In any case it will be remarked that this measurement
of shadows, intervals, or profiles can only be made
when the solar rays strike the moon obliquely in relation
to the observer. When they strike her directly—in
a word, when she is full—all shadow is imperiously
banished from her disc, and observation is no longer
possible.
Galileo, after recognising the existence of the lunar
mountains, was the first to employ the method of calculating
their heights by the shadows they throw. He attributed
to them, as it has already been shown, an average
of 9,000 yards. Hevelius singularly reduced these
figures, which Riccioli, on the contrary, doubled.
All these measures were exaggerated. Herschel,
with his more perfect instruments, approached nearer
the hypsometric truth. But it must be finally
sought in the accounts of modern observers.
Messrs. Boeer and Moedler, the most perfect selenographers
in the whole world, have measured 1,095 lunar mountains.
It results from their calculations that 6 of these
mountains rise above 5,800 metres, and 22 above 4,800.
The highest summit of the moon measures 7,603 metres;
it is, therefore, inferior to those of the earth,
of which some are 1,000 yards higher. But one
remark must be made. If the respective volumes
of the two orbs are compared the lunar mountains are
relatively higher than the terrestrial. The lunar
ones form 1/70 of the diameter of the moon, and the
terrestrial only form 1/140 of the diameter of the
earth. For a terrestrial mountain to attain the
relative proportions of a lunar mountain, its perpendicular
height ought to be 6-1/2 leagues. Now the highest
is not four miles.
Thus, then, to proceed by comparison, the chain of
the Himalayas counts three peaks higher than the lunar
ones, Mount Everest, Kunchinjuga, and Dwalagiri.
Mounts Doerfel and Leibnitz, on the moon, are as high
as Jewahir in the same chain. Newton, Casatus,
Curtius, Short, Tycho, Clavius, Blancanus, Endymion,
the principal summits of Caucasus and the Apennines,
are higher than Mont Blanc. The mountains equal
to Mont Blanc are Moret, Theophylus, and Catharnia;
to Mount Rosa, Piccolomini, Werner, and Harpalus;
to Mount Cervin, Macrobus, Eratosthenes, Albateque,
and Delambre; to the Peak of Teneriffe, Bacon, Cysatus,
Philolaus, and the Alps; to Mount Perdu, in the Pyrenees,
Roemer and Boguslawski; to Etna, Hercules, Atlas,
and Furnerius.
Such are the points of comparison that allow the appreciation
of the altitude of lunar mountains. Now the trajectory
followed by the projectile dragged it precisely towards
that mountainous region of the southern hemisphere
where rise the finest specimens of lunar orography.
TYCHO.
At 6 p.m. the projectile passed the South Pole at
less than thirty miles, a distance equal to that already
reached at the North Pole. The elliptical curve
was, therefore, being rigorously described.
