﻿THE 
  UNFELT 
  EARTHQUAKE. 
  24$ 
  

  

  disturbance, 
  or 
  of 
  its 
  different 
  phases. 
  There 
  is 
  a 
  tolerably 
  close 
  

   agreement 
  between 
  the 
  time 
  of 
  the 
  first 
  disturbance 
  of 
  the 
  horizontal 
  

   force 
  instrument 
  and 
  the 
  times 
  recorded 
  in 
  Italy, 
  as 
  those 
  of 
  

   the 
  arrival 
  of 
  the 
  waves 
  of 
  the 
  first 
  phase, 
  and 
  when 
  we 
  consider 
  that 
  

   this 
  instrument 
  is 
  by 
  its 
  construction 
  especially 
  sensitive 
  to 
  

   mechanical, 
  as 
  well 
  as 
  magnetic, 
  disturbances 
  this 
  agreement 
  is 
  not 
  

   to 
  be 
  wondered 
  at. 
  

  

  When 
  dealing 
  with 
  the 
  records 
  of 
  the 
  Bombay 
  magnetic 
  observa„, 
  

   tory 
  the 
  question 
  of 
  whether 
  the 
  disturbances 
  were 
  mechanical 
  or 
  

   magnetic 
  was 
  discussed, 
  and 
  it 
  was 
  shown 
  that 
  though 
  they 
  might 
  in 
  

   part 
  be 
  explained 
  by 
  the 
  purely 
  mechanical 
  effect 
  of 
  the 
  earthquake 
  

   yet 
  they 
  could 
  not 
  be 
  wholly 
  so 
  explained, 
  and 
  must 
  be 
  attributed 
  in 
  

   part 
  at 
  least 
  to 
  locally 
  induced 
  magnetic 
  disturbances. 
  An 
  examina- 
  

   tion 
  of 
  the 
  irregularities 
  and 
  discrepancies 
  among 
  the 
  records 
  of 
  the 
  

   European 
  observatories 
  points 
  to 
  a 
  similar 
  conclusion, 
  and 
  it 
  seems 
  

   as 
  if 
  here 
  the 
  mechanical 
  effect 
  of 
  the 
  earth 
  waves 
  was 
  completely 
  

   masked 
  by 
  the 
  induced 
  magnetic 
  disturbances 
  ; 
  a 
  conclusion 
  which 
  is 
  

   borne 
  out 
  by 
  the 
  limited 
  number 
  of 
  observatories 
  at 
  which 
  any 
  effect 
  

   was 
  noticed, 
  as 
  compared 
  with 
  the 
  much 
  larger 
  number 
  at 
  which 
  

   nothing 
  was 
  recorded, 
  though 
  the 
  instruments 
  in 
  use 
  were 
  of 
  the 
  

   same 
  type 
  and 
  in 
  some 
  cases 
  identical 
  in 
  construction. 
  

  

  Whatever 
  may 
  be 
  the 
  cause 
  of 
  the 
  disturbances 
  of 
  magnetic 
  

   instruments 
  which 
  are 
  due 
  to 
  distant 
  earthquakes 
  it 
  is 
  evident, 
  from 
  

   the 
  details 
  given 
  above, 
  that 
  the 
  records 
  are 
  useless 
  for 
  comparison 
  

   with 
  those 
  of 
  instruments 
  specially 
  constructed 
  to 
  record 
  the 
  

   mechanical 
  displacements 
  of 
  the 
  earth's 
  surface 
  due 
  to 
  distant 
  earth- 
  

   quakes 
  or 
  other 
  causes. 
  They 
  will 
  consequently 
  be 
  omitted 
  in 
  the 
  

   discussion 
  of 
  the 
  distant 
  records 
  of 
  this 
  earthquake. 
  

  

  We 
  have, 
  then, 
  records 
  which 
  can 
  be 
  utilised 
  from 
  11 
  distinct 
  

   stations, 
  situated 
  at 
  from 
  4,300 
  to 
  4,900 
  miles 
  from 
  the 
  centre, 
  as 
  

   shown 
  in 
  the 
  following 
  tabular 
  statement 
  : 
  — 
  

  

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  245 
  ) 
  

  

  