A Trip to Venus | Page 7

and the resistance of the atmosphere, which grows less as it advances, and send it
away to the moon or some other distant orb."
[Footnote 2: _Engineering_, January 13th, 1893.]
G. "Your spit-fire mode of progression is well enough in theory, but it strikes me as just a
little complicated and risky. I, for one, shouldn't care to emulate Elijah and shoot up to
Heaven in that style."
I. "If it be all right in theory, it will be all right in practice. However, instead of
explosives we might employ compressed air to get the required velocity. In the air-gun or
cannon, as you probably know, a quantity of air, compressed within a chamber of the
breech, is allowed suddenly to expand behind the bullet and eject it from the barrel. Now,
one might manage with a simple gun of this sort, provided it had a very long barrel, and a
series of air chambers at intervals from the breech to the muzzle. Each of these chambers,
beginning at the breech, could be opened in turn as the bullet passed along the barrel, so
that every escaping jet of gas would give it an additional impulse."
_G._ (_with growing interest_). "That sounds neater. You might work the chambers by

electricity."
I. "We could even have an electric gun. Conceive a bobbin wound with insulated wire in
lieu of thread, and having the usual hole through the axis of the frame. If a current of
electricity be sent through the wire, the bobbin will become a hollow magnet or
'solenoid,' and a plug of soft iron placed at one end will be sucked into the hole. In this
experiment we have the germ of a solenoid cannon. The bobbin stands for the gun-barrel,
the plug for the bullet-car, and the magnetism for the ejecting force. We can arrange the
wire and current so as to draw the plug or car right through the hole or barrel, and if we
have a series of solenoids end to end in one straight line, we can switch the current
through each in succession, and send the projectile with gathering velocity through the
interior of them all. In practice the barrel would consist of a long straight tube, wide and
strong enough to contain the bullet-car without flexure, and begirt with giant solenoids at
intervals. Each of the solenoids would be excited by a powerful current, one after the
other, so as to urge the projectile with accelerating speed along the tube, and launch it
into the vast."
G. "That looks still better than the pneumatic gun."
I. "A magnetic gun would have several advantages. For instance, the currents can be sent
through the solenoids in turn as quickly as we desire by means of a commutator in a
convenient spot, for instance, at the butt end of the gun, so as to follow up the bullet with
ease, and give it a planetary flight. By a proper adjustment of the solenoids and currents,
this could be done so gradually as to prevent a starting shock to the occupants of the car.
The velocity attained by the car would, of course, depend on the number and power of the
solenoids. If, for example, each solenoid communicated to the car a velocity of nine yards
per second, a thousand solenoids, each magnetically stronger than another in going from
breech to muzzle, would be required to give a final velocity of five miles a second. In
such a case, the length of the barrel would be at least 1,000 yards. Economy and safety
would determine the best proportions for the gun, but we are now considering the
feasibility of the project, not its cost. With regard to position and supports, the gun might
be constructed along the slope of a hill or mound steep enough to give it the angle or
elevation due to the aim. As the barrel would not have to resist an explosive force, it
should not be difficult to make, and the inside could be lubricated to diminish the friction
of the projectile in passing through it. Moreover, it is conceivable that the car need never
touch the sides, for by a proper adjustment of the magnetism of the solenoids we might
suspend it in mid-air like Mahomet's coffin, and make it glide along the magnetic axis of
the tube."
G. "It seems a promising idea for an actual gun, or an electric despatch and parcel post, or
even a railway. The bullet, I suppose, would be of iron."
I. "Probably; but aluminium is magnetic in a lower degree than iron, and its greater
lightness might prove in its favour. We might also magnetise the car, say by surrounding
it with a coil of wire excited from an accumulator on board. The car, of