﻿222 
  Mr. 
  E. 
  M. 
  Deeley 
  on 
  

  

  Owing 
  to 
  the 
  direct 
  flow 
  of 
  the 
  wind 
  being 
  prevented 
  by- 
  

   trees, 
  buildings, 
  hills, 
  &c, 
  it 
  is 
  by 
  no 
  means 
  easy 
  to 
  observe 
  

   the 
  correct 
  direction 
  of 
  movement. 
  It 
  often 
  happens 
  that 
  a 
  

   wind 
  blowing 
  up 
  a 
  river 
  will 
  follow 
  closely 
  the 
  river 
  

   windings 
  ; 
  passing 
  clouds, 
  especially 
  rain-clouds, 
  also 
  pro- 
  

   duce, 
  for 
  short 
  intervals, 
  marked 
  changes 
  both 
  in 
  the 
  

   direction 
  and 
  force 
  of 
  the 
  wind; 
  but 
  the 
  difficulties 
  that 
  

   are 
  met 
  with 
  in 
  observing 
  the 
  general 
  direction 
  should 
  be 
  

   overcome 
  by 
  the 
  exercise 
  of 
  extreme 
  care 
  so 
  as 
  to 
  obtain 
  a 
  

   result 
  as 
  accurate 
  as 
  possible. 
  The 
  observed 
  results 
  should 
  

   then 
  be 
  recorded 
  in 
  degrees 
  from 
  the 
  true 
  north, 
  working 
  

   clockwise 
  round 
  the 
  compass. 
  

  

  To 
  render 
  the 
  points 
  I 
  wish 
  to 
  draw 
  attention 
  to 
  clear, 
  a 
  

   number 
  of 
  charts 
  or 
  diagrams 
  of 
  cyclonic 
  disturbances 
  &c. 
  

   have 
  been 
  taken 
  from 
  Shaw 
  and 
  Lempfert's 
  paper 
  on 
  " 
  The 
  

   Life 
  History 
  of 
  Surface 
  Air 
  Currents 
  " 
  *. 
  The 
  wind 
  direc- 
  

   tions 
  are 
  sometimes 
  shown 
  by 
  continuous 
  lines 
  instead 
  of 
  

   arrows, 
  and 
  the 
  isobars 
  by 
  dotted 
  lines. 
  In 
  the 
  original 
  

   charts 
  the 
  arrows 
  often 
  show 
  many 
  irregularities 
  in 
  the 
  wind 
  

   directions 
  of 
  the 
  same 
  wind 
  province; 
  but 
  these 
  are 
  due 
  to 
  local 
  

   causes 
  such 
  as 
  hills, 
  falling 
  rain, 
  &c. 
  It 
  is 
  near 
  the 
  centres 
  

   of 
  cyclones 
  that' 
  the 
  errors 
  arising 
  from 
  the 
  methods 
  of 
  obser- 
  

   vation 
  now 
  adopted 
  appear 
  to 
  be 
  most 
  marked. 
  Indeed, 
  until 
  

   strict 
  accuracy 
  is 
  arrived 
  at 
  in 
  recording 
  and 
  plotting 
  obser- 
  

   vations 
  of 
  wind 
  directions, 
  many 
  features 
  of 
  atmospheric 
  

   circulation 
  will 
  continue 
  to 
  be 
  obscure. 
  

  

  Shaw 
  and 
  Lempfert, 
  in 
  the 
  paper 
  already 
  referred 
  to, 
  show 
  

   that 
  the 
  wind 
  directions 
  in 
  cyclones, 
  if 
  they 
  do 
  not 
  always 
  

   close 
  in 
  as 
  regular 
  spirals 
  towards 
  the 
  cyclonic 
  centre, 
  do 
  

   travel 
  in 
  such 
  a 
  way 
  that 
  the 
  air 
  suffers 
  horizontal 
  contraction 
  

   and 
  rises. 
  That 
  this 
  is 
  the 
  case 
  is 
  rendered 
  evident 
  by 
  the 
  

   consideration 
  of 
  the 
  air 
  trajectories 
  they 
  have 
  worked 
  out. 
  

  

  In 
  the 
  case 
  of 
  quite 
  a 
  deep 
  cyclone 
  the 
  difference 
  of 
  

   pressure 
  between 
  the 
  centre 
  and 
  the 
  margin 
  seldom 
  amounts 
  

   to 
  more 
  than 
  one 
  inch 
  of 
  mercury, 
  and 
  this 
  is 
  about 
  the 
  

   change 
  of 
  pressure 
  due 
  to 
  a 
  rise 
  of 
  400 
  feet. 
  To 
  give 
  rise 
  to 
  

   heavy 
  rain, 
  masses 
  of 
  land 
  over 
  which 
  winds 
  are 
  blowing 
  

   and 
  rising 
  as 
  they 
  advance 
  must 
  be 
  much 
  higher 
  than 
  this. 
  

   In 
  a 
  cyclone 
  the 
  rain-producing 
  effect 
  resulting 
  from 
  the 
  

   fall 
  of 
  the 
  barometer 
  is 
  very 
  small 
  indeed. 
  Rain 
  when 
  it 
  does 
  

   fall 
  nearly 
  always 
  results 
  from 
  the 
  rise 
  of 
  air 
  in 
  the 
  cyclone 
  

   or 
  the 
  mounting 
  of 
  one 
  air 
  current 
  over 
  another, 
  the 
  quantity 
  

   of 
  rain 
  depending 
  upon 
  the 
  humidity 
  of 
  the 
  rising 
  air 
  and 
  

   the 
  height 
  to 
  which 
  it 
  is 
  lifted. 
  

  

  According 
  to 
  the 
  old 
  view, 
  the 
  air 
  rises 
  spirally 
  in 
  the 
  

  

  * 
  Meteorological 
  Office 
  Publication 
  No. 
  174. 
  

  

  