ending more and more of his time in Koltukhov's resin laboratory. He liked making new compounds according to Koltukhov's formulas and measuring the electricity in the charged resins. One day Koltukhov sent Yura over to Opratin's laboratory to charge the latest batch of resin. Opratin greeted Yura pleasantly, showed him the electrostatic machine, and helped him to switch it on. Yura looked about with curiosity. There were several people in white overalls at work in the laboratory. One of them, a thickset man with a shaggy head of hair, sat with his back to Yura, at a table on which an aquarium with a wire coil round it and a valve oscillator stood. "Are you doing high frequency experiments?" he asked casually. "Oh, that's just a minor project," Opratin replied with a keen glance at Yura. "Are you interested in high frequencies?" "No, not particularly." A tall, husky man in blue overalls entered the laboratory. To Yura's surprise, this was Uncle Vova Bugrov. "Comrade Benedictov, here's the food for your fish," Bugrov said to Anatole Benedictov in a deep, hoarse voice. The shaggy-haired man sitting beside the valve oscillator turned round, nodded, and took the two paper bags Bugrov was holding out to him. Yura was unable to shift his gaze from the man's broad face and puffy eyelids. "Why, hullo," said Bugrov shaking Yura's hand. "What brings you to our Institute?" "Do you work here?" Yura asked in surprise, his eyes still fixed on Benedictov. "I'm a laboratory technician. I've switched to science now. They think very highly of me here. You know, I'm training a group of scientific workers in wrestling." "What does Benedictov do here?" Yura asked in a low voice. "Benedictov? He's a scientist. He knows all there is to know about fish. Shall I tell you what else I'm doing?" Bugrov asked boastfully. "I'm an inventor, if you want to know. I'm making an electric dynamometer. What d'you think of that?" After charging the resin Yura rushed back to his own Institute and ran up the stairs two at a time. "There's news, Nikolai," he shouted. Panting, he told Nikolai about seeing Benedictov, about the valve oscillator and about Vova Bugrov. Nikolai ran the palm of his hand across his high forehead. "High frequency- and fish? I wonder- But Opratin is studying the level of the Caspian, isn't he?" "Benedictov's the man to ask about the iron boxes." "You think he'd tell you?" During the lunch break Nikolai remained in the deserted laboratory. Sitting at his desk, he cut a thin strip from the sheet of drawing paper on his board. He pinned one end to the desk, twisted the other in a half-curl, and glued the ends together. He sat for a long time staring, in deep thought, at the twisted piece of paper. Then, with a pencil, he drew a line along the edge of the paper until it came full circle. The line ran round both sides of the strip of paper, without Nikolai either lifting his pencil from the paper or crossing the pencil line at any point. This strip of paper was the model of a mathematical paradox known as the Mobius band. From the mathematical point of view the band had no thickness and its surface was not divided into outer and inner surfaces. It was only a surface, and nothing more. A window that mathematics had opened up into the sphere of the Unknown. Nikolai made a second strip twisted in the same direction and tried to put it inside the first one, but this proved to be impossible. By trying to put one strip into another he would have to bring the inner surface of one towards the outer surface of the other. But if neither had an outer surface or an inner surface how could he do this? Nikolai flung the strips on the table and propped up his head on his hand. "What if I made a similar spiral out of copper and linked it up to the output circuit of an oscillator?" He went out to the lounge, pulled Yura away from a game of table tennis, and said: "Do you remember a thing called the Mobius band?" CHAPTER THREE IN WHICH THE SAME BRIGHT IDEA, NECESSITATING FEDOR MATVEYEV'S KNIFE, OCCURS TO BENEDICTOV AND OPRATIN "At last!" Opratin exclaimed, running his eyes across the letter, which was typed on an official letterhead. Ever since summer, Opratin's imagination had been fired by the letters A M D G on Benedictov's box that had contained the missing knife. When Benedictov showed him the box Opratin had immediately recalled the old underground passage in Derbent, the crucifix on the chest of the skeleton, and, lying beside it, the small flat box on a golden chain, with the letters A M D G engraved on it. From what Pavel Koltukhov had said Opratin now knew that there were three boxes, and that the third box, the one in Derbent, contained some sort of "key to the mystery". Opratin had written a number of cautious letters, first to Derbent and then to Moscow, after learning that the agent's equipment had been sent there. Now the long-awaited reply was in his hands. The agent had been a submarine officer in the Italian Tenth Torpedo-Boat Flotilla, notorious for its sudden raids on British naval bases with mines guided by frogmen. Part of the Tenth Flotilla had been transferred to the Crimea in 1942. When the Nazis broke through to the North Caucasus part of the Flotilla had concentrated submarines and frogmen-guided torpedoes at Mariupol on the Sea of Azov for transfer to the Caspian Sea. Vittorio da Castiglione, an officer of the Tenth Flotilla, parachuted down onto the Caspian coast near Derbent on a dark autumn night. His mission had probably been to reconnoitre the underwater approaches to the port of Derbent and note installations that could be attacked with guided torpedoes. But he had wandered into an old quarry and had perished there. Nobody would ever have learned about Vittorio da Castiglione if Opratin had not stumbled over him. "To recapitulate," Opratin said to himself, "one box contained Fedor Matveyev's manuscript and another the knife. But what was in the third box? Probably something very important that would throw light on the entire mystery." Well, he'd soon know what it was all about. Nikolai Opratin rubbed his hands in satisfaction. The Institute of Marine Physics was making preparations to raise the level of the Caspian Sea. This undertaking was based on the extremely simple proposition that a heavy rain can produce one and a half millimetres of precipitation in one minute. If rain poured down constantly on an area of thirty square kilometres of the Caspian day in and day out, the level of the sea would rise three metres in the course of a year. Water for the downpours would have to be "borrowed" from the Black Sea, where there were plans to build a powerful nuclear water boiler. A new Soviet method of obtaining nuclear energy made such an installation possible. As a gigantic fountain of steam gushed forth from the depths of the Black Sea a system of directional antennae would force the endless grey cloud to snake its way over the Caucasus Mountains. On reaching the downpour area in the Caspian Sea the cloud would enter the zone of a powerful electrostatic field. Here the concentrated steam would lose its heat, be converted into water, and pour down on the sea. Laboratory No. 8 was setting up cloud condensation experiments, and this kept Opratin, as head of the laboratory, very busy indeed. The installation had given him a good many sleepless nights. Erection of the installation on a remote, uninhabited island in the Caspian was nearing completion. Opratin was personally supervising the operations. He had in mind certain other plans that were linked up with this installation. The two new members of the staff introduced a somewhat disharmonious note into the carefully planned arrangements in Opratin's laboratory. Shaggy-haired, absent-minded Anatole Benedictov spilled reagents from bottles on the tables, broke a great many vessels and often caused short circuits. He argued with Opratin in a loud voice. Yet Opratin was patient with him, and this was what aroused the greatest astonishment. With Benedictov's arrival the "fish problem" suddenly loomed large in the Institute programme. At any rate, it occupied all the best places in the corridors, for that was where Anatole Benedictov had set up his aquariums. He plagued the assistant manager in charge of supplies with demands for various types of food for his fish. Feeding the fish was one of the duties of the new lab technician, a husky, rosy-cheeked man with slits for eyes and a tuft of reddish hair on top of his head. This was Vova Bugrov. Bugrov very soon felt quite at home in the world of scientific research. As one watched him puttering about beside the spectrograph, softly humming a popular tune, one felt that the delicate cassettes were doomed. "I wonder why Opratin ever took this chap on as a technician," staff members asked one another. "He looks more like a gangster than anything else." To everyone's surprise, though, the new technician turned out to have a light touch; his huge paws handled the precise instruments gently and deftly. Bugrov could do a marvellous soldering job. He put great effort into developing the spectrograms, and he kept a detailed journal (with spelling mistakes in it, true) of the functioning of the various lab instruments and machines. This was more than even Opratin had expected from Bugrov. The motorboat skimmed across the bay towards the open sea. Prow lifted high, it left behind a pair of long, spreading, foamy moustaches. It was a calm, sunny morning in October, with a slight chill in the air. Bugrov, his cap pulled down over his forehead, sat beside the outboard motor. Suddenly he pricked up his ears. Above the steady roar of the motor he caught snatches of an interesting conversation. "No, I don't think they know about the knife," said Nikolai Opratin. "Then why did they come asking to see me?" Anatole Benedictov retorted. "They asked questions, Rita says, about three small iron boxes. But why three? One contained the knife; in the other, you say, they found a manuscript. But where does a third box come from?" "That's my business." Opratin wrapped his raincoat more closely round him. Benedictov tried to light a cigarette but every time he struck a match the wind blew it out. He swore as he kept tossing matches into the water. On reaching the island they guided the boat into a cove with a gently sloping shore. Bugrov cut the motor and nimbly jumped out onto the damp sand. He tied the painter to a length of pipe he had driven into the sand on an earlier visit to the island. Here, on this desolate little island, Laboratory No. 8 of the Institute of Marine Physics had set up an experiment facility. Two months ago a blunt-nose self-propelled barge had pulled its flat belly up onto the sandy shore, and a tractor, followed by a crane on crawler treads, had rolled out of its dark interior with much clanging. An old concrete pillbox built on the island during the war had been converted into a pilot plan for cloud condensation. Benedictov and Opratin climbed to the top of the low but steep rise and disappeared inside the former pillbox. Bugrov remained on the shore. He walked up and down the sand for a while to stretch his legs, then sat down on a rock to think. There was plenty to think about. For two months now he had been punching the clock, something he had never done before in his life- and what was he getting out of it? Where was the knife for which he had agreed to take on the job of lab technician? It was becoming embarrassing. Friends were laughing at him. A steady, full-time job, of all things! In science, too! It was time he gave up working like a horse, they said. Bugrov couldn't have agreed with them more. He would give it up-just as soon as he finished his dynamometer. It would be a beauty! All you'd have to do was step on the footboard and flex your muscles, and the machine would show you how strong you were. There would be no lights or bells, like in the ordinary dynamometers. This one was strictly scientific. All of a sudden Bugrov grew angry with himself. What was he thinking about? The knife was what he needed! Then he would be able to tour provincial towns with an astonishing knife act. He scrambled up the rise and approached the pillbox. After opening the inclining steel door he entered an underground passageway lined with shelves holding storage cells. The passageway led into a round room with a domed ceiling. An internal combustion engine stood there. From this room Bugrov passed through a narrow doorway into what had once been the casemate. The room was crowded with laboratory equipment. Red-hot filaments glowed in an electric fireplace. Nikolai Opratin and Anatole Benedictov sat at a table under a bright light. Bugrov marched to the middle of the room and stood there, hands in pockets, his padded jacket flung open. His face wore an insolent expression. "You promised me the knife," he said. "When will it be ready?" Opratin drummed his fingers on the table. "Look here," he said in an even voice, "if you get on my nerves you'll never lay eyes on the knife at all. Can't you see we haven't set up all the equipment yet? Be patient." "I'm patient, all right," Bugrov replied defiantly. "Too patient, in fact. I'm just warning you. You'd better speed things up." "That will do. Instead of complaining you could put your energies to better use by tinkering with the power generator. You're the one who will be servicing it." Bugrov pushed his cap to the back of his head and left the room. The mutiny on the island had been put down. "I can't see why you have anything to do with that gorilla," Benedictov remarked. Opratin shook his head. "Rank ingratitude, I call it. That gorilla is the person who gets you those ampoules you're so fond of." Benedictov said nothing. "He's right. We'll have to speed things up," Opratin went on. "We won't be here alone forever. We'll have to start work on cloud condensation as well, and that means researchers will be coming here to work. I shan't allow them to see the equipment in the room below, of course, but still- Anyway, I have an idea." He told Benedictov of his talk with Pavel Koltukhov, about the episode mentioned in Fedor Matveyev's manuscript and about the electrets. "Don't you see? The Hindus may very well have used electrets as a source of energy. Electrets have a peculiar property to which I have given a great deal of thought." "Namely?" "A shift in polarity. Sometimes an electret begins to lose its charge within a few hours. The charge drops to zero and then increases again, but now the positive and negative poles have changed places. An electret with altered poles will exist for an indefinite time. Sometimes this happens and sometimes it doesn't. W7hat changes take place in the substance of the electret? What is this zero threshold across which its charge passes? That's the question." "A magnet magnetizes other substances without losing its properties. An electret charges other substances without losing its charge," said Benedictov. He was speaking with his eyes closed, concentrating on his words. "Splendid! That confirms my idea. What we must do is set up an installation in which the knife will transmit the charge. The knife will charge other bodies with its properties, will remake their structure to resemble its own. To put it more exactly, the knife will transmit penetrability." Opratin stared at Benedictov in silence for a few seconds. "Transmit penetrability," he repeated in a low voice. "Use the knife as a transducer. That's a brainwave!" Benedictov coughed to clear his throat and then amplified his idea. "It's a brainwave!" Opratin repeated, striding up and down the room. "Do you mean to say we can do it with living material too?" "Exactly. My experiments with fish make me confident of success." Opratin stopped pacing the floor. "To sum up, we'll make an electret with switched polarity that will create a permanent field. We'll intensify the field with a powerful charge of static electricity, using our Van de Graaff generator. We'll set up the installation in such a way as to make the fields intersect. We'll place Fedor Matveyev's knife, the transmitter of the 'charge,' at one intersection and an ultrashort wave radiator at the other. It will be a kind of cage in which we'll put some of your fish, or maybe dogs. Or anything else, for that matter. We'll keep changing the field intensity and keep on experimenting until we hit on just the right angle!" Opratin's eyes sparkled. He was so excited that he could hardly stand still. "Yes, we'll force that knife to transmit its properties to another object!'" Arguing and interrupting each other, the two scientists proceeded to sketch designs of the future installation. Suddenly Benedictov flung aside his pencil and rose, his joints creaking. "The knife," he said. "We must have the knife. We won't get anywhere without it. I don't think you're searching for it the way you should." "I've combed the sea floor at that place three times." Opratin stopped, then added in a lower voice, "Is there any reason why your wife should want to hinder our work?" "Hinder our work? No, although lately she's been urging me to drop my experiments. But that's all. Why do you ask?" ^Because the knife doesn't seem to be at the bottom of the sea. I have a feeling your wife is concealing it." Benedictov's face grew long. "Impossible. Why should she do that?" "Why should she try to persuade you to give up this line of experiments?" Benedictov did not reply. The electric fireplace threw red shadows across his gloomy face. "Never mind, you leave the knife to me," Opratin said. "I'll get it." CHAPTER FOUR IN WHICH VALERY GORBACHEVSKY'S LITTLE FINGER PLAYS THE LEADING PART Nikolai and Yura were now completely engrossed in the enigmatic Mobius band. Their catch-all notebook was filled to overflowing with formulas and sketches of intertwined bands. "Your idea of using one side is marvellous, Nikolai!" Yura exclaimed. "I'm sure the Mobius band will give us the field we need. Imagine! No pipes! A stream of oil flowing straight through the sea!" Yura's enthusiasm was infectious. "I've estimated," Nikolai said, "that doing away with pipes to transport oil across the Caspian would save about 25,000 tons of steel." "But that's not the main thing," Yura said impatiently. "We'll learn to control surfaces. It'll be an epoch-making discovery!" "Now don't let our imagination run away with you," Nikolai remarked. "We aren't in that class at all. With our limited resources we can only set ourselves a limited goal like increasing the surface tension of a drop of mercury. If we succeed we'll try to do the same with oil." Yura grew downcast. "Is that all?" "No, not quite. Don't spread this all over the Institute and don't say anything, meanwhile, to our chief. Is that clear?" "Yes, strictly confidential," Yura said with a sigh. "The Inquisition put the same kind of pressure on Galileo." The evenings in Cooper Lane were now a busier time than ever. Yura and Nikolai had enlisted the services of three young engineers from the automation department, who helped them to assemble intricate electronic circuits. They often blew the fuses and then had to go out with a candle to repair the damage. Luckily, Nikolai's mother was a patient, kind-hearted woman. One day lab technician Valery Gorbachevsky took Yura aside. "Need any help evenings?" he asked. Yura stared at him. "How do you know what we're doing after working hours?" "I'm not deaf, am I?" "All right, drop in tomorrow at eight. Just keep whatever you see under your hat. Don't mention it to Privalov. What we're doing at home is our own private concern." Valery nodded. "After all, Faraday was once a lab technician too." "Faraday? A lab technician?" "That's right. Not here, of course, but at the Royal Institution of Great Britain. As you can see, a big future lies ahead of you." That evening Yura, a guitar slung over his shoulder, strode briskly down Cooper Lane and turned into the courtyard of Nikolai's house. A series of what sounded like gunshots came from the other side of the archway, where a tall, plump woman was beating a carpet. At sight of Yura she gave a broad smile. "Haven't seen you for a long time," she said. "Good evening, Claudia," said Yura. "Is Nikolai throwing a birthday party?" she asked. "Guests keep coming and coming. Young people, all of them." She smiled again. "My Vova is doing scientific research too nowadays." "Well, give him my best regards." Yura smiled politely and ran up the steps two at a time. He flung open a door from behind which came voices and laughter. Everyone was there. Nikolai and the three other young engineers were tinkering with the instruments. They had the efficient assistance of Valery, who never suspected he was destined to be the hero of the day. "What held you up?" asked Nikolai. "Uncle Vova's wife stopped me for a chat and asked me to pass on her very best regards," Yura replied. "Why the guitar?" "I'll sing you some songs." "Stop twaddling. Come on, let's check the connections." "I'll tell you why I brought the guitar." Yura's tone was now serious. "Our tuning-fork generator is made to oscillate by an electromagnet, isn't it? But the electromagnet means an extra magnetic field, in other words, frequencies that we don't need at all. So I thought-" "That's right," swarthy Hussein Amirov put in. "A guitar can do the work more simply than an electromagnet." The installation stood on a big table behind blue draperies. It consisted of the original mercury heart and valve oscillator with a tuning-fork breaker, to which a twist of copper tubing, an enormous Mobius band, had been added. The output circuit of the valve oscillator was connected to coils surrounding the band. The scales containing the mercury heart stood inside the band. The one-sided Mobius band was expected to produce a field which would sharply increase the surface tension of the mercury and squeeze it so hard that it would stop pulsating. Then, by adding mercury until the heart started beating again they would be able to calculate, from the additional weight, the extent to which surface tension had been stepped up. Once they hit on the right combination of frequencies they could start experimenting with oil. Nikolai switched on the battery of capacitors. To do this he had to crawl under the table and disturb Rex, who was sound asleep there. As Yura checked the connections the neon bulb in the handle of his screwdriver glowed with a twinkling pink light from time to time. "All systems functioning," Yura finally declared. "Breaker frequency is 440 hertz." "Ting, ting, ting" went the tuning-fork gently in the silence of the room. Yura hurriedly tuned his guitar. Next they adjusted the tuning-fork breaker by moving the weights on its prongs. Now all they had to do was touch a guitar 'string, and the contacts of the tuning-fork breaker |would begin to break the high-frequency circuit at the rate of 440 times per second. The mercury heart beat quietly inside the mysterious field of the Mobius band. Our experimenters knew, of course, that a long, boring search lay ahead of them. They knew that an experiment rarely yields the desired result the first time. Still, deep down inside there was the hope that perhaps today a miracle would take place. It didn't. "We'll have to vary the operating factors," said Nikolai. "Will you strike B on the tuning-fork, Valery?" Ting-ting-ting. Yura plucked a guitar string.' There was silence, broken suddenly by a sharp knock on the door. "Who could that be?" Nikolai wondered.' "Mother said she wouldn't return home until late." The young men moved away from the installation and drew the draperies to hide it from view. Only Valery, with his tuning-fork, :and Rex remained behind the draperies. "Let's liven up the party!" shouted Yura. He plucked the strings of the guitar, took a few dancing steps, and began to sing: Why do you wander in the moonlight, Oh black-eyed beauty of mine? Powder in your pocket to poison me with, A locomotive in your pocket to crush me with. Nikolai opened the door and Vova Bugrov, in a striped blue pyjama top, came in. "Hullo, everybody," he said politely, letting his eyes roam about the room. His glance rested on the blue draperies and on the scraps of wire scattered on the floor. Then he shook hands with each of the young men in turn. "Having a party?" he asked. "That's fine. I'll take only a minute of your time, Nikolai." He pulled a rusty spring out of his pocket. "Will you calculate its strength, please?" "You said you'd switched to electric dynamometers," said Yura. "So I have," Bugrov replied with dignity. "This is just something-well, to make a long story short, a couple of pals dropped in and asked me to help them." Nikolai quickly measured the diameter of the spring and the wire to which it was attached, and then took out his slide-rule. "Twenty-eight kilograms." "Thanks." Bugrov picked up the spring and moved towards the door. At that moment there was a crash behind the draperies. The young men exchanged glances. Vova swung round and stared at the draperies. Rex emerged from beneath them, his paws tapping the floor. He stretched and then sniffed at Bugrov's shoes. "Go away, dog," said Bugrov, backing towards the door. "I don't like being sniffed at." Nikolai saw Bugrov out and locked the door behind him. Yura struck another few chords to be on the safe side. Strumming the bass strings, he sang: Powder in your pocket to poison me with, A locomotive in your pocket to crush mo with. Nikolai pulled back the draperies. The scales with the mercury heart had crashed to the floor. The tuning-fork generator lay in a pool of solution with sparkling drops of mercury in it. Valery sat on the table, his face as white as a sheet. He was holding up his right hand and was staring in horror at his extended little finger. That evening Boris Privalov and Pavel Koltukhov remained at the Institute long after everyone else had left. "If you don't mind my saying so, Boris, you're going round the bend about that idea of a pipeline without any pipes," said Koltukhov. "Has Professor Bagbanly gone round the bend too?" Koltukhov said nothing. Privalov looked at his watch and stood up. "By the way, he should be here soon. Would you like to see what we're doing?" They went down to the first floor and walked along a seemingly endless corridor. Privalov unlocked the doors of a room in which a stator from a big dynamo stood. Inside the stator, almost touching the pole shoes and windings, was a coil of glass tubing filled with a pink liquid. The ends of the coil were connected with a tank and a centrifugal pump. "It looks like a high-frequency still for making home-brew liquor," Koltukhov said with a laugh, touching the cold glass with the tips of his fingers. "We're doing two experiments with this apparatus," Privalov explained. "The liquid in the tube is water to which we have added acid to make it a conductor and a colouring substance to make it easier to observe. Now watch. This is the first experiment." At the push of a button a faint hum arose as the centrifugal pump began to drive the pink liquid through the glass coil. "The winding of the stator is not connected with the mains," said Privalov. "It's only connected with the voltmeter. Watch this!" The voltmeter needle trembled and crept towards the right-hand side of the dial. "See that?" "Of course. The liquid is a conductor. It cuts the magnetic lines of force of the stator and induces electromotive force in the windings. There's nothing new about that. A meter in which a liquid passes through a tube of non-magnetic material is based on this principle." "That's true, there's nothing new about it. But whereas the voltage in those meters is insignificant, here-" "Oho!" exclaimed Koltukhov, his eyes on the voltmeter. "How did you manage that?" "Professor Bagbanly," Privalov said shortly. "Now we'll do the experiment the other way round." He switched off the pump. The liquid stopped moving and the voltmeter needle returned to "zero". "Now I'll simply send some current into the stator winding." He pushed another button. Although not driven by the pump, the pink liquid again ran up into the spiral. "Let's make it harder." Privalov turned the knob of a valve. "Keep your eye on the pressure-gauge. I could increase the resistance still more and get a higher pressure. But the fragility of the glass tubes prevents me from doing so. Do you see what I'm getting at?" Koltukhov looked puzzled. His eyes stared fixedly from beneath his grey eyebrows. "Wait a minute," he said. "In other words, a liquid in an electromagnetic field starts moving all by itself. Is this a model of the movement of a liquid through a pipeless pipeline?" "Right. The only difference is that the surface tension of the liquid will take the place of pipes, while a directed field will replace the windings and magnets." " 'The only difference' is a mild way of putting it," Koltukhov muttered. They heard quick footsteps in the corridor. The door opened and Professor Bakhtiar Bagbanly entered. "Ah, our main opponent!" he said as he shook hands with Pavel Koltukhov. "Have you come to see for yourself?" "He's sceptical," said Privalov. "Well, that's part of the scientific approach." Professor Bagbanly ran his eyes over the apparatus, then asked Privalov some technical questions about the experiment. He began to pace the room, a short, stocky, large-headed man with thick grey hair. "What examples do we have of mutual penetrability?" he asked suddenly. "Diffusion," said Privalov. "The diffusion of solids." "Yes, but diffusion calls for specific conditions. Even if you press perfectly polished surfaces of lead and tin together very hard, it will take years before even the slightest penetration takes place. However, if you heat a compressed bundle of lead and tin to 100 degrees a layer of intermingled molecules will appear in their border area within twelve hours. What is it that puts up resistance to transition through the contact zone?" The Professor stopped his pacing and gave the two engineers a thoughtful look. "The surface! That mysterious world of two-dimensional phenomena." He resumed his pacing, meanwhile smoothing; with his fingertips, the grey moustaches beneath his hooked nose. "There's another diffusional phenomenon," he went on, "and that is pressure contact welding. It produces mutual penetration, but you need high temperatures and pressures to do it." "What about welding inside a vacuum?" Privalov asked. "It can be done at a very low pressure and without much heating. What is more, you can join the most diverse materials-steel and glass, for instance. Actually, it isn't so much welding as intensified diffusion." Professor Bagbanly nodded in agreement. "Yes, but why? Possibly, because in a vacuum a surface is free and opens up, as it were, since it borders on empty space. The forces protecting the surface weaken and open up the substance. However, our goal is to intensify diffusion until we attain a state of unhindered mutual penetration. Forcing matter to open its gates, isn't that so?" He traced a question mark in the air with his forefinger. "Is there a lot of matter in solids? The answer is no, there's very little. Actually, an atom has a very insignificant volume. But what is the atom filled with? After all, matter is concentrated in the nucleus of the atom. From the standpoint of density, everything under the sun is as sparse as-" he searched for a comparison-" as sparse as the hair on the head of our friend Pavel Koltukhov." Koltukhov gave a smirk and involuntarily ran a hand over his bald head. "Considered from the position of a mechanical model, matter can easily be penetrated," Professor Bagbanly went on. "Actually, though, we cannot regard matter as a mechanical conglomeration of small spheres situated at a great distance from one another. Powerful internal forces connect all the components and prevent penetration. If those forces did not exist my hand would easily pass through metal." He laid the palm of his hand on the stator. "The probability of physical particles meeting is insignificant. Less probable than peas colliding if two handfuls are thrown towards each other." The Professor wiped his hands on his handkerchief and looked at the two men, his former pupils, as though expecting them to make some objections. "Now I'll formulate the problem," he said, in the same tone of voice he had once used when lecturing to his students. "Hang your ears on the hook of attention. Without changing the mechanical structure of matter we must rearrange its bonds-the bonds between atoms and between molecules-in such a manner that they will be completely neutral when they come into contact with ordinary matter during the period of reciprocal penetration. The internal bonds must be re-arranged! Then we'll achieve penetrability." Koltukhov opened his mouth to make a caustic remark, but just then the telephone rang. Privalov picked up the receiver. "Hullo. Yes, this is me. Is that you, Nikolai? Now take it easy-" He listened for a moment. "What?!" His face changed. "I'll be there in a jiffy." He put down the receiver and glanced at Professor Bagbanly. "We must all rush off at once!" When the blue draperies were pulled across that section of the room Valery realized that an uninvited guest had dropped in. He put down the tuning-fork and, to keep himself busy, examined the connections. It was a good thing he did, for he discovered that one of the weights which regulated the frequency of the tuning-fork breaker was loosely attached, and that the scales on which the mercury heart stood had shifted slightly. "From the vibration, no doubt," Valery said to himself. Carefully, with his little finger, he moved the scales inside the Mobius band while he adjusted the weight with his other hand. At the same moment guitar chords sounded on the other side of the blue draperies and Yura's voice burst into song. "An old-fashioned tune," Valery reflected as he continued to move the scales with his finger. All of a sudden he felt a faint quiver in the little finger. "An electric shock?" he wondered. "No, I haven't touched any metal." To be on the safe side, he thrust his little finger into his mouth. How curious! The finger did not feel his mouth, and his mouth did not feel the finger. He stared fearfully at his finger. It looked perfectly normal. He put it into his mouth again. But again there was no sensation whatsoever. He tried biting the tip of the finger. His teeth came together as though there was nothing between them. Remembering that there was a visitor in the house, Valery stifled a scream. "It took an iron will to keep from shouting," he later said. But his body gave a jerk that dislodged the mercury heart from the scales and overturned the tuning-fork breaker. Professor Bagbanly, Boris Privalov and Pavel Koltukhov hurried up the stairs and burst breathlessly into Nikolai's flat. "Where's Valery?" Privalov demanded. Valery, his face pale and covered with sweat, came into the room. Nikolai excitedly told what had happened. Professor Bagbanly touched Valery's little finger. The tip and the joint next to it were penetrable. The Professor's forefinger passed through them easily and touched his thumb. "Feel anything?" he asked. "No," Valery whispered. It was easy to establish where the penetrability ended. "Light a match," said Professor Bagbanly. "Calm down, young man," he added when he saw Nikolai nervously break a couple of matches as he tried to light them. He turned to Valery. "I want you to put the tip of your finger into the flame of Nikolai's match." Everyone held his breath. Valery looked as though he were walking in his sleep. He slowly put his little finger into the flame. It wavered but its shape did not change. "Do you feel anything?" "Yes," said Valery hoarsely, holding the tip of his finger in the flame. "My fingertip feels warm." The engineers were dumbstruck. They stared in a daze at Valery's little finger. "Thrust your finger into the table," the professor said. Valery obeyed. Half of his finger went into the wood. "Less goes in now," he said. "At first almost the whole finger went in." Professor Bagbanly exchanged glances with Privalov. Then he set about examining the apparatus. "A Mobius band?" he said. "Quite an idea. What did the instruments register when it happened?" "We weren't thinking about penetrability," Yura explained. "We wanted to increase surface tension, using this mercury heart. Valery must have put his hands inside the Mobius band a dozen times without anything happening. But when he moved the weight-and I plucked the strings of my guitar at the same time-something clicked. Valery was so scared he overturned everything, and so we don't know the exact readings." "Automation experts, humph!" Koltukhov remarked, looking the silent, frightened young men up and down. "What's the idea of this clandestine laboratory? I shudder to think of the damage you might have done!" "Have you tuned your guitar since then?" Privalov asked. "No," said Yura. "Then play exactly what you played then. We'll record it," said Professor Bagbanly. "You have a tape recorder here, don't you?" Meanwhile, Valery's little finger was gradually returning to its normal state. He kept testing it against the table. Finally only the very tip of the finger went into the wood. Then, suddenly, he felt his fingertip being pinched, and with a cry he pulled his hand away, leaving a bit of skin in the wood. He immediately thrust his bleeding finger into his mouth. His face broke into a broad smile. "It's ended!" he shouted. The courtyard in Cooper Lane throbbed with music. Strains of music, much of it in a plaintive Oriental key, poured forth through all the open windows from radios, record players and tape recorders. Nikolai had never contributed much to the musical life of the courtyard, but now he aroused the hostility of all his neighbours. Evening after evening there came from his windows the same tiresome strumming of a guitar, accompanied by the thumping of a foot keeping time, and his friend Yura's voice singing: Powder in your pocket to poison me with, A locomotive in your pocket to crush me with. A detailed description of the installation had been sent to the Academy of Sciences in Moscow, together with a long memorandum and the tapes. The young engineers had been ordered to keep their mouths shut and to stop experimenting at home. "You've done enough mischief," said Koltukhov.