﻿THE 
  

   LONDON, 
  EDINBURGH, 
  and 
  DUBLIN 
  

  

  PHILOSOPHICAL 
  MAGAZINE 
  

  

  AND 
  

  

  JOURNAL 
  OF 
  SCIENCE. 
  

  

  ^ 
  ^ 
  

  

  [SIXTH 
  SERIES.] 
  /r 
  

  

  Mr 
  9^ 
  

  

  MARCH1918. 
  V 
  S 
  , 
  d 
  19 
  1Q 
  *' 
  

  

  XXYI. 
  Rain, 
  Wind, 
  and 
  Cyclones. 
  

   By 
  R. 
  M. 
  Deeley, 
  M.Inst.C.E., 
  F.G.S.* 
  

  

  DURING 
  recent 
  years 
  our 
  conceptions 
  respecting 
  the 
  

   conditions 
  obtaining 
  in 
  cyclones 
  have 
  undergone 
  very 
  

   considerable 
  alterations. 
  The 
  old 
  idea, 
  which 
  made 
  a 
  cyclone 
  

   consist 
  of 
  a 
  lower 
  spirally 
  inflowing 
  current 
  of 
  air 
  directed 
  

   towards 
  the 
  centre 
  of 
  an 
  area 
  of 
  low 
  barometric 
  pressure, 
  an 
  

   internal 
  rising 
  current 
  of 
  warm 
  air, 
  and 
  an 
  upper 
  stream 
  of 
  

   air 
  flowing 
  outwards 
  from 
  the 
  same 
  area, 
  requires 
  very 
  con- 
  

   siderable 
  modification 
  in 
  view 
  of 
  modern 
  discoveries. 
  

  

  That 
  the 
  cause 
  of 
  rain 
  is 
  due 
  to 
  the 
  upward 
  flow 
  of 
  masses 
  

   of 
  air, 
  which 
  being 
  cooled 
  below 
  the 
  dew-point 
  by 
  expansion, 
  

   condense 
  out 
  some 
  of 
  their 
  moisture, 
  still 
  holds 
  true 
  ; 
  but 
  the 
  

   distribution 
  of 
  temperature 
  and 
  the 
  actual 
  nature 
  of 
  the 
  air 
  

   circulation 
  prove 
  to 
  be 
  very 
  different 
  from 
  what 
  was 
  once 
  

   thought 
  to 
  be 
  the 
  case. 
  

  

  In 
  all 
  scientific 
  work 
  accurate 
  observation 
  and 
  correct 
  records 
  

   are 
  essential. 
  Here, 
  however, 
  meteorological 
  records 
  fail 
  us- 
  

   in 
  a 
  very 
  important 
  particular. 
  The 
  wind 
  directions 
  shown 
  

   on 
  our 
  charts 
  are 
  not 
  always 
  accurate. 
  In 
  Great 
  Britain, 
  

   for 
  example, 
  wind 
  directions 
  are 
  given 
  to 
  the 
  nearest 
  of 
  

   sixteen 
  points 
  of 
  the 
  compass. 
  It 
  thus 
  comes 
  about 
  that 
  

   winds 
  which 
  are 
  observed 
  to 
  differ 
  in 
  direction 
  only 
  one 
  or 
  

   two 
  degrees 
  from 
  each 
  other, 
  may 
  be 
  charted 
  as 
  differing 
  

   by 
  as 
  much 
  as 
  twenty 
  degrees. 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

   Phil. 
  Mag. 
  S. 
  6. 
  Vol. 
  35. 
  No. 
  207. 
  March 
  1918. 
  R 
  

  

  