﻿Smithsonian 
  Report, 
  1929. 
  — 
  Compton 
  

  

  Plate 
  l 
  

  

  Diagram 
  of 
  the 
  Diffraction 
  

   Grid 
  

  

  OF 
  Waves 
  by 
  a 
  

  

  2. 
  Photograph 
  of 
  Mercury 
  Ripples 
  Diffracted 
  by 
  

   A 
  Grid 
  

  

  