the M. N. 1 began behaving in a most peculiar manner.

She appeared to be acting like a corkscrew. While her bow was
comparatively steady, her stern described a circle in the water
which was churned to mud by the two propellers, each being
revolved in a different direction.

"I'm trying to make the hole bigger just as an amateur
carpenter makes a nail hole bigger, so he can pull out the nail,
by twisting it around," explained Tom. "The motion may be a bit
unpleasant, but it is needful."

And indeed the motion was unpleasant. Tom, veteran airman and
sailor that he was, began to feel a trifle seasick, and Hr.
Hardley was in very evident distress.

Suddenly, however, something happened. The M. N. 1 gave a lurch
to one side and then shot upward so quickly that Ned and Mr.
Damon lost their balance and slumped over on the bench that ran
around three sides of the room.

"Are we free?" cried Mr. Hardley.

"We have come loose from the mud bank," said Tom quietly. "By
boring into it the hole was enlarged sufficiently to enable us to
pull loose. There is no more danger!"

His announcement was received in momentary silence, and then
Ned exclaimed: