AN ACCOUNT OF THE ASTROPHYSICAL 



OBSERVATORY OF THE SMITHSONIAN 



INSTITUTION, 1904-1953 



By Charles G. Abbot, D.Sc. 

 Research Associate, Smithsonian Institution 



The Smithsonian's Astrophysical Observatory was founded by 

 Secretary Samuel P. Langley in 1890. Until 1900 the Observatory's 

 original research activities included developing and improving appa- 

 ratus, and mapping the then little-known infrared spectrimi of the 

 sun. The bolometer, which Langley had invented about 1878, was 

 given photographic registration, tamed to be as quiet and reliable as 

 a mercury thermometer, and used to record small depressions where 

 absorption lines occurred in the solar spectrum. The Observatory's 

 highly exact determinations of the dispersion of rock-salt and fluorite 

 prisms fixed the wavelengths of these absorption lines. Volume 1 of 

 the Annals, describing all of this work, was published in 1900. Expe- 

 ditions to North Carolina and to Sumatra observed the total solar 

 eclipses of 1900 and 1901, and a small eclipse volume was published 

 in 1903. 



The Observatory then took up measurement of the intensity of the 

 sun's radiation, the variability of it, and the transmission of radiation 

 by the earth's atmosphere in the visible and infrared spectrum. The 

 average intensity of solar radiation received by the earth, called the 

 "solar constant," was then unknown between the limits 1.76 and 

 4.0 calories per square centimeter per minute. Solar constant research 

 and the dependence of weather on solar variation principally occupied 

 the Observatory from 1904 through 1953. 



ADMINISTRATION OF THE OBSERVATORY, 1904-1953 



FINANaAL SXH'PORT 



A breakdown of the Observatory's financial support from 1904 

 through 1953 shows that the average yearly support for this period 

 was $37,000. 



SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. 148, NO. 7 



