to all the planetary bodies as well as to the earth. Accordingly, this
was what Newton asserted in respect to all material substance.

[Sidenote: Perturbations accounted for.] But it is a necessary
consequence of this theory that many apparent irregularities and
perturbations of the bodies of the solar system must take place by
reason of the attraction of each upon all the others. If there were but
one planet revolving round the sun, its orbit might be a mathematically
perfect ellipse; but the moment a second is introduced, perturbation
takes place in a variable manner as the bodies change their positions or
distances. An excessive complication must therefore be the consequence
when the number of bodies is great. Indeed, so insurmountable would
these difficulties be, that the mathematical solution of the general
problem of the solar system would be hopeless were it not for the fact
that the planetary bodies are at very great distances from one another,
and their masses, compared with the mass of the sun, very small.

[Sidenote: Results of the theory of gravitation.] Taking the theory of
gravitation in its universal acceptation, Newton, in a manner that looks
as if he were divinely inspired, succeeded in demonstrating the chief
inequalities of the moon and planetary bodies; in determining the figure
of the earth--that it is not a perfect sphere, but an oblate spheroid;
in explaining the precession of the equinoxes and the tides of the
ocean. To such perfection have succeeding mathematicians brought his
theory, that the most complicated movements and irregularities of the
solar system have been satisfactorily accounted for and reduced to
computation. Trusting to these principles, not only has it been found
possible, knowing the mass of a given planet, to determine the
perturbations it may produce in adjacent ones, but even the inverse
problem has been successfully attacked, and from the perturbations the
place and mass of a hitherto unknown planet determined. It was thus
that, from the deviations of Uranus from his theoretical place, the
necessary existence of an exterior disturbing planet was foreseen, and
our times have witnessed the intellectual triumph of mathematicians
directing where the telescope should point in order to find a new
planet. The discovery of Neptune was thus accomplished.

It adds to our admiration of the wonderful intellectual powers of Newton
to know that the mathematical instrument he used was