24 ANNUAL REPORT SMITHSONFAN INSTITUTION, 1919. 



at that ]:)oint by the District government. The incorporation of 

 this land within the park is of very great interest to the public. 



The slight increase in the annual appropriation granted by Con- 

 gress scarcely more than covered the increased cost of maintenance 

 of the park, even by practicing the strictest economy. Lack of 

 funds for grading banks and filling ravines has prevented the com- 

 pletion of work begun three years ago for tlie purpose of obtaining 

 new level spaces for yards and inclosures. 



ASTEOPHYSICAL OBSEKVATORY. 



Several important investigations relating to the war, begun last 

 year, were continued by the staff of the Astrophysical Observatory 

 under the general direction of Dr. C. G. Abbot, in addition to the 

 regular work of the observatory. These researches are mentioned 

 elsewhere in this report under the heading " General considerations." 



At Washington work on solar radiation computations has gone 

 on steadily, and progress has been made with the preparation of a 

 new medium, potassium iodide, for the investigation of the rays 

 beyond where rock salt is transmissible. A new instrument, based 

 upon the principle of the perfect radiator, or " absolutely black body," 

 was constructed for the purpose of measuring nocturnal radiation, 

 such as the earth sends out to space. At the close of the year 

 this instrument was reported as operating successfully on Mount 

 Wilson. 



In view of the fact that the total eclipse of the sun of May 29, 

 1919, would be visible at La Paz, Bolivia, which is not very far from 

 the Smithsonian solar constant observing station at Calama, Chile, 

 a successful expedition was undertaken by Dr. Abbot, Avith the 

 double purpose of observing the eclipse and visiting the Calama 

 station. Good photographs of the phenomenon and also pyrano- 

 metric observations by Mr. A. F. Moore of the brightness of the sky 

 were obtained during the progress of the eclipse. A conference was 

 held with officials of the Argentine Government, which is likely to 

 prove of great value in the future, in that it concerned the employ- 

 ment of solar-radiation measureiftents for weather forecasting by 

 the Argentine meteorological service. At Calama, Chile, Dr. Abbot, 

 in cooperation with the Smithsonian observers there, Messrs. Moore 

 and Leonard Abbot, devised a new method of reducing solar radia- 

 tion observations, so as to determine the solar constant of radiation 

 with at least equal precision to that obtained by the older method, 

 the advantages of the new method being (1) its independence of the 

 variability of atmospheric transparency; (2) the time required is 

 only one-fifth of the former period. 



