﻿232 
  OLDHAM: 
  GREAT 
  EARTHQUAKE 
  OF 
  1897. 
  

  

  Of 
  the 
  two 
  modes 
  of 
  interpreting 
  the 
  records 
  of 
  the 
  first 
  phase, 
  

   that 
  of 
  regarding 
  them 
  as 
  representing 
  angular 
  movements 
  presents 
  

   enormous 
  differences 
  between 
  the 
  results 
  obtained 
  from 
  the 
  different 
  

   instruments, 
  while, 
  if 
  they 
  are 
  regarded 
  as 
  representing 
  linear 
  dis- 
  

   placements, 
  they 
  merely 
  exhibit 
  differences 
  explicable 
  by 
  the 
  varying 
  

   natural 
  and 
  mechanical 
  sensitiveness 
  of 
  the 
  instruments. 
  On 
  the 
  

   other 
  hand, 
  the 
  measures 
  of 
  the 
  second 
  phase 
  present 
  very 
  great 
  

   differences 
  of 
  linear, 
  but 
  not 
  so 
  great 
  of 
  the 
  angular 
  values, 
  in 
  

   which 
  they 
  follow 
  an 
  evident 
  law, 
  that 
  the 
  values 
  are 
  higher 
  as 
  the 
  

   instrument 
  from 
  which 
  they 
  are 
  derived 
  is 
  mechanically 
  freer 
  from 
  

   friction 
  or 
  resistance. 
  

  

  The 
  interpretation 
  of 
  this 
  may 
  be 
  that 
  the 
  earlier 
  disturbances 
  

   are, 
  at 
  any 
  rate 
  largely, 
  the 
  effect 
  of 
  inertia, 
  due 
  to 
  horizontal 
  move- 
  

   ment 
  (condensational 
  waves), 
  while, 
  those 
  at 
  the 
  later 
  period 
  were 
  

   due 
  principally 
  to 
  an 
  actual 
  tilting 
  of 
  the 
  surface, 
  consequent 
  on 
  

   movement 
  of 
  the 
  nature 
  of 
  an 
  undulation 
  (distortional 
  waves). 
  I 
  

  

  As 
  a 
  consequence, 
  Prof. 
  Grablowitz 
  considers 
  that 
  the 
  maximum 
  

   inclination 
  of 
  the 
  surface 
  at 
  Ischia 
  was 
  2", 
  that 
  registered 
  by 
  the 
  water 
  

   level, 
  the 
  only 
  instrument 
  in 
  which 
  adhesion 
  to 
  the 
  sides 
  could 
  com- 
  

   pletely, 
  or 
  nearly 
  so, 
  extinguish 
  the 
  disturbance 
  of 
  the 
  horizontality 
  

   of 
  the 
  surface 
  of 
  the 
  liquid 
  by 
  waves 
  of 
  such 
  period, 
  and 
  the 
  effects 
  

   of 
  inertia 
  felt 
  by 
  other 
  instruments 
  ; 
  while 
  the 
  excess 
  observed 
  on 
  

   the 
  other 
  instruments, 
  even 
  in 
  the 
  spirit 
  levels, 
  is 
  probably 
  to 
  be 
  

   ascribed 
  to 
  inertia 
  consequent 
  on 
  horizontal 
  displacement. 
  The 
  

   oscillation 
  of 
  the 
  spiral 
  spring 
  as 
  observed 
  seems 
  to 
  be 
  sufficiently 
  

   confirmatory 
  of 
  this 
  hypothesis, 
  as 
  it 
  agrees 
  in 
  time 
  with 
  the 
  arrival 
  

   of 
  the 
  undulatory 
  waves, 
  which 
  were 
  accompanied 
  by 
  a 
  considerable 
  

   amount 
  of 
  vertical 
  movement. 
  

  

  I 
  have 
  reproduced 
  the 
  substance 
  of 
  Prof. 
  Grablowitz's 
  account 
  of 
  

   his 
  instruments 
  and 
  the 
  conclusions 
  he 
  drew 
  from 
  their 
  records, 
  not 
  

   merely 
  on 
  account 
  of 
  their 
  intrinsic 
  interest, 
  but 
  also 
  on 
  account 
  of 
  

   the 
  assistance 
  they 
  gave 
  in 
  the 
  interpretation 
  of 
  the 
  records 
  from 
  

  

  1 
  These 
  are 
  different 
  to 
  the 
  distortional 
  Plane 
  waves 
  transmitted 
  through 
  a 
  solid. 
  

   ( 
  232 
  ) 
  

  

  