and a man
dressed as a waiter, whom they had seen in the hallway as they entered,
stepped into the room.

"I came to show you your outfit," he said.

Stepping into the writing room, he grasped the corners of the mantel and
gave a sharp pull. The entire upper half of the mantel swung outward and
came to rest on the writing-table, revealing a compact but wonderfully
well-equipped wireless outfit, including even a wireless detector for
telling the direction a wireless message came from. The boys stared in
astonishment while the waiter grinned.

"What kind of a boarding-house is this, anyway?" asked Lew.

"This ain't no boardin'-house," replied the man. "This is a sort of
headquarters for secret service men from out of town."

"Where's your aerial?" demanded Willie.

"If you go on the roof you'll see it--that is you will if your eyes are
sharp enough."

"I'll bet it's those wire clothes-lines," said Willie.

"Nothin' wrong with your eyes," said the waiter with a smile. "But I
guess there wouldn't be, if the Chief sent you here."

Naturally each of the boys was eager to test the outfit before them.
They crowded round it, sliding the coil, shifting the condenser,
examining this and that, and voicing their approval and pleasure in the
different instruments.

"We may as well begin our watch at once," said Captain Hardy. "Each of
you will have to listen in six hours a day. If we divide the watches
into two tricks of three hours each, it will be easier for you."

The matter was arranged accordingly, and the first trick given to the
most experienced operator, Henry. After the others had seen him take his
seat and adjust his receivers to his head, they withdrew from the
wireless room.

But Henry was far from being in solitude. Sitting apparently alone, he
was listening to a multitude of voices; for before beginning his vigil he
wanted to test out his instruments and see how well they worked and how
sharply they would register sounds. So he sat at his table, tuning now
to this wave length and now to that, now catching a land message and now
one from the sea. Distinctly he caught the signal NAA from the great
navy wireless plant at Arlington. He recognized it before the operator
had finished sending his call signal. Night after night with his
home-made outfit at Central City, Henry had heard this station send forth
the time signals at ten o'clock; and during his brief period as radio man
for Uncle Sam he ha