196 History of the Discovery of the Planet Neptune. 
The orbits of Adams and Le Verrier agree remarkably well 
with each other, but differ sadly from that of Mr. Walker; that 
is, we are compelled to admit that they differ materially from the 
truth. They represent remarkabiy well the direction in whic 
the planet is now seen from the earth, but they give its mean 
distance too great by _ a millions of miles. ‘This dis- 
crepancy is so enormo ve given occasion for the re- 
mark, that the planet amie coe is not the planet pre- 
dicted. by y Le Verrier. Certainly we must concede, that the re- 
gion of space occupied by the planet is very remote from that 
prescribed for it by this mathematician. 
But how has it happened that two astronomers have arrived, 
by independent computations, at almost identically the same re- 
sult, when both are so seriously in error? The answer is obvious. 
Since it was necessary in the first instance, to make some hy- 
pothesis with regard to the distance of the disturbing body from 
the sun, both computers started with that supposition which was 
generally thought most probable. ‘The distance of Saturn from 
the sun is nearly double that of Jupiter; the distance of Uranus 
is almost exactly double that of Saturn ; hence it seemed probable 
that the planet they were in search of, would be found at a dis- 
stance about double that of Uranus. ‘Accordingly, this assump- 
tion was made the basis of their first computations; but neither 
of the computers accepted this as his final result, without attempt- 
ing to verify it. ‘They both varied the assumed distance, and 
found that by bringing the planet a little nearer the sun, the ob- 
served irregularities of Uranus were still better explained. ‘The 
distance of 36°154 (or about 3435 millions of miles) finally 
adopted by Le Verrier, was that which appeared to reconcile all 
the observations most satisfactorily. This anstee corresponds 
to a period of two hundred and seVenteen years. Le Verrier 
found that whether he increased or diminished shee distance, the 
observations of Uranus were not so well represented. He hence 
inferred that the period could not be less than two hundred and 
seven years, nor more than two hundred and thirty-three years. 
According to Professor Peirce of Harvard University, this con- 
clusion was not a legitimate one. ‘The ~~ employed by 
