llions of years--whereas the ordinary perturbations go through their
swings in some hundred thousand years or so at the most. Granted it is
small, but it is terribly persistent; and it always acts in one
direction. Never does it cease: never does it begin to act oppositely
and undo what it has done. It is like the perpetual dropping of water.
There may be only one drop in a twelvemonth, but leave it long enough,
and the hardest stone must be worn away at last.

* * * * *

We have been speaking of millions of years somewhat familiarly; but
what, after all, is a million years that we should not speak familiarly
of it? It is longer than our lifetime, it is true. To the ephemeral
insects whose lifetime is an hour, a year might seem an awful period,
the mid-day sun might seem an almost stationary body, the changes of the
seasons would be unknown, everything but the most fleeting and rapid
changes would appear permanent and at rest. Conversely, if our
life-period embraced myriads of aeons, things which now seem permanent
would then appear as in a perpetual state of flux. A continent would be
sometimes dry, sometimes covered with ocean; the stars we now call fixed
would be moving visibly before our eyes; the earth would be humming on
its axis like a top, and the whole of human history might seem as
fleeting as a cloud of breath on a mirror.

Evolution is always a slow process. To evolve such an animal as a
greyhound from its remote ancestors, according to Mr. Darwin, needs
immense tracts of time; and if the evolution of some feeble animal
crawling on the surface of this planet is slow, shall the stately
evolution of the planetary orbs themselves be hurried? It may be that we
are able to trace the history of the solar system for some thousand
million years or so; but for how much longer time must it not have a
history--a history, and also a future--entirely beyond our ken?

Those who study the stars have impressed upon them the existence of the
most immeasurable distances, which yet are swallowed up as nothing in
the infinitude of space. No less are we compelled to recognize the
existence of incalculable aeons of time, and yet to perceive that these
are but as drops in the ocean of eternity.

FOOTNOTES:

[1] The following account of Mars's motion is from the excellent small
manual of astronomy by Dr. Haughton of Trinity College, Dublin:--(P.
151) "Mars's motion is very unequal; when he first appears