away. What would you
suggest, sir?"

Captain Petersen meditated, while Larry held his breath.

"To turn back," he said at length, in his clear, precise English,
"would in my opinion be to give the laugh to someone whose sense of
humor is already too well developed."

"Exactly!" agreed Professor Stevens, as Larry relaxed in relief.
"Whoever this practical joker is, we will show him he is wasting his
talents--even though it means carrying a supernumerary for the rest of
the voyage."

"Well spoken!" said the captain. "But as far as that is concerned, I
think I can keep Mr. Hunter occupied."

"Then take him, and welcome!"

Whereupon, still elated but now somewhat uneasy, Larry accompanied
Captain Petersen from the mess-room; started to, that is. But at a
glance of sympathy from Diane, he dared call out:

"Say--hold on, folks! I haven't had lunch yet!"

* * * * *

When young Larry Hunter reported to the captain of the _Nereid_, after
this necessary meal, he found that the craft had returned to the
surface.

Assigned a pair of powerful binoculars, he was ordered to stand watch
in the conning-tower and survey the horizon in every direction, in an
effort to sight the vessel that had sent out that mysterious radio,
but though he cast his good brown eyes diligently through those strong
lenses, he saw not so much as a smoke tuft upon the broad, gray-blue
surface of the hazy Atlantic.

Gradually, however, as the afternoon wore away, something else came in
view. Masses of brownish seaweed, supported by small, berry-like
bladders, began drifting by. Far apart at first, they began getting
more and more dense, till at last, with a thrill, he realized that
they were drawing into that strange area known as the Sargasso Sea.

Shortly after this realization dawned, he was ordered below, and as
the tropic sun was sinking over that eery floating tombstone, which
according to Professor Stevens marked a nation's grave, the _Nereid_
submerged.

Down she slid, a hundred fathoms or more, on a long, even glide that
took her deep under that veiling brown blanket.

* * * * *

In the navigating room now, Larry stood with the captain, the
professor and Diane, studying an illuminated panel on which appeared a
cross of five squares, like a box opened out.

The central square reproduced the scene below, while those to left and
right depicted it from port and starboard, an