his shaggy gray hair, and murmured something in German.

"Where did you meet the man?" asked Jack of the young motorcyclist.

"About two miles down the road. He was walking along, sort of talking
to himself, and I was afraid of him. He called to me, and offered me a
half a dollar to deliver this message. I didn't want to at first, but
he said if I didn't he'd hurt me, so I took it. Is it anything bad?"

"We don't know yet," replied Mark.

"No, that is the worst of it," added Professor Roumann. "He has made a
threat, but we can't tell whether or not he will accomplish it. We are
in the dark. He may have done some secret damage to our machinery, and
it will take a careful inspection to show it."

"And will the inspection have to be made now?" asked Jack.

"I think so," answered Professor Henderson gravely. "It would not be
safe to start for the moon and have a breakdown before we got there. We
must wait until morning to begin our trip."

"It will be the safest," spoke the German, and the boys, in spite of
the fact that they were anxious to get under way, were forced to the
same conclusion.

"Then if we're going to camp here for the night," proposed old Andy,
"what's the matter with me and the boys having a hunt for that man?
We've put up with enough from him, and it's time he was punished. If we
let him go on, he'll annoy us all the while, if not now, then after we