ar gentlefolk, drifting softly in
their silver galleons and barges, and enjoying the splendors of "full
earth" poured upon their delightful little world, were accustomed to
fall into charming reveries, as even we hard-headed sons of Adam
occasionally do when the waters under the keel are calm and smooth and
the balmy air of a moonlit night invokes the twin spirits of poetry and
music.

Posidonius, the dominating feature of the shore line here, is an
extraordinary example of the many formations on the moon which are so
different from everything on the earth that astronomers do not find it
easy to bestow upon them names that truly describe them. It may be
called a ring mountain or a ringed plain, for it is both. Its diameter
exceeds sixty miles, and the interior plain lies about 2,000 feet below
the outer surface of the lunar ground. The mountain wall surrounding the
ring is by no means remarkable for elevation, its greatest height not
exceeding 6,000 feet, but, owing to the broad sweep of the curved walls,
the brightness of the plain they inclose, and the picturesque
irregularity of the silhouette of shadow thrown upon the valley floor by
the peaks encircling it, the effect produced upon the observer is very
striking and attractive.

Having finished with Posidonius and glanced across the broken region of
the Taurus Mountains toward the west, we turn next to consider the _Mare
Serenitatis_. This broad gray plain, which, with a slight magnifying
power, certainly looks enough like a sea to justify the first
telescopists in thinking that it might contain water, is about 430 by
425 miles in extent, its area being 125,000 square miles. Running
directly through its middle, nearly in a north and south line, is a
light streak, which even a good opera glass shows. This streak is the
largest and most wonderful of the many similar rays which extend on all
sides from the great crater, or ring, of Tycho in the southern
hemisphere. The ray in question is more than 2,000 miles long, and, like
its shorter congeners, it turns aside for nothing; neither "sea," nor
peak, nor mountain range, nor crater ring, nor gorge, nor canon, is able
to divert it from its course. It ascends all heights and drops into all
depths with perfect indifference, but its continuity is not broken. When
the sun does not illuminate it at a proper angle, however, the
mysterious ray vanishes. Is it a metallic vein, or is it volcanic lava
or ash? Was the globe of the