888), pp. 56 and 122.

CHAPTER II.

LUNAR VOLCANOES.

The surface of the moon presented to our view affords such remarkable
indications of volcanic phenomena of a special kind, that we are
justified in devoting a chapter to their consideration. It is very
tantalising that our beautiful satellite only permits us to look at and
admire one half of her sphere; but it is not a very far-fetched
inference if we feel satisfied that the other half bears a general
resemblance to that which is presented to the earth. It is scarcely
necessary to inform the reader why it is that we never see but one face;
still, for the sake of those who have not thought out the subject I may
state that it is because the moon rotates on her axis exactly in the
time that she performs a revolution round the earth. If this should not
be sufficiently clear, let the reader perform a very simple experiment
for himself, which will probably bring conviction to his mind that the
explanation here given is correct. Let him place an orange in the centre
of a round table, and then let him move round the table from a
starting-point sideways, ever keeping his face directed towards the
orange; and when he has reached his starting-point, he will find that he
has rotated once round while he has performed one revolution round the
table. In this case the performer represents the moon and the orange
the earth.

Now this connection between the earth and her satellite is sufficiently
close to be used as an argument (if not as actual demonstration) that
the earth and the moon were originally portions of the same mass, and
that during some very early stage in the development of the solar system
these bodies parted company, to assume for ever after the relations of
planet and satellite. At the epoch referred to, we may also suppose that
these two masses of matter were in a highly incandescent, if not even
gaseous, state; and we conclude, therefore, that having been once
portions of the same mass, they are composed of similar materials. This
conclusion is of great importance in enabling us to reason from analogy
regarding the origin of the physical features on the moon's surface, and
for the purpose of comparison with those which we find on the surface of
our globe; because it is evident that, if the composition of the moon
were essentially different from that of our earth, we should have no
basis whatever for a comparison of their physical features.

When the m