ULTRA-SHORT-WAVE TRANSMISSION 517 



laced 60-cycle scanning will have a unit time element of 0.17 micro- 

 seconds. This corresponds to a path difference of 51 meters and only 

 a fraction of this is necessary to produce a ghost. A rough estimate of 

 the boundary height range involved in our fading is one-half to five-and- 

 one-half kilometers. The corresponding path difference range is 8 to 

 580 meters. As the fading records show, no matter whether the ''A" 

 or the "B" component predominated, the other component was 

 usually present in amplitude only second to the other. It may be 

 pointed out that where a standing wave system exists, ^"^ reflected 

 components with much larger path differences than those recorded 

 here are almost certain to be found. 



Appendix I 



In the Wwedensky * paper the author applies his theory to one of the 

 experimental curves from a previous paper of ours. He uses the nor- 

 mal earth radius " R," however, without any correction for air re- 

 fraction. If we assume, as a more probable effective earth radius, the 

 value 4/3R,^ the agreement with our curve is markedly improved. 



Appendix II 



In the first Wwedensky paper, Tech. Phys. U. S. S. R. Vol. 2, p. 632, 

 1935 eq. (7, 1) the sign of the term Ir^p sin 2dm should be minus. 



Appendix III 



The fading produced by moving bodies such as airplanes has been 

 referred to in one of our earlier papers.^" It happened one day, during 

 the present investigation, that fading of this type appeared when 

 mechanical recorders were being used and, by speeding up the paper, a 

 record in two polarizations was obtained. The airplane itself (or other 

 cause) was not visible. The results are given in Fig. 19. Again the 

 horizontal component was the worse one. At first the two fadings, 

 both fine and coarse components, were in step; later they passed en- 

 tirely out of step where the fading was so rapid as to smear the paper. 

 These "airplane" fadings were observed, off and on, at other times 

 but were not recorded. 



References 



1. Englund, Crawford and Mumford, Bell System Technical Journal, Vol. 14, p. 369, 



1935. 



2. Brown and Leitch, Proc. I. R. E., Vol. 25, p. 583, 1937; Norton, Proc. I. R. E., 



Vol. 26, p. 115, 1938. 



3. Ross Hull, Q.S.T., Vol. 21, p. 16, 1937, May. 



4. B. Wwedensky, Tech. Phys. U. S. S. R., Vol. 2, p. 624, 1935; Vol. 3, p. 915, 1936; 



Vol. 4, p. 579, 1937. 



