170 EIGHTH ANNUAL REPORT OF 



10, 1795, was the planet Neptune. Tliis conclusion was rendered 

 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 hesitation was 

 created, however, by noting that the missing star in Lalande's maps 

 was marked as doubtful. In order to settle this difficulty, the original 

 manuscript of the astronomer deposited in the Observatory of Paris was 

 referred to. It was then found that L aland e had twice observed the 

 same star; and not finding the right ascension and declination 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 pro- 

 duced 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 observations em- 

 bracing 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, ad- 

 ding much to our knowledge both of Neptune and Uranus. I allude to 

 tire labors of Professor Peirce, of Cambridge. 



It is well known that the planet Neptune was discovered by 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 iiriori 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 

 tlie 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 ena- 

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

 tire 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 scries of profound and beautiful investiga- 

 tions, alternately combining the data of observation with theoretical 

 considerations, these two as'.ronomers have perfected our knowledge of 

 tlie 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 prepai-ed for the press. 



