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  OLDHAM: 
  GREAT 
  EARTHQUAKE 
  OF 
  1897. 
  

  

  cate, 
  and, 
  under 
  the 
  influence 
  of 
  so 
  exceptionally 
  great 
  a 
  disturbance 
  

   as 
  was 
  set 
  up 
  by 
  this 
  earthquake, 
  the 
  record 
  of 
  all 
  but 
  the 
  beginning 
  

   and 
  end 
  was 
  lost. 
  In 
  other 
  cases 
  the 
  rate 
  of 
  travel 
  of 
  the 
  recording 
  

   surface 
  was 
  so 
  slow 
  that 
  the 
  time 
  cannot 
  be 
  accurately 
  determined. 
  

   From 
  the 
  magnetic 
  observatories 
  the 
  replies 
  were 
  mostly 
  negative, 
  

   and 
  in 
  other 
  cases 
  the 
  disturbance 
  was 
  of 
  such 
  a 
  nature 
  as 
  to 
  preclude 
  

   the 
  possibility 
  of 
  exact 
  time 
  determinations. 
  In 
  the 
  following 
  pages 
  

   it 
  has 
  not 
  been 
  considered 
  necessary 
  to 
  refer 
  to 
  these 
  cases, 
  and 
  only 
  

   those 
  records 
  which 
  have 
  given 
  tolerably 
  trustworthy 
  determinations 
  

   of 
  time 
  are 
  referred 
  to. 
  The 
  times 
  as 
  given 
  in 
  the 
  original 
  record 
  

   have 
  in 
  every 
  case 
  been 
  converted 
  into 
  Greenwich 
  mean 
  time. 
  

  

  The 
  records 
  of 
  the 
  cryptoseismic 
  disturbance 
  fall 
  naturally 
  into 
  two 
  

   classes,— 
  those 
  of 
  instruments 
  specially 
  and 
  solely 
  intended 
  to 
  record 
  

   disturbances 
  of 
  the 
  ground, 
  and 
  those 
  of 
  magnetic 
  or 
  electric 
  instru- 
  

   ments, 
  not 
  intended 
  to 
  record 
  movements 
  of 
  the 
  ground 
  on 
  which 
  

   they 
  are 
  set 
  up, 
  though 
  giving 
  evidence 
  of 
  earth 
  movements 
  by 
  an 
  

   irregularity 
  or 
  break 
  in 
  their 
  record. 
  Foremost 
  among 
  those 
  of 
  the 
  

   first 
  class 
  I 
  must 
  place 
  the 
  valuable 
  series 
  of 
  records 
  for 
  which 
  I 
  am 
  

   indebted 
  to 
  Prof. 
  Grablowitz, 
  and 
  not 
  only 
  for 
  the 
  records 
  but 
  

   also 
  for 
  a 
  discussion 
  and 
  comparison 
  of 
  them, 
  from 
  which 
  the 
  nature 
  

   of 
  the 
  series 
  of 
  disturbances 
  is 
  clearly 
  deduced. 
  

  

  Proceeding 
  in 
  the 
  first 
  place 
  to 
  the 
  description 
  of 
  the 
  facts 
  re- 
  

   corded, 
  I 
  shall 
  afterwards 
  discuss 
  their 
  meaning 
  and 
  interpretation. 
  

  

  Casamicciola 
  (Ischia). 
  — 
  I 
  am 
  indebted 
  to 
  Prof. 
  G. 
  Grablowitz, 
  

   Director 
  of 
  the 
  well 
  equipped 
  geodynamic 
  observatory 
  at 
  Casa- 
  

   micciola, 
  for 
  a 
  most 
  interesting 
  account 
  of 
  the 
  effects 
  of 
  the 
  earth- 
  

   quake 
  on 
  his 
  instruments. 
  These 
  are 
  — 
  

  

  (1) 
  A 
  pair 
  of 
  horizontal 
  pendula, 
  arranged 
  so 
  as 
  to 
  complete 
  an 
  electric 
  circuit, 
  

   on 
  the 
  smallest 
  disturbance, 
  by 
  which 
  an 
  alarm 
  is 
  sounded, 
  a 
  time-signal 
  impressed 
  

   on 
  the 
  record 
  of 
  No. 
  (3), 
  and 
  No. 
  (4) 
  set 
  in 
  motion. 
  It 
  acted 
  at 
  nh. 
  19m. 
  3s. 
  

   G. 
  M.T. 
  

  

  (2) 
  The 
  'vasca 
  sismica,' 
  a 
  circular 
  cistern 
  1*56 
  metres 
  diameter 
  and 
  no 
  m. 
  deep 
  

   excavated 
  in 
  the 
  basement 
  of 
  the 
  observatory 
  and 
  filled 
  with 
  water 
  to 
  the 
  depth 
  

   of 
  im. 
  On 
  this 
  there 
  is 
  a 
  float 
  l*5m. 
  diameter, 
  the 
  movements 
  of 
  which 
  are 
  regis- 
  

   tered, 
  with 
  an 
  amplification 
  of 
  92 
  times, 
  on 
  a 
  recording 
  surface 
  moving 
  at 
  the 
  rate 
  

   of 
  about 
  33 
  cm. 
  per 
  hour. 
  

  

  ( 
  228 
  ) 
  

  

  