﻿THE 
  UNFELT 
  EARTHQUAKE. 
  227 
  

  

  Chapter 
  XV.— 
  THE 
  UNFELT 
  EARTHQUAKE. 
  

  

  Beyond 
  the 
  limits 
  of 
  the 
  area 
  over 
  which 
  the 
  earthquake 
  was 
  re- 
  

   cognised 
  without 
  instrumental 
  aid, 
  its 
  effects 
  were 
  impressed 
  on 
  the 
  

   records 
  not 
  only 
  of 
  instruments 
  which 
  have 
  been 
  set 
  up 
  for 
  the 
  special 
  

   purpose 
  of 
  detecting 
  the 
  imperceptible 
  tremors 
  and 
  undulations 
  which 
  

   traverse 
  more 
  or 
  less 
  the 
  whole 
  of 
  the 
  earth, 
  after 
  great 
  earthquakes, 
  

   but 
  also 
  on 
  those 
  of 
  self-recording 
  magnetic 
  and 
  electric 
  instruments. 
  

   After 
  the 
  earthquake 
  every 
  endeavour 
  was 
  made 
  to 
  obtain 
  as 
  

   complete 
  a 
  set 
  of 
  these 
  records 
  as 
  possible, 
  and 
  I 
  have 
  to 
  acknowledge 
  

   the 
  readiness 
  with 
  which 
  information 
  was 
  rendered, 
  and 
  even 
  

   photographs 
  and 
  laborious 
  tracings 
  of 
  the 
  records, 
  made 
  and 
  sent. 
  1 
  

  

  The 
  unfelt 
  disturbances 
  due 
  to 
  distant 
  earthquakes 
  are 
  commonly 
  

   referred 
  to 
  as 
  microseismic, 
  but 
  the 
  term 
  is 
  hardly 
  applicable 
  to 
  

   undulations 
  which, 
  in 
  the 
  case 
  of 
  this 
  earthquake, 
  had 
  a 
  length 
  

   of 
  34 
  miles 
  and 
  caused 
  the 
  ground 
  to 
  rise 
  and 
  fall 
  20 
  inches. 
  2 
  Instead 
  of 
  

   microseismic 
  I 
  would 
  introduce 
  the 
  term 
  cryptoseismic 
  as 
  more 
  

   suitable 
  ; 
  it 
  implies 
  nothing 
  except 
  that 
  the 
  movement 
  is 
  not 
  obvious, 
  

   and 
  is 
  useful 
  to 
  distinguish 
  between 
  the 
  unfelt'movements 
  due 
  to 
  a 
  

   distant 
  earthquake, 
  and 
  the 
  movements 
  due 
  to 
  an 
  earthquake 
  of 
  so 
  

   small 
  an 
  order 
  of 
  magnitude 
  that 
  it 
  never 
  becomes 
  sensible, 
  except 
  

   to 
  very 
  delicate 
  instruments 
  ; 
  to 
  these 
  the 
  term 
  microseismic 
  might 
  

   well 
  be 
  restricted. 
  

  

  The 
  records 
  vary 
  much 
  in 
  value 
  according 
  to 
  the 
  nature 
  of 
  the 
  

   instruments 
  employed. 
  In 
  many 
  cases 
  these 
  were 
  in 
  reality 
  too 
  deli- 
  

  

  1 
  A 
  very 
  detailed 
  account 
  of 
  the 
  records 
  of 
  this 
  earthquake, 
  obtained 
  in 
  Europe, 
  has 
  been 
  

   compiled 
  by 
  Dr. 
  G. 
  Agamennone 
  and 
  published 
  in 
  the 
  Boll. 
  Soc.Sismol. 
  Ital., 
  Ill, 
  pt. 
  ii, 
  pp. 
  249 
  

   —293. 
  In 
  this 
  details 
  are 
  given 
  of 
  some 
  records 
  which 
  I 
  was 
  unable 
  to 
  obtain. 
  The 
  account 
  

   of 
  those 
  referred 
  to 
  is 
  also 
  more 
  detailed 
  and 
  lengthy 
  than 
  that 
  printed 
  in 
  this 
  chapter. 
  

   In 
  some 
  instances 
  the 
  times 
  differ 
  slightly 
  but 
  no 
  alteration 
  has 
  been 
  made 
  in 
  those 
  printed, 
  

   which 
  are 
  the 
  times 
  as 
  originally 
  communicated 
  to 
  me, 
  as 
  the 
  changes 
  were 
  too 
  slight 
  to 
  justify 
  

   the 
  labour 
  of 
  recalculation. 
  For 
  the 
  same 
  reason 
  the 
  details 
  regarding 
  records 
  at 
  stations 
  

   from 
  which 
  1 
  had 
  not 
  previously 
  obtained 
  information 
  have 
  not 
  been 
  incorporated 
  in 
  the 
  

   chapter, 
  with 
  a 
  few 
  exceptions 
  specifically 
  referred 
  to. 
  

  

  8 
  These 
  figures 
  are 
  taken 
  from 
  Prof. 
  Agamennone, 
  Boll. 
  Soc. 
  Sismol. 
  Ital., 
  IV, 
  pt. 
  i, 
  66 
  (i898)r 
  

   They 
  are 
  intended 
  to 
  apply 
  specially 
  to 
  Italy 
  but 
  are 
  equally 
  truelfor 
  the 
  whole 
  of 
  Europe. 
  

  

  Q 
  2 
  ( 
  227 
  ) 
  

  

  