262 ANNTJAL REPORT SMITHSONIAN mSTITUTION, 1961 



satellite passed out of range of the ground station. On the next pass, 

 the sun was again quiet. At 1701 UT, the record showed only the 

 faintest trace of X-ray emission. Throughout the entire sequence of 

 events the Lyman-a flux remained unchanged. 



Many observations are available from the records of Solar Radiation 

 I covering the beginning and ending phases of flares. The enhanced 

 X-ray emission started with the visible flare in every instance and 

 terminated with the decay of the flare. In every case where the X-ray 

 flux exceeded 5 X 10"^ erg cm."^ s"^ in the 2 to 8 A. bandwidth of the 

 X-ray ion chamber, a shortwave fadeout was observed. On July 

 24, 1960, there occurred a sudden disappearance of a large prominence 

 seen above the limb between 0900 UT and 1200 UT. As this event 

 progressed, enhanced X-ray emission was observed on six successive 

 telemetered records, the mean flux reaching 5 X 10"^ erg cm."^ s'^ at 1020 

 UT. There were no flares visible on the disk at that time. 



More sophisticated solar X-ray observatories will undoubtedly be 

 placed in orbit in the near future. It will be extremely interesting 

 to study the detailed correlations between the radio-noise spectra ac- 

 companying these flares and X-ray spectra. As was described by 

 Dr. Alan Maxwell in the 26th James Arthur lecture,^ the radio emission 

 takes a variety of forms associated with thermal excitation, plasma 

 oscillations, and synchrotron emission. Thus far, the closest associa- 

 tion appears to exist between X-ray emission and the centimeter- wave 

 radiation which results from thermal excitation. 



« See Annual Report of the Smithsonian Institution for 1959, p. 299. 



