of blue flame and smoke shot from the detonating exhaust.

"All ready, Harry?" cried Frank to the younger boy who was at his
old station by the engines.

"Ay, ay!" came the response in a hearty tone. "Then let her go."

With a quick movement Frank threw in the clutch.

The mighty propellers began to beat the air with the whirring sound
of a swarm of gigantic locusts in full flight, and after a short run
the great aeroplane took the air in a long graceful rising arc.
Half an hour later, to the watchers in the camp, she was little more
than a speck against the sky.

Frank, his eye constantly on the compass, kept the ship on a true
course for the Moon Mountains which, now that they were flying far
above the dense forest region, lay a rugged mass of blue and brown,
piled like some giant's playthings--on the northwestern horizon.

Even from the distance at which the boys viewed them they conveyed
an almost sinister impression in their rugged shapes. Their harsh
outlines cut the sky in a serrated line like the teeth of a huge
saw.

"Look, look, Frank!" shouted Harry suddenly as they were passing
high over a small clearing.

Both Frank and Ben peered over the side in answer to the boy's
excited hail.