Appendix 5. 



REPORT ON THE ASTROPHYSICAL OBSERVATORY. 



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

 tions of the Smithsonian Astrophysical Observatory for the year 

 ending June 30, 1916. 



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 i)lat 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 equipped 

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

 lometer) the distribution of radiation over the sun's disk. 



During the year apparatus for research has been purchased or con- 

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

 the instrumental equipment is estimated at $1,500. 



WORK OF THE YEAR. 

 1. AT WASHINGTON. 



Some years ago the Institution lent the Harvard College Observa- 

 tory a silver-disk pyrheliometer for use at Arequipa, Peru. By re- 

 quest of Prof. Pickering the observations which had accumulated 

 since August, 1912, were reduced at the Astrophysical Observatory 

 and published by the Smithsonian Institution during the past year.^ 

 Owing to the high altitude of Arequipa the variations of solar radia- 

 tion observed at a fixed zenith distance of the sun (as, for instance, 



1 Arequipa Pyrheliometry, Smithsonian Misc. Coll., Vol. 65, No. 9, 1916. 



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