LEADING OPERATIONS OF THE SMITHSONIAN 



ASTROPHYSICAL OBSERVATORY, 



1895 TO 1955 



By C. G. Abbot 

 Research Associate, Smithsonian Institution 



INTRODUCTION 



Having been associated with the Astrophysical Observatory almost 

 from its inception in 1890, it seems good to me to print, in small com- 

 pass in one place, references to the leading researches and instrumental 

 developments carried out there. It may well be that there are now, 

 and will be in future, those who, for one reason or another, may wish 

 to refer to these events, and will appreciate having easy access to the 

 original sources. 



The list is far from exhaustive, either as regards the work of the 

 Astrophysical Observatory, or references to it. But I believe it is suffi- 

 cient to present a fair picture of what has been accomplished. 



SECTION A 

 Part i. — Improved and new instruments 



1. The bolometer rebuilt and equipped Annals of the Astrophysical Observa- 



with a balancing device close be- tory,'^ vol. i, pp. 47-56, 105-109, 



side it and at constant tempera- 1900; vol. 3, p. 42, 1913. 



ture. Result : The drift nearly 

 eliminated and the wiggle 

 greatly reduced. 



2. Galvanometer. Theory investi- Astrophys. Journ., vol. 18, No. i, July 



gated and new galvanometer of 1903. 



tenfold sensitiveness built. Annals, vol. 1, pp. 244-252, 1900. 



3. Vacuum bolometer with self-con- Annals, vol. 4, pp. 45-64, 1922. 



tained Wheatstone bridge built. 

 Result : Several-fold increase of 

 sensitiveness, and increased 

 steadiness. 



4. Silver-disk pyrheliometer invented. Smithsonian Misc. Coll., vol. 56, No. 



About 100 copies have been 19, 191 1. 



1 Hereafter referred to simply as "Annals." 



SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL 131, NO. 1 



