﻿FOGS 
  AND 
  CLOUDS 
  — 
  HUMPHREYS. 
  219 
  

  

  size 
  of 
  the 
  droplets. 
  The 
  greatest 
  contrast, 
  perhaps, 
  is 
  between 
  the 
  

   brilliant 
  rainbow 
  of 
  the 
  retreating 
  shower 
  and 
  that 
  ill-defined, 
  

   faintly 
  tinged 
  bow 
  one 
  sometimes 
  sees 
  on 
  a 
  sheet 
  of 
  fog. 
  

  

  The 
  halo. 
  — 
  As 
  must 
  be 
  obvious 
  to 
  anyone, 
  the 
  cirrus 
  and 
  other 
  

   very 
  cold 
  clouds 
  nearly 
  always 
  consist 
  of 
  ice 
  crystals. 
  These 
  re- 
  

   flect 
  some 
  of 
  the 
  light 
  that 
  falls 
  upon 
  them; 
  and 
  some 
  of 
  it 
  they 
  

   transmit, 
  bent, 
  or 
  refracted, 
  as 
  we 
  say, 
  out 
  of 
  its 
  course 
  and 
  split 
  

   up 
  into 
  all 
  its 
  colors, 
  but 
  always 
  with 
  the 
  red 
  nearest 
  to 
  the 
  source 
  

   of 
  light. 
  Both 
  the 
  refracted 
  and 
  the 
  reflected 
  light 
  produce 
  various 
  

   bright 
  patterns 
  properly 
  known 
  as 
  halos. 
  

  

  By 
  refraction 
  we 
  get 
  : 
  The 
  very 
  common 
  ring 
  of 
  22° 
  radius 
  about 
  

   the 
  sun 
  or 
  moon 
  (pi. 
  5, 
  fig. 
  2) 
  ; 
  the 
  less 
  frequent 
  ring 
  of 
  46° 
  radius; 
  

   the 
  occasional 
  brilliantly 
  colored 
  arc 
  that 
  has 
  its 
  center 
  directly 
  over- 
  

   head 
  and 
  its 
  convex 
  side 
  next 
  to 
  the 
  sun 
  ; 
  and 
  rarely, 
  numerous 
  other 
  

   splotches 
  and 
  arcs, 
  all 
  more 
  or 
  less 
  distinctly 
  colored, 
  and 
  things 
  

   of 
  beauty 
  and 
  interest. 
  

  

  By 
  reflection, 
  on 
  the 
  other 
  hand, 
  we 
  get 
  only 
  white 
  or 
  color- 
  

   less 
  figures; 
  chiefly, 
  the 
  parhelic 
  circle 
  (pi. 
  5, 
  fig. 
  2) 
  that 
  passes 
  

   through 
  the 
  sun 
  and 
  is 
  parallel 
  to 
  the 
  horizon; 
  and 
  a 
  pillar 
  of 
  light 
  

   that 
  rises 
  straight 
  up 
  through 
  the 
  sun, 
  much 
  as 
  would 
  its 
  reflection 
  

   in 
  rippled 
  water 
  if 
  stood 
  on 
  end. 
  

  

  The 
  corona. 
  — 
  Thin 
  clouds 
  of 
  water 
  droplets 
  also 
  produce 
  beauti- 
  

   ful 
  colored 
  rings 
  about 
  the 
  sun 
  and 
  moon, 
  but 
  usually 
  much 
  smaller 
  

   than 
  the 
  circles 
  formed 
  by 
  refraction 
  through 
  snow 
  crystals, 
  and 
  

   with 
  their 
  colors 
  in 
  reverse 
  order; 
  that 
  is, 
  with 
  the 
  red 
  farthest 
  

   from 
  the 
  source 
  of 
  light 
  instead 
  of 
  nearest 
  to 
  it. 
  These 
  rings, 
  

   known 
  as 
  coronas, 
  are 
  owing 
  to 
  what 
  the 
  physicist 
  calls 
  diffraction, 
  

   or, 
  in 
  this 
  case, 
  the 
  bending 
  of 
  the 
  light 
  around 
  the 
  droplets 
  into 
  

   their 
  shadows. 
  They 
  are 
  most 
  frequently 
  seen 
  about 
  the 
  moon, 
  

   but 
  may 
  be 
  seen 
  even 
  more 
  brilliantly, 
  occasionally 
  in 
  a 
  widening 
  

   series 
  of 
  two 
  or 
  three 
  repetitions 
  of 
  the 
  colors, 
  about 
  the 
  sun, 
  if 
  

   one 
  will 
  use 
  dark 
  glasses 
  to 
  cut 
  down 
  the 
  glare. 
  

  

  Plate 
  26, 
  figure 
  2, 
  from 
  a 
  drawing 
  by 
  Mr. 
  G. 
  A. 
  Clarke, 
  of 
  

   Aberdeen, 
  Scotland, 
  shows 
  a 
  magnificent 
  corona 
  and 
  also 
  contains 
  

   other 
  phenomena 
  observed 
  by 
  him 
  at 
  that 
  place 
  on 
  June 
  13, 
  1921. 
  

   These 
  were: 
  (a) 
  The 
  slightly 
  veiled 
  image 
  of 
  the 
  sun; 
  (b) 
  an 
  

   aureole 
  of 
  faintly 
  colored 
  light 
  close 
  to 
  the 
  sun; 
  (c) 
  a 
  triple 
  corona 
  

   in 
  which 
  the 
  radii 
  of 
  the 
  red 
  or 
  outer 
  borders 
  of 
  the 
  three 
  rings 
  were 
  

   about 
  6°, 
  10°, 
  and 
  16°, 
  respectively; 
  (d) 
  iridescence 
  (see 
  below) 
  

   merged 
  with 
  and 
  extending 
  beyond 
  a 
  portion 
  of 
  the 
  outer 
  coronal 
  

   ring; 
  (e) 
  portions 
  of 
  a 
  fine 
  halo 
  of 
  22° 
  radius, 
  produced 
  by 
  a 
  back- 
  

   ground 
  of 
  thin 
  cirro-stratus. 
  

  

  Cloud 
  iridescence. 
  — 
  Unquestionably 
  the 
  most 
  beautiful 
  thing 
  in 
  all 
  

   the 
  heavens 
  is 
  a 
  magnificent 
  display 
  of 
  iridescent 
  clouds 
  — 
  numerous 
  

  

  