DETERMINATION OF THE ORBIT OF THE PLANET NEPTUNE 



(PROFESSOR CHALLIS). 



[From the Astronomische Nachrichten. No. 596 (1847). Pp. 309 314.] 



IN conformity with a wish expressed by the Vice-Chancellor and the 

 Observatory Syndicate at their ordinary terminal meeting, held on March 

 15, I propose in this Report to carry on, for the information of members 

 of the Senate, the account of proceedings in the Observatory relative to 

 the new planet, a first Report of which was made on December 12 of last 

 year. The theoretical grounds on which a search for the planet was insti- 

 tuted, the manner in which the search was conducted, and the degree of 

 success that attended it, were stated in the former Report, which brought 

 the history of proceedings down to the date at which the planet was dis- 

 covered. I have now to give an account of the subsequent observations 

 both of its position in the heavens, and of its physical appearance, and to 

 state the results respecting the orbit which have been deduced from the 

 observations by calculation. 



A regular series of observations of the planet was commenced on October 

 3, 1846, and continued at all available opportunities, partly with the meridian 

 instruments, and partly with the Northumberland Equatorial, to December 4, 

 soon after which the planet became too faint to observe on the meridian 

 on account of daylight. The observations were subsequently carried on with 

 the Equatorial to January 15. The series was much interrupted by cloudy 

 weather, particularly in the months of December and January. On the whole 

 I have obtained 28 positions of the planet with the meridian instruments, 

 and 25 positions with the Northumberland Equatorial by means of 92 

 differential observations of Right Ascension and as many of North Polar 

 Distance. The Equatorial measures were all referred to the same star, 

 No. 7648 of the British Association Catalogue, the exact place of which 

 was determined by 16 observations with the Transit, and 8 observations 

 with the Mural Circle. I have reason to think that the positions obtained 

 with the equatorial are entitled to very nearly the same weight as those 



