﻿164 
  UR. 
  C. 
  DAVISON 
  ON 
  THE 
  PEMBROKE 
  EARTHQUAKES 
  [May 
  1 
  897, 
  

  

  Iii 
  considering 
  this 
  Table 
  some 
  allowance 
  must 
  be 
  made 
  for 
  

   defective 
  observation 
  and 
  errors 
  of 
  memory 
  ; 
  but 
  it 
  is 
  clear, 
  as 
  a 
  

   first 
  result, 
  that 
  the 
  beginning 
  of 
  the 
  sound 
  generally 
  preceded 
  that 
  

   of 
  the 
  shock, 
  their 
  epochs 
  of 
  maximum 
  intensity 
  coincided, 
  and 
  the 
  

   end 
  of 
  the 
  sound 
  followed 
  that 
  of 
  the 
  shock. 
  

  

  The 
  most 
  notable 
  exception 
  to 
  this 
  rule 
  is 
  the 
  large 
  number 
  of 
  

   places 
  in 
  Pembrokeshire 
  at 
  which 
  the 
  beginning 
  of 
  the 
  sound 
  coincided 
  

   with 
  that 
  of 
  the 
  shock. 
  One 
  reason 
  for 
  this 
  is 
  that 
  the 
  preliminary 
  

   tremors 
  were 
  felt 
  in 
  that 
  county, 
  whereas 
  in 
  other 
  districts 
  the 
  

   beginning 
  of 
  the 
  sound 
  was 
  necessarily 
  referred 
  to 
  the 
  beginning 
  

   of 
  the 
  principal 
  vibrations. 
  For 
  vibrations 
  which 
  are 
  rapid 
  enough 
  

   to 
  be 
  perceived 
  as 
  sound, 
  the 
  ear, 
  with 
  most 
  observers, 
  is 
  a 
  far 
  more 
  

   delicate 
  seismoscope 
  than 
  the 
  body. 
  Moreover, 
  there 
  can 
  be 
  little 
  

   doubt 
  that 
  the 
  seismic 
  focus 
  was 
  many 
  miles 
  in 
  length, 
  and, 
  though 
  

   partly 
  under 
  the 
  sea, 
  extended 
  some 
  distance 
  up 
  the 
  county, 
  so 
  that 
  

   the 
  margins 
  of 
  the 
  focus 
  (from 
  which, 
  I 
  believe, 
  the 
  sound-vibrations 
  

   chiefly 
  come) 
  and 
  the 
  rest 
  of 
  the 
  focus 
  were 
  almost 
  equidistant 
  from 
  

   many 
  of 
  the 
  places 
  of 
  observation. 
  In 
  other 
  parts 
  of 
  the 
  disturbed 
  

   area, 
  but 
  especially 
  in 
  those 
  which 
  lie 
  north 
  and 
  south 
  of 
  the 
  

   epicentre, 
  the 
  beginning 
  of 
  the 
  sound 
  preceded 
  that 
  of 
  the 
  shock, 
  

   because 
  the 
  nearest 
  part 
  of 
  the 
  focus 
  was 
  either 
  the 
  northern 
  or 
  

   southern 
  lateral 
  margin. 
  

  

  At 
  Penzance 
  and 
  St. 
  Goran, 
  in 
  the 
  south 
  of 
  Cornwall, 
  the 
  sound 
  

   is 
  said 
  to 
  have 
  preceded 
  the 
  shock 
  entirely 
  ; 
  and 
  at 
  Lydney, 
  in 
  the 
  

   west 
  of 
  Gloucestershire, 
  to 
  have 
  ceased 
  before 
  the 
  principal 
  vibra- 
  

   tions 
  were 
  felt. 
  These 
  observations 
  seem 
  at 
  first 
  sight 
  to 
  prove 
  

   that 
  the 
  velocity 
  of 
  the 
  sound 
  was 
  greater 
  than 
  that 
  of 
  the 
  larger 
  

   vibrations, 
  but 
  such 
  a 
  conclusion 
  is 
  not 
  sustained 
  by 
  the 
  rest 
  of 
  the 
  

   evidence. 
  At 
  four 
  other 
  places 
  in 
  the 
  south 
  of 
  Cornwall 
  the 
  epochs 
  

   of 
  maximum 
  intensity 
  of 
  the 
  sound 
  and 
  shock 
  are 
  said 
  to 
  have 
  

   coincided, 
  or 
  the 
  end 
  of 
  the 
  sound 
  to 
  have 
  followed 
  that 
  of 
  the 
  shock. 
  

   It 
  is 
  possible 
  that 
  in 
  this 
  district 
  the 
  epoch 
  of 
  maximum 
  intensity 
  

   of 
  the 
  sound 
  may 
  really 
  have 
  preceded 
  that 
  of 
  the 
  shock 
  by 
  a 
  short 
  

   interval, 
  for 
  these 
  epochs 
  are 
  difficult 
  to 
  define 
  with 
  precision. 
  

   This 
  is 
  what 
  we 
  should 
  expect, 
  for 
  the 
  south 
  of 
  Cornwall 
  lies 
  

   almost 
  in 
  the 
  continuation 
  of 
  the 
  supposed 
  fault-line, 
  and 
  the 
  

   loudest 
  sound-vibrations 
  heard 
  there 
  would 
  come 
  from 
  the 
  southern 
  

   margin 
  of 
  the 
  focus. 
  Prom 
  the 
  neighbourhood 
  of 
  Lydney 
  there 
  

   is 
  no 
  other 
  evidence 
  ; 
  but 
  if 
  the 
  sound 
  outraced 
  the 
  shock 
  in 
  one 
  

   direction 
  at 
  right 
  angles 
  to 
  the 
  focus, 
  it 
  would 
  do 
  so 
  also 
  in 
  the 
  other, 
  

   and 
  the 
  observations 
  from 
  the 
  south-east 
  of 
  Ireland 
  are 
  entirely 
  

   opposed 
  to 
  this. 
  On 
  the 
  other 
  hand, 
  the 
  records 
  both 
  from 
  

   Gloucestershire 
  and 
  Ireland 
  are 
  what 
  we 
  should 
  anticipate 
  with 
  a 
  

   westerly 
  hade 
  of 
  the 
  originating 
  fault. 
  

  

  Another 
  explanation 
  of 
  the 
  observations 
  is 
  not 
  impossible. 
  At 
  

   Ballywalter 
  (in 
  Co. 
  Wexford) 
  and 
  Newcastle 
  (in 
  Co. 
  Wicklow) 
  two 
  

   series 
  of 
  vibrations 
  were 
  felt, 
  and 
  the 
  sound 
  was 
  perceived 
  only 
  in 
  

   the 
  interval 
  between 
  them. 
  Now, 
  if 
  the 
  first 
  and 
  slighter 
  series 
  had 
  

   escaped 
  notice, 
  as 
  it 
  seems 
  to 
  have 
  done 
  in 
  some 
  places, 
  the 
  sound 
  

   would 
  to 
  the 
  observers 
  there 
  have 
  appeared 
  to 
  precede 
  the 
  shock 
  

  

  