﻿

  6 
  OLDHAM: 
  GREAT 
  EARTHQUAKE 
  OF 
  iSg-J. 
  

  

  such 
  as 
  can 
  be 
  accepted 
  for 
  comparison. 
  If 
  we 
  exclude 
  them, 
  the 
  area 
  over 
  which 
  

   the 
  shock 
  could 
  have 
  been 
  felt 
  is 
  very 
  much 
  reduced; 
  a 
  rough 
  estimate 
  which 
  

   I 
  have 
  made, 
  and 
  nothing 
  more 
  is 
  possible, 
  places 
  the 
  total 
  area 
  over 
  which 
  the 
  

   shock 
  would 
  have 
  been 
  felt, 
  had 
  it 
  all 
  been 
  dry 
  land, 
  as 
  not 
  more 
  than 
  1,000,000 
  

   square 
  miles. 
  A 
  similar 
  estimate 
  for 
  the 
  1897 
  shock 
  gives 
  about 
  1,750,000 
  square 
  

   miles. 
  

  

  These 
  estimates 
  cannot 
  be 
  regarded 
  as 
  giving 
  an 
  exact 
  ratio 
  of 
  the 
  magnitude 
  

   of 
  (he 
  two 
  shocks. 
  In 
  the 
  case 
  of 
  the 
  Lisbon 
  earthquake 
  the 
  estimate 
  must 
  ne- 
  

   cessarily 
  be 
  very 
  approximate, 
  but 
  it 
  is 
  not 
  probable 
  that 
  it 
  could 
  be 
  raised 
  above 
  

   that 
  of 
  the 
  earthquake 
  of 
  1897. 
  At 
  any 
  rate 
  the 
  facts 
  fully 
  bear 
  out 
  the 
  statement 
  

   that 
  the 
  shock 
  of 
  1897 
  rivalled 
  that 
  of 
  1755 
  in 
  magnitude, 
  and 
  if 
  the 
  doubtful 
  

   records 
  of 
  the 
  latter 
  are 
  excluded, 
  its 
  magnitude 
  was 
  certainly 
  greater. 
  

  

  There 
  is 
  one 
  feature 
  of 
  the 
  1755 
  records 
  which 
  'might 
  lead 
  to 
  a 
  different 
  idea 
  

   and 
  that 
  is 
  the 
  many 
  accounts 
  of 
  its 
  effect 
  on 
  ponds 
  and 
  lakes 
  even 
  as 
  far 
  north 
  as 
  

   Scotland 
  and 
  Denmark, 
  1 
  as 
  contrasted 
  with 
  the 
  absence 
  of 
  similar 
  accounts 
  in 
  the 
  

   case 
  of 
  the 
  1897 
  shock. 
  This 
  is, 
  however, 
  easy 
  of 
  explanation. 
  In 
  a 
  westerly 
  

   direction 
  the 
  country 
  which 
  would 
  occupy 
  the 
  position 
  of 
  England 
  relative 
  to 
  the 
  

   area 
  over 
  which 
  the 
  shock 
  was 
  sensible, 
  is 
  mostly 
  desert, 
  sparsely 
  inhabited 
  and 
  

   devoid 
  of 
  sheets 
  of 
  water. 
  To 
  the 
  south-westwards, 
  in 
  the 
  Peninsula, 
  artificial 
  

   ponds 
  and 
  lakes 
  are 
  not 
  wanting, 
  but 
  there 
  is 
  an 
  absence 
  of 
  educated 
  and 
  intelli- 
  

   gent 
  observers. 
  To 
  the 
  east 
  and 
  north 
  the 
  area 
  over 
  which 
  the 
  shock 
  was 
  felt 
  

   extends 
  into 
  country 
  from 
  which 
  no 
  information 
  can 
  be 
  obtained. 
  

  

  On 
  the 
  other 
  hand, 
  when 
  we 
  consider 
  that 
  the 
  1755 
  shock 
  extended 
  over 
  a 
  

   populous 
  and 
  civilised 
  country, 
  that 
  it 
  attracted 
  universal 
  attention, 
  and 
  that 
  all 
  

   the 
  leading 
  scientific 
  societies 
  and 
  academies 
  of 
  western 
  Europe 
  set 
  themselves 
  to 
  

   collect 
  information 
  regarding 
  it, 
  and 
  when 
  we 
  consider 
  how 
  comparatively 
  few 
  and 
  

   imperfect 
  were 
  the 
  observations 
  collected, 
  even 
  as 
  regards 
  this 
  one 
  point 
  of 
  the 
  

   disturbance 
  of 
  water 
  in 
  ponds, 
  it 
  is 
  not 
  surprising 
  that 
  in 
  the 
  case 
  of 
  the 
  1897 
  

   shock 
  they 
  are 
  altogether 
  wanting. 
  

  

  That 
  similar 
  oscillations 
  of 
  water 
  in 
  tanks 
  took 
  place 
  I 
  do 
  not 
  doubt; 
  we 
  have 
  

   accounts 
  of 
  them 
  within 
  the 
  area 
  over 
  which 
  the 
  shock 
  was 
  felt, 
  and 
  besides 
  those 
  

   mentioned 
  in 
  the 
  text 
  I 
  received 
  numerous 
  accounts 
  of 
  disturbances 
  of 
  water 
  in 
  

   wells 
  having 
  been 
  noticed. 
  There 
  are, 
  besides, 
  two 
  separate 
  accounts, 
  showing 
  

   that, 
  outside 
  the 
  area 
  over 
  which 
  the 
  shock 
  was 
  felt, 
  the 
  undulation 
  of 
  the 
  ground 
  

   was 
  sufficient 
  to 
  make 
  doors 
  swing 
  to 
  and 
  fro. 
  2 
  

  

  For 
  these 
  reasons 
  it 
  does 
  not 
  seem 
  to 
  me 
  that 
  the 
  accounts 
  of 
  the 
  effects 
  of 
  the 
  

   Lisbon 
  earthquake 
  point 
  to 
  its 
  being 
  of 
  greater 
  magnitude, 
  so 
  far 
  as 
  this 
  can 
  be 
  

   measured 
  by 
  the 
  area 
  over 
  which 
  the 
  shock 
  was 
  felt, 
  though 
  it 
  is 
  possible 
  that 
  the 
  

   wave 
  motion 
  was 
  of 
  somewhat 
  different 
  character 
  and 
  gave 
  rise 
  to 
  surface 
  undu- 
  

   lations 
  of 
  greater 
  size 
  and 
  steepness. 
  

  

  1 
  The 
  reputed 
  disturbance 
  of 
  the 
  North 
  American 
  lakes 
  is 
  too 
  doubtfully 
  connected 
  with 
  

   earthquake 
  to 
  be 
  considered. 
  

  

  2 
  Chap. 
  II, 
  p. 
  37. 
  

  

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  376 
  ) 
  

  

  