"Commander," said Captain Wallace, "I beg to report that the pole star has suddenly fallen five degrees south from its position overhead, and the sun has risen to his mid-day position in the sky! I fear we are sailing into a vast polar depression something greater than the description given in our geographies, that the earth is flattened at the poles." "Do you really think, captain," I inquired, "that we are sailing into a hollow place around the pole?" "Why, I am sure of it," said he. "Nothing else can explain the sudden movement of the heavenly bodies. Remember, we have only passed the 85th parallel but a few miles and ought to have the pole star right overhead." "Professor Starbottle has a theory," I said, "that may account for the strange phenomena we witness. Let these gentlemen hear your theory, professor." The professor stated very deliberately what he had already communicated to me, viz.: that we were really descending to the interior of the earth, that the bows of the ship were gradually pointing to its centre, and that if the voyage were continued we would find ourselves swallowed up in a vast polar gulf leading to God knows what infernal regions. The terror inspired by the professor's words was plainly visible on every face. "Let us turn back!" shouted some of the sailors. "My opinion," said the captain, "is that we have entered a polar depression; it is impossible to think that the earth is a hollow shell into which we may sail so easily as this." "If I might venture a remark," said Pilot Rowe, "I think Professor Starbottle is right. If the earth is a hollow shell having a subterranean ocean, we can sail thereon bottom upward and masts downward, just as easily as we sail on the surface of the ocean here." "I believe an interior ocean an impossibility," said the captain. "You're right, sorr," said the master-at-arms, "for what would keep the ship sticking to the wather upside down?" [Illustration: THE TERROR INSPIRED BY THE PROFESSOR'S WORDS WAS PLAINLY VISIBLE ON EVERY FACE.] "I don't say that the earth is absolutely a hollow sphere," said the professor, "but I do say this, we are now sailing into a polar abyss, and if the sun disappears at noon to-day it will be because we have sailed far enough into the gulf to put the ocean over which we have sailed between us and that luminary. If the sun disappears at noon, depend upon it we will never reach the pole, which will forever remain only the ideal axis of the earth." "Do you mean to say," I inquired, "that what men have called the pole is only the mouth of an enormous cavern, perhaps the vestibule of a subterranean world?" "That is precisely the theory I advance to account for this strange ending of our voyage," said the professor. The murmurs of excitement among the men again broke out into wild cries of "Turn back the ship!"