22 



by its magnitude, (9.10;) No. 2, in my opinion, by being 17' south of the geo- 

 centric path. There remained, then, in all the Histoire Celeste, only one star 

 (No. 8) that could have been the planet Neptune. 



The fact that this star afforded the only chance for a Lalande observation of 

 Neptune, and that it was now missing, could leave little doubt on the question 

 of identity. Another consideration strengthened the probability of this conclu- 

 sion ; and this was, its nearness to the point of the loci which had a maximum 



of plausibility, (viz., that of (-r^) == a maximum , b = 0). 



No. 31. The first public announcement of the probable discovery of a La- 

 lande observation of Neptune was made 7 days after its date, viz., on the 9th 

 of February, in the official organ of the Government, (the Washington Union,) 

 in a letter of Lieutenant Maury to the Secretary of the Navy, the Hon. John Y. 

 Mason, dated February the 8th. 



The circumstance of the ( : ) colon placed after the Lalande observation of 

 No. 8, was at this time the only one which was calculated to throw a doubt on 

 this conclusion. Stars Nos. 7 and 8 have nearly the same right ascension, and 

 differ 12'. 7 in declination. One is marked doubtful in R. A. ; the other in Dec. 

 Could they not have been the same .'' Is any star missing from the heavens ? 

 Did Lalande observe Neptune at all .'' Were not the limits of the computed 

 loci of Neptune, May 10, 1795, too restricted .'' Is the observed path of Nep- 

 tune (of only six months) sufficiently well known, to overturn the limits estab- 

 lished by Leverrier for his hypothetical planet, viz., a period of more than 209 

 years, and an eccentricity greater than the present assumed maximum limit ? 

 These were the difficulties under which the hypothesis of identity labored in 

 this country, till the arrival at Washington, (May 19, 1847,) of the news of *M. 

 Mauvais' discovery of the other Lalande observation of Neptune, of May 8, 

 1795. 



No. 32. I shall not here dwell on the particulars relative to the Mauvais disco- 

 very. The news of the probable discovery of the Lalande observation of May 

 10, reached Levei'rier, at Paris, on the same day from Washington and from 

 Altona, (Mr. Peterson's discovery, made March 15, 1847.) The announcement 

 of this fdouble discovery, by Leverrier, to the French Academy, Comptes Ren- 

 dus, 1847, March 29 — the presentation by Captain Lalande, of the Manuscripts 

 of the Histoire Celeste to Arago — his donation of them to the Royal Observa- 



* Comptes Rendus, 1847, April 19th. 



t If I have rightly interpreted the papers relative to the discovery made by Dr. Petersen, it seems that thi-s distinguished 

 astronomer pursued the plan which I had originally proposed to pursue, and in fact had actually commenced, of making a 

 trial catalogue, and then observing tlie heavens for the purpose of finding what stars are now missing. 



If I was able to effect my purpose without the use of the telescope, except for confirmation, and not for discovery, I was 

 perhaps indebted to the more extensive series of observations, Eiu'opean and American, which had been discussed, and 

 which enabled me to restrict the limits of Neptune's place in 1795, more than could be done by Encke's Elements, used 

 by Dr. Petersen, and based on a far shorter period of observations. 



