Appendix 5. 

 KEPORT ON THE ASTROPHYSICAL OBSERVA'^ORY. 



Sir : I have the honor to present the following report on the oper- 

 ations of the Smithsonian Astrophysical Observatory for the year 

 ending June 30, 1912 : 



EQUIPMENT. 



The equipment of the observatory is as follows : 



Ca) At Washington there is an inclosure of about 16,000 square 

 feet, containing five small frame buildings used for observing and 

 computing purposes, three movable frame shelters covering several 

 out-of-door pieces of apparatus, and also one small brick building 

 containing a storage battery and electrical distribution apparatus. 



(h) At Mount Wilson, California, upon a leased plat of ground 

 100 feet square in horizontal projection are located a one-story 

 cement observing structure, designed especially for solar-constant 

 measurements, and also a little frame cottage, 21 feet by 25 feet, for 

 observer's quarters. 



There were no important additions to the instrument equipment 

 of the observatory during the yenv. 



In 1909 the Smithsonian Institution, at the expense of the Hodg- 

 kins fund, erected on the summit of Mount Whitney, California 

 (height 14,502 feet), a stone and steel house to shelter observers 

 who might apply to the Institution for the use of the house to pro- 

 mote investigations in any branch of science. While this structure 

 is not the actual property of the Astrophysical Observatory, it 

 affords an excellent opportunity for observations in connection with 

 those taken on Mount Wilson. 



WORK OF THE YEAR. 

 1. ON THE VARIABILITY OF THE SUN. 



Congress liaving provided funds, an expedition under the im- 

 mediate charge of the Director proceeded in July to Bassour, Algeria, 

 to make there a long series of solar-constant observations simultane- 

 ously with similar observations made by Assistant Aldrich on Mount 

 Wilson. The Algerian expedition included Mr. and Mrs. Abbot and 

 Prof. F. P. Brackett, of Pomona College, California. The apparatus 

 carried was the same used by Mr. Abbot on Mount WMtney in 1909 

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