﻿ISOSEISTS 
  AND 
  SEISMIC 
  AREA, 
  45 
  

  

  ttiis. 
  The 
  two 
  storied 
  houses 
  are 
  built 
  in 
  the 
  same 
  manner, 
  with 
  the 
  

   omission 
  of 
  the 
  top 
  story. 
  

  

  From 
  this 
  description 
  it 
  will 
  be 
  seen 
  that 
  the 
  house 
  is 
  divided 
  by 
  

   two 
  vertical 
  planes 
  into 
  three 
  very 
  distinct 
  portions 
  of 
  very 
  different 
  

   weights 
  and 
  proportions. 
  Consequently 
  when 
  the 
  house 
  is 
  set 
  rock- 
  

   ing 
  each 
  portion 
  will 
  try 
  to 
  swing 
  as 
  an 
  inverted 
  pendulum, 
  with 
  

   its 
  own 
  proper 
  period 
  of 
  oscillation. 
  As 
  this 
  will 
  be 
  different 
  in 
  each 
  

   case, 
  and 
  as 
  the 
  difference 
  is 
  greatest 
  in 
  the 
  case 
  of 
  the 
  main 
  body 
  

   of 
  the 
  building 
  and 
  the 
  south 
  verandah, 
  the 
  different 
  portions, 
  unless 
  

   strongly 
  tied 
  together, 
  will 
  alternately 
  separate 
  and 
  press 
  upon 
  each 
  

   other. 
  

  

  This 
  separation 
  of 
  the 
  verandah 
  from 
  the 
  main 
  body 
  of 
  the 
  

   building 
  was 
  observed 
  by 
  more 
  than 
  one 
  person, 
  and 
  the 
  rate 
  

   at 
  which 
  the 
  separation 
  and 
  return 
  took 
  place, 
  estimated 
  at 
  from 
  

   7 
  to 
  20 
  seconds 
  by 
  different 
  observers, 
  shows 
  that 
  it 
  was 
  not 
  

   directly 
  due 
  to 
  the 
  bending 
  of 
  the 
  house 
  on 
  the 
  top 
  of 
  the 
  earth 
  wave, 
  

   whose 
  period 
  was 
  much 
  quicker, 
  but 
  to 
  a 
  swing 
  communicated 
  to 
  the 
  

   building, 
  and 
  the 
  elastic 
  oscillation 
  of 
  its 
  different 
  parts. 
  Tall 
  

   factory 
  chimneys 
  are 
  known 
  to 
  sway 
  several 
  feet 
  in 
  a 
  high 
  wind, 
  

   and 
  bricks 
  and 
  mortar 
  have 
  sufficient 
  elasticity 
  to 
  allow 
  of 
  a 
  separa- 
  

   tion 
  of 
  several 
  inches 
  between 
  two 
  parts 
  of 
  a 
  tall 
  house 
  swinging 
  

   in 
  opposite 
  directions. 
  

  

  After 
  the 
  earthquake 
  it 
  was 
  found 
  that 
  by 
  far 
  the 
  greater 
  amount 
  

   of 
  the 
  serious 
  damage 
  done 
  was 
  of 
  the 
  character 
  described, 
  and 
  few 
  

   were 
  the 
  houses, 
  even 
  those 
  otherwise 
  little 
  injured, 
  where 
  two 
  

   cracks 
  did 
  not 
  open 
  as 
  shown 
  in 
  fig. 
  3. 
  Moreover, 
  it 
  was 
  found 
  

   that 
  where 
  the 
  main 
  beams 
  supporting 
  the 
  roof 
  and 
  floors 
  ran 
  

   north 
  and 
  south, 
  in 
  the 
  same 
  direction 
  as 
  those 
  of 
  the 
  verandah, 
  and 
  

   hence 
  acted 
  in 
  some 
  degree 
  as 
  ties, 
  the 
  damage 
  was 
  much 
  less 
  than 
  

   when 
  the 
  beams 
  in 
  the 
  main 
  building 
  ran 
  east 
  and 
  west 
  and 
  those 
  

   in 
  the 
  verandah 
  north 
  and 
  south. 
  

  

  Another 
  cause 
  of 
  the 
  damage 
  in 
  Calcutta 
  was 
  the 
  heavy 
  and 
  weak 
  

   balustrades 
  and 
  cornices 
  found 
  on 
  most 
  of 
  the 
  older 
  houses. 
  These 
  

   will 
  be 
  noticed 
  in 
  the 
  views 
  reproduced 
  on 
  Plates 
  XXIII 
  and 
  XXIV, 
  

  

  (4b) 
  

  

  