Chapter Five. The Master Atom.

“Oh! la la! How horribly dull life is! I do wish something really startling would happen, Dick!”

The words were spoken in pretty broken English by Yvette Pasquet, who, charming and chic, as usual, was sitting with Jules and Dick Manton. The adventurous trio were dining al fresco in the leafy garden of the old-world “Hôtel de France” on the river bank at Montigny, that delightful spot on the outskirts of the great Forest of Fontainebleau, a spot beloved by all the artists and littérateurs of Paris.

“Something will happen suddenly, no doubt,” Dick laughed, glancing at his beloved. “It always does!”

“I sincerely hope it will,” declared Jules in good English. “We’re really getting rather rusty. I met Regnier yesterday out at Pré Catalan with Madame Sohet, and he hinted to me that some great mystery had arisen; but he would tell me nothing further.”

“Regnier, as head of the Service, is always well informed, and like an oyster,” Yvette remarked with a laugh. “So I suppose we must wait for something to happen. I hate to be idle.”

“Yes. Something will surely happen very shortly,” said Dick. “I have a curious intuition that we shall very soon be away again on another mission. My intuition never fails me.”

Dick Manton’s words were prophetic, for on that same evening before a meeting of the Royal Society in London, Professor Rudford, the world-famed scientist, made an amazing speech in which he said:

“Could we but solve the problem of releasing and controlling the mighty forces locked up in this piece of chalk, we should have power enough to drive the biggest liner to New York and back. We should have at our disposal energy unlimited. The daily work of the world would be reduced to a few minutes’ tending of automatic machinery. And, I may add, the first nation to solve that problem will have the entire world at its mercy. For no nation, or combination of nations, could stand even against a small people armed with force unlimited and terrible. And—gentlemen—we are on the way to solving that problem!”

As the words fell slowly and calmly from his lips his hearers felt a thrill of ungovernable emotion, almost of apprehension. For they knew well that he spoke only of what he knew, and the measured phrases conjured up in their keen brains not only a picture of a world where labour had been reduced to the vanishing point, but of a world where evil still strove with good, where the enemies of society still strove against the established order of things which they hated, where crime in the hands of the master criminal, armed with force whose potentiality they could only dream of, would be something transcending in sheer horror all the past experiences of tortured humanity.

Supposing the great secret fell into the wrong hands!

The speech at the Royal Society was a nine days’ wonder.

The unthinking Press made merry in the bare idea of a lump of chalk being a source of power. Then the transient impression faded as public attention returned to football and the latest prize-fight. But behind the scenes, in a hundred laboratories, students bent unceasingly over their myriad experiments, striving to wrest from Nature her greatest secret, the mystery of the mighty energy of the atom. Since the day when Madame Curie had discovered that in breaking up, yet seemingly never growing less, radium was shooting off day and night power which never seemed to diminish, the minds of the men of science had been filled with the dream of discovering the secret.

Could they learn to accelerate the process? Could they induce radium to deliver in a few moments the power which, expending itself for centuries untold, never seemed to grow less? Could they learn to control it, or would it, when at last the secret was discovered, prove to be a Frankenstein monster of titanic power, wreaking untold destruction on the world?

A thin, keen-faced man sat facing the British Prime Minister in his private room in Downing Street a few days later. This was Clinton Scott, one of the smartest men of the British Secret Service, a man of wide culture and uncanny knowledge of the underworld of international crime. His profession was the detection of crime; his hobby science in any form.

“We have very disturbing news, Scott,” said the Prime Minister, “and I have sent for you because the problem before us is largely of a scientific nature and I know all about your hobby.”

Clinton Scott smiled.

“You are aware, of course, of the latest developments in the search for some method of releasing and controlling atomic forces,” went on the Prime Minister. “I do not profess to understand them deeply myself, but I have a general idea of what is being done and what success would imply. Professor Rudford, to whom I applied for information on the subject, tells me that such a discovery would revolutionise world conditions. You will understand of your own knowledge all that it implies, and that is why I have sent specially for you in this matter.”

“I am at the country’s service,” replied Scott.

“Now information we have received from Norway suggests very strongly that the problem has been solved,” the other said. “We have no details—nothing in fact very definite at all. But it is certain that some very queer things have been happening. And from what Professor Rudford tells me I am assured that we cannot afford to neglect them. Our ordinary men are useless for this kind of thing. Men with a considerable knowledge of scientific subjects are absolutely necessary. Otherwise matter which, properly understood, would be full of significance will be passed over as of no account and quite minor and unessential incidents will be followed up, and there would be serious waste of time. And time is valuable.”

“I agree that it is,” was the terse reply.

“I want you to go to Norway and look into the matter,” the Prime Minister went on. “Of course I will see that you get all the information we have, and you can select your own assistants.”

Clinton Scott suddenly looked grave.

“Is it known at all?” he asked. “Who is behind this—I mean who has made this discovery? You will appreciate my reason for asking. If it is the work of a genuine man of science there would be no immediate danger, though of course such an invention would upset all ideas of international relations. It is literally true, as no doubt Professor Rudford will have told you, that the nation in exclusive possession of such a secret could dominate the world. But there are one or two men in the world who, with such a secret in their possession, would be a real peril to civilisation.”

“Do you know a man named Lenart Gronvold?” asked the Premier.

Clinton Scott started visibly.

“Do you mean to say he is in it?” he gasped in utter astonishment.

It was the Premier’s turn to be surprised.

“Why—who is he?” he asked. “Professor Rudford had never even heard his name and laughed when I suggested that he could have had anything to do with it.”

“He won’t laugh when he gets some real idea of Gronvold’s ability,” said Scott bitterly. “The man is one of the mysteries of the world of crime,” he went on. “Exactly who he is we don’t know—I mean we know little about his life. But we believe he is Norwegian born, though he has strong Russian characteristics. We know he studied at Leipzig. Tutors who knew him well speak with the utmost admiration of his amazing brain power as a student and the daring of his conceptions. But for some reason he never did well in examinations and attracted no attention whatever outside a very limited circle. Personally, I believe that for some strange reason he deliberately elected not to call attention to himself, for there is not the slightest doubt that he could with ease have captured every honour the University had to bestow. After leaving Leipzig he disappeared for some years. I don’t know how he spent them. But I do know that he is a chemist of amazing ability. He has, moreover, been mixed up with a number of puzzling international crimes, though we have never been able to bring any of them home to him. Do you remember the big bank robbery at Liverpool three years ago?”

The Premier nodded.

“You mean,” he said, “when the bank vaults were blown open with dynamite and half a million in gold stolen?”

“That’s the case,” said Scott. “Only it wasn’t dynamite, there was no explosion. The thick steel and stone walls of the vaulted safe had been melted through as if they had been butter. The story of an explosion was deliberately given out to deceive the thieves. But the fact is that some process was used of which we have no knowledge whatever.”

And he paused, then went on:

“Now I am pretty sure Gronvold was in that. I was called in before anything had been touched. And in one corner I picked up a scrap of paper bearing some queer formulae of which I could make nothing. It had evidently been dropped by accident. And it bore Gronvold’s name. Moreover, as I ascertained by a visit to Leipzig, where I saw some of the old University registers, it was in his handwriting. But where he is, how he got into England, how the burglary was effected and how he got away with such an enormous weight of gold we never could make out. If he is really in this new discovery we are face to face with a terrible problem. The man is absolutely without scruple, and for three years he has had the use of half a million of money for his experiments. He may have done anything in that time.”

“But how did you know of him?” asked the Premier.

“It’s a queer story,” replied the other. “Simmons, one of our men in Christiansand came across, quite by accident, a drunken Norwegian sailor who told a strange story of the blowing up of a mountain by a tiny cartridge placed at the bottom of an old mine shaft. He actually mentioned Gronvold’s name, and claimed to have been one of his assistants. When he became sober he was evidently terribly alarmed at having talked, and denied the whole story. The same day he disappeared, and Simmons has been unable to trace him.”

He went on after a pause:

“Now the blowing up of a mountain is a fact. A hill nearly a thousand feet high in a wild lonely district north-east of Tonstad has absolutely disappeared—levelled out. To have done the work by ordinary means would have meant years of labour and would have cost a fortune. There can be no doubt that some entirely new force has been employed. Officially the occurrence is attributed to a landslide; actually it is and can be nothing of the kind. Now this, coupled with what the Norwegian sailor said, suggests that we ought to look into the matter. Whether the Norwegian Government knows anything about it I do not know, and the matter would be of such importance from the international point of view that we cannot make direct inquiries.”

“Will you take it in hand?” asked the Premier. “Whom will you get to help you? I am afraid the ordinary men would be of very little use.”

“I think I will run over to Paris and see Regnier,” replied Scott. “He has a fellow named Manton who will certainly be useful. He was in our flying corps and was invalided out owing to wounds. He has done some wonderful work and has an entirely new type of aeroplane which he invented and which, by the way, our people would have nothing to do with. Regnier swears by him. He works always with a French girl named Yvette Pasquet, who did some splendid intelligence work during the war, and her brother Jules. They will have nothing to do with anyone else when they are on a case, and they have had some amazing results.”

Crossing to Paris by the afternoon air express Scott the same evening was warmly greeted by Regnier. He rapidly explained his visit. Regnier looked grave.

“I have heard of the man,” he said, “but have never seen him, I don’t think in a case like this you can do better than Manton. He is very well up in all these scientific things; they seem to be a perfect craze with him.”

An hour later, Regnier, Scott, Dick Manton, Yvette, and Jules were closely discussing the problem in Manton’s rooms.

“We have got to find that sailor,” was Dick’s verdict, “and luck is going to have a good deal to do with it. I suppose Simmons is on the look out for him?”

“Yes,” replied Scott, “I wired him at once.”

“Do you think Gronvold and the sailor have quarrelled?” put in Yvette.

“I think not,” was Scott’s reply. “If they had there seems no reason for the man’s alarm. I think he calculated on going back to him. That was Simmons’ view, too.”

Dick, who had been carefully studying a map, looked up.

“Just look here,” he said, “you could hide an army in this place.”

The map was in contour and gave a vivid impression of the wild and desolate country, a broken mass of hills and lakes, stretching north and east from Tonstad.

“Suppose Gronvold is there,” said Dick, “he could hide anything he wanted to. I don’t think he would have travelled far from its base to blow up the hill—that was probably experimental. My idea is that he has established his laboratory somewhere in the hills about there. There is no population and little or no traffic through the district. He must send to one of the towns for supplies, and Christiansand is the most likely. I should guess that the sailor had come there for that purpose and may come again.”

“He did not leave the town by boat,” declared Scott. “Simmons made the most careful inquiries on all the boats in the harbour and no one of his description was seen.”

Three tourists a week later were lodged in a comfortable hotel in the Dronningens Gade, one of the principal streets in the busy port of Christiansand. They were Yvette, Jules, and Scott. Dick had flown the Mohawk direct to the wild district north-east of Tonstad, and with the help of a light tent had pitched a camp in a little wood a couple of miles from the southern edge of the blown-up hill. He had taken pains in the selection of a suitable place and his camp and the Mohawk were so admirably hidden that they were safe from discovery, unless some one actually walked right up to them, a contingency which in that roadless, unpopulated country was extremely unlikely. But though hidden himself he commanded a wide view.

For two days Dick devoted himself to a thorough examination of the surrounding country, quartering it thoroughly either on foot or in the Mohawk. He could however see nothing in the least suspicious.

Then came a surprise.

His only method of receiving news from the others was to “listen in” on the wireless telegraph set with which the Mohawk was fitted for messages which, directed to an address in England, were handed to the Christiansand radio station for dispatch, but were really intended for him. These messages were handed in at eight o’clock precisely and Dick usually got them within half an hour.

On the third day of his watch came the message:

“Sailor located. Travelling north with pack mules. We follow. Osterluis road.”

The man, as he was to learn later, had been spotted by Yvette in Christiansand. She had seen him leave a small café much frequented by sailors, and had been struck by his likeness to the description given by Simmons. She had followed him for some time while he made a variety of purchases at numerous shops, and had been struck by the fact that a mere sailor should evidently have such a large sum of money at his disposal. Luckily she had encountered Simmons, who at once recognised the man and had promptly disappeared to avoid arousing his suspicions.

Yvette was able to learn that all the man’s purchases were being delivered to a small inn on the outskirts of the town, and a few inquiries showed that he had four mules stationed there.

The matter began now to clear up. They were sure of the man; at least he could not leave without his mules and stores. Jules and Scott took up the watch at the inn, while Yvette shadowed the suspect. It was thought best that Simmons should not appear. It soon became evident that the man had no associates in Christiansand. All he did was to visit shops, paying cash for all his purchases and having them sent to the inn where his mules were stabled.

The next day, with his mules heavily loaded, he set out from Christiansand, taking the road to Trygstand and Ostersluis.

Yvette, Jules, and Scott decided to follow him on foot. To have taken horses would have told him he was being followed as soon as he left the road, as they were pretty sure he would, sooner or later. Luckily all three were splendid walkers and felt they would have no trouble in keeping up with the heavily-laden mules. Cramming a few necessities into rucksacks they were soon on the track of their quarry.

Man and mules made steady progress. They were soon through Trygstand and, shortly after, caught sight of the Mohawk high above them and evidently following the road on the watch for them.

With a handkerchief tied to a stick Yvette swiftly signalled to Dick the brief facts, and the Mohawk passed on towards Christiansand. When the sailor and the mules were hidden in a dip in the road Dick landed, and all four held a brief consultation as to their future plans.

As a result Scott put on his best speed and soon passed the sailor who had stopped for a rest. The man was now between two parties on the ground and under observation from Dick from the air. He certainly could not escape.

A few miles beyond Trygstand he suddenly left the high road, and turned westward and north across the open country. Evidently he was not bound for Ostersluis. But where could he be going? For miles there was not even a house in the deserted track of country into which he had plunged.

But it was evident he knew his bearings thoroughly. Hour after hour he jogged along, and soon the pursuers realised that they had been wise not to bring horses. No horse could have crossed the country over which the sure-footed mules went swiftly without a stagger.

At nightfall the man camped. Apparently he paid no attention to the passing of the aeroplane, for he barely glanced at it. Building a small fire under the shelter of a rock, the three pursuers spent a comfortless night. Dick had flown to his camp, intending to pick the party up again at dawn.

Early next morning the man was afoot and continued his journey. He was now in the wild country well to the west of Ostersluis, and travelling due north. Yvette, Jules, and Scott were a mile behind, following with the utmost care not to reveal their presence and so rouse the man’s suspicions.

They had gone but a few miles when the man paused on the flat top of a high hill, which on the side away from them sloped steeply into a deep gorge at the foot of which ran a small stream. They watched him narrowly.

With great care he got the four mules together, standing side by side. He himself took up a position directly in front of them and almost touching the animals’ heads.

A moment later man and mules sank together, apparently into the earth and disappeared!

They could hardly believe their eyes! Surely the man must have gone down the reverse slope of the hill. But they were confident that he had not moved.

They hurried to the spot. Not a sign of any living thing was to be seen! The mystery was profound.

While they stood gazing at one another in speechless amazement, the Mohawk, which they had not perceived above them, dropped vertically downwards and landed a few yards away. Dick sprang out.

“Did you see?” he gasped. “The man and mules went down into some sort of pit. But where was it?”

The flat top of the hill was broken into a series of narrow cracks; apparently the rock of which it was composed was of volcanic origin. They examined it closely, but they could discover nothing which offered a solution of the mystery.

Dick described closely what he had seen from the sky. It agreed with what the others had observed. The man had got the mules together, and all had sunk slowly downward. Dick had seen the black mouth of the pit for a few moments and a blaze of light. Then the pit had disappeared, and the ground resumed its normal appearance.

“We shall have to camp here to-night,” said Dick. “We must get to the bottom of this. We shall have to take turns to watch. In the meantime we had better have a look round.”

Having closely examined the top of the hill, they turned to the deep gorge and descended to the bottom. The stream, they found, issued from the hill itself, flowing out from a low tunnel high enough to admit the passage of a man. From it also issued a cloud of mist which spread over the bottom of the little valley in a thick blanket which completely concealed the surface of the ground from anyone at the top of the hill.

But still more remarkable was that the bed of the little stream was deeply covered with what appeared to be recently melted lava. In many places it was still hot, and the water, they found, was nearly boiling. The first traces of this were found at the mouth of the tunnel from which the stream emerged, and for hundreds of yards the molten rock could be traced, as though it had poured from the tunnel and flowed down the bed of the brook.

Wood and water were available in abundance, and soon they had pitched their camp, near enough to the top of the mysterious hill to enable them to watch it closely and yet well concealed so that if the man reappeared they would have no difficulty in escaping observation.

The first watch fell to Yvette, and with a revolver ready for instant use, she prepared to spend a couple of lonely hours on the edge of the hill. The camp was but a quarter of a mile away so that a shot would bring her speedy help at any time.

A brilliant moon lit up the country for miles.

There was no trace of any living thing. Everything was still and silent.

Yvette had been on watch about an hour when she became aware that the air was full of a dull murmur of sound. She listened intently. There was no mistake about it. A dull throbbing noise was distinctly discernible.

She walked round the flat top of the hill, looking keenly in every direction and trying to locate the position from which the mysterious sound was coming. But it was in vain.

Glancing into the gorge, she saw a strange and terrible phenomenon. The course of the little brook was traced in a dull fiery glow. Clouds of steam were rising thickly into the night air; she could plainly hear the sharp hiss of water on something hot.

She ran swiftly down the hill. At the bottom she paused on the edge of the stream. The water had disappeared and in its place ran a river of molten rock! Through her boots she felt the heat of the ground.

Returning to the top of the hill she waited for Dick, who was now almost due to relieve her. In a few moments he appeared and listened in amazement as she gasped out her story.

The dull, throbbing noise was still audible.

“Machinery,” said Dick laconically, “but where?”

Suddenly he flung himself on his face, and pressed his ear close to the ground.

“Listen,” he said.

Yvette followed his example. There could be no mistake; the mysterious sound was coming from the ground beneath their feet! The earth was full of muffled thunder.

Dick took from his pocket a hammer and struck a sharp blow on the flat rock beneath their feet. It rang hollow! Unmistakably they were standing on the roof of a cavern.

Walking to the camp they roused the others and told them what they had seen and heard.

“We have got to catch that sailor if we wait here a month,” said Scott. “He must come out again some time. But how about food?”

“We have enough tinned stuff in the Mohawk for a week,” said Dick, “so we shall be all right for a few days. In the meantime we must watch the place closely.”

Next day passed without incident until evening was drawing on. Then Yvette, who was watching the top of the hill while the others rested, at six o’clock gave a low whistle. She was lying on the ground keeping observation between a couple of rocks which hid her completely. In a moment the others had crawled to her side.

“Look!” she said.

On the top of the hill, three hundred yards away, stood the sailor and the four mules, clearly silhouetted against the evening glow. He had appeared suddenly, Yvette told them, just on the spot where he had disappeared on the previous day.

“We must get him,” said Dick.

The man with the mules started to return along the way he had come. They saw at once that the path he was taking would bring him close to them.

With the mules unloaded the man evidently had no intention of walking. He mounted one of the animals and rode towards them at a fast trot.

He was within twenty yards when Dick aimed his revolver and fired. The mule the man was riding bolted, throwing its rider heavily. Before he could recover himself he was bound and helpless. The other three mules stampeded wildly and were soon out of sight.

Carried to the camp the man soon recovered. But he resolutely refused to say a word.

“Well,” said Dick. “We must try to get into the cave. Perhaps the tunnel out of which the brook runs will lead us to it.”

They were soon at the mouth of the strange tunnel. There was no sign of the molten matter of the previous night. The stream, thick with mud, flowed sluggishly, but the water was cool, and the ground, which the night before had been too hot to walk upon, was now not more than uncomfortably warm.

With Dick leading, Scott and Yvette next in order, and Jules bringing up the rear they entered the mouth of the tunnel. There was, they found, just room for them to pass, stooping low and walking knee deep in the little stream. They were, of course, in total darkness, for Dick was afraid to show a light for fear of betraying their presence.

For a hundred yards Dick groped his way onward. Then his outstretched hands struck something soft. It was a kind of curtain hung across the stream, thick and heavy.

Cautiously he slightly raised one corner and peered through. The sight that struck his eyes filled them with amazement.

They were at the entrance to an enormous chamber, a hundred and fifty yards across, dimly lighted by a single big electric lamp, the only one alight out of dozens which hung from the roof. The floor sloped steeply upwards at the far end where they could make out a kind of platform, reaching nearly to the roof and with steps leading downward into the great hall. All round the side were a series of openings, apparently small chambers cut into the solid rock. From one of these the stream they had followed seemed to issue, crossing the floor of the great cave in a narrow deep channel.

But what fascinated Dick’s attention was a great table, apparently of iron, which occupied the centre of the cave. It was heavily constructed and seemed to be based on massive legs which went down into the rock. Upon it stood a strange machine unlike anything he had ever seen before and of the use of which he could not form the smallest idea. Surmounted by two huge governor balls, it was a complicated mass of polished wheels, of some metal which Dick could not identify, and which gleamed with a strange radiance in the light of the huge electric lamp overhead. From the machine a bewildering mass of wires led to a series of points at the face of the rock.

So much Dick could make out in the dim light. He was keenly anxious to learn more. But how was it to be done? No sign of any human being was to be seen, but he could not imagine that what lay before their eyes was the work of the solitary sailor who now lay bound in their camp.

At any rate they could not remain where they were. Dick decided to try to gain entrance to one of the wall chambers where they could shelter with a better chance of seeing what would happen in this underground home of mystery. But which should they choose?

Some of the chambers were half-way to the roof and were reached by steps cut in the solid rock. Dick decided on one of these not far from where they were standing. They crept cautiously from their hiding-place and stole along to the bottom of the cave. A moment later they were at the foot of the steps. These they hastily climbed, and soon found themselves in a fair-sized cave, fifteen or sixteen feet above the floor of the main cavern and commanding a good view of the entire area. It was dry and warm and formed an ideal post of observation, provided their presence remained undiscovered.

Suddenly a blaze of light struck their eyes. Some one had turned on the whole of the electric lamps which hung in clusters from the roof.

Peering cautiously out they saw, to their amazement, half a dozen men issue from different chambers near the floor of the cave. All wore big round spectacles of deep blue glass and were clothed in close-fitting garments of rubber, with heavy gauntletted gloves of the same material. Apparently they could not see well, for the spectacles must have been almost impervious to ordinary light.

One of the men, fixing his spectacles on more firmly and, drawing his rubber overall more closely around him, approached the strange machine which stood on the table. The others proceeded to the points at which the wires from the machine reached the side of the cave. Here they took up some kind of tool which looked like a gigantic blowpipe and stood ready as if awaiting a signal.

A low whistle sounded from the man at the table, as he grasped a small wheel and gave it a quick turn.

An instant later an appalling blaze of light burst from the strange machine, and the cave was filled with a roar of sound, a terrible deep drone of such frightful intensity that the hidden watchers shuddered as if with actual physical agony. Dick felt the sweat start suddenly from his forehead and pour down his face. Anxiously he glanced towards Yvette. She lay with her face buried in her arms, her body trembling convulsively. Scott and Jules, their faces white as chalk, were gazing at the unearthly light which streamed from the whirling machine, shading their eyes with their hands to shelter them from its blinding radiance. They could not look at it for more than a few seconds; it was like trying to gaze at the sun at midday.

Taking a letter from his pocket, Dick bored a tiny hole in it with his scarf pin. Through this hole he found he could see in comparative comfort. He signed to the others to do the same, and soon all four—for Yvette quickly recovered her self-possession—were eagerly watching the strange scene before them. Speech, in the deafening noise by which they were surrounded, was, of course, out of the question.

The man at the great table in the centre of the cavern evidently had a task of great difficulty to control the movements of the strange machine, which he seemed to do by means of a large wheel something like the steering wheel of a steamer. Long streamers of flame shot from it in all directions, and as its mass of wheels revolved at terrific speed it shook and trembled as if it would actually leap from the table.

In the meantime the men at the rock face were hard at work with big blowpipes, from the muzzles of which shot streams of fire of such intensity that the solid rock seemed to melt away like butter. The molten matter was led by ducts in the ground through a grid of some metal, evidently highly refractory to heat, for it appeared to do no more than glow white-hot even in the terrific temperature of the melted rock. After passing through this grid the molten matter was led to the bed of the stream, from which the water had in some manner been cut off, and flowed out the way Dick and his companions had entered.

What was the object of the work?

Dick could not guess, but every now and again one of the men would walk to the grid and with a long implement shaped like a hoe would scrape off something adhering to the bars, which he deposited in a big tank of water. Dick determined that, sooner or later, he would obtain a specimen.

But in the meantime their position was decidedly precarious. If they were observed there was no possible way of escape, for the tunnel by which they had entered was barred by the stream of molten matter. They could only lie still and hope that no one would enter the gallery in which they lay concealed.

After two hours of work, the man at the table stopped the machine, and all the men straightened out for a rest. Evidently they were very much exhausted. The lights were extinguished, except for the single one which was burning when they entered, and the men returned to their quarters, evidently almost falling with weariness. Dick came to the conclusion that they could only carry on the work on which they were engaged for a short time and that after that sleep and rest were imperative. The flow of molten metal had stopped and the water was again allowed to flow along its ordinary channel, from whence it sent up huge clouds of dense steam.

This gave Dick his chance.

Sending the others to the mouth of the exit, he cautiously crept towards the tank in which were deposited the scrapings from the grid which filtered the molten rock. He reached it safely, and plunging in his arm up to the shoulder, abstracted a couple of handfuls of what seemed like heavy shot. These he placed at once in his pocket.

He was about to return to the others when his attention was caught by the queer platform at the one end of the cave. Looking at this carefully he found that it was really a huge lift, and at once the mysterious disappearance of the sailor and the mules was explained. It was evident that the top of the lift was really the thin covering of rock which had sounded hollow when tapped and that this had been so cut that when the lift forced it into position only traces of ragged crevices were left on the surface. Dick could not but admire the ingenuity with which this approach to the subterranean retreat had been devised.

Presently he heard a heavy knocking above his head and, guessing the cause, shrank back for shelter into the mouth of a small cave adjoining. A moment later a man emerged from one of the other chambers and approached the lift. Dick was curious to see how it worked. There was, as he could see, a small electric motor fitted to it, but where could the necessary power come from?

The new-comer carried in his hand a tiny machine which was in every respect a duplicate in miniature of the big one on the central table. But it was so small that the man carried it easily in one hand. From it ran a pair of electric cables which the man proceeded to connect with the terminals of the motor.

Placing the machine on the ground he gave the wheel a sharp turn. Immediately the tiny machine began to revolve, throwing out flashes and flames exactly like the larger one but on a miniature scale.

Clearly, however, there was considerable power in it, for the lift at once commenced to descend. On it stood a man whom Dick instantly recognised as Gronvold. And he was accompanied by the sailor whom Dick had left safely tied up in their camp. Evidently Gronvold had found and released him.

Their position was now indeed one of terrible gravity.

As soon as the lift reached the bottom the two men stepped off and the lift reascended, moving upward with an ease which showed the tremendous power developed by the tiny machine. Here, indeed, was something of which Dick had had no previous experience.

The three men crossed the cave to the shelter occupied by the man who worked the big machine, who was evidently the captain, and Dick knew there was no time to be lost.

Directly the men entered the shelter, Dick dashed across the cave to join the others, snatching out his revolver as he ran.

He had nearly reached them, when a whistle blew and instantly half a dozen men rushed from different caves. They were discovered!

“Take care of Yvette, Jules!” Dick yelled as, with Scott at his side, he faced round to the men who were rushing at them from three sides.

Instantly Yvette and Jules plunged into the tunnel. Dick and Scott backed after them with drawn revolvers threatening the men in the cave.

For a moment the leaders hesitated; apparently they were not aimed. Then Gronvold rushed to the front, followed by the captain, both carrying curious weapons which looked like heavy pistols.

All four men fired simultaneously. Dick saw the captain drop, evidently shot dead, and heard a bullet whiz past him and strike the rock behind. A burst of flame singed his hair, and he felt the hot breath of it on his face.

Then Gronvold fired at Scott. The effect as the bullet struck him was strange and awful. His body actually disappeared in a mass of flame under the impact of some projectile of unimaginable power and energy. At the same instant Dick slipped on a projecting bit of rock and fell heavily on his head. As he lost consciousness he heard the crack of a revolver behind him. Yvette and Jules, hearing the shots, had returned in the nick of time. Jules snatched up Dick and carried him down the tunnel, while Yvette very coolly shot down Gronvold just as he was reloading his terrible weapon.

When Dick recovered his senses he found himself lying on the ground at the entrance to the tunnel, his head pillowed on Yvette’s arm as she tried to pour some brandy between his lips. He could feel the sobs which shook her, and even felt a tear on his face. Jules stood on guard at the entrance to the tunnel, his revolver ready for instant action in case of pursuit.

As Dick opened his eyes, Yvette gave a gasp of relief.

“Oh, dearest, I thought you were dead!” she sobbed and burst into tears. A moment later she turned away blushing scarlet. She had betrayed her secret at last. And even in his confused state Dick felt a thrill of triumphant joy.

His head spinning he staggered to his feet. But he would have fallen if Yvette had not caught him.

“Sit down, Dick,” she said peremptorily. “Jules can look after this place.”

Dick obeyed, perforce; he was so sick and giddy that he could have done nothing even if the expected attack had come.

But it never came. Suddenly as they stood there, tense and waiting, a terrific convulsion shook the earth. With a terrible roar the great cavern collapsed and a vast burst of smoke and flame vomited to the sky, and a deep crater was left by the subsidence. Sick and dizzy, with showers of stones falling all around them, they stood aghast while explosion after explosion rent the air, rendering the crater deeper. It was some minutes before quiet reigned again and, white and shaken, after their nerve-racking experience, they were able to collect their shaken faculties and make an examination of the scene.

The hill beneath which the cavern was located had practically disappeared; in its place was left nothing but a heap of torn and tumbled earth and rock. Its dreadful secret was safe, for the cave and its contents, and the men who had wielded such titanic forces, were buried deep under tens of thousands of tons of débris.

Perhaps it was as well, Dick thought. There are some forms of knowledge which mortals ought not to possess; there are some powers which they are not fit to handle.

Whatever secret Gronvold had discovered, it rested with him for ever on the very scene of his ill-omened labours. What had gone wrong in the depths of the cavern they could not even imagine, but it was evident that the mysterious force which Gronvold had called into existence, whatever it was, had destroyed him and his companions. And it was almost by a miracle that Dick, Yvette, and Jules had escaped.

Slowly and painfully they made their way back to their camp, and for the first time Dick became conscious of the great weight of the double handful of shot which he had taken from the tank. He drew some of it out and examined it by the light of the fire. As he did so he gave a cry of surprise. For the “shot” was nothing more or less than tiny nuggets of virgin gold.

Here was an addition to the mystery. As Dick knew perfectly well, there was not an atom of gold-bearing rock within hundreds of miles of where they stood.

It was evident that one of the secrets of Gronvold’s invention was that it gave him the power of actually bringing about the transmutation of substances. There was some element in the rock which was susceptible of being changed into gold by a process at which they could not even guess. But if this were so, Gronvold had indeed, as they suspected, been able to solve the problem of loosing the incredible force contained in the atom. His discovery was, as Dick at once realised, on the lines of the latest development of scientific thought.

Dick was to see the problem solved in later years by more reputable investigators.

But he could never forget his strange encounter with the wonderful but misguided genius whose career had been so terribly brought to an end by the dread power he had himself evoked.