“Capital!” cried the major; “but do you know that, at nine
dollars a pound, this projectile will cost—-”
“One hundred and seventy-three thousand and fifty dollars ($173,050).
I know it quite well. But fear not, my friends; the money will not
be wanting for our enterprise. I will answer for it. Now what say
you to aluminum, gentlemen?”
“Adopted!” replied the three members of the committee. So ended
the first meeting. The question of the projectile was
definitely settled.
CHAPTER VII
HISTORY OF THE CANNON
The resolutions passed at the last meeting produced a great
effect out of doors. Timid people took fright at the idea of
a shot weighing 20,000 pounds being launched into space; they
asked what cannon could ever transmit a sufficient velocity to
such a mighty mass. The minutes of the second meeting were
destined triumphantly to answer such questions. The following
evening the discussion was renewed.
“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, to-day is
with the dimensions of the cannon.”
“Now, up to the present time,” said Barbicane, “our longest guns
have not exceeded twenty-five 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?”
“Ordinarily the length of a gun is twenty to twenty-five times
the diameter of the shot, and its weight two hundred and
thirty-five to two hundred and forty times that of the shot.”
“That is not enough,” cried J. T. Maston impetuously.
“I agree with you, my good friend; and, in fact, following this
proportion for a projectile nine feet in diameter, weighing 30,000
pounds, the gun would only have a length of two hundred and twenty-
five feet, and a weight of 7,200,000 pounds.”
“Ridiculous!” rejoined Maston. “As well take a pistol.”