June 4, 1921 delunger and whittemore: radio fading 



255 



daytime but quickly loses this property by the recombination of the 

 ions at night. 



(5) The Heaviside surface, permanently ionized, and an almost 

 perfect conductor. 



The boundaries of these layers are obviously not absolutely horizon- 

 tal surfaces. The stratosphere is ionized during the day only, the 

 sun's rays being the cause of the ionization. The permanently ionized 

 region above the Heaviside surface is the region of permanent aurora, 



Heamide surface 



Stratosphere 

 ^Isothermal layer) 



Ior)/zed fyay onk/) 



100 km. 



/^Radioactive layer 



Earth's surface 



Fig. 1. — Vertical cross-section of the earth's atmosphere. 



and is so good a conductor that the waves cannot penetrate it. Any 

 waves reaching it can only slide along it, just as waves slide along the 

 even less perfectly conducting surface of the earth. 



Previous explanations of radio transmission phenomena have con- 

 sidered the waves as being constantly reflected back and forth or 

 progressively refracted between the Heaviside surface and the earth, 

 both by day and by night, their intensity being reduced in the day- 

 time by the ionization in the stratosphere. That view does not ex- 

 plain why the waves have the characteristics of ground absorption 



