18 ANNUAI, REPORT SMITHSONIAN" INSTITUTION, 19 31 



of rarities. To illustrate the unusual importance of the year's 

 additions, it may be said that 63 species were shown for the first 

 time in the National Zoological Park. 



Visitors to the park totaled 2,171,515, a slight decrease from the 

 previous year's total. The fact that there was not a greater decline 

 in number of visitors, as there was in other similar institutions owing 

 to the present economic depression, was due to the great public in- 

 terest shown in the new reptile exhibits. Attendance of school 

 groups numbered 649 from 21 States, comprising 34,026 individuals. 



The new reptile house was opened on February 27, 1931, with a 

 reception attended by 3,000 people. The building contains special 

 lighting and ventilating systems and all the modern features known 

 for the best exhibition of animals. Since its opening it has become 

 the most popular building in the entire park. The most urgently 

 needed additional building is one for small mammals and the great 

 apes; plans for this building are now being prepared under an 

 appropriation by Congress for the purpose. 



ASTROPHYSICAL OBSERVATORY 



A large part of the year's work was devoted to the preparation 

 of text, tables, and illustrations for Volume V of the Annals of 

 the Astrophysical Observatory, which will cover the results of 

 observations made at the several stations since August, 1920. The 

 entire manuscript was sent to the printer toward the end of June. 



The three stations at Montezuma, Chile, Table Mountain, Calif., 

 and Mount Brukkaros, Southwest Africa, have continued observa- 

 tions of the radiation of the sun on all possible days. The results 

 from the last two stations have not proved as satisfactory as those 

 from Montezuma, and considerable effort has been expended on im- 

 proving them. During the year new varieties of the short method 

 of determining the solar constant of radiation, applicable to condi- 

 tions at Table Mountain and Mount Brukkaros, have been worked 

 out, with resulting great improvement in the values from these two 

 stations. 



Upon the completion of the reduction of all the solar constant 

 observations from the three field stations interesting results have 

 been derived from their comparison. Whereas the probable error 

 of the monthly mean values since 1920 is less than 0.1 per cent, 

 the extreme range of the solar-constant values is 2.8 per cent. The 

 march of solar variation since 1920 may be expressed very faith- 

 fully as the sum of five regular periodicities of 68, 45, 25, 11, and 

 8 month intervals. The curve of temperatures at Washington, D. C, 

 and Williston, N. Dak., may also be represented by the sum of 

 these same periodicities with the addition of an 18-month period. 



