198 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1931 



6. Nearly 2,000 solar-constant measurements at Washington, Bas- 

 sour, Mount Wilson, and Mount Whitney from 1902 to 1920, yielding 

 a mean value of 1.94 calories per square centimeter per minute, and 

 proving that the sun is variable. 



T. Many determinations of the distribution of energy over the 

 sun's disk for various wave lengths. 



8. Many determinations of the distribution of energy in the solar 

 spectrum, yielding estimates of the effective temperature of the sun. 



9. Development of the recording balloon pryheliometer and deter- 

 mination therewith of the solar radiation at 25,000 meters altitude. 



10. Development of the pyranometer, an instrument for measuring 

 sky radiation. 



11. A new brief method of solar-constant determination, whereby 

 five independent values per day are obtained with minimum atmos- 

 pheric influence. 



12. Dail}^ observations of the variability of the sun at several 

 widely separated high-altitude desert stations beginning with the 

 year 1920. 



13. Determination of the march of variation of the monthly mean 

 values of the solar constant of radiation for the past 12 years with 

 an accuracy sufficient for all purposes. 



14. Discovery that the sun's radiation varies in five continuing 

 regular periodicities. 



15. Indications that the weather is to a considerable degree gov- 

 erned by solar changes and is probably predictable therefrom. 



IC. B3^-products of the research which include determinations of 

 atmospheric transparency, precipitable water, and ozone content. 



With hope that the apparent connection between solar variation 

 and the weather will be verified and will lead to improved methods 

 of long-range forecasting, my colleagues and I are going on with 

 solar-radiation studies, introducing such improvements as may help 

 to establish a more exact record of the solar variation available for 

 all future time. 



