CHAPTER II.
HOW CAN WE GET TO THE OTHER PLANETS?
The next evening promised well, and I kept my appointment, butunfortunately a slight haze gathered in the sky and prevented us frommaking further observations. While hoping in vain for it to clear away,Professor Gazen and I talked over the possibility of journeying to otherworlds. The gist of our argument was afterwards published in aconversation, entitled "Can we reach the other planets?" which appearedin _The Day after To-morrow_. It ran as follows:
_I_. (_the writer_). "Do you think we shall ever be able to leave theearth and travel through space to Mars or Venus, and the other membersof 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 beenaccounted miracles in ancient times."
_G_. "No doubt, and hence people are apt to suppose that science can doeverything; 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 wetry."
_G_. "Not always; but in this case I think we know. The celestial bodiesare evidently isolated in space, and the tenants of one cannot pass toanother. We are confined to our own planet."
_I_. "A similar objection might have been urged against the plan ofColumbus."
_G_. "That was different. Columbus only sailed through unknown seas to adistant continent. We are free to explore every nook and cranny of theearth, but how shall we cross the immense void which parts us fromanother world, except on the wings of the imagination?"
_I_. "Great discoveries and inventions are born of dreams. There areminds which can foresee what lies before us, and the march of sciencebrings it within our reach. All or nearly all our great scientificvictories have been foretold, and they have generally been achieved bymore than one person when the time came. The telescope was a dream forages, so was the telephone, steam and electric locomotion, aerialnavigation. Why should we scout the dream of visiting other worlds,which is at least as old as Lucian? Ere long, and perhaps before thecentury is out, we shall be flying through the air to the variouscountries of the globe. In succeeding centuries what is to hinder usfrom travelling through space to different planets?"
_G_. "Quite impossible. Consider the tremendous distance--the lifelessvacuum--that separates us even from the moon. Two hundred and fortythousand miles of empty space."
_I_. "Some ten times round the world. Well, is that tremendous vacuumabsolutely impassable?"
_G_. "To any but Jules Verne and his hero, the illustrious Barbicane,president of the Gun Club."[1]
[Footnote 1: _The Voyage a la Lune_, by Jules Verne.]
_I_. "Jules Verne has an original mind, and his ideas, thoughextravagant, are not without value. Some of them have been realised, andit may be worth while to examine his notion of firing a shot from theearth to the moon. The projectile, if I remember, was an aluminium shellin the shape of a conical bullet, and contained three men, a dog or two,and several fowls, together with provisions and instruments. It was airtight, warmed and illuminated with coal gas, and the oxygen forbreathing was got from chlorate of potash, while the carbonic acidproduced by the lungs and gas-burners was absorbed with caustic potashto keep the air pure. This bullet-car was fired from a colossalcast-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 ofgun-cotton was calculated to give the projectile a velocity sufficientto carry it past the 'dead-point,' where the gravity of the earth uponit was just balanced by that of the moon, and enable it to fall towardsthe moon for the rest of the way. The sudden shock of the discharge onthe car and its occupants was broken by means of spring buffers andwater 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 likeseven miles a second."
_I_. "His estimate was too high. An initial velocity of 9,000 yards, orfive miles a second, would carry a projectile beyond the sensibleattraction of the earth towards the moon, the planets, or anywhere; inshort, to an infinite distance. Indeed, a slightly lower velocity wouldsuffice in the case of the moon, owing to her attraction."
_G_. "But how are we to give the bullet that velocity? I believe thehighest velocity obtained from a single discharge of cordite, one of ourbest explosives, was rather less than 4,000 feet, or only aboutthree-quarters of a mile per second. With such a velocity, theprojectile would simply rise to a great height and then fall back to theground."
_I_. "Both of these drawbacks can be overcome. We are not limited to asingle discharge. Dr. S. Tolver Preston, the well-known writer onmolecular science, has pointed out that a very high velocity can be gotby the use of a compound gun, or, in other words, a gun which firesanother gun as a projectile.[2] Imagine a first gun of enormousdimensions loaded with a smaller gun, which in turn is loaded with thebullet. The discharge of the first gun shoots the second gun into theair, with a certain velocity. If, now, the second gun, at the instant itleaves the muzzle of the first, is fired automatically, say byutilising the first discharge to press a spring which can react on ahammer or needle, the bullet will acquire a velocity due to bothdischarges, and equivalent to the velocity of the second gun at the timeit was fired plus the velocity produced by the explosion of its owncharge. In this way, by employing a series of guns, fired from eachother in succession, we can graduate the starting shock, and give thebullet a final velocity sufficient to raise it against gravity, and theresistance of the atmosphere, which grows less as it advances, and sendit 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, butit 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 therequired velocity. In the air-gun or cannon, as you probably know, aquantity of air, compressed within a chamber of the breech, is allowedsuddenly 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 verylong barrel, and a series of air chambers at intervals from the breechto the muzzle. Each of these chambers, beginning at the breech, could beopened in turn as the bullet passed along the barrel, so that everyescaping jet of gas would give it an additional impulse."
_G._ (_with growing interest_). "That sounds neater. You might work thechambers by electricity."
_I_. "We could even have an electric gun. Conceive a bobbin wound withinsulated wire in lieu of thread, and having the usual hole through theaxis 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 softiron placed at one end will be sucked into the hole. In this experimentwe have the germ of a solenoid cannon. The bobbin stands for thegun-barrel, the plug for the bullet-car, and the magnetism for theejecting force. We can arrange the wire and current so as to draw theplug or car right through the hole or barrel, and if we have a series ofsolenoids end to end in one straight line, we can switch the currentthrough each in succession, and send the projectile with gatheringvelocity through the interior of them all. In practice the barrel wouldconsist of a long straight tube, wide and strong enough to contain thebullet-car without flexure, and begirt with giant solenoids atintervals. Each of the solenoids would be excited by a powerful current,one after the other, so as to urge the projectile with acceleratingspeed along the tube, and launch it into the vast."
_G_. "That looks still better than the pneumatic gun."
_I_. "A magnetic gun would have seve
ral advantages. For instance, thecurrents can be sent through the solenoids in turn as quickly as wedesire by means of a commutator in a convenient spot, for instance, atthe butt end of the gun, so as to follow up the bullet with ease, andgive it a planetary flight. By a proper adjustment of the solenoids andcurrents, this could be done so gradually as to prevent a starting shockto the occupants of the car. The velocity attained by the car would, ofcourse, depend on the number and power of the solenoids. If, forexample, each solenoid communicated to the car a velocity of nine yardsper second, a thousand solenoids, each magnetically stronger thananother in going from breech to muzzle, would be required to give afinal velocity of five miles a second. In such a case, the length of thebarrel would be at least 1,000 yards. Economy and safety would determinethe best proportions for the gun, but we are now considering thefeasibility of the project, not its cost. With regard to position andsupports, the gun might be constructed along the slope of a hill ormound steep enough to give it the angle or elevation due to the aim. Asthe barrel would not have to resist an explosive force, it should not bedifficult to make, and the inside could be lubricated to diminish thefriction of the projectile in passing through it. Moreover, it isconceivable that the car need never touch the sides, for by a properadjustment of the magnetism of the solenoids we might suspend it inmid-air like Mahomet's coffin, and make it glide along the magnetic axisof the tube."
_G_. "It seems a promising idea for an actual gun, or an electricdespatch 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 alsomagnetise the car, say by surrounding it with a coil of wire excitedfrom an accumulator on board. The car, of course, would be hermeticallysealed, but it would have doors and windows which could be opened atpleasure. In open space it would be warmed and lighted by the sun, andin 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 interiorcould be lined with a non-conductor. Liquefied oxygen or air forbreathing, and condensed fare would sustain the inmates; and on thewhole they might enjoy a comfortable passage through the void, takingscientific observations, and talking over their experiences."
_G_. "It would be a novel observatory, quite free from atmospherictroubles. They might be able to make some astronomical discoveries."
_I_. "A novel laboratory as well, for in space beyond the attraction ofthe earth there would be no gravity. The travellers would not feel asense of weight, but as the change would be gradual they would getaccustomed 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, andanything put overboard would neither fall nor rise, but simply floatalongside. 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 mighthit the moon, with its large disc and comparatively short range,provided no wandering meteorite diverted the bullet from its course; butit would be impossible to hit a planet, such as Venus or Mars, a merepoint of light, and thirty or forty million miles away, especially asboth the earth and planet are in rapid motion. A flying rifle-shot froma lightning express at a distant swallow would have more chance ofsuccess. If you missed the mark, the projectile would wheel round theplanet, and either become its satellite or return towards the earth likethat of Jules Verne in his fascinating romance."
_I_. "Jules Verne, and other writers on this subject, appear to haveassumed that all the initial effort should come from the cannon. Perhapsit did not suit his literary purpose to employ any other driving force.At all events he possessed one in the rockets of Michel Ardan, thegenial Frenchman of the party, which were intended to break the fall ofthe projectile on the moon."
_G_. "If I recollect, they were actually fired to give the car a fillipwhen it reached the dead-point on its way back to the earth."
_I_. "Even in a vacuum, where an ordinary propeller could not act, thebullet may become a prime mover, and co-operate with the gun. A rocketcan burn without an atmosphere, and the recoil of the rushing fumes willimpel the car onwards."
_G_. "Do you think a rocket would have sufficient power to be of anyservice?"
_I_. "Ten or twelve large rockets, capable of exerting a united backpressure of one and a half tons during five or six minutes on a car ofthat weight at the earth's surface, would give it in free space avelocity of two miles a second, which, of course, would not be lost byfriction."
_G_. "So that it would not be absolutely necessary to give theprojectile an initial velocity of five miles a second."
_I_. "No; and, besides, we are not solely dependent on the rocket. A jetof gas, at a very high pressure, escaping from an orifice into thevacuum or ether, would give us a very high propelling force. Bycompressing air, oxygen, or coal-gas (useful otherwise) in ironcylinders with closed vents, which could be opened, we should have astore of energy serviceable at any time to drive the car. In this way apressure or thrust of several tons on the square inch might be appliedto the car as long as we had gas to push it forwards."
_G_. "Certainly, and by applying the pressure, whether from the rocketor 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 youwanted to go."
_I_. "Moreover, beyond the range of gravitation, we could steer andtravel by pumping out the respired air, or occasionally projecting apebble from the car through a stuffing box in the wall, or else byfiring a shot from a pistol."
_G_. "You might even have a battery of machine guns on board, anddecimate the hosts of heaven."
_I_. "Our bullets would fly straight enough, anyhow, and I suppose theywould hit something in course of time."
_G_. "If they struck the earth they would be solemnly registered asfalling stars."
_I_. "Certainly they would be burnt up in passing through the atmosphereof a planet and do no harm to its inhabitants."
_G_. "Well, now, granting that you could propel the car, and thatalthough your gun was badly aimed you could steer towards a planet, howlong would the journey take?"
_I_. "The self-movement of the car would enable us to save time, whichis a matter of the first importance on such a trip. In the plan of JulesVerne, the bullet derives all its motion from the initial effort, andconsequently 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 couldmaintain the velocity of the car, however, we should accomplish thedistance in thirteen hours at a speed of five miles a second, and moreor less in proportion."
_G_. "About as long as the journey from London to Aberdeen by rail. Whatabout Mars or Venus?"
_I_. "At the same speed we should cover the 36,000,000 miles to theseplanets in 2,000 hours, or 84 days, that is, about three months. With aspeed of ten miles a second, which is not impossible, we could reachthem 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 notafraid you will be dissipated like a meteorite by the intense heat offriction with the planet's atmosphere, or else be smashed to atoms bythe 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. Theatmosphere of the approaching planet would act as a kind of buffer, andthe fall of the car could be further checked by our means of recoil, andalso by a large parachute. We should probably be able to descend quiteslowly 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 fromthe car when it was nearing the ground."
_G_. "I
presume you are taking into account the velocity of the planetin its orbit? That of the earth is 18 miles a second, or a hundred timesfaster than a rifle bullet; that of Venus, which is nearer the sun, is afew miles more; and that of Mars, which is further from the sun, israther less."
_I_. "For that reason the more distant planets would be preferable toland on. Uranus, for instance, has an orbital velocity of four miles asecond, and his gravity is about three-fourths that of the earth.Moreover, his axis lies almost exactly on the plane of the ecliptic, sothat we could choose a waiting place on his orbit where the line of hisaxis lay in the direction of his motion, and simply descend on one ofhis poles, at which the stationary atmosphere would not whirl the car,and where we might also profit by an ascending current of air. Theattraction of the sun is so slight at the distance of Uranus, that astone flung out of the car would have no perceptible motion, as itwould 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, oneounce 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 oneand a half tons at rest on the orbit of the planet. Indeed, the vitiatedair, escaping from the car through a small hole by its own pressure,would probably serve the purpose. Just before the planet came up, and inthe nick of time we could fire some rockets, and give the car a velocityof 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 asafe descent. Our parachutes would be out, and at the first contact withthe atmosphere, the car would probably be blown away; but it would soonacquire the velocity of the planet, and gradually sink downwards to thesurface."
_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, bothMars and Venus are inhabited by intelligent beings, we should probablybe able to construct another cannon and return the way we came."
_G_. (_smiling_). "Well, I confess the project does not look soimpracticable as it did. After all, travelling in a vacuum seems ratherpleasant. One of these days, I suppose, we astronomers will be packed inbullets and fired into the ether to observe eclipses and comets' tails."
_I_. "In all that has been said we have confined ourselves to ways andmeans already known; but science is young, and we shall probablydiscover new sources of energy. It may even be possible to dispense withthe gun, and travel in a locomotive car. Lord Kelvin has shown that ifLessage's hypothesis of gravitation be correct, a crystal or other bodymay be found which is lighter along one axis than another, and thus wemay be able to draw an unlimited supply of power from gravity by simplychanging the position of the crystal; for example, by raising it whenlighter, and letting it fall when heavier. This form of 'perpetualmotion' might be equally obtainable if Dr. Preston's[3] theory of anether as the cause of gravity be true. Indeed, Professor Poynting is nowengaged in searching for such a crystal, which, if discovered, willupset the second law of thermo-dynamics. I merely mention this to showthat science is on the track of concealed motive powers derived fromthe ether, and we cannot now tell what the engines of the future will belike. For ought we know, the time is coming when there will be a regularmail service between the earth and Mars or Venus, cheap trips toMercury, and exploring expeditions to Jupiter, Saturn, or Uranus."
[Footnote 3: _Philosophical Magazine_, February, 1895.]