REPORT OP THE SECRETARY 109 



2. When a sun-spot group is carried by the solar rotation across 

 the central diameter of the visible disk, then the solar constant 

 value declines, and usually has a minimum on the day following 

 such central transit. 



3. When many spot groups, faculae, or long strings of dark 

 hydrogen flocculi indicate that great solar activity is prevailing, the 

 solar constant is high. 



4. When a long quiescent period occurs in solar activity, the solar 

 constant values steadily decline. 



These rules connecting the solar radiation with the sun's visible 

 appearance seem to hold some promise of quantitative development. 

 Possibly there may be found some formula for computing solar 

 constant values by the aid of direct solar photographs and hydrogen 

 and calcium spectroheliograms, which may enable the solar radiation 

 values to be expressed with fair approximation for the past quarter 

 of a century. If so, it will be of great advantage. 



PERSONNEL 



In addition to the changes of personnel above mentioned, Mr. 

 William H. Hoover was temporarily engaged as assistant beginning 

 March 12, 1923. He is in training to be director of the proposed 

 solar radiation observatory of the Argentine Government at La 

 Quiaca, Argentina. Mr. Hoover spent some time in Washington 

 and some upon Mount Harqua Hala, Ariz. Mrs. Arline Leary 

 served as temporary computer, beginning April 16, 1923. Both of 

 these assistants were paid from funds given for the purpose by 

 Mr. John A. Roebling. 



SUMMARY 



A comparison of two years of results on the variation of solar 

 radiation observed at Mount Harqua Hala, Ariz., and Montezuma, 

 Chile, shows close accord between the stations and agreement be- 

 tween them in showing forth solar changes of both long and short 

 interval types. "Monthly mean values of both stations indicate a 

 long continued decline of the output of solar radiation beginning in 

 November, 1921, and continuing at least until September, 1922. 

 This is in some respects the most remarkable solar change on record. 

 Great improvements have been made at both stations, and their ob- 

 servations have been put as far as possible on exactly equal footing. 

 It is believed that beginning January 1, 1924, there will be still 

 closer accord in their reuslts. Definite correspondences have been 

 observed between the variation of the sun's radiation and the varia- 

 tion of the most marked of its visible features. Several new deter- 

 minations of the form of the sun's energy spectrum distribution 



