"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.