It was a bright, sunshiny morning a week later. The Southern Cross was
now in sub-tropic waters, steaming steadily along under blue skies and
through smooth azure water flecked here and there with masses of
yellow gulf weed.

The boys were in a group forward watching the flying fish that fled
like coveys of frightened birds as the bow of the polar ship cut
through the water. Under Dr. Gregg's care Billy and Harry had quite
recovered from their sea-sickness.

"Off there to the southeast somewhere is the treasure galleon and the
Sargasso Sea," said Harry, indicating the purplish haze that hung on
the horizon. [Footnote: See Vol. 4 of this series, The Boy Aviators'
Treasure Quest; or, The Golden Galleon.]

"Yes, and off there is the South Pole," rejoined Frank, pointing due
south, "I wish the old Southern Cross could make better speed, I'm
impatient to be there."

"And I'm impatient to solve some of the mystery of this voyage," put
in Billy, "here we've been at sea a week and Captain Hazzard hasn't
told us yet anything about that--that,--well you know, that ship you
spoke about, Frank."

"He will tell us all in good time," rejoined the other, "and now
instead of wasting speculation on something we are bound not to find
out till we do find it out, let's go aft to the wireless room and
polish up a bit."

The Southern Cross carried a wireless apparatus which had been