f^ [ 120 ] 



that one of the stars observed by l.alande on the night of May 10, 1795, 

 was the planet Neptune. This conchision was rendered ahuo^t certainty by 

 the observation, made on the first clear night, that all the stars iu the cluster 

 above mentioned were found in place, except the one previously fixed upon 

 as the new planet. Some doubt was created, however, by noting that the 

 missing star in Lalande's maps was marked as doubtful. In order to set- 

 tle 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 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 indi- 

 cated doubtful. The planet had moved during the interval of observa- 

 tion, 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 obser- 

 vations 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 tlie body would describe were 

 there no other planets in tlie system. This orbit has been investigated 

 by anotlier of our countrymen in a series of profound and lieautiful re- 

 searches, 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 by mathe- 

 matical deductions from the perturbations observed in Uranus, and ihat 

 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 chmensions, 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 discovering tlie 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 produce in the planet Uranus. His fiiud 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 ITSl, for 

 correct tables for determining its position in the heavens. Professor Peirce 

 also investigated the action of all the other planets on Neptune, and his 

 results enabled Mr. Walker, by applying them to his elliptical orbit, to coin- 

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

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

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

 alternately combining the data of observation witli theoretical consider- 

 ations, these two astronnmers 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. Tl^ie details ol Mr. 

 Peirce's paper have not yet been prepared for the press. Tiiey will prob- 

 ably be given in due time to the world as a part of the Smithsonian Con 

 tributions. 



