of Europium. Hurry."

As the elevator shot downward, the old professor endeavored to congratulate Holden on his appointment.

"Forget it. This was your idea, and they should have named you leader of the expedition, but that really doesn't make much difference. Anything you say goes, see?"

A crowd was milling around the entrance to the Western Hemisphere tunnel. An official tried to stop Holden and his companion as they pushed their way through the crowd.

"The liner is leaving. You can't go in there."

"Oh, we can't, huh? Here."

A single glance at the paper shoved under his nose, and the gatekeeper came to life.

"Right this way, you're just in time."

The three ran out on top of the building, where the beautiful silver shape of the liner floated at the top of a short tower. An officer was just giving the command to cast loose, but as Holden shouted to him, he countermanded it, for special orders from the Union had to be obeyed, even if schedules were spoiled.

Nodding their thanks to the now obsequious gateman, the two scientists hurried up the ladder that had been dropped for them; again came the shouted "Cast off," and the huge liner, impelled by powerful motors, rose rapidly to the high altitude at which she traveled.

"Message for you, sir," said a pleasant voice at Holden's elbow, and he turned. A neatly uniformed boy held out to him a thin envelope. Breaking the seal, he read rapidly.

"Will you show us in to the Captain, please," he addressed the boy as he finished the message.

The lad nodded, and led them down a long hall to the bow of the ship and up to the bridge.

"Mr. Holden, I presume? And Professor Erickson? I am Captain Linet."

The Captain was an immense man, well over six feet, with the build of a prizefighter. His face was pleasant, but there was an expression of intense sorrow in his deep blue eyes.

"I understand that you have been appointed to head an expedition to the moon, the nature of which has not been revealed, but which will do away forever with the earthquakes which have become so prevalent. I wish to join that expedition. My beloved wife was in New York at the time of the last quake. You understand."

Holden nodded sympathetically. He would be glad to have all the men like this he could find, and he expressed that opinion to the Captain.

"Thank you. I will resign my position when we reach San Francisco, and will await your orders."

"But, Captain," Holden asked, "how did you know that I was head of the expedition?"

"Oh, the news has been broadcast everywhere, with instructions to give you any aid possible. But no information was given as to the exact nature of the trip. Could I be trusted—?"

"Why certainly. We are going to destroy the moon, wipe it out of existence, so that it will cease to exert the tremendous gravitational pull that has been causing—."

At that moment a petty officer appeared behind the Captain.

"Have you any further orders concerning the cargo to be dumped at New Orleans?"

"No. I thought I gave you to understand that there were to be no more additions to that cargo. Didn't you hear me?"

"I beg your pardon, sir," the man said, and walked away.

"I wonder how much of our conversation he heard?" mused Erickson. "But then, I suppose it makes no difference."

After a few minutes of conversation, Holden asked the Captain if they could be shown their cabins, so that they could get a few hours of rest before reaching their destination. The request was readily granted, and in a few minutes Holden was alone in a neat little room, furnished with a comfortable chair, tables along two walls, and a very pleasant looking berth built into the third side. The professor had a similar place a few doors down the hall.

Holden threw off his shoes and coat and tumbled into the berth. The events of the last weeks were spinning in his head, and a procession of visions passed before his eyes. That terrible catastrophe, the trip to Europe, to the capitol of the World Union, and now, the appointment as leader of the most important expedition in the history of the universe, with the possible exception of that first epoch-making voyage to Mars back in 2350.

Another vision appeared before his eyes. Jean! Jean, his own sweetheart, the one person in the world who mattered, gone now for a full year. Why had she decided to make the voyage to Mars? What could have happened to the ill-fated Gloriana, with her hundreds of passengers and valuable cargo? A year ago she had left; and, as some people said, merely drifted out into space, never to be heard from again.

A deep sob shook Holden's body as he thought of that beautiful girl, who, laughing at his fears, had stepped into the space flyer with a smile on her lips, promising to come back in a year and marry him.

At last, however, these memories gave way before exhaustion, and he fell into a sleep, troubled by strange dreams. It seemed that a great serpent had attacked him, and, flinging its coils about his body, was slowly squeezing out his life. Suddenly, he was wide awake. Strong hands were on his throat, the thumbs were pressed tight against his larynx.

He struggled to gain his breath, to shout for help, but the pressure closed his throat. In another moment it would be too late. Then his mind cleared; raising both hands to the back of his neck, he grasped the little fingers of his assailant, and pulled with all his strength. The man gave a cry of pain and anger and relaxed his grip. Holden gulped in a breath of air, and flung himself from his berth, endeavoring to catch and hold the coward who had attacked in the dark. The man, however, was wiry and quick. With a sudden jerk he wriggled loose, gained the door and was gone. When Holden reached the corridor, no one was in sight. Quickly he walked to Professor Erickson's room, awakened him, and told him what had happened.

Erickson rang up a steward, who promised to do everything in his power to apprehend the culprit.

"Who could it have been?" asked Erickson.

"I haven't the slightest idea. I have no enemies that I know of. I'm not carrying any valuables. It was probably a case of mistaken identity."

The incident was dismissed with that interpretation, and it was several weeks before Holden thought of it again, but then he wished fervently that he had investigated more thoroughly.

CHAPTER II

A Midnight Attack

It was midnight when the liner reached San Francisco, but Holden insisted on going at once to the offices of the Interplanetary Transportation Company, where work was carried on day and night. Fortunately they found an official of the company who had sufficient power to carry out their instructions.

It is unnecessary to go into the details of the meeting, or of the ensuing days. The unlimited power given Holden, together with the vital importance of his mission, brought everyone into instant cooperation.

Three mammoth space ships were turned over to the gang of mechanics he had hired, to be fitted with projectors for the anti-gravitational screens. Thousands of chemists all over the world dropped their work to prepare the precious hexoxen while others extracted Europium from the rare minerals in which it was found. Special freight ships were sent out to gather together the supply of these materials upon which the fate of the earth depended, and rapidly the great quantities of the chemical necessary were stored in the ships.

Captain Linet had proven true to his word, and, with his great executive ability, had made himself invaluable.

It was a pleasant sight to see the huge old Captain, veteran of many a storm in the air, conferring with the slim young Holden, whose pleasant features and soft voice gave no real notion of the immense energy, fiery courage and scientific knowledge which he possessed.

Crews for the three ships had to be assembled. Holden