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 moyable frame shelters covering several out-of-door pieces of apparatus, 
and also one small brick building containing a storage battery and electrical 
distribution apparatus. 
(bo) 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. 
WORK 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 fgrtunately 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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