by utilising the first discharge to press a spring which can react on a hammer or needle, the bullet will acquire a velocity due to both discharges, and equivalent to the velocity of the second gun at the time it was fired plus the velocity produced by the explosion of its own charge.  In this way, by employing a series of guns, fired from each other in succession, we can graduate the starting shock, and give the bullet a final velocity sufficient to raise it against gravity, 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.”