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"My dear colleagues," said Barbicane, without further preamble,
"the subject now before us is the construction of the engine,
its length, its composition, and its weight. It is probable
that we shall end by giving it gigantic dimensions; but however
great may be the difficulties in the way, our mechanical genius
will readily surmount them. Be good enough, then, to give me
your attention, and do not hesitate to make objections at the close.
I have no fear of them. The problem before us is how to communicate
an initial force of 12,000 yards per second to a shell of 108
inches in diameter, weighing 20,000 pounds. Now when a projectile
is launched into space, what happens to it? It is acted upon by
three independent forces: the resistance of the air, the attraction
of the earth, and the force of impulsion with which it is endowed.
Let us examine these three forces. The resistance of the air is of
little importance. The atmosphere of the earth does not exceed
forty miles. Now, with the given rapidity, the projectile will
have traversed this in five seconds, and the period is too brief
for the resistance of the medium to be regarded otherwise than
as insignificant. Proceding, then, to the attraction of the earth,
that is, the weight of the shell, we know that this weight will
diminish in the inverse ratio of the square of the distance.
When a body left to itself falls to the surface of the earth, it
falls five feet in the first second; and if the same body were
removed 257,542 miles further off, in other words, to the distance
of the moon, its fall would be reduced to about half a line in the
first second. That is almost equivalent to a state of perfect rest.
Our business, then, is to overcome progressively this action
of gravitation. The mode of accomplishing that is by the force
of impulsion."
"There's the difficulty," broke in the major.
"True," replied the president; "but we will overcome that, for
the force of impulsion will depend on the length of the engine
and the powder employed, the latter being limited only by the
resisting power of the former. Our business, then, today is
with the dimensions of the cannon."
"Now, up to the present time," said Barbicane, "our longest guns
have not exceeded twentyfive feet in length. We shall
therefore astonish the world by the dimensions we shall be
obliged to adopt. It must evidently be, then, a gun of great
range, since the length of the piece will increase the detention
of the gas accumulated behind the projectile; but there is no
advantage in passing certain limits."
"Quite so," said the major. "What is the rule in such a case?"
