Morning found the travelers above a great, grassy plain, dotted here
and there with negro settlements which were separated by rivers,
lakes or thin patches of forest.

"Well, we'll speed up a bit," decided Tom after breakfast, which was
eaten to the weird accompaniment of hundreds of native warning-
drums, beaten by the superstitious blacks.

Tom went to the engine room, and turned on more speed. He was about
to go back to the pilot house, to set the automatic steering
apparatus to coincide with the course mapped out, when there was a
crash of metal, an ominous snapping and buzzing sound, followed by a
sudden silence.

"What's that?" cried Ned, who was in the motor compartment with his
chum.

"Something's gone wrong!" exclaimed the young inventor, as he sprang
back toward the engine. The propellers had ceased revolving, and as
there was no gas in the bag at that time, it having been decided to
save the vapor for future needs, the Black Hawk began falling toward
the earth.

"We're going down!" yelled Ned.

"Yes, the main motor has broken!" exclaimed Tom. "We'll have to
descend to repair it."

"Say!" yelled Mr. Damon, rushing in, "we're right over a big African