﻿90 
  OLDHAM: 
  GREAT 
  EARTHQUAKE 
  OF 
  1897. 
  

  

  is 
  cut 
  is 
  weaker 
  than 
  the 
  shank 
  ; 
  if 
  the 
  screw 
  thread 
  ends 
  

   abruptly 
  the 
  bolt 
  will 
  always 
  give 
  way 
  at 
  the 
  junction 
  of 
  the 
  two 
  

   parts, 
  this 
  being 
  a 
  point 
  which 
  is 
  weaker 
  than 
  any 
  other 
  in 
  the 
  bolt, 
  

   and, 
  paradoxical 
  as 
  it 
  may 
  seem, 
  that 
  bolt 
  may 
  actually 
  be 
  made 
  

   stronger 
  by 
  weakening 
  the 
  stronger 
  part 
  till 
  the 
  strength 
  of 
  the 
  bolt 
  

   is 
  equal 
  at 
  every 
  point 
  of 
  its 
  length. 
  

  

  This 
  principle 
  is 
  of 
  universal 
  application, 
  and 
  from 
  it 
  we 
  see 
  

   how 
  the 
  heaping 
  up 
  of 
  an 
  embankment 
  on 
  the 
  surface 
  of 
  the 
  

   alluvium 
  produces 
  a 
  line 
  of 
  weakness 
  along 
  its 
  base 
  on 
  either 
  side, 
  

   Besides 
  this 
  cause 
  of 
  weakness, 
  we 
  have 
  the 
  fact 
  that 
  the 
  material 
  

   for 
  the 
  embankment 
  is 
  usually 
  derived 
  from 
  a 
  row 
  of 
  borrow-pits 
  

   on 
  either 
  side 
  of 
  the 
  bank. 
  These 
  two 
  causes 
  acting 
  together 
  give 
  

   rise 
  to 
  a 
  special 
  aptitude 
  for 
  fracture, 
  and 
  we 
  find 
  nearly 
  every- 
  

   where 
  throughout 
  northern 
  Bengal 
  and 
  lower 
  Assam 
  that 
  the 
  

   roads 
  and 
  railway 
  lines 
  were 
  bounded 
  on 
  either 
  side 
  by 
  a 
  set 
  of 
  

   fissures 
  running 
  parallel 
  to 
  the 
  road 
  in 
  all 
  such 
  places 
  where 
  

   fractures 
  have 
  not, 
  for 
  other 
  reasons, 
  been 
  formed 
  across 
  the 
  road. 
  

  

  There 
  was 
  a 
  very 
  noticeable 
  tendency 
  for 
  fissures, 
  of 
  the 
  nature 
  

   now 
  being 
  considered, 
  to 
  range 
  themselves 
  parallel 
  to 
  each 
  other, 
  

   and 
  at 
  first 
  the 
  direction 
  was 
  not 
  unnaturally 
  presumed 
  to 
  be 
  at 
  

   right 
  angles 
  to 
  the 
  direction 
  of 
  propagation 
  of 
  the 
  earthquake 
  wave. 
  

   This 
  assumption 
  was, 
  however, 
  found 
  to 
  be 
  untenable 
  and 
  no 
  such 
  

   general 
  rule 
  applicable. 
  Whether 
  any 
  connection 
  might 
  have 
  held 
  

   good 
  between 
  the 
  direction 
  of 
  the 
  fissures 
  and 
  that 
  of 
  the 
  visible 
  

   surface 
  waves 
  cannot 
  be 
  decided, 
  as 
  the 
  observations 
  are 
  too 
  scanty. 
  

   It 
  is 
  certain 
  that 
  these 
  undulations 
  did 
  not 
  necessarily 
  travel 
  in 
  the 
  

   same 
  direction 
  as 
  the 
  earthquake 
  wave, 
  1 
  and 
  it 
  is 
  possible 
  that 
  where 
  

   the 
  movement 
  was 
  sufficient 
  to 
  cause 
  fissures 
  to 
  be 
  formed, 
  they 
  

   followed 
  the 
  direction 
  of 
  the 
  crests 
  and 
  hollows 
  of 
  the 
  surface 
  

   waves. 
  Even 
  if 
  we 
  suppose, 
  what 
  is 
  probable 
  enough, 
  that 
  the 
  

   direction 
  of 
  propagation 
  of 
  these 
  waves 
  is 
  largely 
  governed 
  by 
  local 
  

   peculiarities 
  of 
  the 
  constitution 
  of 
  the 
  surface 
  layer 
  of 
  the 
  alluvium, 
  

  

  1 
  See 
  Chap, 
  II, 
  pp. 
  20, 
  26, 
  36, 
  40. 
  

  

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