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PERIODICITY IN SOLAR VARIATION' 



By C. G. abbot 



Secretary, Smithsonian Institution 



AND 



GLADYS T. BOND 



Statistical Assistant, Smithsonian Astrophysical Observatory 

 (With 2 Plates) 



Long ago, Secretary Langley induced Congress to support the study 

 of solar radiation at the Smithsonian Astrophysical Observatory. He 

 pointed out that all life and all weather depend on it. He held out the 

 possibility and hope that a sufficient knowledge of solar radiation and 

 of its behavior in our atmosphere might even enable meteorologists to 

 forecast long in advance the fat years and the lean years as Joseph is 

 said to have done in Egypt. 



After 40 years of research, we have results which seem to us to 

 justify in some degree Langley's hope. We have not yet, it is true, 

 tried the bold venture of long-range forecasting, but we have evidence 

 to present to the Academy today that the sun's output of radiation is 

 variable ; that its variation is periodic ; that the United States weather 

 departures from normal are periodic ; and that nearly all of the ranges 

 of weather departures from normal are comprised in a series of peri- 

 odicities which are identical with those found in the sun. We expect 

 to discover by a little more research whether we have here real cause 

 and effect. If it should prove so, we need not emphasize the value of 

 such knowledge. 



For more than 25 years the staff of the Smithsonian Astrophysical 

 Observatory has been measuring the intensity of solar radiation. At 

 first, in Washington, w^e further developed the method devised by 

 Langley and used by him about 50 years ago at Allegheny and at 

 Mount Whitney. We devised the silver-disk pyrheliometer for ordi- 

 nary daily measurements of the total intensity of solar radiation at the 

 station. We also devised the water-flow and the water-stir standard 

 pyrheliometers, whereby we reduced the scale of measurement to 



^ Paper presented before the National Academy of Sciences, April 26, 1932 

 Smithsonian Miscellaneous Collections, Vol. 87, No. 9 



