﻿A. 
  W. 
  Buff 
  — 
  Seiches 
  on 
  the 
  Bay 
  of 
  Fundy. 
  411 
  

  

  33, 
  36, 
  38, 
  40, 
  42, 
  43, 
  47, 
  50, 
  50, 
  45, 
  43, 
  43, 
  46, 
  46, 
  40, 
  40, 
  39, 
  

   35, 
  27 
  fathoms, 
  or 
  a 
  mean 
  of 
  34'4 
  fathoms. 
  Reducing 
  to 
  feet 
  

   and 
  substituting 
  in 
  either 
  formula 
  we 
  have, 
  for 
  binodal 
  vibra- 
  

   tions, 
  a 
  period 
  of 
  87 
  minutes, 
  and 
  for 
  trinodal, 
  43*5 
  minutes. 
  

   Now 
  the 
  period 
  of 
  the 
  " 
  secondary 
  undulations 
  " 
  is, 
  according 
  

   to 
  Mr. 
  Dawson, 
  " 
  about 
  40 
  minutes." 
  If 
  an 
  allowance 
  of 
  

   two 
  miles 
  had 
  been 
  made 
  for 
  the 
  depth 
  of 
  the 
  indentation 
  

   referred 
  to, 
  and 
  the 
  corresponding 
  soundings 
  omitted, 
  the 
  cal- 
  

   culated 
  period 
  for 
  low 
  water 
  would 
  become 
  very 
  nearly 
  40 
  

   minutes. 
  On 
  the 
  other 
  hand, 
  it 
  will 
  be 
  shown 
  below 
  that 
  the 
  

   observed 
  period 
  is 
  possibly 
  more 
  nearly 
  43 
  minutes. 
  In 
  any 
  

   case 
  the 
  evidence 
  that 
  these 
  "secondary 
  undulations" 
  are 
  also 
  

   trinodal 
  vibrations 
  seems 
  strong 
  if 
  not 
  conclusive. 
  

  

  Next, 
  as 
  to 
  the 
  difference 
  of 
  vibration 
  period 
  at 
  high 
  water 
  

   and 
  at 
  low 
  water, 
  it 
  can 
  be 
  calculated 
  that 
  for 
  a 
  difference 
  of 
  

   20 
  feet 
  (about 
  the 
  mean 
  range 
  at 
  St. 
  John), 
  the 
  period 
  should 
  

   be 
  two 
  minutes 
  less 
  at 
  high 
  water 
  than 
  at 
  low 
  water. 
  To 
  

   enable 
  me 
  to 
  test 
  this 
  point, 
  Mr. 
  Dawson 
  has 
  kindly 
  supplied 
  

   me 
  traces 
  of 
  all 
  the 
  records 
  of 
  secondary 
  undulations 
  at 
  present 
  

   available 
  and 
  sufficiently 
  well 
  defined 
  to 
  give 
  a 
  reliable 
  esti- 
  

   mate. 
  Unfortunately 
  these 
  can 
  hardly 
  be 
  considered 
  sufficient 
  

   to 
  establish 
  the 
  point, 
  but 
  such 
  as 
  they 
  are, 
  they 
  are 
  given. 
  

   For 
  low 
  water 
  the 
  periods 
  are 
  41, 
  45, 
  45, 
  39, 
  40, 
  32, 
  49, 
  53, 
  

   giving 
  a 
  mean 
  of 
  43 
  minutes 
  ; 
  for 
  high 
  water, 
  43, 
  35, 
  43, 
  40, 
  

   46, 
  giving 
  a 
  mean 
  of 
  41*4. 
  The 
  former 
  mean 
  is 
  1*6 
  minutes 
  

   greater 
  than 
  the 
  latter, 
  but 
  the 
  data 
  are 
  insufficient 
  to 
  justify 
  

   much 
  reliance 
  being 
  placed 
  on 
  this 
  argument. 
  The 
  apparent 
  

   variability 
  of 
  period 
  shown 
  by 
  the 
  above 
  figures 
  may 
  be 
  readily 
  

   accounted 
  for. 
  In 
  the 
  first 
  place 
  every 
  slight 
  barometric 
  

   change 
  or 
  change 
  of 
  wind 
  produces 
  a 
  corresponding 
  change 
  of 
  

   level 
  and 
  this 
  is 
  superposed 
  on 
  the 
  " 
  secondary 
  undulations," 
  

   producing 
  an 
  apparent 
  variation 
  of 
  period. 
  Secondly, 
  the 
  

   irregularities 
  of 
  coast 
  line 
  may 
  have 
  an 
  effect. 
  Thirdly, 
  and 
  

   perhaps 
  most 
  important 
  of 
  all, 
  different 
  modes 
  of 
  vibration 
  

   may 
  co-exist 
  in 
  different 
  proportions 
  at 
  different 
  times, 
  so 
  that 
  

   the 
  resultant 
  period 
  may 
  at 
  some 
  time 
  be 
  more 
  nearly 
  that 
  of 
  

   "binodal 
  vibration, 
  at 
  others 
  of 
  trinodal, 
  etc. 
  Thus, 
  a 
  higher 
  

   mode 
  of 
  vibration 
  co-existing 
  with 
  the 
  prevailing 
  mode 
  might 
  

   account 
  for 
  the 
  " 
  notches 
  " 
  observed 
  by 
  Airy 
  in 
  the 
  secondary 
  

   undulations 
  at 
  Malta. 
  

  

  As 
  regards 
  the 
  relation 
  of 
  the 
  phases 
  of 
  vibration 
  at 
  oppo- 
  

   site 
  sides 
  of 
  the 
  bay, 
  no 
  information 
  is 
  at 
  hand. 
  St. 
  John 
  is 
  

   the 
  only 
  point 
  on 
  the 
  bay 
  at 
  which 
  there 
  is 
  a 
  recording 
  tide- 
  

   gauge. 
  Another 
  at 
  Digby, 
  on 
  the 
  opposite 
  side 
  of 
  the 
  bay, 
  

   would 
  probably 
  settle 
  the 
  matter 
  in 
  a 
  month 
  ; 
  but 
  the 
  cost 
  of 
  

   erecting 
  a 
  gauge 
  suitable 
  for 
  such 
  work 
  is 
  considerable. 
  I 
  

   hope 
  on 
  some 
  occasion, 
  when 
  the 
  water 
  is 
  calm 
  and 
  " 
  secondary 
  

  

  