﻿206 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1922. 
  

  

  When 
  the 
  obstruction 
  is 
  only 
  a 
  peak 
  the 
  crest 
  cloud 
  is 
  apt 
  to 
  ba 
  

   called 
  a 
  cap, 
  hat, 
  cowl, 
  hood, 
  and 
  the 
  like, 
  all 
  of 
  which 
  are 
  recog- 
  

   nized 
  signs 
  of 
  bad 
  weather, 
  as, 
  for 
  instance: 
  

  

  " 
  When 
  Falkland 
  Hill 
  puts 
  on 
  his 
  cap, 
  

   The 
  Howe 
  o' 
  Fife 
  will 
  get 
  a 
  drap. 
  

  

  " 
  When 
  Traprain 
  puts 
  on 
  his 
  hat, 
  

   The 
  Lothian 
  lads 
  may 
  look 
  to 
  that. 
  

  

  " 
  When 
  Rubenslaw 
  puts 
  on 
  his 
  cowl, 
  

  

  The 
  Dunion 
  on 
  his 
  hood, 
  

   Then 
  a' 
  the 
  wives 
  of 
  Teviotside 
  

  

  Ken 
  there 
  will 
  be 
  a 
  flood." 
  

  

  Riffle 
  cloud. 
  — 
  Very 
  often 
  the 
  crest 
  cloud 
  along 
  a 
  mountain 
  ridge 
  

   is 
  paralleled 
  by 
  a 
  similar 
  but 
  smaller 
  cloud 
  over 
  the 
  leeward 
  valley, 
  

   or 
  plain 
  in 
  the 
  case 
  of 
  the 
  exceptional 
  isolated 
  mountain. 
  The 
  

   wind, 
  deflected 
  in 
  a 
  great 
  wave 
  over 
  the 
  mountain, 
  rises 
  in 
  a 
  series 
  

   of 
  decreasing 
  billows 
  beyond, 
  like 
  the 
  waves 
  cr 
  riffles 
  in 
  a 
  river 
  due 
  

   to 
  a 
  ledge 
  of 
  rock, 
  or 
  other 
  obstruction, 
  on 
  the 
  bottom 
  — 
  hence 
  the 
  

   name 
  " 
  riffle 
  cloud." 
  

  

  The 
  process 
  by 
  which 
  the 
  crest 
  cloud 
  is 
  formed 
  along 
  the 
  ridge 
  

   of 
  the 
  mountain 
  and 
  restricted 
  thereto, 
  that 
  is, 
  the 
  cooling 
  of 
  the 
  

   air 
  by 
  ascent 
  on 
  the 
  windward 
  side 
  and 
  its 
  warming 
  by 
  descent 
  on 
  

   the 
  lee 
  side, 
  occurs 
  also 
  in 
  the 
  rising 
  and 
  falling 
  air 
  on 
  the 
  wind- 
  

   ward 
  and 
  the 
  lee 
  sides 
  respectively 
  of 
  the 
  series 
  of 
  air 
  waves, 
  or 
  giant 
  

   riffles, 
  induced 
  by 
  the 
  mountain 
  obstruction 
  to 
  the 
  wind. 
  Hence, 
  

   when 
  the 
  crest 
  cloud 
  is 
  at 
  all 
  heavy 
  the 
  top 
  of 
  the 
  first 
  and 
  largest 
  

   wave 
  is 
  apt 
  to 
  be 
  clouded; 
  even 
  the 
  second 
  wave 
  occasionally 
  shows 
  

   some 
  cloud, 
  but 
  the 
  third 
  rarely 
  if 
  ever. 
  

  

  The 
  crest 
  cloud 
  and 
  the 
  riffle 
  cloud, 
  since 
  they 
  show 
  the 
  presence 
  

   of 
  humid 
  winds, 
  are 
  excellent 
  signs 
  of 
  rain, 
  or 
  snow, 
  in 
  a 
  few 
  

   hours. 
  The 
  order 
  of 
  occurrence 
  is: 
  Formation 
  of 
  the 
  crest 
  cloud; 
  

   thickening 
  of 
  the 
  crest 
  cloud 
  and 
  forming 
  of 
  the 
  riffle 
  cloud 
  ; 
  growth 
  

   and 
  union 
  of 
  these 
  two 
  clouds 
  and 
  the 
  complete 
  covering 
  of 
  the 
  

   sky 
  ; 
  onset 
  of 
  rain 
  or 
  snow. 
  

  

  Banner 
  cloud. 
  — 
  The 
  banner 
  cloud 
  (pi. 
  21, 
  fig. 
  1) 
  suggests 
  a 
  great 
  

   white 
  flag, 
  whence 
  its 
  name, 
  floating 
  from 
  a 
  tall 
  mountain 
  peak. 
  

   In 
  strong 
  winds 
  the 
  atmospheric 
  pressure 
  to 
  the 
  immediate 
  leeward 
  

   of 
  such 
  a 
  peak 
  is 
  more 
  or 
  less 
  reduced. 
  If 
  the 
  humidity 
  is 
  right 
  

   this 
  causes 
  a 
  cloud 
  through 
  the 
  resulting 
  cooling, 
  aided, 
  no 
  doubt, 
  

   in 
  many 
  cases, 
  by 
  the 
  cold 
  walls 
  of 
  the 
  peak 
  itself. 
  Here 
  too, 
  as 
  

   in 
  the 
  preceding 
  cases, 
  the 
  cloud 
  is 
  stationary, 
  but 
  its 
  substance 
  in 
  

   rapid 
  flux 
  through 
  condensation 
  on 
  one 
  side 
  and 
  evaporation 
  on 
  

   the 
  other. 
  

  

  