﻿RATE 
  OF 
  PROPAGATION. 
  73 
  

  

  Sth 
  minute 
  was 
  . 
  120 
  miles. 
  

  

  6th 
  „ 
  „ 
  120 
  „ 
  

  

  7th 
  „ 
  140 
  „ 
  

  

  8th 
  „ 
  „ 
  »5o 
  » 
  

  

  9th 
  „ 
  „ 
  l6 
  ° 
  » 
  

  

  From 
  these 
  tables 
  it 
  will 
  be 
  seen 
  that 
  the 
  slowest 
  rate 
  of 
  travel 
  

   seems 
  to 
  have 
  been 
  in 
  the 
  third 
  minute 
  and 
  the 
  third 
  hundred 
  miles. 
  

   Onveither 
  side 
  of 
  this 
  limit, 
  as 
  we 
  approach 
  the 
  centre 
  or 
  recede 
  from 
  

   it, 
  there 
  is 
  seen 
  to 
  be 
  a 
  steady 
  and 
  regular 
  increase 
  in 
  the 
  rate 
  of 
  

   travel. 
  This 
  is 
  evident 
  from 
  the 
  diagram 
  if 
  it 
  is 
  borne 
  in 
  mind 
  that, 
  

   from 
  the 
  manner 
  in 
  which 
  it 
  was 
  constructed, 
  the 
  rate 
  of 
  travel 
  is 
  

   indicated 
  by 
  the 
  slope 
  of 
  the 
  line 
  drawn, 
  the 
  more 
  nearly 
  horizontal 
  

   this 
  is 
  the 
  greater 
  the 
  velocity 
  indicated, 
  and 
  the 
  more 
  inclined 
  the 
  

   slower 
  the 
  rate 
  of 
  travel. 
  If 
  the 
  diagram 
  is 
  examined, 
  it 
  will 
  be 
  

   seen 
  that 
  the 
  line 
  can 
  be 
  divided 
  into 
  two 
  parts, 
  one 
  near 
  the 
  origin 
  

   w 
  ? 
  hich 
  is 
  concave 
  upwards 
  — 
  indicating 
  that 
  the 
  rate 
  of 
  travel 
  is 
  

   diminishing 
  — 
  and 
  the 
  other 
  away 
  from 
  the 
  origin, 
  which 
  is 
  convex 
  

   upwards, 
  indicating 
  a 
  progressive 
  increase 
  in 
  the 
  rate 
  of 
  travel, 
  

   The 
  point 
  of 
  junction 
  of 
  these 
  two 
  parts 
  of 
  the 
  hodograph 
  is 
  that 
  

   where 
  the 
  rate 
  of 
  travel 
  was 
  least 
  and 
  lies 
  at 
  about 
  280 
  miles 
  

   from 
  the 
  origin. 
  

  

  The, 
  form 
  of 
  the 
  hodograph 
  drawn 
  on 
  Plate 
  XXXIX 
  resembles 
  

   that 
  of 
  Schmidt's 
  hodograph 
  1 
  , 
  based 
  on 
  the 
  assumption 
  of 
  a 
  higher 
  

   rate 
  of 
  transmission 
  of 
  the 
  earthquake 
  wave 
  in 
  the 
  deeper 
  seated 
  than 
  

   in 
  the 
  more 
  superficial 
  portions 
  of 
  the 
  earth's 
  crust, 
  and 
  also 
  the 
  form 
  

   of 
  the 
  same 
  author's 
  modification 
  of 
  Seebach's 
  hyperbola, 
  3 
  when 
  the 
  

   curvature 
  of 
  the 
  earth's 
  surface 
  is 
  taken 
  into 
  consideration, 
  and 
  this 
  

   might, 
  at 
  first 
  sight, 
  seem 
  to 
  favour 
  its 
  acceptance 
  as 
  the 
  true 
  one. 
  

   On 
  closer 
  examination, 
  however, 
  it 
  is 
  found 
  that 
  the 
  acceleration 
  at 
  a 
  

   distance 
  from 
  the 
  epicentre 
  is 
  too 
  small 
  to 
  be 
  accounted 
  for 
  by 
  either 
  

   of 
  the 
  hypotheses 
  taken 
  separately, 
  and 
  still 
  more 
  so 
  by 
  the 
  combin- 
  

   ed 
  effects 
  of 
  the 
  two 
  causes, 
  i.e., 
  of 
  the 
  known 
  curvature 
  of 
  the 
  

  

  1 
  Jahresheft 
  Ver. 
  f. 
  vaterl. 
  Naturkunde 
  in 
  Wurttemberg, 
  1888, 
  p. 
  254. 
  

   3 
  Ibid, 
  1890, 
  p. 
  227. 
  

  

  (73 
  ) 
  

  

  