revealed to Le Verrier that he was endowed with the powers requisite
for dealing with the subtlest instruments of mathematical analysis.
When he was twenty-eight years old, his first great astronomical
investigation was brought forth. It will be necessary to enter into
some explanation as to the nature of this, inasmuch as it was the
commencement of the life-work which he was to pursue.

If but a single planet revolved around the sun, then the orbit of
that planet would be an ellipse, and the shape and size, as well as
the position of the ellipse, would never alter. One revolution after
another would be traced out, exactly in the same manner, in
compliance with the force continuously exerted by the sun. Suppose,
however, that a second planet be introduced into the system. The sun
will exert its attraction on this second planet also, and it will
likewise describe an orbit round the central globe. We can, however,
no longer assert that the orbit in which either of the planets moves
remains exactly an ellipse. We may, indeed, assume that the mass of
the sun is enormously greater than that of either of the planets. In
this case the attraction of the sun is a force of such preponderating
magnitude, that the actual path of each planet remains nearly the
same as if the other planet were absent. But it is impossible for
the orbit of each planet not to be affected in some degree by the
attraction of the other planet. The general law of nature asserts
that every body in space attracts every other body. So long as there
is only a single planet, it is the single attraction between the sun
and that planet which is the sole controlling principle of the
movement, and in consequence of it the ellipse is described. But
when a second planet is introduced, each of the two bodies is not
only subject to the attraction of the sun, but each one of the
planets attracts the other. It is true that this mutual attraction