224 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 31 



the modulations of the carrier wave do not affect the record appreci- 

 ably and the results obtained are independent of the nature of the 

 program broadcasted. Realizing the importance of the investigation, 

 the broadcasting station scrupulously maintains a constant energy 

 output in its antenna current, and each night before the observers 

 begin work the receiving set is carefully calibrated by means of a 

 small local oscillator in the laboratory placed in close proximity to 

 the receiving set. The output of the local oscillator necessary to 

 maintain full deflection of the recorder in the receiving circuit is then 

 read from the micro-ammeter in the circuit. The constant of the 

 apparatus for the evening is thus determined. In this way local 



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ARSANGEHENT OF APPARATUS 



Figure 10. — Diagram of radio receiving circuit for recording intensities in the carrier 



wave 



sources of error, both at the broadcasting and receiving ends, are 

 eliminated and the resulting measure of the variable reception from 

 night to night may be attributed to the changing electrical condi- 

 tions of the atmosphere through which the broadcasted wave travels 

 en route to the receiving station. 



Opinions differ as to just what happens when a broadcasted wave 

 travels over the earth. Some believe that an ether wave is propa- 

 gated which is reflected back to earth from an ionized layer of the 

 earth's atmosphere, known as the Kennelly-Heaviside layer, which 

 lies some 70 kilometers above the earth's surface. Others maintain 

 that the electric wave is refracted rather than reflected from such a 

 layer. Whatever the mechanism, the wave appears to be turned back 

 by this ionized layer of the earth's atmosphere. Any change in the. 



