﻿THE 
  BOMBAY 
  MAGNETIC 
  OBSERVATORY. 
  \Si 
  

  

  increase 
  or 
  decrease 
  of 
  declination. 
  It 
  may 
  be 
  noted 
  that 
  the 
  intensity 
  of 
  the 
  

   mechanical 
  disturbance 
  was 
  feeble, 
  and 
  the 
  motion 
  observed 
  at 
  the 
  time 
  of 
  the 
  dis- 
  

   turbance 
  showed 
  no 
  evidence 
  of 
  any 
  great, 
  much 
  less 
  violent, 
  movements. 
  Finally 
  

   the 
  peculiar 
  character 
  of 
  the 
  trace 
  of 
  this 
  instrument, 
  as 
  will 
  be 
  seen 
  later 
  on, 
  leaves 
  

   no 
  reasonable 
  doubt 
  that 
  the 
  disturbance 
  was 
  due 
  to 
  magnetic 
  action, 
  which 
  must 
  

   have 
  accompanied 
  the 
  seismic 
  disturbance, 
  possibly 
  as 
  effect 
  of 
  a 
  cause. 
  

  

  5. 
  The 
  case 
  of 
  the 
  Horizontal 
  Force 
  Magnetograph 
  is, 
  however, 
  different. 
  

   From 
  the 
  peculiar 
  nature 
  of 
  the 
  bifilar 
  suspension, 
  it 
  becomes 
  obvious 
  that 
  the 
  

   tension 
  of 
  the 
  wires 
  being 
  a 
  principal 
  factor 
  in 
  the 
  general 
  formula 
  for 
  the 
  con- 
  

   dition 
  of 
  equilibrium, 
  it 
  must 
  be 
  affected 
  by 
  any 
  sudden 
  displacement 
  of 
  the 
  points 
  

   of 
  suspension. 
  A 
  distortional 
  wave, 
  for 
  instance, 
  suddenly 
  lifting 
  the 
  points 
  of 
  

   suspension 
  would 
  result 
  in 
  increasing 
  the 
  tension, 
  and 
  any 
  sudden 
  depression 
  

   would 
  for 
  a 
  moment 
  reduce 
  the 
  tension. 
  A 
  lateral 
  movement, 
  also, 
  is 
  likely 
  to 
  

   temporally 
  alter 
  the 
  conditions 
  of 
  equilibrium, 
  and 
  this 
  Magnetograph, 
  therefore, 
  

   appears 
  to 
  have 
  been 
  disturbed 
  by 
  the 
  combined 
  action 
  of 
  both 
  mechanical 
  and 
  

   magnetical 
  disturbances; 
  in 
  this 
  instance 
  more 
  perhaps 
  by 
  the 
  latter 
  than 
  by 
  the 
  

   former, 
  which 
  was 
  feeble 
  as 
  stated 
  above. 
  The 
  trace 
  shows 
  some 
  evidence 
  of 
  

   being: 
  affected 
  by 
  two 
  causes 
  superimposed 
  upon 
  each 
  other, 
  specially 
  at 
  the 
  end 
  

   of 
  the 
  disturbance, 
  where 
  the 
  blurred 
  trace, 
  probably 
  due 
  to 
  change 
  in 
  the 
  focal 
  

   distance 
  caused 
  by 
  a 
  slight 
  displacement 
  of 
  the 
  mirror, 
  appears 
  suddenly 
  to 
  pass 
  

   from 
  a 
  faint 
  to 
  a 
  somewhat 
  deep 
  impression, 
  bounded 
  by 
  convex 
  curves. 
  

  

  6. 
  Movement 
  in 
  the 
  Vertical 
  Force 
  Magnetograph 
  now 
  remains 
  to 
  be 
  inquired 
  

   into. 
  That 
  the 
  centre 
  of 
  gravity 
  and 
  point 
  of 
  support 
  of 
  the 
  magnet 
  in 
  this 
  instru- 
  

   ment, 
  do 
  not 
  coincide, 
  and 
  may 
  cause 
  rotation, 
  and, 
  therefore, 
  movement 
  

   of 
  the 
  magnet, 
  is 
  self-evident; 
  but 
  from 
  the 
  conditions 
  cf 
  the 
  magnet 
  and 
  the 
  

   quantity 
  of 
  motion 
  observed, 
  it 
  does 
  not 
  seem 
  probable 
  that 
  the 
  motion 
  was 
  

   due 
  to 
  mechanical 
  causes. 
  This 
  instrument 
  is 
  under 
  an 
  exhausted 
  receiver 
  

   but 
  .its 
  knife 
  edge 
  is 
  somewhat 
  faulty, 
  and 
  this 
  Magnetograph, 
  therefore, 
  

   is 
  peculiarly 
  sensitive 
  to 
  shocks,— 
  an 
  accidental 
  fall 
  of 
  a 
  lamp-chimney, 
  heavy 
  

   tread 
  of 
  visitors, 
  and 
  even 
  a 
  slight 
  knock 
  of 
  the 
  hand 
  results 
  in 
  dislocation 
  of 
  

   the 
  curve. 
  And 
  such 
  dislocations 
  being 
  frequent, 
  special 
  care 
  is 
  always 
  taken 
  to 
  

   guard 
  the 
  instruments 
  from 
  such 
  accidents. 
  And 
  yet 
  no 
  dislocation 
  of 
  the 
  curve 
  

   is 
  noticed 
  during 
  the 
  earthquake, 
  which 
  more 
  or 
  less 
  establishes 
  the 
  fact 
  that 
  move, 
  

   ments 
  of 
  the 
  earth 
  must 
  have 
  been 
  very 
  feeble. 
  But 
  the 
  instrument 
  does 
  show 
  

   vibrations, 
  which 
  naturally 
  leads 
  to 
  the 
  inference 
  that 
  they 
  must 
  have 
  been 
  caused 
  

   by 
  some 
  magnetic 
  action, 
  the 
  first 
  vibration 
  of 
  which 
  is 
  timed 
  to 
  have 
  taken 
  place 
  

   exactly 
  when 
  the 
  Declination 
  trace 
  is 
  just 
  lost 
  by 
  the 
  second 
  wave. 
  

  

  7. 
  And 
  it 
  would 
  thus 
  appear 
  as 
  if 
  the 
  seismic 
  convulsion 
  was 
  in 
  some 
  way 
  the 
  

   cause 
  of 
  the 
  magnetic 
  action, 
  the 
  latter 
  phenomenon 
  running 
  parallel 
  to 
  the 
  

   former, 
  increasing 
  as 
  it 
  increased 
  and 
  subsiding 
  as 
  it 
  subsided, 
  every 
  seismic 
  wave 
  

   having 
  its 
  companion 
  effect 
  in 
  a 
  magnetic 
  wave. 
  

  

  8. 
  With 
  regard 
  to 
  the 
  direction. 
  Since 
  the 
  Barograph 
  would 
  not 
  show 
  any 
  

   indication 
  of 
  direction, 
  nor 
  the 
  Magnetographs, 
  all 
  of 
  which 
  appear 
  to 
  have 
  been 
  

   disturbed 
  by 
  magnetic 
  action, 
  it 
  is 
  difficult 
  to 
  come 
  to 
  any 
  definite 
  conclusions, 
  

   Except, 
  perhaps, 
  in 
  the 
  case 
  of 
  Declination, 
  the 
  suggestive 
  explanations 
  given 
  

   later 
  on, 
  if 
  true, 
  would 
  point 
  at 
  least 
  that 
  the 
  direction 
  of 
  the 
  magnetic 
  

  

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