That would be unfortunate," he said, with his frosty smile. "Stanley
assures us this glass is unbreakable. He means commercially unbreakable.
What would happen to it if it were submitted to the strain of being
flung against a rock pile--in addition to the enormous stress of the
water pressure--I don't know. It's your job to see that we don't have to
find out!"

* * * * *

It had been planned to test the sphere empty first to see how it stood
the strain.

We drifted to a full stop over the center of Penguin Deep where we were
to gamble our lives in a game with Neptune. Sea anchors were rigged to
lessen our drift and the donkey engine was geared to the first cable
drum.

There was an impressive row of these drums, each holding an interminable
length of three-quarter-inch cable. The bulk of a mile of steel cable
has to be seen to be believed!

The glass sphere was lifted from the hold, delicately for all its
enormous weight, and swung over the rail preparatory to being lowered
into the depths.

Not until that moment did I notice two things: that there was no
fastening of any kind to keep the thick lid in place: and that the
three-quarter-inch cable looked like a pack thread in comparison to the
ponderous bulk it strained to support.

"We couldn't use a heavier cable," said the Professor, "because of the
strain. We're overloading the hoist as it is. As for the lid being
fastened down--I think you'll find it will be pressed into place
securely enough!"

There was unanimous silence as the great globe slipped into the
sea--down and down until the last reflection of the morning sun ceased
to shimmer from its surface. Drum after drum was played out, till the
first mate held his hand up to check the engineer.

"Five thousand feet, sir," he called to Stanley.

"Haul it back up. And let us hope," Stanley added fervently, "that we'll
find the gadget in one piece."

* * * * *

The engine began to snort rhythmically. Dripping, vibrating, the coils
of cable began to crawl back in place on the drums. There was a glint
under the surface again as the sunlight reflected on the nearing sphere.

The great ball flashed out of the water, and a cheer burst from the
throats of all of us. It was absolutely unharmed. Only--there was a
beading of fine moisture inside the thick globe. What that could mean,
none of us could figure out.

"Difference in temperature?" worri