172 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1951 



and the outbreak of "northern lights," as well as erratic disturbances 

 to the aiming of delicate compasses, has been a matter of widespread 

 knowledge for perhaps a century or more. With the advent of radio 

 we have learned that the passage of a large spot group past the central 

 meridian of the sun generally heralds by about one day the onset of 

 poor long-distance radio reception. In recent years the origin of 

 many seemingly cyclical phenomena have been blamed on the sunspots. 

 Such things, for example, as business cycles and the quality of wines 

 have been suspected of cyclical variations in phase with the sunspot 

 changes. Most of these speculative suspected correlations I regard 

 as inadequately substantiated. 



More recently we have gained undeniable evidence of a whole gamut 

 of new and unexpected influences of sun on earth. Theory tells us 

 that these new influences ought to be intimately associated with the 

 solar atmosphere, even though our observational studies have not yet 

 revealed the clues that allow us to explain what we observe. The work 

 of the Australian radio-scientists Pawsey, Yabsley, Payne-Scott, Wild, 

 and others, supplemented by work in England by Ryle, in France by 

 Denisse, in the United States by Reber, Burrows, Hagen, and by still 

 others, has indicated to us that the sun is, at times, a powerful trans- 

 mitter of very short-wave radio pulses, sometimes thousands of times 

 as powerful as we seem to be able to explain. Here is one of the most 

 fertile new fields of research. And it has potential significance of a 

 most practical sort. One scientist, Kiepenheuer of the Fraunhof er In- 

 stitute in Germany, even goes so far as to speculate tentatively that 

 substantial effects on the rate of gi'owth of plants and animals may 

 occur when the solar radiations at radio wavelengths of about 1 meter 

 grow abnormally intense. 



The known effects on radio reception have given birth to a whole 

 science of radio-propagation prediction and analysis. Work of this 

 sort makes up one of the main tasks of the Central Radio Propagation 

 Laboratory of the National Bureau of Standards in Washington. The 

 activity of the sun is the principal sustaining source not only of the 

 radio-reflecting layers so intensively studied at that laboratory but also 

 of the day-to-day and hour-to-hour changes in the character of those 

 layers predicted at the National Bureau of Standards. The sun, ac- 

 cording to the studies done there, behaves in a far more complex fashion 

 than a simple luminous sphere of gas at the established solar surface 

 temperature of 6,000° Kelvin. Brilliant prominences known as "solar 

 flares" for example, can send radiation to the earth with the velocity 

 of light that in turn can cause a complete blackout of long-distance 

 radio communications on the entire sunlit hemisphere of the earth — 

 the well-known "Bellinger effect" first noted by the pioneer in radio 

 propagation analysis, J. H. Dellinger. 



