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."[1]
[Footnote 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."
[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."
_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[3] 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."
[Footnote 3: _Philosophical Magazine_, February, 1895.]