Appendix 5. 



KEPOET ON THE ASTEOPHYSICAL OBSERVATORY. 



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

 operations of the Smithsonian Astrophysical Observatory for the 

 year ending June 30, 1915 : 



EQUIPMENT. 



The equipment of the observatory is as follows : 



(a) 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. 



(6) At Mount Wilson, Cal., upon a leased plat of ground 100 feet 

 square, in horizontal projection, are located a one-story cement ob- 

 serving structure, designed especially for solar-constant measure- 

 ments, and also a little frame cottage, 21 feet by 25 feet, for observer's 

 quarters. 



Upon the observing shelter at Mount Wilson there is a tower 40 

 feet high above the 12-foot piers which had been prepared in the 

 original construction of the building. This tower is being equipped 

 with a tower telescope for use when observing (with the spectro- 

 bolometer) the distribution of radiation over the sun's disk. This 

 has been made possible by an appropriation by Congress of $2,000 

 for this f)urpose. 



During the year apparatus for research has been purchased or 

 constructed at the observatory shop. The value of these additions to 

 the instrumental equipment, no^t counting the tower equipment above 

 mentioned, is estimated at about $500. 



WORK OF THE OBSERVATORY. 

 AT WASHINGTON. 



Observations were made for the testing of pyrheliometers. As in 

 former years several silver-disk pyrheliometers were prepared and 

 sent abroad by the Institution after standardization at the Astro- 

 physical Observatory. 



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