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possesses two distinct movements,
the first being that of rotation upon her axis, the second that of
revolution round the earth, accomplishing both in the same time—that is
to say, in 27-1/3 days.
    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
Observatory about the moon's movement of rotation they began to make
themselves uneasy about her movement of revolution round the earth, and
twenty scientific reviews quickly gave them the information they wanted.
They then learnt that the firmament, with its infinite stars, may be
looked upon as a vast dial upon which the moon moves, indicating the
time to all the inhabitants of the earth; that it is in this movement
that the Queen of Night shows herself in her different phases, that she
is full when she is in opposition with the sun—that is to say, when the
three bodies are on a line with each other, the earth being in the
centre; that the moon is new when she is in conjunction with the
sun—that is to say, when she is between the sun and the earth; lastly,
that the moon is in her first or last quarter when she makes, with the
sun and the earth, a right angle of which she occupies the apex.
    Some perspicacious Yankees inferred in consequence that eclipses could
only take place at the periods of conjunction or opposition, and their
reasoning was just. In conjunction the moon can eclipse the sun, whilst
in opposition it is the earth that can eclipse him in her turn; and the
reason these eclipses do not happen twice in a lunar month is because
the plane upon which the moon moves is elliptical like that of the
earth.
    As to the height which the Queen of Night can attain above the horizon,
the letter from the Observatory of Cambridge contained all that can be
said about it. Every one knew that this height varies according to the
latitude of the place where the observation is taken. But the only zones
of the globe where the moon reaches her zenith—that is to say, where
she is directly above the heads of the spectators—are necessarily
comprised between the 28th parallels and the equator. Hence the
important recommendation given to attempt the experiment upon some point
in this part of the globe, in order that the projectile may be hurled
perpendicularly, and may thus more quickly escape the attraction