Appendix 5. 



KEPORT 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, 1913 : 



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. 



(h) At Mount Wilson, Cal., upon a leased plot of ground 100 

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

 observing structure, designed especially for solar-constant measure- 

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

 quarters. 



During the year there was erected upon the observing shelter at 

 Mount Wilson a tower 40 feet high above the 12-foot piers which 

 had been prepared in the original construction of the building. This 

 tower is now being equipped as a tower telescope for use when ob- 

 serving (with the spectrobolometer) the distribution of radiation 

 over the sun's disk. The cost of the tower and its apparatus has thus 

 far been about $1,400. 



Other pieces of apparatus for research have been purchased or 

 constructed at the observatory shop. The value of these additions 

 to the instrumental equipment, not counting the tower above men- 

 tioned and its equipment, is estimated at $1,500. 



WORK OF THE YEAR. 



1. ON THE SOLAR CONSTANT OF RADIATION. 



When Volume II of the Annals of the Astrophysical Observatory 

 was published in 1908 the standard scale of measurement of solar 

 radiation had not yet been established. Several supposedly standard 

 pyrheliometers for the purpose of fixing the true scale of radiation 



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