22 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
The equipment of the Zoological Park, both as regards the accom- 
modations for the collections and facilities for visitors, is still in- 
adequate and is inferior to that of other establishments of the kind 
of equal importance. 
Many of the animals are kept in temporary quarters that are in- 
sufficient in size, more or less insanitary, and quite costly to maintain. 
This is particularly true of the fine series of birds, which includes 
some of exceptional interest and rarity. The rough temporary build- 
ing in which they are now kept is too small for the exhibition of the 
entire collection and tle conditions are such that it is difficult to keep 
the birds in a good state of health. In a suitable structure the bird 
collection would be one of the most attractive features of the park. 
Permanent paddocks are also needed for the hardy deer, wild 
sheep, goats, and cattle, which are now scattered in temporary inclo- 
sures, some of them altogether unsuitable. 
A new bridge across Rock Creek is urgently needed to replace the 
present temporary log structure, and it should be of a permanent 
character and sufficiently wide to provide for the greatly increased 
travel when the valley of Rock Creek is fully developed. 
The roadways and walks in the park were greatly improved at the 
cost of a special appropriation for that purpose. Nearly a mile of 
the roads were treated either by reshaping and supplying a top layer 
of stone or by regrading and furnishing the entire thickness of road- 
bed metal. About 1? miles of walks were also laid or repaired and steps 
were constructed where grades had before been too steep. A consid- 
erable amount of work was also done to provide proper drainage. 
ASTROPHYSICAL OBSERVATORY. 
The Astrophysical Observatory has been engaged in three principal 
lines of work during the year. 
Observations by the spectrobolometric method were continued in 
order to confirm the view referred to in last year’s report that the 
determinations of the intensity of the solar radiation outside the 
earth’s atmosphere are independent of the observer’s altitude above 
sea level, provided the conditions are otherwise good. Observations 
for the “ solar constant ” were accordingly taken on Mount Whitney 
in the summer of 1910, where opportunity was afforded also for 
measurements of the brightness of the sky by day and by night, the 
influence of the water vapor on the sun’s spectrum, and the distribu- 
tion of the sun’s energy spectrum outside the atmosphere. The re- 
sults of these observations show no discrepancy due to altitude be- 
tween Mount Wilson (5,840 feet) and Mount Whitney (14,502 feet). 
It also seemed important to confirm by further observation the 
variability of the solar constant of radiation. Observations were ac- 
cordingly continued daily at Mount Wilson until November 10, 1910, 
