﻿Smithsonian 
  Report 
  1922. 
  — 
  Humphreys. 
  

  

  Plate 
  I. 
  

  

  

  I. 
  Radiation 
  Fog, 
  Loudoun 
  Valley, 
  Va. 
  

   (A. 
  .). 
  Weed, 
  photo.) 
  

  

  2. 
  Advection 
  Fog, 
  Seen 
  from 
  Mount 
  Wilson, 
  Calif. 
  

   i 
  I-'. 
  Ellerman, 
  photo.) 
  

  

  