"If you want to know how to propel spaceships,” began Harry, "and mark you, I’m not saying anything one way or the other about the existence of flying saucers—then you must forget magnetism. You must go straight to gravity—that’s the basic force of the universe, after all. But it’s going to be a tricky force to handle, and if you don’t believe me just listen to what happened only last year to a scientist down in Australia. I shouldn’t really tell you this, I suppose, because I’m not sure of its security classification, but if there’s any trouble I’ll swear that I never said a word.
"The Aussies, as you may know, have always been pretty hot on scientific research, and they had one team working on fast reactors—those house-broken atomic bombs which are so much more compact than the old uranium piles. The head of the group was a bright but rather impetuous young nuclear physicist I’ll call Dr. Cavor. That, of course, wasn’t his real name, but it’s a very appropriate one. You’ll all recollect, I’m sure, the scientist Cavor in Wells’ First Men in the Moon, and the wonderful gravity-screening material cavorite he discovered?
"I’m afraid dear old Wells didn’t go into the question of cavorite very thoroughly. As he put it, it was opaque to gravity just as a sheet of metal is opaque to light. Anything placed above a horizontal sheet of cavorite, therefore, became weightless and floated up into space.
"Well, it isn’t as simple as that. Weight represents energy—an enormous amount of it—which can’t just be destroyed without any fuss. You’d have to put a terrific amount of work into even a small object in order to make it weightless. Antigravity screens of the cavorite type, therefore, are quite impossible—they’re in the same class as perpetual motion.”
"Three" of my friends have made perpetual motion machines,” began our unwanted visitor rather stuffily. Harry didn’t let him get any further: he just steamed on and ignored the interruption.
"Now, our Australian Dr. Cavor wasn’t searching for antigravity, or anything like it. In pure science, you can be pretty sure that nothing fundamental is ever discovered by anyone who’s actually looking for it—that’s half the fun of the game. Dr. Cavor was interested in producing atomic power: what he found was antigravity. And it was quite some time before he realised that was what he’d discovered.
"What happened, I gather, was this: The reactor was of a novel and rather daring design, and there was quite a possibility that it might blow up when the last pieces of fissile material were inserted. So it was assembled by remote control in one of Australia’s numerous convenient deserts, all the final operations being observed through TV sets.
"Well, there was no explosion—which would have caused a nasty radioactive mess and wasted a lot of money, but wouldn’t have damaged anything except a lot of reputations. What actually happened was much more unexpected, and much more difficult to explain.
"When the last piece of enriched uranium was inserted, the control rods pulled out, and the reactor brought up to criticality—everything went dead. The meters in the remote control room, two miles from the reactor, all dropped back to zero. The TV screen went blank. Cavor and his colleagues waited for the bang, but there wasn’t one. They looked at each other for a moment with many wild surmises: then, without a word, they climbed up out of the buried control chamber.
'The reactor building was completely unchanged: it sat out there in the desert, a commonplace cube of brick holding a million pounds’ worth of fissile material and several years of careful design and development. Cavor wasted no time: he grabbed the Jeep, switched on a portable Geiger counter, and hurried off to see what had happened.
"He recovered consciousness in hospital a couple of hours later. There was little wrong with him apart from a bad headache, which was nothing to the one his experiment was going to give him during the next few days. It seemed that when he got to within twenty feet of the reactor, his Jeep had hit something with a terrific crash. Cavor had got tangled in the steering wheel and had a nice collection of bruises: the Geiger counter, oddly enough, was quite undamaged and was still clucking away quietly to itself, detecting no more than the normal cosmic-ray background.
"Seen from a distance, it had looked a perfectly normal sort of accident, that might have been caused by the Jeep going into a rut. But Cavor hadn’t been driving all that fast, luckily for him; and anyway there was no rut at the scene of the crash. What the Jeep had run into was something quite impossible. It was an invisible wall, apparently the lower rim of a hemispherical dome, which entirely surrounded the reactor. Stones thrown up in the air slid back to the ground along the surface of this dome, and it also extended underground as far as digging could be carried out. It seemed as if the reactor was at the exact center of an impenetrable, spherical shell.
"Of course, this was marvellous news and Cavor was out of bed in no time, scattering nurses in all directions. He had no idea what had happened, but it was a lot more exciting than the humdrum piece of nuclear engineering that had started the whole business.
"By now you’re probably all wondering what the devil a sphere of force—as you science-fiction writers would call it—has to do with antigravity. So I’ll jump several days and give you the answers that Cavor and his team discovered only after much hard work and the consumption of many gallons of that potent Australian Beer.
'The reactor, when it had been energised, had somehow produced an antigravity field. All the matter inside a twenty-foot-radius sphere had been made weightless, and the enormous amount of energy needed to do this had been extracted, in some utterly mysterious manner, from the uranium in the pile. Calculations showed that the amount of energy in the reactor was just sufficient to do the job.' Presumably the sphere of force would have been larger still if there had been more ergs available in the power source.
”1 can hear someone just waiting to ask a question, so I’ll anticipate them. Why didn’t this weightless sphere of earth and air float up into space? Well, the earth was held together by its cohesion, anyway, so there was no reason why it should go wandering off. As for the air, that was forced to stay inside the zone of zero gravity for a most surprising and subtle reason which leads me to the crux of this whole peculiar business.
"Better fasten your seat belts for the next bit: we’ve got a bumpy passage ahead. Those of you who know something about potential theory won’t have any trouble, and I’ll do my best to make it as easy as I can for the rest.
"People who talk glibly about antigravity seldom stop to consider its implications, so let’s look at a few fundamentals. As I’ve already said, weight implies energy—lots of it. That energy is entirely due to Earth’s gravity field. If you remove an objects weight, that’s precisely equivalent to taking it clear outside Earth’s gravity. And any rocket engineer will tell you how much energy that requires.”
Harry turned to me and said: 'There’s an analogy I’d like to borrow from one of your books, Arthur, that puts across the point I’m trying to make. You know—comparing the fight against Earth’s gravity to climbing out of a deep pit.”
"You’re welcome,” I said. "I pinched it from Doc Richardson, anyway.”
"Oh,” replied Harry. "I thought it was too good to be original. Well, here we go. If you hang on to this really very simple idea, you’ll be O.K. To take an object clear away from the Earth requires as much work as lifting it four thousand miles against the steady drag of normal gravity. Now, the matter inside Cavor’s zone of force was still on the Earth’s surface, but it was weightless. From the energy point of view, therefore, it was outside the Earth’s gravity field. It was inaccessible as if it was on top of a four-thousand-mile-high mountain.
"Cavor could stand outside the antigravity zone
and look into it from a point a few inches away. To cross those few inches, he would have to do as much work as if he climbed Everest seven hundred times. It wasn’t surprising that the Jeep stopped in a hurry. No material object had stopped it, but from the point of view of dynamics it had run smack into a cliff four thousand miles
high.....
"I can see some blank looks that are not entirely due to the lateness of the hour. Never mind: if you don’t get all this, just take my word for it. It won’t spoil your appreciation of what follows—at least, I hope not.
"Cavor had realised at once that he had made one of the most important discoveries of the age, though it was some time before he worked out just what was going on. The final clue to the antigravitational nature of the field came when they shot a rifle bullet into it and observed the trajectory with a high-speed camera. Ingenious, don’t you think?
"The next problem was to experiment with the field’s generator and to find just what had happened inside the reactor when it had been switched on. This was a problem indeed. The reactor was there in plain sight, twenty feet away. But to reach it would require slightly more energy than going to the Moon..... _
"Cavor was not disheartened by this, nor by the inexplicable failure of the reactor to respond to any of its remote controls. He theorised that it had been completely drained of energy, if one can use a rather misleading term, and that little if any power was needed to maintain the antigravity field once it had been set up. This was one of the many things that could only be determined by examination on the spot. So by hook or by crook, Dr. Cavor would have to go there.
"His first idea was to use an electrically driven trolley, supplied with power through cables which it dragged behind it as it advanced into the field. A hundred-horsepower generator, running continuously for seventeen hours, would supply enough energy to take a man of average weight on the perilous twenty-foot journey. A velocity of slightly over a foot an hour did not seem much to boast about, until you remembered that advancing one foot into the antigravity field was equivalent to a two-hundred-mile vertical climb.
'The theory was sound, but in practice the electric trolley wouldn’t work. It started to push its way into the field, but began to skid after it had traversed half an inch. The reason was obvious when one started to think about it. Though the power was there, the traction wasn’t. No wheeled vehicle could climb a gradient of two hundred miles per foot.
"This minor setback did not discourage Dr. Cavor. The answer, he realised at once, was to produce the traction at a point outside the field. When you wanted to lift a load vertically, you didn’t use a cart: you used a jack or an hydraulic ram.
"The result of this argument was one of the oddest vehicles ever built. A small but comfortable cage, containing sufficient provisions to last a man for several days, was mounted at the end of a twenty-foot-long horizontal girder. The whole device was supported off the ground by balloon tires, and the theory was that the cage could be pushed right into the centre of the field by a machine which would remain outside its influence. After some thought, it was decided that the best prime mover would be the common or garden bulldozer.
"A test was made with some rabbits in the passenger compartment—and I can’t help thinking that there was an interesting psychological point here. The experimenters were trying to get it both ways: as scientists they’d be pleased if their subjects got back alive, and as Australians they’d be just as happy if they got back dead. But perhaps I’m being a little too fanciful.... (You know, of course, how Australians feel about rabbits.)
"The bulldozer chugged away hour after hour, forcing the weight of the girder and its insignificant payload up the enormous gradient. It was an uncanny sight—all this energy being expended to move a couple of rabbits twenty feet across a perfectly horizontal plain. The subjects of the experiment could be observed throughout the operation: they seemed to be perfectly happy and quite unaware of their historic r61e.
"The passenger compartment reached the centre of the field, was held there for an hour, and then the girder was slowly backed out again. The rabbits were alive, in good health, and to nobody’s particular surprise there were now six of them.
"Dr. Cavor, naturally, insisted on being the first human being to venture into a zero-gravity field. He loaded up the compartment with torsion balances, radiation detectors, and periscopes so that he could look into the reactor when he finally got to it. Then he gave the signal, the bulldozer started chugging, and the strange journey began.
"There was, naturally, telephone communication from the passenger compartment to the outside world. Ordinary sound waves couldn’t cross the barrier, for reasons which were still a little obscure, but radio and telephone both worked without difficulty. Cavor kept up a running commentary as he was edged forward into the field, describing his own reactions and relaying instrument readings to his colleagues.
"The first thing that happened to him, though he had expected it, was nevertheless rather unsettling. During the first few inches of his advance, as he moved through the fringe of the field, the direction of the vertical seemed to swing around. 'Up’ was no longer toward the sky: it was now in the direction of the reactor hut. To Cavor, it felt as if he was being pushed up the face of a vertical cliff, with the reactor twenty feet above him. For the first time, his eyes and his ordinary human senses told him the same story as his scientific training. He could see that the centre of the field was, gravitywise, higher than the place from which he had come. However, imagination still boggled at the thought of all the energy it would need to climb that innocent-looking twenty feet, and the hundreds of gallons of diesel fuel that must be burned to get him there.
"There was nothing else of interest to report on the journey itself, and at last, twenty hours after he had started, Cavor arrived at his destination. The wall of the reactor hut was right beside him, though to him it seemed not a wall but an unsupported floor sticking out at right angles from the cliff up which he had risen. The entrance was just above his head, like a trapdoor through which he would have to climb. This would present no great difficulty, for Dr. Cavor was an energetic young man, extremely eager to find just how he had created this miracle.
"Slightly too eager, in fact. For as he tried to work his way into the door, he slipped and fell off the platform that had carried him there.
"That was the last anyone ever saw of him—but it wasn’t the last they heard of him. Oh dear no! He made a very big noise indeed.....
"You’ll see why when you consider the situation in which this unfortunate scientist now found himself. Hundreds of kilowatt-hours of energy had been pushed into him—enough to lift him to the Moon and beyond. All that work had been needed to take him to a point of zero gravitational potential. As soon as he lost his means of support, that energy began to reappear. To get back to our earlier and very picturesque analogy—the poor doctor had slipped off the edge of the four-thousand-mile-high mountain he had ascended.
"He fell back the twenty feet that had taken almost a day to climb. 'Ah, what a fall was there, my countrymen!’ It was precisely equivalent, in terms of energy, to a free drop from the remotest stars down to the surface of the Earth. And you all know how much velocity an object acquires in that fall. It’s the same velocity that’s needed to get it there in the first place—the famous velocity of escape. Seven miles a second, or twenty-five thousand miles an hour.
"That’s what Dr. Cavor was doing by the time he got back to his starting point. Or to be more accurate, that’s the speed he involuntarily tried to reach. As soon as he passed Mach 1 or 2, however, air resistance began to have its little say. Dr. Cavor’s funeral pyre was the finest, and indeed the only, meteor display ever to take place entirely at sea level.....
"I’m sorry that this story hasn’t got a happy ending. In fact, it hasn’t got an ending at all, because that sphere of zero gravitational potential is still sitting there in the Australian desert, apparently doing nothing at all but in fact producing ever-increasing amounts of frustration in scientific and official circles. I don’t see how the authorities can hope to keep it secret much longer. Sometimes I think how odd it is that the world’s tallest mountain is in Australia—and that though it’s four thousand miles high the airliners often fly right over it without knowing it’s there.”
That is why the sequel seems a little unfair. A month later, someone brought a very odd publication to one of our meetings. It was nicely printed and laid out with professional skill, the misuse of which was sad to behold. The thing was called Flying Saucer Revelations—and there on the front page was a full and detailed account of the story Purvis had told us. It was printed absolutely straight—and what was much worse than that, from poor Harry’s point of view, was that it was attributed to him by name.
Since then he has had 4,375 letters on the subject, most of them from California: 24 called him a liar; 4,205 believed him absolutely. (The remaining ones he couldn’t decipher and their contents still remain a matter of speculation.)
I’m afraid he’s never quite got over it, and I sometimes think he’s going to spend the rest of his life trying to stop people believing the one story he never expected to be taken seriously.
There may be a moral here. For the life of me I can’t find it.
Arthur C. Clarke’s famous collection, Tales from the White Hart, was apparently inspired in part by Dunsany’s Jorkens series, quite independently of the Pratt and de Camp series about Gavagan’s Bar.
Tales From the Spaceport Bar Page 5
