ationary, merely undulating with the roll and heave of the ocean.

Hurrying to the cabin, Captain Henderson opened the side window
shutters, turned off the electric lights and peered out.

"I can't see anything," he said. "Yet I should be able to, as we are not
very deep."

The gage showed that the ship was submerged only thirty feet, and at
that depth there should have been no difficulty in seeing, at least
dimly, objects under water. But the windows showed as black as night.

"Bring me one of the portable searchlights," called Mr. Henderson.

Washington brought one, operated by a storage battery. Holding it so the
reflector cast the beams out of the bull's-eye and into the water on the
opposite side, the inventor peered forth.

"I was afraid of this!" he murmured.

"What is it?" asked Jack.

"We are caught in the Sargasso Sea," replied Mr. Henderson.

"The Sargasso Sea?" repeated Mark, in a questioning tone. "What is
that?"

"It is a great sea of grass," replied the captain. "An immense ocean of
sea weed, that sometimes floats on the surface and sometimes a little
below. The stalks or blades of the grass are very long and closely
matted together."

"Is there any danger?" asked Andy in some alarm.

"Very much," answered the professor quietly. "A ship, once fairly
entangled in the grass or sea weed, seldom gets out. If it is a sailing
ship the weed clings to the rudder, making steerage impossible, and even
in a strong wind the ship cannot get free of the mass. The grass winds
about the propellers of steamships, and holds them as tight as in a
vise.

"Sometimes a great storm may tear the mass of weed loose from the bottom
of the ocean, and then the ship is free. But the Sargasso Sea is the
graveyard of many a fine vessel."

The pumps were set going. Anxiously everyone watched the gage. The
pointer never moved, but remained at thirty feet. The _Porpoise_ was
caught.

"Well, since we can't go up, let us see if we can go down," said the
inventor. "Perhaps we can dive under the sea weed."

The cocks of the tanks were opened and the water rushed in. Under the
weight of it the ship should have sunk to the bottom. Instead it
remained just where it was, thirty feet below the surface.

"Try the screw again," suggested Andy, "Maybe we can back out."

The big propeller in the tube was started going in a reverse direction,
but the _Porpoise_ only moved a few feet and then stopped. To go forward
was equally imp