APPENDIX 8 

 REPORT ON THE ASTROPHYSICAL OBSERVATORY 



Sir: I have the honor to submit the following report on the 

 activities of the Astrophysical Observatory for the fiscal year ended 

 June 30, 1938 : 



WORK AT WASHINGTON 

 REOOMPUTATION 8 



The recomputation of solar-constant values under the direction of 

 L. B. Aldrich, referred to in last year's report, was the main business. 

 A considerable force of extra computers was employed on a job 

 basis under grants-in-aid from John A. Roebling. Also a consider- 

 able force of W. P. A. workers was assigned to the project. With 

 the regular force and these extra workers the immense task is nearly 

 completed. It is hoped to finish the entire recomputations and com- 

 parisons of solar-constant results from all stations by January 1939, 

 so as to make up a homogeneous series of daily values from 1923 

 to the present time. 



STELLAR SPECTRUM ENERGY CURVES 



In 1922, 1923, 1928, and 1934, attempts were made, in cooperation 

 with the Mount Wilson Observatory, to measure the distribution of 

 energy in the spectra of some of the brighter stars. The measure- 

 ments were made in the focus of the 100-inch reflecting telescope. 

 Results of some value were reached in 1923 and 1928, using a pris- 

 matic spectroscope and the radiometer. In 1934 it was attempted, 

 in cooperation with Dr. Joel Stebbins, to observe at 10 wave lengths 

 selected by Christiansen filters, employing a photoelectric cell. Un- 

 fortunately, owing to the great inequality of sensitiveness of the cell 

 for different wave lengths of radiation, these observations proved 

 valueless. 



Since 1934 repeated attempts have been made at Washington to 

 devise a radiation-measuring instrument with a black absorbing sur- 

 face. We desired to attain sufficient sensitiveness to get good meas- 

 urements with the Christiansen filters for stars as faint as third 

 magnitude. In the opinion of able astronomers this would be a 

 highly valuable accomplishment, indeed one of the most interesting 



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