170 Benjamin Peirce. 
When, in 1846, 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 necessarily to the assigned 
Leverrier had proposed to himself to solve the following prob- 
em :—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 cor- 
rect 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 pro- 
the place in that orbit, as is well known, was less than one de- 
gree, as seen from the earth, from the actual place where Galle 
found Neptune. 
Yet Professor Peirce declared that Leverrier’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 éclat which the world had given 
them. But Leverrier 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 mo 
tion 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 motions had the ratios 2:5 and 1:2, and that 
the reasonings of Leverrier were thereby vitiated. Nota little 
controversy has come from these papers of Professor Peirce; 
and we cannot say that the last word in regard to the question 
has even yet been spoken. As is not unusual in like discus 
sions, there is probably a portion of truth and a portion of error 
