﻿2I 
  4 
  

  

  OLDHAM 
  ; 
  GREAT 
  EARTHQUAKE 
  OF 
  1897. 
  

  

  Subsequently, 
  when 
  investigating 
  the 
  Neapolitan 
  earthquake 
  of 
  

   1 
  S 
  5 
  7, 
  he 
  found 
  that 
  at 
  the 
  Certosa 
  de 
  St. 
  Lorenzo, 
  near 
  Padula, 
  a 
  

   number 
  of 
  pinnacles 
  had 
  been 
  twisted 
  all 
  in 
  the 
  same 
  direction, 
  and 
  

   recognising 
  the 
  inapplicability 
  of 
  his 
  former 
  hypothesis, 
  proposed 
  an 
  

   alternative 
  one, 
  as 
  follows 
  1 
  : 
  — 
  

  

  " 
  Now 
  there 
  are 
  two 
  distinct 
  trains 
  of 
  earthquake 
  causation, 
  by 
  either 
  of 
  which 
  

   bodies 
  may 
  be 
  twisted 
  on 
  their 
  bases. 
  First, 
  by 
  the 
  action 
  of 
  a 
  single 
  shock, 
  when 
  

   the 
  centre 
  of 
  adherence 
  of 
  the 
  base 
  of 
  the 
  object, 
  lies 
  to 
  one 
  side 
  or 
  other 
  of 
  the 
  

   vertical 
  plane 
  passing 
  through 
  the 
  centre 
  of 
  gravity, 
  and 
  the 
  line 
  of 
  the 
  wave- 
  

   path. 
  Second, 
  by 
  the 
  conjoint 
  action 
  of 
  two 
  closely 
  successive 
  shocks. 
  By 
  the 
  

   first 
  shock, 
  the 
  body 
  is 
  tilted 
  up 
  from 
  its 
  base, 
  but 
  not 
  overthrown, 
  so 
  that 
  for 
  a 
  

   time, 
  greater 
  or 
  less, 
  it 
  rests 
  wholly 
  upon 
  one 
  edge 
  of 
  its 
  base 
  ; 
  while 
  thus 
  poised 
  

   if 
  another 
  shock 
  bear 
  upon 
  it, 
  in 
  any 
  direction 
  transverse 
  to 
  the 
  first, 
  it 
  acts 
  as 
  

   usual, 
  at 
  the 
  centre 
  of 
  gravity 
  of 
  the 
  body, 
  to 
  displace 
  it 
  by 
  inertia, 
  in 
  the 
  contrary 
  

   direction 
  to 
  the 
  wave 
  transit 
  ; 
  but 
  the 
  body 
  is 
  held, 
  more 
  or 
  less, 
  by 
  friction 
  at 
  the 
  

   edge 
  momentarily 
  in 
  contact 
  with 
  its 
  support, 
  and 
  there 
  only 
  ; 
  but 
  this 
  edge 
  must 
  

  

  EtoW. 
  

  

  1*P 
  shock 
  . 
  

  

  &-boW. 
  

  

  C 
  

  

  B. 
  

  

  IS. 
  I&shock, 
  

  

  K 
  

  

  x> 
  

  

  -w. 
  * 
  

  

  r. 
  

  

  2*. 
  JDieW. 
  

  

  |S 
  

  

  Fig. 
  19. 
  Diagram 
  (after 
  Mallet) 
  to 
  illustrate 
  the 
  effect 
  of 
  two 
  shocks 
  in 
  causing 
  rotation. 
  

  

  always 
  lie 
  to 
  one 
  side 
  of 
  the 
  vertical 
  plane 
  passing 
  through 
  the 
  centre 
  of 
  gravity 
  

   in 
  the 
  direction 
  of 
  the 
  wave-path 
  : 
  hence 
  the 
  tilted 
  body, 
  while 
  relapsing 
  upon 
  its 
  

   base, 
  also 
  rotates, 
  round 
  some 
  point 
  situated 
  in 
  the 
  edge 
  of 
  its 
  base 
  upon 
  which 
  it 
  

   had 
  been 
  tilted, 
  and 
  thus 
  it 
  comes 
  to 
  rest 
  in 
  a 
  new 
  position, 
  having 
  twisted 
  more 
  

   or 
  less 
  round 
  a 
  vertical 
  axis. 
  

  

  1 
  R. 
  Mallet. 
  The 
  great 
  Neapolitan 
  earthquake 
  of 
  1857. 
  London 
  1862, 
  Vol. 
  I, 
  p. 
  376. 
  The 
  

   s 
  ame 
  explanation 
  is 
  given 
  by 
  R.Falb, 
  apparently 
  independently 
  arrived 
  at, 
  in 
  his 
  Gedanken 
  

   und 
  Studien 
  uber 
  den 
  Vulcanismus, 
  8°, 
  Graz, 
  1875, 
  p. 
  223. 
  

  

  ( 
  2.4 
  ) 
  

  

  