﻿FOGS 
  AND 
  CLOUDS 
  — 
  HUMPHREYS. 
  199 
  

  

  or 
  reflection 
  class 
  are 
  (1) 
  the 
  parhelic 
  circle, 
  a 
  white 
  band 
  of 
  light 
  

   passing 
  around 
  the 
  sky 
  parallel 
  to 
  the 
  horizon 
  and 
  through 
  the 
  sun 
  

   (pi. 
  5, 
  fig. 
  2) 
  ; 
  and 
  (2) 
  the 
  sun 
  pillar, 
  a 
  vertical 
  column 
  of 
  white 
  

   light 
  extending 
  directly 
  above 
  and 
  below 
  the 
  sun. 
  

  

  These 
  halos 
  are 
  positive 
  proof 
  that 
  the 
  cirro-stratus 
  clouds, 
  like 
  

   the 
  cirrus 
  from 
  which 
  they 
  frequently 
  are 
  developed, 
  also 
  consist, 
  

   normally, 
  of 
  myriads 
  of 
  ice 
  crystals. 
  

  

  Whenever 
  the 
  cirro-stratus 
  cloud 
  (pi. 
  5, 
  fig. 
  1) 
  has 
  developed 
  from 
  

   a 
  cirrus 
  it 
  may 
  be 
  assumed 
  that 
  rain 
  or 
  snow, 
  as 
  determined 
  by 
  the 
  

   temperature, 
  probably 
  will 
  soon 
  follow, 
  not 
  out 
  of 
  the 
  cirro-stratus, 
  

   of 
  course, 
  but 
  from 
  an 
  approaching 
  nimbus, 
  or 
  rain 
  cloud. 
  

  

  Though 
  denser 
  than 
  the 
  cirrus, 
  the 
  cirro-stratus 
  still 
  is 
  so 
  thin 
  as 
  

   to 
  leave 
  the 
  outline 
  of 
  the 
  sun 
  sharply 
  defined. 
  

  

  3. 
  Cirro-cumulus 
  (Ci.-Cu.) 
  — 
  "Mackerel 
  Sky. 
  — 
  Small 
  rounded 
  

   masses 
  or 
  white 
  flakes 
  without 
  shadow, 
  or 
  showing 
  very 
  slight 
  

   shadow; 
  arranged 
  in 
  groups 
  and 
  often 
  in 
  lines. 
  French, 
  Moutons 
  — 
  

   German, 
  Schdfchen-ioolken.' 
  1 
  '' 
  (PL 
  6, 
  figs. 
  1 
  and 
  2.) 
  

  

  The 
  term 
  " 
  mackerel 
  sky 
  " 
  is 
  an 
  abbreviation 
  of 
  " 
  mackerel-back 
  

   sky," 
  so 
  named 
  because 
  of 
  the 
  frequent 
  resemblance 
  of 
  rows 
  of 
  cirro- 
  

   cumuli 
  to 
  the 
  patterns 
  (not 
  the 
  scales) 
  on 
  the 
  backs 
  of 
  one 
  or 
  more 
  

   species 
  of 
  mackerel. 
  When 
  the 
  cirro-cumuli 
  are 
  small, 
  numerous, 
  

   and 
  without 
  order 
  or 
  pattern, 
  they 
  often 
  are 
  called 
  " 
  curdle 
  sky." 
  

   (PL 
  6, 
  fig. 
  2.) 
  

  

  All 
  forms 
  of 
  the 
  cirro-cumulus 
  appear 
  to 
  be 
  due 
  to 
  small 
  local 
  

   convections. 
  Those 
  occurring 
  in 
  rows 
  presumably 
  are 
  on 
  the 
  crests 
  

   of 
  air 
  waves 
  or 
  billows 
  at 
  the 
  interface 
  between 
  wind 
  layers 
  of 
  

   unequal 
  speeds 
  or 
  different 
  directions, 
  or 
  both, 
  and 
  commonly 
  un- 
  

   equal 
  also 
  in 
  temperature 
  and 
  humidity. 
  The 
  cirro-cumulus, 
  through 
  

   turbulence 
  or 
  other 
  cause, 
  often 
  merges 
  into 
  a 
  more 
  or 
  less 
  uniform, 
  

   stratified 
  cloud, 
  especially 
  the 
  cirro-stratus. 
  

  

  The 
  fact 
  that 
  the 
  cirro-cumuli 
  cast 
  but 
  faint 
  shadows, 
  if 
  any, 
  and 
  

   that 
  the 
  sharp 
  outline 
  of 
  the 
  sun 
  is 
  visible 
  through 
  them 
  shows 
  that 
  

   they 
  are 
  quite 
  thin 
  and 
  contain 
  but 
  little 
  cloud 
  material. 
  

  

  4. 
  Alto-cumulus 
  (A.-Cu). 
  — 
  "Larger 
  rounded 
  masses, 
  lohite 
  or 
  

   grayish, 
  partially 
  shaded, 
  arranged 
  in 
  groups 
  or 
  lines, 
  and 
  often 
  so 
  

   crowded 
  together 
  in 
  the 
  middle 
  region 
  that 
  the 
  cloudlets 
  join. 
  The 
  

   separate 
  masses 
  are 
  generally 
  larger 
  and 
  more 
  compact 
  (resembling 
  

   strato-cumulus) 
  in 
  the 
  middle 
  region 
  of 
  the 
  group, 
  but 
  the 
  denseness 
  

   of 
  the 
  layer 
  varies 
  and 
  sometimes 
  is 
  so 
  attenuated 
  that 
  the 
  individual 
  

   masses 
  assume 
  the 
  appearance 
  of 
  sheets 
  or 
  thin 
  flakes 
  of 
  considerable 
  

   extent 
  with 
  hardly 
  any 
  shading. 
  At 
  the 
  margin 
  of 
  the 
  group 
  they 
  

   form 
  smaller 
  cloudlets 
  resembling 
  those 
  of 
  cirro-cumulus. 
  The 
  cloud- 
  

   lets 
  often 
  group 
  themselves 
  in 
  parallel 
  lines, 
  arranged 
  in 
  one 
  or 
  more 
  

   directions." 
  (PL 
  7, 
  figs. 
  1 
  and 
  2; 
  pi. 
  8, 
  figs. 
  1 
  and 
  2; 
  pi. 
  9, 
  fig. 
  1.) 
  

  

  