" said Tom.

"Yes," replied Dick Sand, "and now it prevents the interior air from
being renewed."

"Could we not make a hole in the wall above the level of the water?"
asked the old black.

"Doubtless, Tom; but if we have five feet of water within, there are
perhaps six or seven, even more, without."

"You think, Mr. Dick--?"

"I think, Tom, that the water, rising inside the ant-hill, has
compressed the air in the upper part, and that this air now makes an
obstacle to prevent the water from rising higher. But if we pierce a
hole in the wall by which the air would escape, either the water would
still rise till it reached the outside level, or if it passed the
hole, it would rise to that point where the compressed air would again
keep it back. We must be here like workmen in a diving-bell."

"What must be done?" asked Tom.

"Reflect well before acting," replied Dick Sand. "An imprudence might
cost us our lives!"

The young novice's observation was very true.

In comparing the cone to a submerged bell, he was right. Only in that
apparatus the air is constantly renewed by means of pumps. The divers
breathe comfortably, and they suffer no other inconveniences than
those resulting from a prolonged sojourn in a compressed atmosphere,
no longer at a normal pressure.

But here, beside those inconveniences, space was already reduced a
third by the invasion of the water. As to the air, it would only be
renewed if they put it in communication with the outer atmosphere by
means of a hole.

Could they, without running the danger spoken of by Dick Sand, pierce
that hole? Would not the situation be aggravated by it?

What was certain was, that the water now rested at a level which only
two causes could make it exceed, namely: if they pierced a hole, and
the level of the rising waters was higher outside, or if the height
of this rising water should still increase. In either of these cases,
only a narrow space would remain inside the cone, where the air, not
renewed, would be still more compressed.

But might not the ant-hill be torn from the ground and overthrown by
the inundation, to the extreme danger of those within it? No, no more
than a beaver's hut, so firmly did it adhere by its base.

Then, the event most to be feared was the persistence of the storm,
and, consequently, the increase of the inundation. Thirty feet of
water on the plain would cover the cone with eighteen feet of water,
and bear on the air within