argument was afterwards published in a conversation, entitled "Can we reach the other planets?" which appeared in The Day after To-morrow. It ran as follows:

I. (the writer). "Do you think we shall ever be able to leave the earth and travel through space to Mars or Venus, and the other members of the Solar System?"

G. (Checking an impulse to smile and shaking his head), "Oh, no! Never."

I. "Yet science is working miracles, or what would have been accounted miracles in ancient times."

G. "No doubt, and hence people are apt to suppose that science can do everything; but after all Nature has set bounds to her achievements."

I. "Still, we don't know what we can and what we cannot do until we try."

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]

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."

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