to tidal action on the moon itself must, therefore,
be much in excess of anything which we here experience. It is, in
consequence, probable that such a tidal drag, extending over a very long
period of time, has resulted in slowing down the moon's rotation to its
present rate.

The fact that we never see but one side of the moon has given rise from
time to time to fantastic speculations with regard to the other side.
Some, indeed, have wished to imagine that our satellite is shaped like
an egg, the more pointed end being directed away from us. We are here,
of course, faced with a riddle, which is all the more tantalising from
its appearing for ever insoluble to men, chained as they are to the
earth. However, it seems going too far to suppose that any abnormal
conditions necessarily exist at the other side of the moon. As a matter
of fact, indeed, small portions of that side are brought into our view
from time to time in consequence of slight irregularities in the moon's
movement; and these portions differ in no way from those which we
ordinarily see. On the whole, we obtain a view of about 60 per cent. of
the entire lunar surface; that is to say, a good deal more than
one-half.

The actual diameter of the moon is about 2163 miles, which is somewhat
more than one-quarter the diameter of the earth. For a satellite,
therefore, she seems very large compared with her primary, the earth;
when we consider that Jupiter's greatest satellite, although nearly
twice as broad as our moon, has a diameter only one twenty-fifth that of
Jupiter. Furthermore, the moon moves around the earth comparatively
slowly, making only about thirteen revolutions during the entire year.
Seen from space, therefore, she would not give the impression of a
circling body, as other satellites do. Her revolutions are, indeed,
relatively so very slow that she would appear rather like a smaller
planet accompanying the earth in its orbit. In view of all this, some
astronomers are inclined to regard the earth and moon rather as a
"double planet" than as a system of planet and satellite.

When the moon is full she attracts more attention perhaps than in any of
her other phases. The moon, in order to be full, must needs be in that
region of the heavens exactly opposite to the sun. The sun _appears_ to
go once entirely round the sky in the course of a year, and the moon
performs the same journey in the space of about a month. The moon, when
full, having got hal