﻿Smithsonian 
  Report 
  1922. 
  — 
  Humphreys. 
  

  

  Plate 
  9. 
  

  

  I. 
  Billow 
  Cloud 
  (Form 
  of 
  Alto-cumulus). 
  

  

  (A. 
  J. 
  Henry, 
  photo.) 
  

  

  2. 
  Alto-stratus 
  and 
  Advection 
  Fog, 
  Seen 
  from 
  Mount 
  Wilson, 
  

  

  Calif. 
  

  

  (F. 
  Ellcrman, 
  photo.) 
  

  

  