ants on
the moon, it does not necessarily follow that the night will never
come when, through some mightier medium than any ever yet
constructed or conceived, we shall descry, beside mountains and
valleys, also peopled plains and populous cities animating the fair
features of this beautiful orb. One valuable auxiliary of the
telescope, destined to play an important part in lunar discovery,
must not be overlooked. Mr. Norman Lockyer says, "With reference
to the moon, if we wish to map her correctly, it is now no longer
necessary to depend on ordinary eye observations alone; it is
perfectly clear that by means of an image of the moon, taken by
photography, we are able to fix many points on the lunar surface."
[427] With telescopic and photographic lenses in skilled hands, and
a wealth of inventive genius in fertile brains, we can afford to wait a
long while before we close the debate with a final negative.

In the meantime, eyes and glasses giving us no satisfaction, we turn
to scientific _induction_. Speculation is a kind of mental mirror, that
before now has anticipated or supplemented the visions of sense.
Not being practical astronomers ourselves, we have to follow the
counsel of that unknown authority who bids us believe the expert.
But expertness being the fruit of experience, we may be puzzled to
tell who have attained that rank. We will inquire, however, with due
docility, of the oracles of scientific research. It is agreed on all sides
that to render the moon habitable by beings at all akin with our own
kind, there must be within or upon that body an atmosphere, water,
changing seasons, and the alternations of day and night. We know
that changes occur in the moon, from cold to heat, and from
darkness to light. But the lunar day is as long as 291 of ours; so that
each portion of the surface is exposed to, or turned from, the sun for
nearly 14 days. This long exposure produces excessive heat, and the
long darkness excessive cold. Such extremities of temperature are
unfavourable to the existence of beings at all like those living upon
the earth, especially if the moon be without water and atmosphere.
As these two desiderata seem indispensable to lunar inhabitation,
we may chiefly consider the question, Do these conditions exist? If
so, inductive reasoning will lead us to the inference, which
subsequent experience will strengthen, that the moon is inhabited
like its superior planet. But if not, life on the satellite