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