don't you go up, Tom?"

"I'm trying to," answered the young inventor. "Something seems to be
the matter." He pulled the speed lever over a few more notches, and
increased the power of the gas machine. Still the Black Hawk did not
rise.

"Bless my handkerchief box!" cried Mr. Damon, "what's the matter?"

"I don't know," answered Tom. "We seem to be held fast."

He further increased the speed of the propellers, and the gas
machine was set to make vapor at its fullest capacity, and force it
into the bag. Still the craft was held to the earth.

"Maybe the gas has no effect in this climate," called Ned.

"It can't be that," replied Tom. "The gas will operate anywhere. It
worked all right today."

Suddenly she airship moved up a little way, and then seemed to be
pulled down again, hitting the ground with a bump.

"Something is holding us!" cried Tom. "We're anchored to earth! I
must see what it is!" and, catching up his electric rifle, he dashed
out of the cabin.