248 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 11 



is violent at night, these tendencies being more pronounced the shorter 

 the wave-length. Thus abnormally great distances are obtained at 

 night by stations using short waves, even though the power employed 

 is as small as one kilowatt. Signals from such stations in the north- 

 eastern part of the United States have been heard across the Atlantic, 

 and off the coast of South America, as well as across the North Ameri- 

 can continent. 



The phenomenon of fading is much better known among amateurs 

 than among commercial radio men because amateurs do most of their 

 radio transmitting and receiving at night and they are limited by law 

 to short wave-lengths. The great fluctuations in the intensity of 

 signals and the extraordinary distances of transmission at night which 

 have been reported by amateurs have not been taken very seriously 

 by professional radio men because there are so many difficulties with 

 radio apparatus that reliable results are hard to get. 



What is probably the most comprehensive series ever made of co- 

 operative transmission tests on the phenomenon of fading was con- 

 ducted during the past year through the cooperation of the American 

 Radio Relay League and the Bureau of Standards. Transmission 

 took place from stations at a number of points in the northwest quar- 

 ter of the United States according to a prearranged schedule, and 

 simultaneous records of received signal intensity were made by about 

 one hundred specially appointed receiving operators. Through the 

 hearty and enthusiastic cooperation of the officers and members of 

 the American Radio Relay League it has been possible to obtain 

 many thousands of these records and to gain a great deal of informa- 

 tion which it would be difficult if not impossible to obtain otherwise 

 without an enormous expenditure. The handling of the records 

 made during these tests as well as many details of the management 

 of the tests have been in the hands of Mr. S. Kruse at the Bureau of 

 Standards. These tests have given an opportunity to confirm in a 

 statistical way what had previously been the impressions received 

 by operators and experimenters in the course of receiving signals for 

 other purposes. 



Fading of signals as well as signals of abnormal intensity are ob- 

 tained only at distances beyond which the absorption has been found 

 to be appreciable. On 200 meter communication, fading is not often 

 found within a distance of 20 miles from the transmitting station, but 

 fading is usually found at a distance of GO miles or more from the trans- 

 mitting station. 



