152 CARNEGIE INSTITUTION 



seriously undertaken by Professor Porro at Turin and Dr. H. S. 

 Davis in this country. The latter has been aided by the Trustees 

 of the Gould fund. The question whether anything to promote 

 the work can be done by the Carnegie Institution is respectfully 

 submitted. 



4. Attention has recently been called by Professor Rambaut to a 

 remarkable series of observations made by Professor Hornsby at the 

 Radcliffe Observatory, Oxford, beginning in 1774, which he is de- 

 sirous to reduce. From his report it would seem that the results 

 may be of special value. It therefore seems desirable to investigate 

 the question of their precision and of the character of the results to 

 be derived from them. When this is done the question of provid- 

 ing for their complete reduction could be considered. 



Respectfully submitted. 



Simon Newcomb. 

 Washington, October 8, igo2. 



Appendix F to Report of Committee on Astronomy. 



PROGRESS AND PRESENT STATE OF CELESTIAL 

 PHOTOMETRY AND PHOTOGRAPHY. 



By E. C. Pickering. 



Celestial Photometry. 



The earliest estimates of the relative brightness of stars are recorded 

 by Ptolemy in the Almagest, but careful comparisons, capable of 

 revealing small changes in brightness, were first made by Sir Wil- 

 liam Herschel. The inadequacy of visual estimates was recognized 

 by Sir John Herschel while engaged in extending and improving 

 his father's work. This led to the constructions of the first stellar 

 photometer, by which the light of a star was compared with a minute 

 image of the Moon, adjustable in distance from the eye. The full 

 possibilities of comparisons made without instrumental aid for large 

 numbers of stars were realized by Argelander, whose Uranometria 

 Nova, giving the approximate magnitudes and places of 3,256 stars, 

 was published in 1S43. This was followed twenty years later by 

 the monumental Bonner Durchmustenuig giving the positions and 

 magnitudes of 324,189 stars in the northern heavens, in the prepa- 



