﻿THE 
  BOMBAY 
  MAGNETIC 
  OBSERVATORY, 
  

  

  85 
  

  

  19. 
  The 
  Observatory 
  has 
  two 
  Vertical 
  Force 
  Magnet 
  ographs, 
  both 
  of 
  which 
  

   show 
  the 
  two 
  waves 
  clearly. 
  The 
  maximum 
  effect 
  of 
  the 
  first 
  disturbance 
  coincides 
  

   in 
  time 
  with 
  the 
  greatest 
  disturbance 
  in 
  the 
  Declination 
  Magnetograph. 
  The 
  

   amplitudes 
  of 
  the 
  vibrations 
  above 
  the 
  curve 
  are 
  somewhat 
  smaller 
  than 
  those 
  be- 
  

   low 
  the 
  curve 
  (this 
  is 
  more 
  clearly 
  shown 
  in 
  Vertical 
  Force 
  No. 
  2) 
  which 
  shows 
  

   a 
  slight 
  decrease 
  in 
  Vertical 
  Force 
  during 
  the 
  t 
  ime 
  of 
  disturbance. 
  It 
  may 
  be 
  

   noted 
  that 
  the 
  time 
  of 
  vibration 
  of 
  this 
  magnet 
  is 
  535 
  seconds, 
  about 
  the 
  same 
  

   as 
  that 
  of 
  Declination 
  magnet. 
  

  

  21. 
  Summary.— 
  Disturbanceof 
  magnetical 
  and 
  meteorological 
  instruments 
  at 
  

   Government 
  Observatory, 
  Colaba, 
  Bombay, 
  during 
  the 
  earthquake 
  of 
  12th 
  June 
  

   1897. 
  

  

  

  

  H 
  

  

  our. 
  

  

  Minute 
  

  

  Declination, 
  1st 
  shock. 
  

  

  ( 
  Commencement 
  . 
  

   * 
  lEnd 
  . 
  

  

  m 
  

  

  16 
  

   16 
  

  

  5 
  

   7 
  

  

  Most 
  intense, 
  2nd 
  shock, 
  maximum 
  

  

  effect 
  

  

  . 
  

  

  16 
  

  

  8'5 
  

  

  Fnd 
  of 
  Disturbance 
  

  

  

  

  16 
  

  

  34 
  

  

  Horizontal 
  Force, 
  1st 
  shock 
  

  

  J 
  Commencement 
  

   ' 
  (End 
  . 
  

  

  • 
  

  

  16 
  

   16 
  

  

  2*5 
  

  

  55 
  

  

  End 
  of 
  Disturbance 
  . 
  • 
  

  

  

  

  16 
  

  

  36 
  

  

  Vertical 
  Force, 
  1st 
  shock 
  . 
  

  

  J 
  Commencement 
  

   • 
  I 
  End 
  . 
  

  

  • 
  

  

  16 
  

   16 
  

  

  6'5 
  

  

  10 
  

  

  2nd 
  shock 
  

  

  ( 
  Commencement 
  . 
  

   1 
  End 
  . 
  

  

  • 
  

  

  )6 
  

   16 
  

  

  10 
  

   14 
  

  

  Barograph, 
  1st 
  shock 
  

  

  {"Commencement 
  . 
  

   . 
  < 
  Maximum 
  effect 
  

   (.End 
  . 
  

  

  • 
  

  

  16 
  

   16 
  

   16 
  

  

  5 
  "5 
  

   125 
  

  

  I 
  have 
  here 
  reproduced 
  only 
  so 
  much 
  of 
  Mr. 
  Moos' 
  account 
  as 
  

   deals 
  with 
  the 
  observed 
  facts 
  ; 
  it 
  will 
  be 
  seen 
  that 
  he 
  attributes 
  the 
  

   effect 
  to 
  magnetic 
  causes 
  in 
  the 
  main, 
  and 
  in 
  the 
  original 
  this 
  is 
  

   treated 
  at 
  greater 
  length. 
  The 
  matter 
  is 
  one 
  of 
  importance, 
  as 
  it 
  

   affects 
  the 
  question 
  of 
  whether 
  the 
  time 
  records 
  obtained 
  from 
  the 
  

   disturbance 
  of 
  magnetic 
  instruments 
  by 
  earthquakes 
  may 
  be 
  taken 
  as 
  

   accurately 
  representing 
  the 
  passage 
  of 
  the 
  earthquake 
  wave. 
  

  

  The 
  disturbance 
  of 
  magnetic 
  instruments 
  by 
  earthquakes 
  has 
  

   been 
  frequently 
  observed 
  , 
  but 
  the 
  cause 
  has 
  been 
  a 
  matter 
  of 
  dis- 
  

   cussion, 
  and 
  experiments 
  have 
  been 
  made 
  to 
  determine 
  whether 
  it 
  

   was 
  purely 
  mechanical 
  or 
  wholly 
  or 
  in 
  part 
  magnetic. 
  M. 
  Moureaux, 
  

   Chief 
  of 
  the 
  Magnetic 
  Observatory 
  of 
  Pare 
  Saint-Maur, 
  Paris, 
  had 
  a 
  

   duplicate 
  of 
  his 
  horizontal 
  force 
  magnetograph 
  prepared, 
  substituting 
  

  

  1 
  185 
  ) 
  

  

  