Astronomy 581 



only 2". 3 in longitude, o". 7 in latitude. The normals formed 

 from modern observations differ about o". 3, which gives no 

 support to the suspicion of a trans- Neptunian planet, although 

 nothing is definitely settled, as a planet exterior to Neptune 

 might exist and yet give small evidence of its attractions dur- 

 ing the years 1 795-1863. The standard system of star-places 

 adopted is that of Gould. The mass of Uranus resulting 

 from the discussion is 21 Q ^. Observations with the great 

 telescope in Washington (made by Newcomb in 1874 and 

 later) give 22 6oo- 



New elements of the planet are deduced, two of which 

 may well be quoted here, viz. : Mean distance, 30.07055 ; 

 periodic time, 164.782 Julian years. 



THE ORBIT OF URANUS 



PROFESSOR NEWCOMB'S " Investigation of the Orbit of Uranus," 

 with tables of its motion, was published as No. 262 of the 

 "Contributions to Knowledge" in 1873. 



The work was undertaken as early as 1859, and the orbit 

 of Neptune, just referred to, was a part of the general re- 

 search. 



The first chapter of the work is devoted to a method of 

 development of the perturbations which is novel in many 

 respects, and is especially suited to the particular problem in 

 hand. With improved elements and methods the research 

 was again begun in 1868, and carried to its termination in 

 1873, by the aid of the Smithsonian Institution and of the 

 "American Ephemeris." 



In the Report for 1872 Professor Newcomb presents some 

 considerations on the scope of his researches, from which the 

 following is taken. 



