HOW CAN WE GET TO THE OTHER PLANETS?
The next evening promised well, and I kept my appointment, but unfortunately a slight haze gathered in the sky and prevented us from making further observations. While hoping in vain for it to clear away, Professor Gazen and I talked over the possibility of journeying to other worlds. The gist of our 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."
 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. 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."
 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 course, would be hermetically sealed, but it would have doors and windows which could be opened at pleasure. In open space it would be warmed and lighted by the sun, and in the shadow of a planet, if need were, by coal-gas and electricity. In either case, to temper the extremes of heat or cold, the interior could be lined with a non-conductor. Liquefied oxygen or air for breathing, and condensed fare would sustain the inmates; and on the whole they might enjoy a comfortable passage through the void, taking scientific observations, and talking over their experiences."
G. "It would be a novel observatory, quite free from atmospheric troubles. They might be able to make some astronomical discoveries."
I. "A novel laboratory as well, for in space beyond the attraction of the earth there would be no gravity. The travellers would not feel a sense of weight, but as the change would be gradual they would get accustomed to it, and suffer no inconvenience."
G. "They would keep their gravity in losing it."
I. "The car, meeting with practically no resistance in the ether, would tend to move in the same direction with the same velocity, and anything put overboard would neither fall nor rise, but simply float alongside. When the car came within the sensible attraction of the moon, its velocity would gradually increase as they approached each other."
G. "Always supposing the aim of the gun to have been exact. You might hit the moon, with its large disc and comparatively short range, provided no wandering meteorite diverted the bullet from its course; but it would be impossible to hit a planet, such as Venus or Mars, a mere point of light, and thirty or forty million miles away, especially as both the earth and planet are in rapid motion. A flying rifle-shot from a lightning express at a distant swallow would have more chance of success. If you missed the mark, the projectile would wheel round the planet, and either become its satellite or return towards the earth like that of Jules Verne in his fascinating romance."
I. "Jules Verne, and other writers on this subject, appear to have assumed that all the initial effort should come from the cannon. Perhaps it did not suit his literary purpose to employ any other driving force. At all events he possessed one in the rockets of Michel Ardan, the genial Frenchman of the party, which were intended to break the fall of the projectile on the moon."
G. "If I recollect, they were actually fired to give the car a fillip when it reached the dead-point on its way back to the earth."
I. "Even in a vacuum, where an ordinary propeller could not act, the bullet may become a prime mover, and co-operate with the gun. A rocket can burn without an atmosphere, and the recoil of the rushing fumes will impel the car onwards."
G. "Do you think a rocket would have sufficient power to be of any service?"
I. "Ten or twelve large rockets, capable of exerting a united back pressure of one and a half tons during five or six minutes on a car of that weight at the earth's surface, would give it in free space a velocity of two miles a second, which, of course, would not be lost by friction."
G. "So that it would not be absolutely necessary to give the projectile an initial velocity of five miles a second."
I. "No; and, besides, we are not solely dependent on the rocket. A jet of gas, at a very high pressure, escaping from an orifice into the vacuum or ether, would give us a very high propelling force. By compressing air, oxygen, or coal-gas (useful otherwise) in iron cylinders with closed vents, which could be opened, we should have a store of energy serviceable at any time to drive the car. In this way a pressure or thrust of several tons on the square inch might be applied to the car as long as we had gas to push it forwards."
G. "Certainly, and by applying the pressure, whether from the rocket or the gas, to the front and sides, as well as to the rear of the car, you would be able to regulate the speed, and direct the car wherever you wanted to go."
I. "Moreover, beyond the range of gravitation, we could steer and travel by pumping out the respired air, or occasionally projecting a pebble from the car through a stuffing box in the wall, or else by firing a shot from a pistol."
G. "You might even have a battery of machine guns on board, and decimate the hosts of heaven."
I. "Our bullets would fly straight enough, anyhow, and I suppose they would hit something in course of time."
G. "If they struck the earth they would be solemnly registered as falling stars."
I. "Certainly they would be burnt up in passing through the atmosphere of a planet and do no harm to its inhabitants."
G. "Well, now, granting that you could propel the car, and that although your gun was badly aimed you could steer towards a planet, how long would the journey take?"
I. "The self-movement of the car would enable us to save time, which is a matter of the first importance on such a trip. In the plan of Jules Verne, the bullet derives all its motion from the initial effort, and consequently slows down as it rises against the earth's attraction, until it begins again to quicken under the gravitation of the moon. Hence his voyage to our satellite occupied four days. As we could maintain the velocity of the car, however, we should accomplish the distance in thirteen hours at a speed of five miles a second, and more or less in proportion."
G. "About as long as the journey from London to Aberdeen by rail. What about Mars or Venus?"
I. "At the same speed we should cover the 36,000,000 miles to these planets in 2,000 hours, or 84 days, that is, about three months. With a speed of ten miles a second, which is not impossible, we could reach them in six weeks."
G. "One could scarcely go round the world in the same time. But, having got to a planet, how are you going to land on it? Are you not afraid you will be dissipated like a meteorite by the intense heat of friction with the planet's atmosphere, or else be smashed to atoms by the shock?"
I. "We might steer by the stars to a point on the planet's orbit, mathematically fixed in advance, and wait there until it comes up. The atmosphere of the approaching planet would act as a kind of buffer, and the fall of the car could be further checked by our means of recoil, and also by a large parachute. We should probably be able to descend quite slowly to the surface in this way without damage; but in case of peril, we could have small parachutes in readiness as life-buoys, and leap from the car when it was nearing the ground."
G. "I presume you are taking into account the velocity of the planet in its orbit? That of the earth is 18 miles a second, or a hundred times faster than a rifle bullet; that of Venus, which is nearer the sun, is a few miles more; and that of Mars, which is further from the sun, is rather less."
I. "For that reason the more distant planets would be preferable to land on. Uranus, for instance, has an orbital velocity of four miles a second, and his gravity is about three-fourths that of the earth. Moreover, his axis lies almost exactly on the plane of the ecliptic, so that we could choose a waiting place on his orbit where the line of his axis lay in the direction of his motion, and simply descend on one of his poles, at which the stationary atmosphere would not whirl the car, and where we might also profit by an ascending current of air. The attraction of the sun is so slight at the distance of Uranus, that a stone flung out of the car would have no perceptible motion, as it would only fall towards the sun a mere fraction of an inch per second, or some 355 feet an hour; hence, as Dr. Preston has calculated, one ounce of matter ejected from the car towards the sun every five minutes, with a velocity of 880 feet a second, would suffice to keep a car of one and a half tons at rest on the orbit of the planet. Indeed, the vitiated air, escaping from the car through a small hole by its own pressure, would probably serve the purpose. Just before the planet came up, and in the nick of time we could fire some rockets, and give the car a velocity of two or three miles a second in the direction of the planet's motion, so that he would overtake us, with a speed not over great to ensure a safe descent. Our parachutes would be out, and at the first contact with the atmosphere, the car would probably be blown away; but it would soon acquire the velocity of the planet, and gradually sink downwards to the surface."
G. "What puzzles me is how you are to get back to the earth."
I. "Whoever goes must take the risk; but if, as appears likely, both Mars and Venus are inhabited by intelligent beings, we should probably be able to construct another cannon and return the way we came."
G. (smiling). "Well, I confess the project does not look so impracticable as it did. After all, travelling in a vacuum seems rather pleasant. One of these days, I suppose, we astronomers will be packed in bullets and fired into the ether to observe eclipses and comets' tails."
I. "In all that has been said we have confined ourselves to ways and means already known; but science is young, and we shall probably discover new sources of energy. It may even be possible to dispense with the gun, and travel in a locomotive car. Lord Kelvin has shown that if Lessage's hypothesis of gravitation be correct, a crystal or other body may be found which is lighter along one axis than another, and thus we may be able to draw an unlimited supply of power from gravity by simply changing the position of the crystal; for example, by raising it when lighter, and letting it fall when heavier. This form of 'perpetual motion' might be equally obtainable if Dr. Preston's theory of an ether as the cause of gravity be true. Indeed, Professor Poynting is now engaged in searching for such a crystal, which, if discovered, will upset the second law of thermo-dynamics. I merely mention this to show that science is on the track of concealed motive powers derived from the ether, and we cannot now tell what the engines of the future will be like. For ought we know, the time is coming when there will be a regular mail service between the earth and Mars or Venus, cheap trips to Mercury, and exploring expeditions to Jupiter, Saturn, or Uranus."