APPENDIX 5. 



REPORT ON THE ASTROPHYSICAL OBSERVATORY. 



Sir : The Astrophysical Observatory was conducted under the fol- 

 lowing passage of the sundry civil act approved July 19, 1919 : 



Astrophysical Observatory : For maintenance of Astrophysical Observatory, 

 under the direction of the Smithsonian Institution, including assistants, pur- 

 chase of necessary books and periodicals, apparatus, making necessary obser- 

 vations in high altitudes, repairs and alterations of buildings, and miscella- 

 neous expenses, $13,000. 



The observatory occupies a number of frame structures within an 

 inclosure of about 16,000 square feet south of the Smithsonian ad- 

 ministration building at Washington, and also a cement observing 

 station and frame cottage for observers on a plot of 10,000 square 

 feet leased from the Carnegie Solar Observatory, on Mount Wilson, 

 Calif. 



The present value of the buildings and equipment is estimated at 

 $50,000. This estimate contemplates the cost required to replace the 

 outfit for the purpose of the investigation. 



WORK OF THE YEAR. 



At Washington. — Much labor was expended on the preparation 

 of tables of results for publication in Volume IV of the Annals of 

 the Observatory. 



Under Mr. Fowle's direction, the Mount Wilson observations of 

 1919 were reduced and compared with those obtained by Smith- 

 sonian observers in Chile. An experiment had been made in using 

 rolled stellite instead of cast stellite to prepare new spectroscope 

 mirrors for the South American work. As these mirrors were not 

 quite finished when Director Abbot went south to observe the eclipse 

 of May 28 (as related in last year's report) he took with him the 

 Mount Wilson spectroscope mirrors, intending that the new ones 

 should replace them on Mount Wilson. Unfortunately, they proved 

 unsuitable owing to a gradual alteration of figure after completion, 

 but were nevertheless used on Mount Wilson by Mr. Aldrich for the 

 experiments of 1919. 



The matter is mentioned here because the defective mirrors intro- 

 duced stray light in the spectrum, which led to a systematic error of 2 

 per cent (in defect) in the Mount Wilson solar constant values of 

 1919. Considerable additional labor was required in the reductions 

 on this account. Furthermore, the sky was unusually hazy and 

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