﻿ROTATION 
  OF 
  PILLARS. 
  22-1 
  

  

  particle 
  in 
  a 
  more 
  or 
  less 
  circular 
  course. 
  Here 
  there 
  would 
  be 
  no 
  

   angular 
  rotation, 
  but 
  over 
  a 
  larger 
  or 
  smaller 
  area 
  the 
  whole 
  ground 
  

   would 
  be 
  caused 
  to 
  move 
  in 
  small 
  circles, 
  and 
  a 
  pillar 
  or 
  similar 
  object 
  

   fractured 
  from 
  its 
  base, 
  would 
  be 
  caused 
  to 
  tilt 
  and 
  roll 
  round 
  on 
  its 
  

   edge 
  and 
  so 
  rotate 
  with 
  regard 
  to 
  its 
  original 
  position. 
  

  

  It 
  does 
  not 
  seem, 
  however, 
  that 
  the 
  term 
  ' 
  vorticose* 
  is 
  necessa- 
  

   rily 
  restricted 
  to 
  so 
  simple 
  a 
  form 
  of 
  movement 
  as 
  this,, 
  for 
  I 
  

   find 
  in 
  Mr. 
  Mallet's 
  account 
  of 
  the 
  Neapolitan 
  earthquake 
  a 
  state- 
  

   ment 
  that 
  the 
  Syndic 
  of 
  Padula, 
  was 
  of 
  opinion 
  that 
  the 
  shock 
  was 
  

   ' 
  vorticose 
  ' 
  or 
  at 
  least 
  in 
  various 
  directions 
  transverse 
  to 
  the 
  main 
  

   one 
  and 
  so 
  close 
  together 
  in 
  time 
  that 
  it 
  was 
  impossible 
  to 
  regard 
  the 
  

   earthquake 
  as 
  other 
  than 
  a 
  prolonged 
  and 
  irregular 
  succession 
  of 
  

   oscillations, 
  lasting 
  several 
  seconds. 
  1 
  From 
  this 
  it 
  is 
  evident 
  that 
  the 
  

   term 
  vorticose 
  is 
  applied 
  to 
  shocks 
  in 
  which 
  no 
  definite 
  direction 
  of 
  

   movement 
  can 
  be 
  noticed, 
  but 
  where 
  the 
  apparent 
  direction 
  seems 
  

   to 
  vary 
  or 
  revolve. 
  This 
  interpretation 
  finds 
  its 
  explanation 
  in 
  

   the 
  diagrams 
  of 
  the 
  seismographs 
  which 
  have 
  been 
  invented 
  and 
  

   taken 
  into 
  use 
  in 
  Japan. 
  

  

  Fig. 
  22. 
  Diagram 
  of 
  vorticose 
  motion. 
  

  

  To 
  take 
  the 
  simplest 
  case 
  first, 
  suppose 
  the 
  movement 
  of 
  the 
  

   wave 
  particle 
  to 
  be 
  circular, 
  neglecting 
  for 
  the 
  moment 
  any 
  move* 
  

  

  1 
  Great 
  Neapolitan 
  Earthquake, 
  1857, 
  h 
  P« 
  368. 
  

  

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  221 
  ) 
  

  

  