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ANNUAL EEPOKT SMITHSONIAN INSTITUTION, 19 3 2 



which composes the sun. It is to be regarded like the stirring 



of a fire with a poker, which brings up from below the hotter 



materials, and throws out temporarily a greater radiation in our 

 rooms. 



The short-period changes of solar radiation, which rim their 

 courses in a few days, are probably caused in other ways. We may 

 suppose that patches of increased or diminished radiating power 

 form occasionally on the solar surface. An example of this, indeed, 

 is often seen in the bright f aculae which surround sun spots. On the 

 other hand, there may be areas of diminished intensity above the sun 



