s 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 as