Once more he turned, as to a magnet, to the machine that was his handiwork.

The fifteen-foot sphere was an earth-borer--Guinness's own invention.

In it he had utilized for the first time for boring purposes the newly developed atomic disintegrators. Many holes equally s.p.a.ced over the sphere were the outlets for the dissolving ray--most of them on the bottom and alternating with them on the bottom and sides were the outlets of powerful rocket propulsion tubes, which would enable it to rise easily from the hole it would presently blast into the earth. A small, tight-fitting door gave entrance to the double-walled interior, where, in spite of the s.p.a.ce taken up by batteries and mechanisms and an enclosed gyroscope for keeping the borer on an even keel, there was room for several people.

The earth-borer had been designed not so much for scientific investigation as the specific purpose of reaching a rich store of radium ore buried four miles below the Guinness desert camp. Many geologists and mining engineers knew that the radium was there, for their instruments had proven it often; but no one up to then knew how to get to it. David Guinness did--first. The borer had been constructed in his laboratory in San Francisco, then dismantled and freighted to the little desert town of Palmdale, from whence Holmes had brought the parts to their isolated camp by truck. Strict secrecy had been kept. Rather than risk a.s.sistants they had done all the work themselves.

Fifteen minutes pa.s.sed by, while the slight figure of the inventor puttered about the interior of the sphere, brightly lit by a detachable searchlight, inspecting all mechanisms in preparation for their descent. Sue stood by the door watching him, now and then turning to scan the desert for the returning Phil.

It was then, startlingly sudden, that there cracked through the velvet night the faint, distant sound of a gun. And it came from the direction of the water-hole.

Sue's face went white, and she trembled. Without a word her father stepped out of the borer and looked at her.

"That was a gun!" he said. "Phil didn't have one with him, did he?"

"No," Sue whispered. "And--why, there's n.o.body within miles of here!"

The two looked at each other with alarm and wonder. Then, from one of the broken patches of scrub that ringed the s.p.a.ce in which the borer stood, came a mocking voice.

"Ah, you're mistaken, Sue," it affirmed. "But that was a gun."

David Guinness jerked around, as did his daughter. The man who had spoken stood only ten yards away, clearly outlined in the bright moonlight--a tall, well-built man, standing quite at ease, surveying them pleasantly. His smile did not change when old Guinness cried:

"Quade! James Quade!"

The man nodded and came slowly forward. He might have been considered handsome, had it not been for his thin, mocking lips and a swarthy complexion.

"What are you doing here?" demanded Guinness angrily. "And what do you mean--'it was a gun?' Have you--"

"Easy, easy--one thing at a time," said Quade, still smiling. "About the gun--well, your young friend Holmes said, he'd be right back, but I--I'm afraid he won't be."

Sue Guinness's lips formed a frightened word:

"Why?"

Quade made a short movement with his left hand, as is brushing the query aside. "Let's talk about something more pleasant," he said, and looked back at the professor. "The radium, and your borer, for instance. I hear you're all ready to go down."

David Guinness gasped. "How did you know--?" he began, but a surge of anger choked him, and his fists clenched. He stepped forward. But something came to life in James Quade's right hand and pointed menacingly at him. It was the stubby black shape of an automatic.

"Keep back, you old fool!" Quade said harshly. "I don't want to have to shoot you!"

Unwillingly, Guinness came to a stop. "What have you done with young Holmes?" he demanded.

"Never mind about him now," said Quade, smiling again. "Perhaps I'll explain later. At the moment there's something much more interesting to do. Possibly you'll be surprised to hear it, but we're all going to take a little ride in this machine of yours, Professor. Down. About four miles. I'll have to ask you to do the driving. You will, won't you--without making a fuss?"

Guinness's face worked furiously. "Why, you're crazy, Quade!" he sputtered. "I certainly won't!"

"No?" asked Quade softly. The automatic he held veered around, till it was pointing directly at the girl. "I wouldn't want to have to shoot Sue--say--through the hand...." His finger tightened perceptibly on the trigger.

"You're mad, man!" Guinness burst out. "You're crazy! What's the idea--"

"In due time I'll tell you. But now I'll ask you just once more,"

Quade persisted. "Will you enter that borer, or must I--" He broke off with an expressive shrug.

David Guinness was powerless. He had not the slightest idea what Quade might be about; the one thought that broke through his fear and anger was that the man was mad, and had better be humored. He trembled, and a tight sensation came to his throat at sight of the steady gun trained on his daughter. He dared not trifle.

"I'll do it," he said.

James Quade laughed. "That's better. You always were essentially reasonable, though somewhat impulsive for a man of your age. The rash way you severed our partnership, for instance.... But enough of that.

I think we'd better leave immediately. Into the sphere, please. You first, Miss Guinness."

"Must she come?"

"I'm afraid so. I can't very well leave her here all unprotected, can I?"

Quade's voice was soft and suave, but an undercurrent of sarcasm ran through it. Guinness winced under it; his whole body was trembling with suppressed rage and indignation. As he stepped to the door of the earth-borer he turned and asked:

"How did you know our plans? About the radium?--the borer?"

Quade told him. "Have you forgotten," he said, "that you talked the matter over with me before we split last year? I simply had the laboratory watched, and when you got new financial backing from young Holmes, and came here. I followed you. Simple, eh?... Well, enough of this. Get inside. You first, Sue."

Trembling, the girl obeyed, and when her father hesitated Quade jammed his gun viciously into his ribs and pushed him to the door. "Inside!"

he hissed, and reluctantly, hatred in his eyes, the professor stepped into the control compartment after Sue. Quade gave a last quick glance around and, with gun ever wary, pa.s.sed inside. The door slammed shut: there was a click as its lock shot over. The sphere was a sealed ball of metal.

Inside, David Guinness obeyed the automatic's imperious gesture and pulled a shiny-handled lever slowly back, and the hush that rested over the Mojave was shattered by a tremendous bellow, a roar that shook the very earth. It was the disintegrating blast, hurled out of the bottom in many fan-shaped rays. The coa.r.s.e gray sand beneath the machine stirred and flew wildly; the sphere vibrated madly; and then the thunder lowered in tone to a mighty humming and the earth-borer began to drop. Slowly it fell, at first, then more rapidly. The shiny top came level with the ground: disappeared; and in a moment there was nothing left but a gaping hole where a short while before a round monster of metal had stood. The hole was hot and dark, and from it came a steadily diminishing thunder....

For a long time no one in the earth-borer spoke--didn't even try to--for though the thunder of the disintegrators was muted, inside, to a steady drone, conversation was almost impossible. The three were crowded quite close in the spherical inner control compartment. Sue sat on a little collapsible stool by the bowed, but by no means subdued, figure of Professor David Guinness, while Quade sat on the wire guard of the gyroscope, which was in the exact center of the floor.

The depth gauge showed two hundred feet. Already the three people were numb from the vibration; they hardly felt any sensation at all, save one of great weight pressing inwards. The compartment was fairly cool and the air good--kept so by the automatic air rectifiers and the insulation, which shut out the heat born of their pa.s.sage.

Quade had been carefully watching Guinness's manipulation of the controls, when he was struck by a thought. At once he stood up, and shouted in the elderly inventor's ear: "Try the rockets! I want to be sure this thing will go back up!"

Without a word Guinness shoved back the lever controlling the disintegrators, at the same time whirling a small wheel full over. The thudding drone died away to a whisper, and was replaced by sharper thundering, as the stream of the propulsion rockets beneath the sphere was released. A delicate needle trembled on a gauge, danced at the figure two hundred, then crept back to one-ninety ... one-sixty ...

one-forty.... Quade's eyes took in everything.

"Excellent, Guinness!" he yelled. "Now--down once more!"

The rockets were slowly cut; the borer jarred at the bottom of its hole; again the disintegrators droned out. The sphere dug rapidly into the warm ground, biting lower and lower. At ten miles an hour it blasted a path to depths. .h.i.therto unattainable to man, sweeping away rock and gravel and sand--everything that stood in its way. The depth gauge rose to two thousand, then steadily to three and four. So it went on for nearly half an hour.

At the end of that time, at a depth of nearly four miles, Quade got stiffly to his feet and once more shouted into the professor's ear.

"We ought to be close to that radium, now," he said. "I think--"