ULTRA-SIIORT-WAVE TRANSMISSION PHENOMENA 



217 



then veering slightly to the left to follow the main New York-to- 

 Chicago airplane route. Flights were made at 8000, 5000, 2500, and 

 1000 feet (2440, 1525, 763, and 305 meters) above sea level, and the 

 results are given in Figs. 15 to 20 inclusive. Fig. 21 gives a map of 

 the country. 



In these figures the experimental curves are supplemented by the- 

 oretical ones, these latter being calculated by assuming the earth at the 

 reflection point to be equivalent to a plane surface medium of a dielec- 



10 20 30 40 SO 60 70 80 90 100 110 120 130 140 150 

 MILES FROM TRANSMITTER 



Fig. 17 — Flight from transmitter. Altitude — 5000 feet; 

 wave-length — 4.3 meters, June 29, 1931. 



trie constant 10 and a resistivity of 10,000 ohms per cm. cube and 100 

 feet (30 meters) above sea level. This point, for the outermost deep 

 minimum, varied in location from 1.5 miles out, for the 1000-foot flight, 

 to 2 miles out, for the 8000-foot flight, with corresponding angles of 

 incidence of 88 and 88.5 degrees. The area involved is fairly level and 

 open. The earth's curvature is taken into account and refraction cor- 

 rections are applied using the Schelleng, Burrows, and Ferrell formula. 

 As shown in Fig. 15 the fit at the extreme distances is considerably im- 

 proved by this latter correction, thus indicating its validity. The deep 



