Read From the Earth to the Moon; and, Round the Moon for Free Online Page B

which touched upon the enterprise of the Gun Club.
The letter of the Observatory of Cambridge was published by them,
and commented upon with unreserved approval.
    Until that time most people had been ignorant of the mode in which
the distance which separates the moon from the earth is calculated.
They took advantage of this fact to explain to them that this
distance was obtained by measuring the parallax of the moon.
The term parallax proving "caviare to the general," they further
explained that it meant the angle formed by the inclination of two
straight lines drawn from either extremity of the earth's radius
to the moon. On doubts being expressed as to the correctness of
this method, they immediately proved that not only was the mean
distance 234,347 miles, but that astronomers could not possibly
be in error in their estimate by more than seventy miles either way.
    To those who were not familiar with the motions of the moon,
they demonstrated that she possesses two distinct motions, the
first being that of rotation upon her axis, the second being
that of revolution round the earth, accomplishing both together
in an equal period of time, that is to say, in twenty-seven and
one-third days.
    The motion of rotation is that which produces day and night on
the surface of the moon; save that there is only one day and one
night in the lunar month, each lasting three hundred and
fifty-four and one-third hours. But, happily for her, the face
turned toward the terrestrial globe is illuminated by it with an
intensity equal to that of fourteen moons. As to the other
face, always invisible to us, it has of necessity three hundred
and fifty-four hours of absolute night, tempered only by that
"pale glimmer which falls upon it from the stars."
    Some well-intentioned, but rather obstinate persons, could not
at first comprehend how, if the moon displays invariably the
same face to the earth during her revolution, she can describe
one turn round herself. To such they answered, "Go into your
dining-room, and walk round the table in such a way as to always
keep your face turned toward the center; by the time you will
have achieved one complete round you will have completed one
turn around yourself, since your eye will have traversed
successively every point of the room. Well, then, the room is
the heavens, the table is the earth, and the moon is yourself."
And they would go away delighted.
    So, then the moon displays invariably the same face to the
earth; nevertheless, to be quite exact, it is necessary to add
that, in consequence of certain fluctuations of north and south,
and of west and east, termed her libration, she permits rather
more than half, that is to say, five-sevenths, to be seen.
    As soon as the ignoramuses came to understand as much as the
director of the observatory himself knew, they began to worry
themselves regarding her revolution round the earth, whereupon
twenty scientific reviews immediately came to the rescue.
They pointed out to them that the firmament, with its infinitude
of stars, may be considered as one vast dial-plate, upon which the
moon travels, indicating the true time to all the inhabitants of
the earth; that it is during this movement that the Queen of
Night exhibits her different phases; that the moon is full when she is in opposition with the sun, that is when the three
bodies are on the same straight line, the earth occupying the
center; that she is new when she is in conjunction with the
sun, that is, when she is between it and the earth; and, lastly
that she is in her first or last quarter, when she makes
with the sun and the earth an angle of which she herself occupies
the apex.
    Regarding the altitude which the moon attains above the horizon,
the letter of the Cambridge Observatory had said all that was to
be said in this respect. Every one knew that this altitude
varies according to the latitude of the observer. But the only
zones of the globe in which the moon passes the zenith, that is,
the point