But they disappeared every now and
then under thick vapory spots, which are never seen on the Lunar disc.
They were the thin concentric cloud rings that surround the terrestrial
sphere.
However, the travellers' eyes were soon able to trace the rest of the
Earth's surface not only with facility, but even to follow its outline
with absolute delight. This was in consequence of two different
phenomena, one of which they could easily account for; but the other
they could not explain without Barbican's assistance. No wonder. Never
before had mortal eye beheld such a sight. Let us take each in its turn.
We all know that the ashy light by means of which we perceive what is
called the _Old Moon in the Young Moon's arms_ is due to the
Earth-shine, or the reflection of the solar rays from the Earth to the
Moon. By a phenomenon exactly identical, the travellers could now see
that portion of the Earth's surface which was unillumined by the Sun;
only, as, in consequence of the different areas of the respective
surfaces, the _Earthlight_ is thirteen times more intense than the
_Moonlight_, the dark portion of the Earth's disc appeared considerably
more adumbrated than the _Old Moon_.
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