﻿35- 
  OLDHAM: 
  GREAT 
  EAttlHQUAKE 
  OF 
  1 
  897. 
  

  

  of 
  Ensign 
  Spooner 
  at 
  Sylhet, 
  and 
  the 
  gate 
  pillars 
  of 
  the 
  Church 
  at 
  the 
  same 
  

   place. 
  In 
  the 
  case 
  of 
  such 
  verj' 
  squat 
  pillars, 
  or 
  overthrown 
  portions 
  of 
  pillars, 
  

   as 
  these, 
  it 
  is 
  probable 
  that 
  overthrow 
  is 
  not 
  due 
  to 
  high 
  horizontal 
  acceleration, 
  

   but 
  to 
  a 
  large 
  vertical 
  component 
  of 
  the 
  motion. 
  They 
  must 
  in 
  fact 
  be 
  looked 
  

   upon 
  as 
  modified 
  cases 
  of 
  projection, 
  and 
  it 
  may 
  be 
  doubted 
  whether 
  the 
  formula 
  

   can 
  be 
  depended 
  on 
  in 
  those 
  cases 
  where 
  the 
  proportions 
  of 
  the 
  object 
  overthrown 
  

   are 
  such 
  as 
  to 
  give 
  accelerations 
  of 
  over 
  about 
  12 
  feet 
  per 
  sec. 
  per 
  sec. 
  

  

  It 
  will 
  be 
  seen 
  that 
  at 
  Gauhati 
  these 
  are 
  a 
  number 
  of 
  cases 
  of 
  overthrow 
  givmg 
  

   values 
  of 
  / 
  ranging 
  up 
  to 
  17 
  ft. 
  per 
  sec. 
  per 
  sec. 
  Excluding 
  the 
  high 
  values 
  

   as 
  suggested 
  in 
  the 
  last 
  paragraph, 
  we 
  get 
  an 
  average 
  acceleration 
  of 
  about 
  

   12 
  ft. 
  per 
  sec. 
  per 
  sec. 
  while 
  the 
  objects 
  projected 
  by 
  the 
  earthquake 
  (excluding 
  

   the 
  tomb 
  of 
  Mrs. 
  Lamb, 
  where 
  the 
  projected 
  pillar 
  seems 
  to 
  have 
  rolled 
  after 
  

   touching 
  the 
  ground), 
  we 
  have 
  a 
  velocity 
  wave 
  particle 
  of 
  from 
  6 
  ft. 
  to 
  8f 
  ft. 
  

   per 
  sec. 
  

  

  If 
  the 
  motion 
  of 
  the 
  wave-particle 
  was 
  a 
  simple 
  harmonic 
  one, 
  as 
  it 
  would 
  be 
  in 
  a 
  

   purely 
  elastic 
  wave, 
  and 
  as 
  it 
  has 
  generally 
  been 
  supposed 
  that 
  it 
  may 
  be 
  assumed 
  

   to 
  have 
  been, 
  without 
  any 
  material 
  error, 
  in 
  the 
  case 
  of 
  an 
  earthquake, 
  it 
  would 
  

   be 
  possible 
  to 
  calculate, 
  from 
  these 
  data, 
  both 
  the 
  amplitude 
  and 
  period 
  of 
  the 
  wave 
  

   motion. 
  1 
  But 
  if 
  we 
  attempt 
  to 
  combine 
  the 
  acceleration 
  and 
  velocity 
  deduced 
  

   we 
  obtain 
  a 
  wave 
  period 
  of 
  about 
  4 
  seconds, 
  and 
  an 
  amplitude 
  of 
  about 
  4 
  feet, 
  

   both 
  results 
  which 
  are 
  preposterously 
  impossible. 
  

  

  The 
  difficulty 
  is 
  somewhat 
  diminished, 
  though 
  not 
  removed, 
  if 
  we 
  remember 
  

   that 
  the 
  tabulated 
  values 
  of 
  the 
  maximum 
  acceleration 
  are 
  those 
  of 
  the 
  horizontal 
  

   component 
  only, 
  and 
  that 
  the 
  fact 
  of 
  stones 
  having 
  been 
  projected 
  upwards 
  shows 
  

   that 
  the 
  vertical 
  component 
  of 
  the 
  acceleration 
  must 
  have 
  been 
  greater 
  than 
  that 
  

   of 
  gravity. 
  Taking 
  it 
  as 
  only 
  equal, 
  that 
  is 
  at 
  32 
  ft. 
  per 
  sec. 
  per 
  sec, 
  and 
  the 
  

   horizontal 
  component 
  as 
  12 
  ft. 
  per 
  sec. 
  per 
  sec. 
  we 
  get 
  the 
  resultant 
  total 
  acceler- 
  

   ation 
  as 
  at 
  least 
  34 
  ft. 
  per 
  sec. 
  per 
  sec. 
  Combining 
  this 
  with 
  a 
  maximum 
  velocity 
  

   of 
  8 
  ft. 
  per 
  sec. 
  we 
  find 
  that, 
  on 
  the 
  supposition 
  that 
  this 
  velocity 
  and 
  acceleration 
  

   were 
  due 
  to 
  a 
  purely 
  elastic 
  vibration, 
  the 
  amplitude 
  would 
  have 
  been 
  about 
  2 
  ft. 
  

   and 
  the 
  period 
  i£ 
  sec, 
  while 
  if 
  the 
  maximum 
  velocity 
  was 
  only 
  6 
  ft. 
  per 
  sec. 
  the 
  

   amplitude 
  would 
  be 
  I 
  ft. 
  and 
  the 
  period 
  1 
  sec. 
  

  

  Here 
  there 
  is 
  nothing 
  to 
  find 
  fault 
  with 
  in 
  the 
  deduced 
  period 
  of 
  the 
  wave, 
  but 
  

   the 
  amplitudes, 
  involving 
  a 
  total 
  range 
  of 
  motion 
  of 
  4 
  feet 
  and 
  2 
  feet, 
  respectively, 
  

   are 
  far 
  beyond 
  what 
  there 
  is 
  any 
  reason 
  to 
  believe 
  took 
  place 
  ; 
  and 
  it 
  must 
  be 
  

   remembered 
  that 
  the 
  maximum 
  acceleration 
  and 
  the 
  maximum 
  velocity 
  of 
  wave- 
  

   particle 
  were 
  certainly 
  not 
  less 
  than 
  the 
  amounts 
  utilized 
  in 
  making 
  this 
  calculation, 
  

   but 
  were 
  probably 
  greater. 
  

  

  ' 
  From 
  the 
  formula 
  for 
  simple 
  harmonic 
  motion 
  

   2 
  -n 
  a 
  >_ 
  

  

  Wc 
  obtain 
  

  

  •Dt 
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