THE SMITHSONIAN INSTITUTION CLAEK. 153 



One of the principal aims in establishing the park was to promote 

 the preservation of races of animals threatened with extinction, such 

 as the American bison, which once roamed in vast herds over the 

 western plains and was rapidly disappearing before the advance of 

 railroads and the rapacity of hmiters. Several bison were secured 

 for the park and have thrived here, and through the efforts of the 

 Smithsonian Institution and others the Government was aroused to 

 establish preserves in the West where the bison breeds freely. 



There are several large cages for birds in the park. The great 

 " flight cage," 158 feet long by 50 feet in width and height, is built 

 over several full-grown trees and has a running stream of water sup- 

 plying pools for the convenience of the birds, which are mainly 

 herons, stolks, cranes, cormorants, gulls, and pelicans. 



Among the particularly important exhibits is a fine collection of 

 ungulates, or hoofed animals, no less than 50 species of wild cattle, 

 deer, sheep, goats, antelopes, horses, and their Idndred being repre- 

 sented, many of them by breeding herds. There is also a valuable 

 collection of North American water fowl, a specially prepared breed- 

 ing lake being set aside for the wild ducks, geese, and swans of this 

 continent. 



ASTROPHYSICAL OBSERVATORY. 



The Astrophysical Observatory, founded in 1890, investigates solar 

 radiation, and in general, solar phenomena, and has produced a 

 complete chart, made by automatic processes, which shows in detail 

 the so-called invisible spectrum. The work of this Observatory is 

 especially directed to thuse .portions of the energy of the sun that 

 affect through its radiation the climate and the crops. 



Through the use of speciallv designed pyrheliometers attached 

 to free balloons, observations liave been made of the intensity of 

 solar radiation at various elevations up to a height of more than 

 80,000 feet above sea level. Special studies have been made of 

 the solar constant and of the distribution of radiation over the 

 sun's disk. The principal astrophysical w^ork is carried on at the 

 observatory in the Smithsonian Park in Washington and at Mount 

 Wilson and Mount Whitney in California. On the summit of 

 Mount Whitney the Institution has constructed a shelter for the 

 general use of obser^ ers. Expeditions to various parts of the world 

 have been made for observation of eclipses of the sun and other 

 special studies. 



As the result of researches made by the observatory during the 

 period from 1900 to 1915 it is found that the average value of heat 

 emitted by the sun is 1.932 calories per minute per square centi- 

 meter, and that the heat emitted in a year equals that obtained by 



