124 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1931 



A. F. Moore. Walter Watson, jr., reported for duty as assistant at 

 Montezuma February 1, 1931. 



SUMMARY 



The principal work accomplished has been the development of 

 new methods and the complete reduction of all solar-constant obser- 

 vations made at the field stations since 1920. The results with 

 accompanying text and illustrations have been collected and sent to 

 press as Volume V of the Annals of the Observatory. Comparison 

 of values shows that the variation of the sun indicated by monthly 

 mean values since 1920 is determined with sufficient accuracy for 

 all purposes. The probable error of monthly means is less than 0.1 

 per cent. Solar changes found since 1920 range to 2.8 per cent. 

 Daily observations are less satisfactory than monthly means, but 

 improvements are proposed. An expedition is in Southwest Africa 

 endeavoring to discover a site for a solar radiation observatory equal 

 to Montezuma, Chile. A new instrument for the periodic analysis 

 of solar and weather data is nearly completed. 



On the whole the outcome of 10 years of intensive study of solar 

 radiation, as brought together in the text of Volume V of the Annals 

 of the Observatory now in press, is very interesting. It encourages 

 great hope that the causes of weather may be traced in solar variation 

 to such a degree as to enable the skilled meteorologist to forecast 

 principal changes of weather far in advance. 



Respectfully submitted. 



C. G. Abbot, Director. 



The Secretary, 



Smithsonian Institution. 



