446 BENJAMIN PEIRCE. 



suiting Astronomer until 1867. The high place which the "American 

 Epheraeris " has ever held among like publications is greatly due to 

 the character given to it by Fi-ofessor Peirce in these its earliest 

 yeai's. 



When, in 18-46, Galle discovered the planet Neptune in the place 

 pointed out to him by Leverrier, Professor Peirce took the liveliest 

 interest in the admirable researches of Leverrier and Adams. He 

 entered with zest into all the questions which were thus raised. What 

 is the orbit of the new planet ? What its mass ? How much do they 

 differ from the assigned orbits and masses ? Does the new planet 

 explain all the irregularities of Uranus ? Did the data lead neces- 

 sarily to the assigned place, and to it alone ? 



The results of his investigations were at various times given to this 

 Academy, but more especially on the 4th of April, 1848. He then 

 gave the perturbations of longitude and radius vector of Uranus by 

 Neptune, and announced that Neptune and either of the two hypo- 

 thetical planets of Leverrier and Adams would equally explain the 

 observations of Uranus, within reasonable limits of error. 



Leverrier had proposed to himself to solve the following problem. 

 From the observed irregularities of the planet Uranus to compute the 

 elements of the orbit of an assumed exterior planet that has caused 

 these irregularities. He ought perhaps to have limited himself to the 

 other problem, to which he gave so correct an answer, where among 

 the stars astronomers must look in order to see the disturbing body. 

 The elements of the orbit could be had from observations when once 

 the planet was seen. He found for the unknown planet an orbit and 

 a mass by processes that will always command the admiration of men ; 

 and the place in that orbit, as is well known, was less than one degree, 

 as seen from the earth, from the actual place where Galle found 

 Neptune. 



Yet Professor Peirce declared that Leverrler's geometric planet and 

 Neptune were not the same bodies. He praised without question the 

 work of Leverrier and of Adams, asserting for them their right to 

 all the praise and eclat which the world had given them. But Lever- 

 rier had distinctly stated that the planet which disturbed Uranus 

 could not be at a less mean distance from the sun than 35 ; that is, 

 that no planet that was within this distance could cause the observed 

 irregularities of the motion of Uranus. Neptune, however, is at a 

 distance of only 30, and does account for the perturbations of Uranus. 



In this and in other communications Professor Peirce claimed that 

 the perturbations changed their character at the points where the mean 



