APPENDIX 6 



REPORT ON THE ASTROPHYSICAL OBSERVATORY 



Sir: I have the honor to submit the following report on the activ- 

 ities of the Astrophysical Observatory for the fiscal year ended June 

 30, 1933: 



PLANT AND OBJECTS 



This observator}^ operates regularly the central station at Wash- 

 ington and two field stations for observing solar radiation on Table 

 Mountain, Calif., and Mount Montezuma, Chile. The observatory 

 controls a station on Mount Wilson, Calif., where occasional expedi- 

 tions are sent for special investigations, one of which is mentioned 

 below. 



The observatory is continuing the measurements of the solar con- 

 stant of radiation referred to in former reports and forming the 

 principal theme of volumes II, III, IV, and V of its annals. 



WORK IN WASHINGTON 



With the publication of volume V of the annals there was available 

 a long series of solar-constant measurements adapted for study of the 

 variation of the sun and the dependence of terrestrial temperatures 

 thereon. Seven regular periodicities were discovered in the variation 

 of the sun, having intervals of approxmiately 7, 8, 11, 21, 25, 45, and 

 68 months. The observations reported in volume V of the annals 

 closed with the year 1930. A revision of the periodicities based upon 

 observations from 1924 to 1932 was undertaken by Dr. Abbot. The 

 periodic terms when summed u]) represented the fluctuation within 

 an average departure of less than one tenth of 1 percent. He ven- 

 tured to forecast the fluctuation of the solar radiation to the end of 

 the year 1934 as based on this analysis. The observations followed 

 the prediction as closely as could be expected up to about May 1, 

 1933, when a divergence of about three fourths of 1 percent began 

 to disclose itself: The results came higher than expected. Whether 

 this divergence is due to a slight change of scale of the instruments 

 at Table Mountain from whence the observations are alone available 

 at present, to a failure of the empirical method of reduction there on 

 account of the very unusual humid and hazy summer, or to a real 

 divergence of solar radiation from the trend indicated by former 



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