102 REPORT OF THE SECRETARY. 



ASTROPHYSICAL OBSERVATOItY. 



As already mentioned, this exhibit occupied the south court of the main 

 pavilion, which could be entered only from the court devoted to the Smith- 

 sonian j)roper. At previous expositions, the exhibit of this Bureau consisted 

 of publications, charts of the infra-red spectrum, and other charts relating to 

 astrophysics, some small pieces of apparatus, and a series of transparent 

 photographs of solar eclipses and of sun spots. All these objects were exhibited 

 at St. Louis, and in addition a working exhibit wa,s prepared. This consisted, 

 tirst, of a bolometer connected with a galvanometer, on which was attached 

 a mirror which threw a spot of light on a horizontal scale, so that any change 

 of temperature in the bolometer would be transmitted to the galvanometer 

 and the spot could be seen to move. This change of temperature could be 

 brought about b.v a visitor simply holding his hand over a hole in the case 

 in which the bolometer was placed. The whole exhibit was carefully labeled, 

 and there was scarcely a moment during the da.v when visitors could not be 

 found watching the workings of this delicate instrument for measuring slight 

 changes in temperature. 



The other moving exhibit consisted of a large two-mirrored coelostat. specially 

 constructed for this exposition, which, as l)efore mentioned, was located about 

 30 feet south of the Government building, opposite the court in which the astro- 

 physical exhibit was made. This coelostat on sunny days reflected a large l)eam 

 of sunlight through a window into a dark room which occupied over half of the 

 astrophysical court. Part of the beam of sunlight was thrown through a tele- 

 scope, which in turn threw a large image of the sun on tlie north wall of the dark 

 room. At scarcely any time during the seven months of the exposition was 

 the visitor unable to find large sun-spots, or groups of si)ots, on this image. 

 Another portion of the beam of light was reflected by a series of mirrors to a 

 grating of speculum metal, which in turn threw a brilliant solar spectrum 

 around the east and south walls of the dark room. To make this exhibit more 

 intelligil)le to the public, a descriptive illustrated jiamphlet. written by the 

 director, was distributed gratuitously to those desiring copies. 



NATIONAL ZOOLOGICAL PARK. 



At jirevious expositions the exhibit of the National Zoological Park has con- 

 sisted of pictures of the buildings and jtaddocks in the park, with the addition, 

 usually, of a small model of the park itself. It was felt that such a representa- 

 tion of this Bureau at the St. lionis Exposition would be in:ule(iuate, and, after 

 a careful consideration of possibilities, an extensive exhiliit of birds, placed in 

 a cage large enough to permit them to fly about, was decided upon. The cage 

 was 228 feet long, 84 feet wide, and 50 feet high, and was erected by the Super- 

 Aising Architect of the Treasury Department at the request of the representa- 

 tive of the Institution from the appropriation for Government huildings, at a 

 cost of about $17,.^>0(). This cage, which was designed by the superintendent of 

 the park, was prob.ibly (he largest of its kind ever built. It was traversed by 

 a central arched passageway, open to the public, extending the entire length of 

 the cage. As already mentioned, the cage was situated 100 or 200 yards south 

 of the main building, in a small valley, amid trees, several of which were in- 

 closed by the cage. It was divided into two portions by a longitudinal jiarti- 

 tion. In the north half were confined the larger birds, among which were 

 gulls, three species of wild geese, trumpeter swans. Cuban flamingos, roseate 

 siioonliills, four species of ibis, three siiecies of heron, demoiselle cranes, white 

 pelicans, brown pelicans, Eurui)ean pelicans, and other birds, such as darters. 



