if a siren whistle was being blown.

"'Pears like there's goin' t' be a tumultuous demonstration of
sub-maxiliary contortions in th' empherial regions contiguous t' th'
upper atmosphere!" exclaimed Washington, entering from the engine room
into the conning tower.

"What's the trouble?" asked Mr. Henderson.

"Terrible big black cloud chasin' us from behind!" exclaimed the
colored man.

Noting the alarm in Washington's voice the professor glanced from the
rear window. What he saw caused him to exclaim:

"It's a cyclone! We must drop down to avoid it!"

He sprang to a lever controlling the gas and yanked it toward him.
There was a shrill hissing sound, and a second later the Mermaid began
to sink. The boys watching the gages on the wall of the tower, saw
that the craft was falling rapidly.

But, with a rush and roar, the terrible wind was upon them. It caught
the craft in its fearful grip and heeled it over as a ship careens to
the ocean blast.

"It's a storm in the upper regions! We'll find it calm below!" cried
the professor above the howling of the gale. He opened the gas outlet
wider and the ship fell more rapidly.