
  here, 
  

   Shillong, 
  — 
  At 
  Shillong 
  the 
  seismometer 
  shed 
  is 
  close 
  to 
  the 
  hospital, 
  and 
  was 
  

   the 
  only 
  building 
  left 
  standing 
  after 
  the 
  earthquake. 
  It 
  was 
  used 
  by 
  the 
  hospital 
  

   assistant 
  to 
  shelter 
  the 
  patients, 
  and 
  all 
  that 
  is 
  known 
  of 
  the 
  effect 
  of 
  the 
  earth- 
  

   quake 
  is 
  that 
  all 
  nine 
  cylinders 
  were 
  upset 
  in 
  a 
  north-north-easterly 
  direction. 
  

   The 
  cylinders 
  were 
  not 
  reerected 
  for 
  three 
  days, 
  during 
  which 
  several 
  shocks 
  

  

  ( 
  35? 
  ) 
  

  

  