s fingers came in contact
with a silver dollar and a disc of celluloid. Of a sudden an eager
light flashed into his eyes. "What kind of money did that Mexican
have?" he demanded.

"Some silver," said the Chief indifferently.

"Of what denominations?"

"Dollars. He had three of them."

"What was done with that money?" asked the captain with an earnestness
that was almost tragic.

"Oh! The greaser made such a disturbance that the jailer let him keep
it. He's got it with him in the jail."

A great sigh burst from Captain Hardy's lips. "Telegraph your men
instantly," he cried, "to get those dollars. That Mexican is no
smuggler. He's a spy. He's the man who carries the messages across
the border. The messages are on the dollars. And here's the key to
the cipher!"

And he drew from his pocket and laid before the Chief a battered silver
dollar and a curiously marked celluloid disc.

CHAPTER XVI

AN UNEXPECTED MESSAGE

"Was he surprised?" cried the four boys of the wireless patrol, as
their captain entered the living-room after his trip to the secret
service offices.

Captain Hardy chuckled. "I think he was," he said. "But for a time it
was I who was surprised. The Chief knew from his own men all about
yesterday's message. One of them picked it up. What's more, he has a
lot of amateurs in different parts of the country listening in, just as
you are doing, and they picked up yesterday's message at enough
different points to indicate the line of the secret stations we are
after. The messages are crossing the border somewhere near El Paso.
But the Germans are getting them across in some way other than by
wireless. They know we'd spot their outfit quick. The Chief thinks
some one telephones the messages the last lap and that a messenger
carries them into Mexico."

"And what about the dollar and the disc?" asked Roy. "What did the
Chief think of them?"

"Well, he was surprised. And what's more, we got hold of that dollar
at exactly the right moment. The secret service men arrested a Mexican
who was wading the Rio Grande at El Paso last night. They searched him
and found nothing on him that seemed incriminating. They questioned
him and the fellow finally said he had smuggled some tobacco into this
country, so they put him in jail as a smuggler. The fellow had some
money he had gotten for his tobacco--and it was three silver dollars!
The secret service men down there knew nothing of wh