REPORT OF THE SECRETARY 5 



United States for the interchange with other countries of govern- 

 mental and scientific documents. During the year the service handled 

 719,121 packages of such matter, an increase of 61,775 over the 

 previous year. The weight of these packages was 656,119 pounds. 

 The Government franking privilege was extended to cover a number 

 of South and Central American countries, and packages for those 

 countries were therefore sent direct to their destinations by mail in- 

 stead of through the respective exchange bureaus. Shipments of 

 exchanges to Spain have been suspended since August 1936, and those 

 to China since August 1937. At the close of the year, however, a large 

 consignment was being prepared for shipment to the Chinese Bureau 

 of International Exchanges, which had moved its office from Nanking 

 to Chungking. 



National Zoological Park. — The outstanding feature of the year 

 was the addition to the collection of the large number of animals, 

 birds, and reptiles brought back by the National Geographic 

 Society-Smithsonian Expedition to the East Indies. The actual num- 

 ber of specimens was 879, consisting of 121 mammals of 46 species, 

 649 birds of 93 species, and 109 reptiles of 30 species. The new large 

 mammal house described in last year's report was stocked with ani- 

 mals during August and September 1937, the difficult task of trans- 

 ferring such large creatures as elephants, hippopotamuses, and 

 rhinoceroses being accomplished without mishap. Visitors for the 

 year again increased in number, the total reaching 3,127,650. This 

 included 1,374 organizations, mainly schools, with a total of 70,371 

 individuals. Among the additions to the animal collection may be 

 mentioned 34 mammals born and 30 birds hatched in the Park. The 

 total number of animals in the collection at the close of the year was 

 2,754, an increase of 412 over last year. The most urgent need of 

 the Park is a new building for the restaurant and concession stand. 



Astrophysical Observatory. — The main business of the year was the 

 recomputation of all solar-constant values from 1923 to the present 

 time. This immense task was nearly completed at the close of the 

 year, and it is hoped that by January 1939 a homogeneous series of 

 daily values will be available. A highly sensitive instrument to 

 measure the distribution of energy in the spectra of some of the 

 brighter stars was constructed by Dr. Abbot and Mr. Hoover, and in 

 May 1938 Mr. Hoover took the apparatus to Mount Wilson, Calif., 

 to make new measurements of the stellar spectrum energy and also 

 to make studies of the growth of plants in monochromatic rays. By 

 way of anticipating next year's report, it may be said that gratifying 

 progress was made in both researches. At the request of the Weather 

 Bureau, construction was begun of a duplicate of the atmospheric 

 turbidity and moisture apparatus used by the Institution in testing 



