gravity of the system is somewhat displaced--itself a matter of no
great account--but also that the orbit of the original planet ceases
to be circled and becomes elliptical, and this for the evident reason
that the sphere will be drawn somewhat away from the sun when the
second planet happens to lie in the part of its orbit immediately
outside of its position, in which case the pull is away from the solar
centre; while, on the other hand, when the new planet was on the other
side of the sun, its pull would serve to intensify the attraction
which drew the first sphere toward the centre of gravity. As the
pulling action of the three bodies upon each other, as well as upon
their equatorial protuberances, would vary with every change in their
relative position, however slight, the variations in the form of their
orbits, even if the spheres were but three in number, would be very
important. The consequences of these perturbations will appear in the
sequel.

In our solar system, though there are but eight great planets, the
group of asteroids, and perhaps a score of satellites, the variety of
orbital and axial movement which is developed taxes the computing
genius of the ablest astronomer. The path which our earth follows
around the sun, though it may in general and for convenience be
described as a variable ellipse, is, in fact, a line of such
complication that if we should essay a diagram of it on the scale of
this page it would not be possible to represent any considerable part
of its deviations. These, in fact, would elude depiction, even if the
draughtsman had a sheet for his drawing as large as the orbit itself,
for every particle of matter in space, even if it be lodged beyond the
limits of the farthest stars revealed to us by the telescope,
exercises a certain attraction, which, however small, is effective on
the mass of the earth. Science has to render its conclusions in