160 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



the way in which electric waves travel were erroneous. Such, never- 

 theless, is the way in which science has groped into the unknown. 

 Somebody experimenting with wireless and listening in found himself 

 quite unconsciously eavesdropping on Marconi waves from far-away 

 Europe. Instantly the thought about how wireless waves travel had 

 to be changed. Evidently the ether waves followed the curvature of 

 the earth and did not travel in straight lines after all. This led Pro- 

 fessor Kennelly of Harvard to postulate that there must exist high 

 above the earth's surface, perhaps 100 miles or so up, an electrified 

 conducting layer from which the electromagnetic waves emitted from 

 the powerful antennae were reflected back to earth. The earth's 

 upper atmosphere, therefore, in his mind formed a conducting layer 

 and imprisoned the radio waves between the earth's surface and space 

 outside. A few months after Professor Kennelly published his idea, 

 the English scientist, Oliver Heaviside, announced a similar conclusion 

 quite independently. In honor of these two distinguished men this 

 upper region of the earth's atmosphere that is electrically ionized is 

 commonly referred to as the Kennelly-Heaviside layer, also designated 

 as the E layer. 



If we look at a diagram (pi. 2) which presents a vertical section of 

 the earth and its atmosphere, we see that this Kennelly-Heaviside layer 

 exists at an altitude of from 80-100 kilometers. Radio waves emitted 

 from a sending station in all directions arriving in this ionized region 

 have their velocity and direction changed as they penetrate further 

 and further into the region, until at length they are bent back to 

 earth again, reaching receiving stations hundreds and sometimes 

 thousands of miles from the source whence they were broadcast. This 

 region lies far above the stratosphere and generally above the region 

 that is usually regarded as that where ozone is manufactured. This 

 E layer is particularly favorable for reflecting or turning back radio 

 waves of the frequencies which are most generally used for commer- 

 cial broadcasting in connection with our entertainment programs. 

 Radio waves of much shorter wave lengths or of higher frequencies 

 penetrate and actually traverse through this region until they reach 

 what appears to be another ionized region called the F layer originally 

 postulated by Professor Appleton of England. This F layer lies some 

 200 kilometers high or in the territory where auroral streamers stage 

 their gorgeous displays. If the ionization of these upper regions is 

 more intense as we near the period of maximum sunspot activity, one 

 might well expect that some change might be observed in connection 

 with radio transmission. 



Anticipating a new field of research, a Boston radio engineer, Mr. 

 G. W. Pickard, and myself became interested in the making of quan- 

 titative measurements of radio reception during the last sunspot 

 maximum of 1928 in an endeavor to discover if such anticipated effects 



