162 EIGHTH ANNUAL REPORT OF 



of May 10, 1795, was the planet Neptune. This conclusion was ren- 

 dered almost certainty by the observation, made on the first clear night, 

 that all the stars in the cluster above mentioned were found in place, 

 except the one previously fixed upon as the new planet. Some hesi- 

 tation was created, however, b} r noting that the missing star in Lalande's 

 maps was marked as doubtful. In order to seitle this difficulty, the 

 original manuscript of the astronomer deposited in the Observatory of 

 Paris was referred to. It was then found that Lalande had twice ob- 

 served the same star ; and not finding the right ascension and declina- 

 tion each time the same, and not dreaming it was a planet, he selected 

 one of the observations for publication, marking the position indicated 

 doubtful. The planet had moved during the interval of observation, 

 and thus produced the discrepancy. By allowing for the movement 

 during the time elapsed, the two observations precisely agree. There 

 could, therefore, be no longer any doubt that this star, observed and 

 mapped fifty years ago as a fixed star, was in reality the planet Neptune. 

 Mr. Walker, availing himself of this discovery, had now a series of ob- 

 servations embracing not a few months of the motion of the planet, but 

 which carried it back fifty years. From these data he was enabled to 

 deduce a pure elliptical orbit, or one which the body would describe 

 were there no other planets in the system. This orbit has been 

 investigated by another of our countrymen in a series of profound and 

 beautiful researches, adding much to our knowledge both of Neptune 

 and Uranus. I allude to the labors of Professor Peirce, of Cambridge. 

 It is well known that the planet Neptune was discovered b}r mathe- 

 matical deductions from the perturbations observed in Uranus, and that 

 Leverrier and Adams, the independent authors of this discovery, not 

 only pointed out the direction in which the unseen planet was to be 

 found, but also, from a priori considerations, gave the dimensions, form, 

 and position of the orbit it describes around the sun. The direction 

 indicated was the true one, but the elements of the orbit were widely 

 different from those subsequently found to belong to the actual orbit of 

 the planet. Professor Peirce submitted the data used by Leverrier and 

 Adams to a new and critical examination, and succeeded in discover- 

 ing the cause of their error, and of verifying the conclusions of Mr. 

 Walker. He afterwards proceeded to consider the inverse problem, 

 viz : that of deducing the perturbations which Neptune ought to pro- 

 duce in the planet Uranus. His final results gave a perfect explanation 

 of all the anomalies in the motions of Uranus, and furnished the data, 

 for the first time since its discovery in 1781 , for correct tables for 

 determining its position in the heavens. Professor Peirce also investi- 

 gated the action of all the other planets on Neptune, and his results en- 

 abled Mr. Walker, by applying them to his elliptical orbit, to compare 

 the actual with the calculated place of the planet. This led to a further 

 correction of the elliptical orbit, and a more perfect table of calculated 

 places. In this way, by a series of profound and beautiful investiga- 

 tions, alternately combining the data of observation with theoretical 

 considerations, these two astronomers have perfected our knowledge of 

 the motion of the most distant planets of our system, and furnished the 

 means of giving their past and future position through all time. The 

 details of Mr. Peirce's paper have not yet been prepared for the press. 



