The destroyer staggered for a moment, and the entire central section of the ill-fated ship disappeared. The bow and stern came together with a rush and went down in a swirling maelstrom of water. The plane lurched in the air as a thundering crash rose from the sea.

The second destroyer, in no way daunted by the fate of her colleague, rushed to the attack. Dr. Bird pounded his key frantically in an attempt to turn her back. His message was too late or was misunderstood. Straight over the submarine went the second ship. Again came the red flash. The forward half of the destroyer disappeared and the stern slid down into a huge hole which had opened in the water.

"He's invulnerable!" cried the doctor. He pounded his key with feverish rapidity. The two remaining destroyers slackened speed and veered off. Slowly, as though loath to turn their backs on the enemy, they headed out for the broad Atlantic and comparative safety.

The submarine went slowly on her way. She did not turn west at the mouth of the Potomac but continued on up the bay. As long as there was light enough, the doctor's plane kept above her but the fading light soon made it impossible to see her. When she had disappeared from view, the doctor reluctantly gave the word to return to Washington.

"Where do you suppose he will attack next, Doctor?" asked Carnes when they sat again in the doctor's private laboratory.

"Washington, of course," said Dr. Bird absently as he looked up from a pile of telegrams he was running through.

"Why Washington?"

"Use your head. Representatives of every civilized power are in Washington now at the President's invitation to consider means of halting the anti-religious activities of the Soviets. The destruction of the city and the killing of these men would be a telling blow for Russia to strike."

"But, Doctor, you don't think--"

"Excuse me, Carnes; that will keep. Let me read these telegrams."

For half an hour silence reigned in the laboratory. Dr. Bird laid down the last message with a sigh.

"Carnes," he said, "I'm check-mated. I sent out a hundred ultra-sensitive short wave receivers yesterday. Four of them were located within fifty miles of Wilmington, North Carolina. One of these four was destroyed, but none of the others detected a sign of a wave during the attack. One of them was within a hundred feet of the edge of the hole. If he isn't using a ray of some sort, what on earth is he using?"

"It looked like a flash of red light when it came from the submarine."

"Yes, but it couldn't be light. Let me think."

The doctor sat for a few minutes with corrugated brows. Suddenly he sprang to his feet.

"I deserve to be beaten," he cried. "Why didn't I think of that possibility before?"

He hurried into his laboratory and brought out a small box with a gla.s.s front. From the top projected a spike topped with a ball.

Through the gla.s.s, Carnes could see a thin sheet of metal hanging pendant from the spike.

"An electroscope," explained the doctor. "That sheet of metal is really two sheets of gold-leaf, at present stuck together. If I rub a piece of hard rubber with a woolen cloth, the rod will become charged with static electricity. If I then touch the ball with it, the charge is transferred to the electroscope and causes the two sheets of gold-leaf to stand apart at an angle. Watch me."

He took a hard rubber rod and rubbed it briskly on his coat sleeve. As he touched the ball of the electroscope the sheets of gold-leaf separated and stood apart at a right angle.

"As long as the air remains non-conducting, the two bits of gold-leaf will hold that position. The air, however, is not a perfect insulator and the charge will gradually leak off. If I bring a bit of radioactive substance, for instance, pitchblende, near the electroscope, the charge will leak rapidly. Do you understand?"

"Yes, but how is that going to help us?"

"Saranoff is accomplishing his result by artificially compressing the atoms. It is inevitable that he will do it imperfectly, and some electrons will be loosened and escape. These electrons, traveling up through the earth will make the air conducting. To-morrow we will have a means of locating the borer under ground."

"Once you locate it, how will you fight it?"

"That is the problem I must work out to-night."

"Could we bury a charge of explosive and blow it up?"

"Ordinary explosives would be useless," the doctor answered. "They would react in the same manner as other substances, and would be rendered harmless. Radite might do the work if it could be placed in the path, but it couldn't be. We may locate the position and depth of the borer, but long before we could dig and blast a hole deep enough to place a charge of radite before it, it would have pa.s.sed on or changed direction. No, Carnes, old dear, the only solution that I can see is to turn his own guns on him. If I can, before morning, duplicate his device, we can train it on the spot where he is and reduce him and his machine to a pinch of yellow powder."

"Can you do it, Doctor?"

"What one man's brain can device, another man's brain can duplicate.

The only question is that of time. I am confident that Saranoff will attack Washington to-morrow. If I can do the job to-night, we may save the city. If not--At any rate, Carnes, your job will be to see that the President and all of the heads of the government are out of the city by morning. The President may refuse to leave. Knowing him as I do, I rather expect he will."

"In that case, the issue is in the hands of the G.o.ds. Now get out of here. I want to work. Report back at daybreak with a car."

Dr. Bird turned back to his laboratory.

"He must be using a ray of some sort, possibly a radium emanation," he muttered to himself. "That would have no wave motion and might accomplish the result, although I would expect the exact opposite from it. The first thing to do is to examine that powder with a spectroscope and see if I can get a clue to the electronic arrangement."

When Carnes arrived at the Bureau of Standards at dawn be rubbed his eyes in astonishment. The buildings were lighted up and the grounds swarmed with workmen. Before the buildings were lined up a dozen trucks and twice that many touring cars. A cordon of police held back the curious. Carnes' gold badge won him an entrance and he hurried up the stairs to Dr. Bird's laboratory. The doctor's face was drawn and haggard, but his eyes glowed with a feverish light. Workmen were carrying down huge boxes.

"What's up, Doctor?" demanded the detective.

"Oh, you got here at last, did you? You're just in time. If you'd been fifteen minutes later, you would have found us gone."

"Gone where?"

"Out into Maryland in an attempt to stop Saranoff in his progress toward Washington."

"Have you found your means of combating him?"

"I hope so, although it is not what I started out to get. Did you bring a car as I told you?"

"It's waiting below."

"Good enough. I'll go in it. Williams, are those projectors all loaded?"

"Yes, Dr. Bird. The magnet will be ready to go in five minutes. The electroscopes and the other light stuff are all loaded and ready to move."

"You have done well. I'll let you bring the trucks and heavy equipment while I go ahead with the instruments. Take the road out toward Upper Marlboro. If I don't meet you before, stop there for orders."

"Very well, Doctor."

"Come on, Carnes, let's go."