The movement of rotation is the one that causes night and day on the
surface of the moon, only there is but one day and one night in a lunar
month, and they each last 354-1/3 hours. But, happily, the face, turned
towards the terrestrial globe, is lighted by it with an intensity equal
to the light of fourteen moons. As to the other face, the one always
invisible, it has naturally 354 hours of absolute night, tempered only
by "the pale light that falls from the stars." This phenomenon is due
solely to the peculiarity that the movements of rotation and revolution
are accomplished in rigorously equal periods, a phenomenon which,
according to Cassini and Herschel, is common to the satellites of
Jupiter, and, very probably to the other satellites.

Some well-disposed but rather unyielding minds did not quite understand
at first how, if the moon invariably shows the same face to the earth
during her revolution, she describes one turn round herself in the same
period of time. To such it was answered--"Go into your dining-room, and
turn round the table so as always to keep your face towards the centre;
when your circular walk is ended you will have described one circle
round yourselves, since your eye will have successively traversed every
point of the room. Well, then, the room is the heavens, the table is the
earth, and you are the moon!"

And they go away delighted with the comparison.

Thus, then, the moon always presents the same face to the earth; still,
to be quite exact, it should be added that in consequence of certain
fluctuations from north to south and from west to east, called
libration, she shows rather more than the half of her disc, about 0.57.

When the ignoramuses knew as much as the director of the Cambridge