﻿ROTATION 
  OF 
  PILLARS. 
  223 
  

  

  give 
  it 
  a 
  slight 
  positive 
  rotation. 
  As 
  soon, 
  however, 
  as 
  the 
  direction 
  

  

  Fig. 
  23. 
  Diagram 
  of' 
  rotation 
  by 
  vorticose 
  motion. 
  

  

  of 
  the 
  movement 
  changes 
  and 
  the 
  particle 
  begins 
  to 
  return 
  from 
  2 
  to 
  

   3, 
  a 
  much 
  more 
  powerful 
  tendency 
  to 
  rotate 
  the 
  column 
  in 
  a 
  negative 
  

   direction 
  round 
  1 
  will 
  be 
  set 
  up, 
  and 
  the 
  column 
  at 
  the 
  same 
  time 
  

   tilted 
  over 
  on 
  its 
  edge 
  towards 
  2, 
  The 
  same 
  thing 
  will 
  happen 
  when 
  

   the 
  particle 
  returns 
  from 
  3 
  towards 
  4 
  and 
  so 
  on, 
  each 
  successive 
  tilt 
  

   being 
  accompanied 
  by 
  a 
  further 
  twist 
  in 
  a 
  negative 
  direction. 
  As 
  

   before, 
  the 
  distance 
  of 
  the 
  centre 
  of 
  the 
  column 
  from 
  its 
  original 
  

   position 
  will 
  be 
  less 
  than 
  it 
  had 
  there 
  been 
  merely 
  a 
  single 
  tilt 
  and 
  

   twist. 
  1 
  

  

  Of 
  these 
  two 
  explanations 
  the 
  latter 
  seems 
  more 
  in 
  conformity 
  

   with 
  the 
  facts 
  observed 
  than 
  the 
  former. 
  The 
  first 
  would 
  require 
  

   that 
  the 
  crushing 
  of 
  the 
  edges 
  should 
  be 
  tolerably 
  uniform 
  all 
  round, 
  

  

  1 
  This 
  chapter 
  was 
  written 
  and 
  set 
  up 
  in 
  type 
  before 
  I 
  was 
  aware 
  of 
  a 
  paper 
  by 
  Mr. 
  C. 
  

   Davison 
  on 
  the 
  theory 
  of 
  vorticose 
  earthquake 
  shocks 
  (Geol. 
  Mag., 
  dec 
  2, 
  IX, 
  257 
  — 
  266, 
  1S82), 
  

   which 
  would 
  otherwise 
  have 
  been 
  referred 
  to 
  in 
  the 
  text. 
  He 
  explains 
  the 
  vorticose 
  shock 
  

   much 
  in 
  the 
  same 
  way 
  as 
  that 
  adopted 
  in 
  the 
  text, 
  i.e. 
  as 
  a 
  movement 
  to 
  and 
  fro 
  in 
  a 
  gradually 
  

   changing 
  direction, 
  and 
  points 
  out 
  how 
  such 
  must 
  necessarily 
  result 
  with 
  a 
  focus 
  of 
  any 
  size, 
  in 
  

   the 
  neighbourhood 
  of 
  the 
  epicentre, 
  from 
  the 
  fact 
  that 
  the 
  impulses 
  reaching 
  a 
  spot 
  at 
  succes- 
  

   sive 
  intervals 
  of 
  time 
  come 
  from 
  different 
  parts 
  of 
  the 
  focus 
  and 
  hence 
  from 
  different 
  directions. 
  

   The 
  manner 
  in 
  which 
  such 
  a 
  form 
  of 
  movement 
  leads 
  to 
  the 
  rotation 
  of 
  solid 
  objects 
  is 
  not 
  

   discussed, 
  but 
  it 
  is 
  held 
  (p. 
  264) 
  that 
  the 
  objection 
  to 
  the 
  vorticose 
  theory 
  urged 
  Mr. 
  Darwin 
  (in 
  

   1839) 
  that 
  under 
  every 
  object 
  so 
  turned 
  there 
  must 
  have 
  been 
  a 
  separate 
  vorticose 
  movement, 
  

   loses 
  its 
  force 
  on 
  the 
  view 
  there 
  presented. 
  It 
  is 
  evident, 
  however, 
  from 
  the 
  extracts 
  quoted 
  

   in 
  this 
  chapter 
  that 
  the 
  vorticose 
  motion, 
  as 
  understood 
  by 
  Darwin 
  and 
  Mallet, 
  was 
  something 
  

   very 
  different 
  to 
  that 
  whose 
  possibility 
  has 
  been 
  demonstrated 
  by 
  Mr. 
  Davison, 
  whose 
  existence 
  

   has 
  been 
  proved 
  by 
  the 
  researches 
  of 
  Prof. 
  Milne 
  and 
  others 
  in 
  Japan, 
  and 
  whose 
  actuality 
  is 
  

   adopted 
  in 
  this 
  memoir 
  as 
  a 
  satisfactory 
  means 
  of 
  explaining 
  the 
  rotation 
  ol 
  objects 
  by 
  an 
  

   earthquake. 
  

  

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  223 
  ) 
  

  

  