an Crater of the Moon,' but, in my opinion, Copernicus is,
owing to its position and grandeur, much more worthy of that dignity.
Tycho is fine in itself, but is not so favourably situated, being
surrounded by other formations somewhat in the same way as St. Paul's
Cathedral is surrounded and shut in, for the most part, by other and
meaner buildings.

"How much more should we appreciate the splendid proportions and majesty
of our Metropolitan Cathedral if we could view it as an isolated
building with a fine open space all around it!"

"I quite agree with that, Professor," remarked John, "and I have always
thought it a great pity that Sir Christopher Wren was not allowed to
carry out his original plan in this respect."

We were looking at the Carpathian range of mountains just to the
northward of Copernicus, when M'Allister touched my arm, exclaiming,
"Look, Professor, at all those tiny craters near the western side of
Copernicus. Why, there are so many of them that the ground for miles
round looks like a honeycomb, and in some places there are straight rows
of them!"

"Yes," I said, "this part of the lunar surface is simply riddled with
tiny craterlets, and some of them are utilised as tests for the
definition of our telescopes. I have heard it remarked that a map of
this part of the moon presents almost the appearance of the froth on a
glass of stout when it has settled down, the very numerous tiny
air-bubbles of different sizes representing the craterlets; and really
it does bear such a resemblance.

"Almost due east of Copernicus is another bright and isolated ring-plain
named Kepler, after the celebrated astronomer. This is some twenty-two
miles in diameter and surrounded by very bright streaks of light,
extending in some directions over seventy miles, the whole nimbus of
light covering an area of nearly ten thousand square miles. These really
are streaks, not ridges, for, as you will see, nearly all the surface
surrounding this formation is flat and level.

"Some of the streaks from Kepler radiate in the direction of
Aristarchus, others towards Copernicus, cutting right through the rays
from those formations. From this it is gathered that Copernicus was
formed first, then Aristarchus, and Kepler still later on in the moon's
history.

"The surrounding wall of Kepler is comparatively low with respect to
the lunar surface level, but the depth of the crater is nearly ten
thousand feet below the mountain peaks.