t
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--Hello, 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