The night was moonless; only the great untroubled stars wondered down at this daring venture into the unknown. Stern hummed a tune to keep his spirits up. Running easily over the monotonous dark swells with a fair following breeze, he passed an hour or two. He sat down, braced the tiller, and resigned himself to contemplation of the mysteries that had been and that still must be. And very sweet to him was the sense of protection, of guardianship, wherein he held the sleeping girl, in the shelter of the little cabin. He must have dozed, sitting there inactive and alone. How long? He could not tell. All that he knew was, suddenly, that he had wakened to full consciousness, and that a sense of uneasiness, of fear, of peril, hung about him. Up he started, with an exclamation which he suppressed just in time to avoid waking Beatrice. Through all, over all, a vast, dull roar was making itself heard--a sound as though of mighty waters rushing, leaping, echoing to the sky that droned the echo back again. Whence came it? Stern could not tell. From nowhere, from everywhere; the hum and vibrant blur of that tremendous sound seemed universal. "My God, what's that?" Allan exclaimed, peering ahead with eyes widened by a sudden stabbing fear. "I've got Beatrice aboard, here; I can't let anything happen to her!" The gibbous moon, red and sullen, was just beginning to thrust its strangely mottled face above the uneasy moving plain of waters. Far off to southward a dim headland showed; even as Stern looked it drifted backward and away. Suddenly he got a terrifying sense of speed. The headland must have lain five miles to south of him; yet in a few moments, even as he watched, it had gone into the vague obliteration of a vastly greater distance. "What's happening?" thought Stern. The wind had died; it seemed as though the waters were moving with the wind, as fast as the wind; the yawl was keeping pace with it, even as a floating balloon drifts in a storm, unfeeling it. Deep, dull, booming, ominous, the roar continued. The sail flapped idle on the mast. Stern could distinguish a long line of foam that slid away, past the boat, as only foam slides on a swift current. He peered, in the gloom, to port; and all at once, far on the horizon, saw a thing that stopped his heart a moment, then thrashed it into furious activity. Off there in a direction he judged as almost due northeast, a tenuous, rising veil of vapor blotted out the lesser stars and dimmed the brighter ones. Even in that imperfect light he could see something of the sinuous drift of that strange cloud. Quickly he lashed the tiller, crept forward and climbed the mast, his night-glasses slung over his shoulder. Holding by one hand, he tried to concentrate his vision through the glasses, but they failed to show him even as much as the naked eye could discern.