[Investigations on Light and Heat published with Appropriation from the Kumford Fund.] 



IV. 



Stellar Photography. 

 By EDWARD C. PICKERING. 



Presented March 10, 1886. 



The experiments to be described below were mainly conducted by the aid of an 

 appropriation made in June, 1885, from the Bache Fund of the National Academy 

 of Sciences. Numerous prehminary experiments had been made with a grant from 

 the Rumford Fund of the American Academy. My attention was directed to stellar 

 photography in 1882, by Mr. W. H. Pickering. Many of the preliminary experi- 

 ments were made by him, and his advice was followed regarding the photographic 

 processes to be employed. In the later work, he has rendered important aid by 

 his advice, and by making many auxiliary experiments in his photographic labo- 

 ratory at the Massachusetts Institute of Technology. The actual exposures and 

 development of the photographs have been made by several assistants in turn. 

 From June 11, 1885, to October 16, 1885, this work was intrusted to Mr. A. 11. 

 Whittemore ; from October 17, 1885, to January 26, 1886, to Mr. H. Helm Clay- 

 ton ; and from February 2, 1886, to the present time, to Mr. Willard P. Gerrish. 

 To the skill and perseverance shown by these gentlemen the success attained is 

 largely due. 



The following subjects are discussed below in turn: — 



History of Stellar Photography. 



Preliminary Experiments, 1882 to 1885. 



Description of the Photographic Apparatus finally adopted. 



Theoretical Considerations entering into the Problem of Stellar Photography. 



Trails formed by Stars when their apparent Motion is not wholly corrected 



by the Motion of the Telescope. 

 Construction of Charts by Photography. 

 Stellar Spectra. 



Brighter Stars in the Pleiades. 

 Close Polar Stars. 



