SOLAR RADIATION AND ATMOSPHERE — STETSON 171 



roimdings are so activated as to change materially the cosmic environ- 

 ment of the earth is a question still unanswered. 



In summary, we have reviewed a few of the important ways in 

 which the sun and the atmosphere are closely associated. The solar 

 cycle marked by the coming and going of sunspots appears definitely 

 to be reflected in geomagnetic phenomena of the earth, in the ioniza- 

 tion of the upper atmosphere affecting all radio communication, in 

 climatic cycles of the past and in a somewhat complex manner with 

 weather variations today. Perhaps some day terrestrial effects yet 

 to be discovered may in turn become predictable through cycles that 

 follow law and order. Difficult as the pursuit of such investigations 

 may be, results already attained are a stimulus to sustained effort, and 

 we are becoming increasingly conscious withal of a more intimate re- 

 lationship between the earth and its cosmic environment than could 

 have been suspected a decade or two ago. In this cosmic environment 

 we may be assured the sun will play a major role. 



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