"We'll, there's no accounting for boys nowadays," sighed Mr. Barr,
"however, you needn't worry about this money--there'll be plenty of
it and it'll all be good honest coin."

"What do you wish us to do?" demanded Frank.

"Just this: Mr. Beasley here and me is in on a deal in ivory. That
is, we were, but the big cache we had hoarded up in the Kuroworo
Mountains in the Bambara country has been stolen by a rival trader,
an Arab named Muley-Hassan. We know where he's hidden it and we
know, too, that he won't dare to bring it out till he thinks that we
aren't watching him. Now the time is ripe for a big deal in Ivory.
There is a shortage in the market. Prices will go up sky high. If
we get it out in time we'll make a barrel of coin, but if we don't
we stand to lose heavily."

Mr. Beasley gave a groan; to the boys' amazement he seemed to be
about to collapse. Lathrop too looked ill and anxious. Old Barr
paid no attention, however, but went on.

"Now, I heard about you boys and your air-ship, and I heard, too,
that you was planning a little trip to Africa and thought you might
like to combine business and pleasure."

He drew from his pocket a much-thumbed, crudely drawn map and spread
it out on the table. How he obtained it, the boys never learned
exactly, but they heard later that a treacherous attendant of the
ivory dealer had sold it to him for a good round sum.

"This country down here," he said, indicating it with a black rimmed