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BELL SYSTEM TECHNICAL JOURNAL 



The factor a will be recognized to be the absorption factor of the 

 famihar Austen-Cohen empirical formula, which may be expressed as 



e = 0.009 -^e- 



a 



ndi^) 



in which 



P = radiated power in watts, 

 d = distance in kilometers, 

 X = wave-length in kilometers, 

 a = absorption factor, 

 e = in volts per meter. 



The first term represents the decrease in strength due merely to the 

 spreading out of the waves; the second term, the decrease due to the 



D/stance /horn StiJf/bn /n /VJ/es. 



Fig. 3 — Effect pf the terrain in reducing the field strength of a broadcast transmitting 

 station. 5 kilowatts in antenna, frequency 610 kilocycles, wave-length 492 meters 



absorption of the wave energy by the imperfect conductivity of the 

 earth's surface. 



The curves given in Fig. 3 are derived from a considerable amount 

 of data taken in the course of field strength surveys of the New York 



