Appendix 5. 



EEPOET ON THE ASTEOPHYSICAL OBSEKVATORY. 



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. 



(b) 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 purpose. 



During the year apparatus for research has been purchased or 

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

 the instrumental equipment, not 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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