REPORT OF THE SECRETARY. 101 



these computers temporarily was borne by a gift of Mr. John A. 

 Roebling. At the close of the fiscal year the computations of the 

 Annals had been very nearly completed. The manuscript of the vol- 

 ume was also almost ready for publication, and it is hoped to put the 

 whole to press early in the autumn of 1921. 



As usual, a large amount of delicate instrument work has been 

 done by Mr. A. Kramer, instrument maker, and still more delicate 

 parts have been prepared by Mr. L. B. Aldrich, of the observatory 

 staff. They have prepared and standardized a number of pyrhelio- 

 meters, pyranometers, galvanometers, and bolometers for the use of 

 the observatory and its stations. 



By invitation of Dr. George E. Hale, director of the Solar Observ- 

 atory at Mount Wilson, Calif., Dr. Abbot has undertaken the prep- 

 aration of a special spectrobolometer for the observation of the energy 

 spectra of the stars in the same manner in which we are accustomed 

 to observe the energy spectrum of the sun. This outfit comprises a 

 special spectroscope, a vacuum bolometer of special dimensions and 

 construction, and a vacuum galvanometer designed to be of the very 

 highest order of sensitiveness. The construction of this apparatus 

 had been almost completed at the close of the fiscal year. 



Work in the field. — As stated in last year's report, by the gener- 

 osity of Mr. John A. Roebling, of Bernards ville, N. J., not only has 

 the private station of the Smithsonian Institution located near Cal- 

 ama, Chile, been removed to the top of a mountain about 8 miles 

 farther south, but the station of the Astrophysical Observatory has 

 been relocated on the mountain called Harqua Hala, situated about 100 

 miles to the northwest of Phoenix, Ariz. In June, 1920, Dr. Abbot 

 selected the site for the latter station and arranged with local con- 

 tractors for the erection of an adobe building about 40 feet long, 

 10 feet wide, of two stories. The lower story, underground, was 

 designed for the instruments, and the upper story for a dwelling 

 house and computing rooms for the observers. Proceeding from 

 Arizona to Mount Wilson, Dr. Abbot was joined early in July by Mr. 

 L. B. Aldrich, and together they carried out at Mount Wilson, in 

 July, August, and part of September, the usual observations on the 

 solar constant of radiation and on the distribution of radiation over 

 the sun's disk. In addition, they conducted a number of other in- 

 vestigations, including a redetermination of the constants of the 

 secondary pyrheliometers employed in the research, a redetermina- 

 tion of the transmission of the spectrobolometer for different wave 

 lengths, various investigations with the pyranometer and the 

 Angstrom pyrgeometer, and, assisted by Mrs. Abbot, investigations 

 on the use of solar radiation for cooking purposes. 



The solar cooking outfit erected on Mount Wilson some years ago 

 was in 1920. for the first time, brought to a reasonable degree of per- 



