A long and learned talk was started on this subject between Altamont and the Doctor, simplified, however, as much as possible for the benefit of Bell and Johnson. Hatteras took no part in it, and even when they went on to speculate about the earth's centre, and discussed several of the theories that had been advanced respecting it, he seemed not to hear; it was evident his thoughts were far away. Among other opinions put forth was one in our own days, which greatly excited Altamont's surprise. It was held that there was an immense opening at the poles which led into the heart of the earth, and that it was out of the opening that the light of the Aurora Borealis streamed. This was gravely stated, and Captain Synness, a countryman of our own, actually proposed that Sir Humphrey Davy, Humboldt, and Arago should undertake an expedition through it, but they refused." "And quite right too," said Altamont. "So say I; but you see, my friends, what absurdities imagination has conjured up about these regions, and how, sooner or later, the simple reality comes to light." CHAPTER XXIV. MOUNT HATTERAS. After this conversation they all made themselves as comfortable as they could, and lay down to sleep. All, except Hatteras; and why could this extraordinary man not sleep like the others? Was not the purpose of his life attained now? Had he not realized his most daring project? Why could he not rest? Indeed, might not one have supposed that, after the strain his nervous system had undergone, he would long for rest? But no, he grew more and more excited, and it was not the thought of returning that so affected him. Was he bent on going farther still? Had his passion for travel no limits? Was the world too small for him now he had circumnavigated it. Whatever might be the cause, he could not sleep; yet this first night at the Pole was clear and calm. The isle was absolutely uninhabited--not a bird was to be seen in this burning atmosphere, not an animal on these scoriae-covered rocks, not a fish in these seething waters. Next morning, when Altamont, and the others awoke, Hatteras was gone. Feeling uneasy at his absence, they hurried out of the grotto in search of him. [Illustration: There he was standing on a rock, gazing fixedly at the top of the mountain.--P.242] There he was standing on a rock, gazing fixedly at the top of the mountain. His instruments were in his hand, and he was evidently calculating the exact longitude and latitude. The Doctor went towards him and spoke, but it was long before he could rouse him from his absorbing contemplations. At last the captain seemed to understand, and Clawbonny said, while he examined him with a keen scrutinizing glance-- "Let us go round the island. Here we are, all ready for our last excursion." "The last!" repeated Hatteras, as if in a dream. "Yes!, the last truly, but," he added, with more animation, "the most wonderful."