G. "Not always; but in this case I think we know. The celestial bodies are evidently isolated in space, and the tenants of one cannot pass to another. We are confined to our own planet."
I. "A similar objection might have been urged against the plan of Columbus."
G. "That was different. Columbus only sailed through unknown seas to a distant continent. We are free to explore every nook and cranny of the earth, but how shall we cross the immense void which parts us from another world, except on the wings of the imagination?"
I. "Great discoveries and inventions are born of dreams. There are minds which can foresee what lies before us, and the march of science brings it within our reach. All or nearly all our great scientific victories have been foretold, and they have generally been achieved by more than one person when the time came. The telescope was a dream for ages, so was the telephone, steam and electric locomotion, aerial navigation. Why should we scout the dream of visiting other worlds, which is at least as old as Lucian? Ere long, and perhaps before the century is out, we shall be flying through the air to the various countries of the globe. In succeeding centuries what is to hinder us from travelling through space to different planets?"
G. "Quite impossible. Consider the tremendous distance—the lifeless vacuum—that separates us even from the moon. Two hundred and forty thousand miles of empty space."
I. "Some ten times round the world. Well, is that tremendous vacuum absolutely impassable?"
G. "To any but Jules Verne and his hero, the illustrious Barbicane, president of the Gun Club."[1]
[1] The Voyage à la Lune, by Jules Verne.
I. "Jules Verne has an original mind, and his ideas, though extravagant, are not without value. Some of them have been realised, and it may be worth while to examine his notion of firing a shot from the earth to the moon. The projectile, if I remember, was an aluminium shell in the shape of a conical bullet, and contained three men, a dog or two, and several fowls, together with provisions and instruments. It was air tight, warmed and illuminated with coal gas, and the oxygen for breathing was got from chlorate of potash, while the carbonic acid produced by the lungs and gas-burners was absorbed with caustic potash to keep the air pure. This bullet-car was fired from a colossal cast-iron gun founded in the sand. It was aimed at a point in the sky, the zenith, in fact, where it would strike the moon four days later, that is, after it had crossed the intervening space. The charge of gun-cotton was calculated to give the projectile a velocity sufficient to carry it past the 'dead-point,' where the gravity of the earth upon it was just balanced by that of the moon, and enable it to fall towards the moon for the rest of the way. The sudden shock of the discharge on the car and its occupants was broken by means of spring buffers and water pressure."
G. "The last arrangement was altogether inadequate."
I. "It was certainly a defect in the scheme."
G. "Besides, the initial velocity of the bullet to carry it beyond the 'dead-point,' was, I think, 12,000 yards a second, or something like seven miles a second."
I. "His estimate was too high. An initial velocity of 9,000 yards, or five miles a second, would carry a projectile beyond the sensible attraction of the earth towards the moon, the planets, or anywhere; in short, to an infinite distance. Indeed, a slightly lower velocity would suffice in the case of the moon, owing to her attraction."
G. "But how are we to give the bullet that velocity? I believe the highest velocity obtained from a single discharge of cordite, one of our best explosives, was rather less than 4,000 feet, or only about three-quarters of a mile per second. With such a velocity, the projectile would simply rise to a great height and then fall back to the ground."
I. "Both of these drawbacks can be overcome. We are not limited to a single discharge. Dr. S. Tolver Preston, the well-known writer on molecular science, has pointed out that a very high velocity can be got by the use of a compound gun, or, in other words, a gun which fires another gun as a projectile.[2] Imagine a first gun of enormous dimensions loaded with a smaller gun, which in turn is loaded with the bullet. The discharge of the first gun shoots the second gun into the air, with a certain velocity. If, now, the second gun, at the instant it leaves the muzzle of the first, is fired automatically, say 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."
[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