Towards morning the ascending movement became accelerated. If the heat increased, instead of diminishing, as we approached nearer to the surface of the globe, this effect was due to local causes alone, and those volcanic. The manner of our locomotion left no doubt in my mind. An enormous force, a force of hundreds of atmospheres, generated by the extreme pressure of confined vapours, was driving us irresistibly forward. But to what numberless dangers it exposed us!
Soon lurid lights began to penetrate the vertical gallery which widened as we went up. Right and left I could see deep channels, like huge tunnels, out of which escaped dense volumes of smoke; tongues of fire lapped the walls, which crackled and sputtered under the intense heat.
"See, see, my uncle!" I cried.
"Well, those are only sulphureous flames and vapours, which one must expect to see in an eruption. They are quite natural."
"But suppose they should wrap us round."
"But they won't wrap us round."
"But we shall be stifled."
"We shall not be stifled at all. The gallery is widening, and if it becomes necessary, we shall abandon the raft, and creep into a crevice."
"But the water—the rising water?"
"There is no more water, Axel; only a lava paste, which is bearing us up on its surface to the top of the crater."