He raced down the stairs with the detective at his heels. He went along the line of touring cars and spoke briefly to the drivers. He climbed into the car which Carnes had brought. As it started the other cars fell in behind it. At a speed of forty miles an hour, with a detachment of motorcycle police leading the van, the cavalcade rolled out through the deserted streets of Washington. Once clear of the city, the speed was increased.

"Did you persuade the President to leave?" asked the doctor.

"There wasn't a chance. The papers panned him so much for following my advice at Charleston that he has turned stubborn. He says that if all the forces of the government can't protect him against one man, he is willing to die."

"We've got to save him," said Dr. Bird grimly. "h.e.l.lo, there's the Chesapeake ahead."

The doctor studied the country.

"We are about opposite the place where we left that sub last night. I fancy that Saranoff will operate from there, for it didn't move during the last half hour we watched it. We'll go back inland a mile or two and spread out. I have no idea how far his radiations will affect the electroscopes, but we'll try four hundred-yard intervals to start.

That will enable us to cover a line twelve miles long."

He picked up a megaphone and spoke to the line of cars behind him.

"Take up four hundred yard intervals when we spread out," he said.

"Every man keep his headphone on and listen for orders. Follow my car until it stops, then turn north and south and drop your men at intervals."

He reentered the car and led the way back for two miles. He halted his car at a crossroad. The cars following him turned and went to the north and south. Besides Carnes and the doctor, the car held two men from the Bureau. As they climbed out, Carnes saw that one of them carried a portable radio sending set, while the other bore an electroscope and a rubber rod. The radio operator set up his device, while the other man rubbed his coat sleeve briskly with the hard rubber and then touched the ball of the electroscope with it. The two bits of gold-leaf spread out.

"While we're waiting, I'll explain something of this to you, Carnes,"

said the doctor. "At four hundred-yard intervals are men with electroscopes like this one. My attempt to locate Saranoff by means of wave detectors was a failure. That proved that the ray he was using is not of the wave type. The other common ray is the cathode ray type which does not consist of vibrations but of a stream of electrons, negative particles of electricity, traveling in straight lines of high velocity. He must be knocking loose some of the electrons when he collapses the atoms. The rate of discharge of these electroscopes will give us a clue to the nearness of his device."

"Once you locate him, how do you propose to attack him?"

"The obvious method, that of using his own ray against him, fell down.

However, in attempting to produce it, I stumbled on another weapon which may be equally effective. I am going to try to use an exact opposite of his ray. The cathode ray, when properly used, will bombard the atoms and knock electrons loose. I perfected last night a device on which I have been working for months. It is a super-cathode ray. I tested it on the yellow powder and find that I can successfully reverse Saranoff's process. He can contract matter together until it occupies less than one one-thousandth of its original volume. My ray will destroy this effect and restore matter to something like its original condition."

"And the effect will be?"

"Use your imagination. He blasts out a hole by condensing the rock to a pinch of yellow powder. He moves forward into the hole he has made.

I come along and reverse his process. The yellow powder expands to its original volume and the hole he has made ceases to exist. What must happen to the foreign body which had been introduced into the hole that is no longer a hole?"

Carnes whistled.

"At any rate, I hope that I am never in a hole when that happens."

"And I devoutly hope that Saranoff is. I met with one difficulty. My ray will not penetrate the depth of solid rock which separates his borer from the surface."

"Then how will you reach him to crush him? You don't expect to drill down ahead of him?"

"That is my stroke of genius, Carnes. I am going to make him bore the hole down which my ray will travel to accomplish his destruction. The cathode ray and rays of that type--"

"Pardon me, Doctor," interrupted the radio operator. "I have just received a message from the squadron leader of the planes patrolling the bay. He states that every inch of the Chesapeake Bay and the Potomac River have been examined and no submarine is visible."

"I expected that. He will have opened a cavern under the earth, in which his craft is safe from aerial observation. Once the borer has left it, it is invulnerable no longer."

"What reply shall I make?"

"Tell him to keep up a constant patrol. Three navy subs with radite-charged torpedos are on their way up the bay, together with half a dozen destroyers. The subs will scout for such a hole as I have described and will attack his sub if they find it. The destroyers will stand by and support them."

The operator turned to his instrument. The electroscope observer claimed the doctor's attention.

"There is a steady leak here, Doctor," he said. "I get a discharge in eleven minutes."

"Probably a result of his work in opening the hiding place for his submarine last night. Keep it charged, Jones."

"What did you say about the cathode ray, Doctor?" asked Carnes.

"The cathode ray? Oh, yes. I said that rays of that type were attracted by--h.e.l.lo, look there!"

From a point a mile to the north a ball of red fire streaked up into the air. A moment later similar signals rose from other watchers in the line.

"It works, Carnes!" cried the doctor as he rushed for the car. "We've got him this time!"

The car raced along the road. At the first man who had signalled, it slackened speed. The doctor leaned out.

"What is your discharge rate?" he called.

"Eight minutes. Doctor."

The car rolled on. Dr. Bird repeated the question at the next post and was told that the electroscope there was losing its charge in seven minutes. The next man reported four minutes and the next man, one minute. The following station reported three minutes.

"It's right along here somewhere!" cried the doctor. "Summon everyone to this point and take up twenty-yard intervals."

From the north and south the cars came racing in. The instruments were spread out along a new line twenty yards apart. As the borer was located the intervals were decreased to fifteen feet. Dr. Bird thrust a long white rod into the ground.

"His path lies under here," he said. "Into the cars and go back a mile and test again."

The borer was making slow progress, and it was half an hour before Dr.

Bird drove the second stake in the ground. With a transit he took the bearing of the path and laid it out on a large scale map.

"We'll stop him between Marr and Ritchie," he announced. "Jones, I am going back and set up my apparatus. Keep track of his movements. If he changes direction, let me know at once."

The doctor's car tore off to the west. Near Upper Marlboro, he met the convoy of trucks and led them to the selected spot. The trucks were unloaded and the apparatus laid out. Attached to a huge transformer were a dozen strange-looking projectors. What puzzled Carnes most was a huge built-up steel bar wound about with heavy cable. Dr. Bird had this bar erected on a truck and located it with great exactness. The projectors were set up in a battery just east of the bar.

"How about power?" asked the doctor.

"We'll have it in five minutes," replied one of the men. "A power transmission line carrying twenty-two thousand pa.s.ses within two hundred yards of here. We are phoning now to have the power cut off.

As soon as the line is dead we'll cut it and bring the ends here."

The electrician was good at his word. In five minutes the power line had been cut and cables spliced to the ends. The cables were brought to the doctor's apparatus and the main lines were rigged to the ends of the cable wound around the bar. In parallel on taps, the projectors were connected. Huge oil-switches were placed in both lines.