The materials available to the mathematician
for the solution of this problem were to be derived solely from the
discrepancies between the calculated places in which Uranus should be
found, taking into account the known causes of disturbance, and the
actual places in which observation had shown the planet to exist.
Here was indeed an unprecedented problem, and one of extraordinary
difficulty. Le Verrier, however, faced it, and, to the astonishment
of the world, succeeded in carrying it through to a brilliant
solution. We cannot here attempt to enter into any account of the
mathematical investigations that were necessary. All that we can do
is to give a general indication of the method which had to be
adopted.
Let us suppose that a planet is revolving outside Uranus, at a
distance which is suggested by the several distances at which the
other planets are dispersed around the sun. Let us assume that this
outer planet has started on its course, in a prescribed path, and
that it has a certain mass. It will, of course, disturb the motion
of Uranus, and in consequence of that disturbance Uranus will follow
a path the nature of which can be determined by calculation. It
will, however, generally be found that the path so ascertained does
not tally with the actual path which observations have indicated for
Uranus.
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