294 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
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Ha Light Curve 
Flare NO6 WIO 
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= { ! I I 
14930 15°C0™ 152 30m 1E"90™ U.T. 
Ficure 4.—Comparison of Ha@ flare light curve (McMath-Hulbert Observatory) and 
concomitant short-wave fade, 5 MC, WWV (Cornell), Sept. 15, 1951. 
The reason that the predictions are not always accurate is that the 
visible radiation from the sun does not by itself produce terrestrial 
events, which are caused by the increased flux of ultraviolet radiation 
and particles that may accompany the increases in visible hight. Un- 
fortunately, the mechanism of the emission of radiation by solar flares 
is very poorly understood and we cannot at present predict their 
ultraviolet radiations from observation of the visible light. ‘To com- 
