﻿306 
  Scientific 
  Intelligence. 
  

  

  tances 
  / 
  by 
  R. 
  D. 
  Oldham, 
  Geological 
  Survey 
  of 
  India. 
  (Abstract.) 
  

   — 
  When 
  preparing 
  a 
  report 
  on 
  the 
  great 
  Indian 
  earthquake 
  

   of 
  12th 
  June, 
  1897, 
  the 
  author 
  noticed 
  that 
  the 
  European 
  records 
  

   of 
  this 
  earthquake 
  showed 
  a 
  phase 
  of 
  increased 
  disturbance 
  in 
  

   what 
  are 
  commonly 
  called 
  the 
  preliminary 
  tremors, 
  making, 
  with 
  

   the 
  great 
  undulations, 
  three 
  phases 
  of 
  motion. 
  He 
  suggested 
  

   that 
  these 
  three 
  phases 
  represented 
  the 
  arrival 
  of 
  (1) 
  the 
  conden- 
  

   sational, 
  (2) 
  the 
  distortional 
  waves 
  traveling 
  through 
  the 
  earth, 
  

   and 
  (3) 
  surface 
  undulations 
  traveling 
  round 
  the 
  earth. 
  The 
  

   present 
  paper 
  is 
  an 
  attempt 
  to 
  verify 
  these 
  suggestions 
  by 
  a 
  com- 
  

   parison 
  with 
  other 
  earthquakes. 
  

  

  For 
  this 
  purpose 
  a 
  selection 
  has 
  been 
  made 
  from 
  the 
  published 
  

   records 
  of 
  those 
  earthquakes 
  which 
  fulfil 
  the 
  conditions 
  (1) 
  that 
  

   the 
  place 
  of 
  origin 
  shall 
  be 
  known 
  within 
  1° 
  of 
  arc, 
  (2) 
  that 
  the 
  

   time 
  of 
  origin 
  shall 
  be 
  known 
  within 
  a 
  limit 
  of 
  error 
  of 
  one 
  

   minute, 
  (3) 
  that 
  there 
  shall 
  be 
  a 
  sufficient 
  number 
  of 
  records, 
  dis- 
  

   tant 
  more 
  than 
  20° 
  of 
  arc 
  from 
  the 
  origin, 
  to 
  serve 
  as 
  a 
  check 
  on 
  

   each 
  other. 
  Eleven 
  distinct 
  shocks, 
  representing 
  seven 
  great 
  

   earthquakes, 
  are 
  found 
  to 
  satisfy 
  these 
  conditions, 
  and 
  in 
  every 
  

   case 
  the 
  same 
  three-phase 
  character 
  as 
  was 
  recognized 
  in 
  the 
  

   earthquake 
  of 
  12th 
  June, 
  1897, 
  is 
  found. 
  A 
  comparison 
  of 
  time 
  

   intervals 
  and 
  apparent 
  rates 
  of 
  propagation 
  shows 
  that 
  the 
  coin- 
  

   cidence 
  is 
  not 
  accidental, 
  but 
  represents 
  the 
  separation 
  of 
  three 
  

   distinct 
  types 
  of 
  wave 
  motion 
  having 
  different 
  rates 
  of 
  propa- 
  

   gation. 
  

  

  On 
  plotting 
  the 
  records 
  it 
  is 
  found 
  that 
  the 
  time 
  curves 
  of 
  the 
  

   first 
  two 
  phases 
  form 
  curved 
  lines, 
  indicating 
  an 
  increase 
  of 
  

   apparent 
  velocity 
  with 
  distance 
  from 
  the 
  origin, 
  such 
  that, 
  apply- 
  

   ing 
  Rudzki's 
  investigation, 
  the 
  wave 
  motion 
  represented 
  by 
  these 
  

   two 
  phases 
  must 
  have 
  traveled 
  through 
  the 
  earth, 
  along 
  curved 
  

   wave 
  paths, 
  convex 
  towards 
  the 
  center 
  of 
  the 
  earth, 
  and 
  with 
  a 
  

   rate 
  of 
  propagation 
  which 
  increases 
  with 
  the 
  distance 
  from 
  the 
  

   surface. 
  On 
  continuing 
  these 
  curves, 
  by 
  extrapolation, 
  to 
  the 
  

   origin, 
  they 
  give 
  rates 
  of 
  propagation 
  in 
  very 
  fair 
  concordance 
  

   with 
  the 
  rates 
  of 
  propagation 
  of 
  condensational 
  and 
  distortional 
  

   plane 
  waves 
  which 
  may 
  be 
  expected 
  to 
  obtain 
  in 
  continuous 
  rock 
  

   at 
  some 
  distance 
  from 
  the 
  surface 
  of 
  the 
  earth. 
  

  

  The 
  waves 
  of 
  the 
  third 
  phase 
  show 
  no 
  such 
  increase 
  of 
  rate 
  of 
  

   propagation 
  with 
  distance 
  from 
  the 
  origin. 
  The 
  rate 
  of 
  propaga- 
  

   tion 
  is 
  uniform 
  at 
  all 
  distances 
  ; 
  from 
  which 
  it 
  is 
  concluded 
  that 
  

   the 
  great 
  undulations 
  of 
  the 
  third 
  phase 
  are 
  surface 
  waves, 
  travel- 
  

   ing 
  with 
  a 
  uniform 
  rate 
  of 
  propagation 
  round 
  the 
  surface 
  of 
  the 
  

   earth. 
  It 
  is 
  also 
  found 
  that 
  the 
  waves 
  of 
  this 
  phase 
  set 
  up 
  by 
  

   great 
  earthquakes 
  travel 
  faster 
  than 
  those 
  set 
  up 
  by 
  lesser 
  ones, 
  

   and 
  from 
  this 
  it 
  is 
  concluded 
  that 
  the 
  rate 
  of 
  propagation 
  of 
  these 
  

   waves 
  is 
  in 
  some 
  way 
  a 
  function 
  of 
  their 
  size, 
  thus 
  affording 
  a 
  

   confirmation 
  of 
  Lord 
  Kelvin's 
  suggestion 
  that 
  their 
  propagation 
  

   is 
  in 
  part 
  gravitational. 
  

  

  The 
  general 
  conclusion 
  is 
  that 
  in 
  the 
  complete 
  record 
  of 
  a 
  dis- 
  

   tant 
  earthquake, 
  three 
  distinct 
  types 
  of 
  wave 
  motion 
  can 
  be 
  

  

  