228 



ANNUAL EEPOET SMITHSONIAN INSTITUTION, 19 31 



Further studies of the lunar effect are being pursued at the Perkins 

 Observatory which give promise of evaluating further corrections 

 to the radio curve for more direct comparison with the curve of 

 sun-spot numbers. 



Perhaps the most remarkable result of our correlation study has 

 been the discovery that radio apparatus has become an effective tool 

 in the study of solar radiation. Furthermore, since meteorological 

 changes are correlatable with changes in^ radio reception, it is but 

 fair to specify that a new method has been evolved which may ulti- 

 mately lead to important correlation between sun spots and the 



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l6oo 



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Figure 13. — Curve showing changing intensity of WBBM at Delaware, Ohio, as 

 function of solar altitude 



weather. To this end researches will be continued in these closely 

 related lines at the Perkins Observatory. 



Grateful acknowledgement is due the American Academy of Arts 

 and Sciences for grants from the Rumford Fund to aid in the pur- 

 chase of apparatus for this new field of research in radiation, and 

 to the American Association for the Advancement of Science for 

 assistance in the making of the observations and reductions. 



In conclusion, it may be said that investigations in radio trans- 

 mission, together with researches in the change in the earth's mag- 

 netism and electricity and the ultra-violet radiation of the sun, may 

 yet prove to furnish the most definite data as to changes in the 

 sun itself. 



