﻿THE 
  BOMBAY 
  MAGNETIC 
  OBSERVATORY. 
  

  

  ■83 
  

  

  strongly 
  than 
  before 
  at 
  about 
  um. 
  This 
  goes 
  on, 
  but 
  the 
  magnetic 
  action 
  now 
  

   becomes 
  less 
  and 
  less 
  intense 
  (presumably 
  therefore 
  the 
  cause 
  of 
  the 
  disturbance 
  

   of 
  the 
  seismic 
  waves 
  also) 
  and 
  the 
  amplitude 
  of 
  the 
  vibrations 
  falling 
  within 
  the 
  

   limit 
  of 
  photographic 
  action, 
  the 
  record 
  runs 
  beautifully 
  clear 
  after 
  this, 
  and 
  every 
  

   wave 
  is 
  registered 
  following 
  its 
  predecessor 
  with 
  more 
  or 
  less 
  rhythmic 
  precision 
  

   the 
  intensity 
  of 
  the 
  disturbance 
  getting 
  less 
  and 
  less 
  till, 
  at 
  about 
  34 
  minutes 
  past 
  

   the 
  hour, 
  the 
  disturbed 
  trace 
  runs 
  into 
  normal 
  curve 
  once 
  more. 
  

  

  11. 
  However, 
  one 
  singular 
  feature 
  in 
  the 
  trace, 
  which 
  is 
  clearly 
  visible 
  in 
  the 
  

   latter 
  part 
  of 
  the 
  disturbed 
  curve, 
  must 
  also 
  be 
  explained, 
  vies 
  : 
  the 
  running 
  of 
  

   the 
  vibration 
  lines 
  into 
  each 
  other 
  by 
  a 
  zig-zag 
  kind 
  of 
  trace. 
  The 
  most 
  

   plausible 
  explanation 
  appears 
  to 
  be 
  the 
  following: 
  — 
  

  

  12. 
  Assuming 
  the 
  normal 
  curve 
  to 
  be 
  the 
  zero 
  for 
  the 
  time, 
  ordinary 
  vibrations 
  

   caused 
  by 
  momentary 
  disturbance, 
  would 
  take 
  place 
  above 
  and 
  below 
  this 
  zero 
  

   with 
  equal 
  amplitudes. 
  But 
  from 
  the 
  nature 
  of 
  the 
  appearance 
  of 
  the 
  zig-zag 
  curve 
  

   ft 
  seems 
  as 
  if 
  the 
  advancing 
  seismic 
  wave 
  of 
  condensation 
  caused 
  a 
  decrement 
  in 
  the 
  

   declination 
  and 
  compelled 
  vibrations 
  about 
  a 
  displaced 
  zero 
  higher 
  up 
  the 
  curve, 
  

   while 
  during 
  the 
  receding 
  wave 
  (as 
  it 
  passed 
  away) 
  the 
  reverse 
  and 
  opposite 
  effect 
  

   followed, 
  the 
  declination 
  increasing, 
  the 
  vibrations 
  were 
  Caused 
  about 
  a 
  lowered 
  zero 
  

   each 
  phenomenon 
  of 
  course 
  having 
  its 
  maximum 
  and 
  minimum 
  effect. 
  Fourteen 
  

   such 
  waves 
  in 
  all 
  can 
  be 
  delected 
  on 
  the 
  trace, 
  the 
  2nd 
  or 
  3rd 
  of 
  which, 
  more 
  pos- 
  

   sibly 
  the 
  2nd, 
  was 
  the 
  most 
  intense, 
  and 
  each 
  complete 
  wave 
  was 
  followed 
  by 
  

   another 
  after 
  an 
  average 
  interval 
  of 
  about 
  2 
  m. 
  The 
  maximum 
  effect 
  of 
  the 
  

   advancing 
  and 
  the 
  retreating 
  parts 
  of 
  the 
  wave 
  being 
  recorded 
  at 
  the 
  average 
  

   interval 
  of 
  about 
  1 
  m. 
  

  

  

  Disturbance 
  in 
  Declination 
  Magnetograph. 
  

  

  Wave. 
  

  

  [Maximum 
  effect 
  showing 
  

  

  Maximum 
  effect 
  showing 
  

  

  

  

  decreased 
  declination. 
  

  

  increased 
  declination. 
  

  

  

  

  

  

  

  Commencement 
  

   of 
  ■disturbance. 
  

  

  

  

  h. 
  m. 
  

  

  h. 
  m. 
  

  

  h. 
  m. 
  

  

  ISt 
  

  

  

  16 
  6 
  

  

  16 
  7 
  

  

  16 
  5 
  

  

  2nd 
  

  

  

  8-5 
  

  

  95 
  

  

  

  3rd 
  

  

  

  10.5 
  

  

  n"5 
  

  

  

  4th 
  

  

  

  12.5 
  

  

  I3'5 
  

  

  

  5th 
  

  

  

  15 
  

  

  16 
  

  

  

  6th 
  

  

  

  17 
  

  

  18 
  

  

  

  7th 
  

  

  

  19-5 
  

  

  20-5 
  

  

  

  8th 
  

  

  

  21 
  5 
  

  

  22*5 
  

  

  

  gth 
  

  

  

  24 
  

  

  25 
  

  

  

  loth 
  

  

  

  26 
  

  

  27 
  

  

  

  nth 
  

  

  

  28 
  

  

  29 
  

  

  

  1 
  2th 
  

  

  

  30 
  

  

  31 
  

  

  End 
  of 
  disturb- 
  

  

  13th 
  

  

  

  31*5 
  

  

  32 
  5 
  

  

  ance. 
  

  

  14th 
  

  

  

  33'5 
  

  

  

  16 
  34 
  

  

  ( 
  183 
  ) 
  

  

  