Appendix V. 



REPORT ON THE ASTROPHYSICAL 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, 1911: 



EQUIPMENT. 



The equipment of the observatory is as follows: 



(a) At Washington there is an inclosure of about 16,000 square feet, con- 

 taining 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. 



(&) 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 year. 



In 1909 the Smithsonian Institution, at the expense of the Hodgkins 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 promote 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. 



WOKK OF THE YEAR. 



In order to thoroughly confirm the results obtained on the summit of Mount 

 Whitney (4,420 meters or 14,502 feet) in 1909, discussed in my last annual 

 report, an expedition again occupied that place in August, 1910. The person- 

 nel consisted of the director and Mr. G. F. Marsh, of Lone Pine, California. 

 Nearly all of the equipment for spectrobolometric work had been left on Mount 

 Whitney through the winter and was found in good condition. Additional 

 apparatus for measuring the brightness of the sky by day and by night was 

 carried up by pack train under the care of Mr. Elder, of Lone Pine. The good 

 fortune which had attended the 1909 expedition failed for a moment in 1910, 

 and one mule, carrying the silver-disk pyrheliometer and other loading, rolled 

 off among the rocks and was killed. The pyrheliometer fortunately received 

 no injury. 



Solar-constant measurements were made successfully on Mount Whitney in 

 1910 on three successive days. Mr. Fowle made solar-constant observations 

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