Though the Arcadians pretended
they had inhabited the earth at an epoch before the moon existed, though
Simplicius believed her immovable and fastened to the crystal vault,
though Tacitus looked upon her as a fragment broken off from the solar
orbit, and Clearch, the disciple of Aristotle, made of her a polished
mirror upon which were reflected the images of the ocean—though, in
short, others only saw in her a mass of vapours exhaled by the earth, or
a globe half fire and half ice that turned on itself, other savants,
by means of wise observations and without optical instruments, suspected
most of the laws that govern the Queen of Night.
Thus Thales of Miletus, B.C. 460, gave out the opinion that the moon was
lighted up by the sun. Aristarchus of Samos gave the right explanation
of her phases. Cleomenus taught that she shone by reflected light.
Berose the Chaldean discovered that the duration of her movement of
rotation was equal to that of her movement of revolution, and he thus
explained why the moon always presented the same side. Lastly,
Hipparchus, 200 years before the Christian era, discovered some
inequalities in the apparent movements of the earth's satellite.
These different observations were afterwards confirmed, and other
astronomers profited by them. Ptolemy in the second century, and the
Arabian Aboul Wefa in the tenth, completed the remarks of Hipparchus on
the inequalities that the moon undergoes whilst following the undulating
line of its orbit under the action of the sun. Then Copernicus, in the
fifteenth century, and Tycho Brahe, in the sixteenth, completely exposed
the system of the world and the part that the moon plays amongst the
celestial bodies.
At that epoch her movements were pretty well known, but very little of
her physical constitution was known. It was then that Galileo explained
the phenomena of light produced in certain phases by the existence of
mountains, to which he gave an average height of 27,000 feet.
After him, Hevelius, an astronomer of Dantzig, lowered the highest
altitudes to 15,000 feet; but his contemporary, Riccioli, brought them
up again to 21,000 feet.
Herschel, at the end of the eighteenth century, armed with a powerful
telescope, considerably reduced the preceding measurements. He gave a
height of 11,400 feet to the highest mountains, and brought down the
average of different heights to little more than 2,400 feet. But
Herschel was mistaken too, and the observations of Schroeter, Louville,
Halley, Nasmyth, Bianchini, Pastorff, Lohrman, Gruithuysen, and
especially the patient studies of MM. Boeer and Moedler, were necessary
to definitely resolve the question. Thanks to these savants, the
elevation of the mountains of the moon is now perfectly known. Boeer and
Moedler measured 1,905 different elevations, of which six exceed 15,000
feet and twenty-two exceed 14,400 feet. Their highest summit towers to a
height of 22,606 feet above the surface of the lunar disc.
At the same time the survey of the moon was being completed; she
appeared riddled with craters, and her essentially volcanic nature was
affirmed by each observation. From the absence of refraction in the rays
of the planets occulted by her it is concluded that she can have no
atmosphere. This absence of air entails absence of water; it therefore
became manifest that the Selenites, in order to live under such
conditions, must have a special organisation, and differ singularly from
the inhabitants of the earth.
Lastly, thanks to new methods, more perfected instruments searched the
moon without intermission, leaving not a point of her surface
unexplored, and yet her diameter measures 2,150 miles; her surface is
one-thirteenth of the surface of the globe, and her volume
one-forty-ninth of the volume of the terrestrial spheroid; but none of
her secrets could escape the astronomers' eyes, and these clever
savants carried their wonderful observations still further.
Thus they remarked that when the moon was at her full the disc appeared
in certain places striped with white lines, and during her phases
striped with black lines. By prosecuting the study of these with greater
precision they succeeded in making out the exact nature of these lines.
They are long and narrow furrows sunk between parallel ridges, bordering
generally upon the edges of the craters; their length varied from ten to
one hundred miles, and their width was about 1,600 yards. Astronomers
called them furrows, and that was all they could do; they could not
ascertain whether they were the dried-up beds of ancient rivers or not.
The Americans hope, some day or other, to determine this geological
question. They also undertake to reconnoitre the series of parallel
ramparts discovered on the surface of the moon by Gruithuysen, a learned
professor of Munich, who considered them to be a system of elevated
fortifications raised by Selenite engineers. These two still obscure
points, and doubtless many others, can only be definitely settled by
direct communication with the moon.
As to the intensity of her light there is nothing more to be learnt; it
is 300,000 times weaker than that of the sun, and its heat has no
appreciable action upon thermometers; as to the phenomenon known as the
"ashy light," it is naturally explained by the effect of the sun's rays
transmitted from the earth to the moon, and which seem to complete the
lunar disc when it presents a crescent form during its first and last
phases.
Such was the state of knowledge acquired respecting the earth's
satellite which the Gun Club undertook to perfect under all its aspects,
cosmographical, geographical, geological, political, and moral.
*
The immediate effect of Barbicane's proposition was that of bringing out
all astronomical facts relative to the Queen of Night. Everybody began
to study her assiduously. It seemed as if the moon had appeared on the
horizon for the first time, and that no one had ever seen her in the sky
before. She became the fashion; she was the lion of the day, without
appearing less modest on that account, and took her place amongst the
"stars" without being any the prouder. The newspapers revived old
anecdotes in which this "Sun of the wolves" played a part; they recalled
the influence which the ignorance of past ages had ascribed to her; they
sang about her in every tone; a little more and they would have quoted
her witty sayings; the whole of America was filled with selenomania.
The scientific journals treated the question which touched upon the
enterprise of the Gun Club more specially; they published the letter
from the Observatory of Cambridge, they commented upon it and approved
of it without reserve.
In short, even the most ignorant Yankee was no longer allowed to be
ignorant of a single fact relative to his satellite, nor, to the oldest
women amongst them, to have any superstitions about her left. Science
flooded them; it penetrated into their eyes and ears; it was impossible
to be an ass—in astronomy.
Until then many people did not know how the distance between the earth
and the moon had been calculated. This fact was taken advantage of to
explain to them that it was done by measuring the parallax of the moon.
If the word "parallax" seemed new to them, they were told it was the
angle formed by two straight lines drawn from either extremity of the
earth's radius to the moon. If they were in doubt about the perfection
of this method, it was immediately proved to them that not only was the
mean distance 234,347 miles, but that astronomers were right to within
seventy miles.
To those who were not familiar with the movements of the moon, the
newspapers demonstrated daily that she 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.
1 comment