ent was
far more horizontal than vertical. As for discovering the exact depth to
which we had attained, nothing could be easier. The Professor as he
advanced measured the angles of deviation and inclination; but he kept
the result of his observations to himself.

About eight o'clock in the evening, my uncle gave the signal for
halting. Hans seated himself on the ground. The lamps were hung to
fissures in the lava rock. We were now in a large cavern where air was
not wanting. On the contrary, it abounded. What could be the cause of
this--to what atmospheric agitation could be ascribed this draught? But
this was a question which I did not care to discuss just then. Fatigue
and hunger made me incapable of reasoning. An unceasing march of seven
hours had not been kept up without great exhaustion. I was really and
truly worn out; and delighted enough I was to hear the word Halt.

Hans laid out some provisions on a lump of lava, and we each supped with
keen relish. One thing, however, caused us great uneasiness--our water
reserve was already half exhausted. My uncle had full confidence in
finding subterranean resources, but hitherto we had completely failed in
so doing. I could not help calling my uncle's attention to the
circumstance.

"And you are surprised at this total absence of springs?" he said.

"Doubtless--I am very uneasy on the point. We have certainly not enough
water to last us five days."

"Be quite easy on that matter," continued my uncle. "I answer for it we
shall find plenty of water--in fact, far more than we shall want."

"But when?"

"When we once get through this crust of lava. How can you expect springs
to force their way through these solid stone walls?"

"But what is there to prove that this concrete mass of lava does not
extend to the centre of the earth? I don't think we have as yet done
much in a vertical way."

"What puts that into your head, my boy?" asked my uncle mildly.

"Well, it appears to me that if we had descended very far below the
level of the sea--we should find it rather hotter than we have."

"According to your system," said my uncle; "but what does the
thermometer say?"

"Scarcely fifteen degrees by Reaumur, which is only an increase of nine
since our departure."

"Well, and what conclusion does that bring you to?" inquired the
Professor.

"The deduction I draw from this is very simple. According to the most
exact observations, the augmentation of the temperature of