have come upon
the wreck so soon."

At that moment a man entered the cabin.

"Trouble, Mr. Swift!" he reported.

"What kind?" asked Tom.

"Our propellers are tangled with a mass of serpent weed," was the
answer. "They're both fouled, and we can't budge."

"Bless my anchor chain!" ejaculated Mr. Damon. "Stuck again!"

CHAPTER XX

THE DEVIL FISH

It was true. The long sinuous strands of ocean grass, known under the
name of "serpent weed," had caught around the whirling propellers and
there had been wound and twisted very tightly. Just as sometimes the
stern line gets so tightly twisted around a motor boat propeller as to
require hours of work with an axe to free it, the seaweed was twisted
around the blades of the M. N. 1.

Slowly the undersea craft came to a stop, and there she remained,
floating freely enough, but a few feet above the bottom of the ocean.
There was a look of alarm on the faces of Ned and Mr. Damon, but Tom
Swift smiled.

"This is annoying, and may cause us delay," he announced, "but there is
no danger."

"How are we to get free from the weed?" asked Mr. Damon. "We can't move
if it's wound around our propellers, can we?"

"Not very well," Tom answered. "But all that will have to be done will
be for some of us to put on diving suits, go out and chop the strands
of weed away. We can do it more easily than could an ordinary vessel,
for they would have to go into dry dock for the purpose. I think I'll
go out myself. I want to look around a little."

"I'll go with you," said Ned. "As long as we haven't seen any sharks I
don't mind."

"Nor gigantic starfish, either," added Tom with a smile, and Ned nodded
in agreement.

"We might try reversing the propellers," suggested the man from the
engine room, who had come in with the information about the serpent
weed. "The chief didn't like to try that. We saw the weed from our
observation windows and stopped as soon as we felt we had fouled it."

"That was right," commended Tom. "Well, try reversing. It can't do any
harm, and it may make it easier for us to free the propellers when we
go out."

He went to the engine room himself to see that everything was properly
attended to. Slowly the motors were reversed, and only a slight current
was given them, as, with the resistance of the tightly wound weed, too
powerful a force might burn out the insulation.

Slowly the starting lever was thrown over. There was a low humming and
whining as