At length, just as I had completed my hasty lunch, there occurred a sudden but perceptible darkening of the atmosphere which seemed to indicate that the expected change was now imminent, and, springing up the companion-way to the deck, I found a most extraordinary scene awaiting me. The thickness that had hitherto pervaded the atmosphere had vanished, as if by magic, leaving the air astonishingly clear and transparent right to the boundary of the horizon, and revealing a vast expanse of dense, livid, purple-grey cloud, which had overspread the north-western half of the heavens, and was at the precise moment passing over and shutting out the sun from view. The edge of the cloud was as straight and sharply defined as though it had been trimmed with a knife, and it divided the firmament into two almost equal portions, the larger of which was a beautiful expanse of clear, serene, unclouded blue; while the other hung livid and threatening above us, with the promise of a raving tornado lurking within its black bosom. Immediately overhead the colour of this immense cloud curtain was a cold, slaty blue, from whence, as the eye travelled down its expanse toward the north-western horizon, the hue became darker until where it met the water it was as black as night; while, underneath it, the sea undulated restlessly, with the writhings of an angry serpent, showing a surface as lustreless and of the same colour as molten lead. Low down in the bosom of the cloud could be seen occasional palpitating quiverings, as though the fires within it were striving to burst their way through, and presently, quite at the horizon, a flash of lightning sparked vividly out of it. "Are the topsail halliards all ready for running, Mr Forbes?" said I. "All ready, sir," was the reply; and, turning away, the mate walked quietly forward, throwing the falls off the pins on his way. A minute later I heard him telling Joe to stand by the fore-topsail halliards, and the rest of the men to lay aft to the braces, following them along the deck and stationing himself at the main-topsail halliards in readiness to let them run. At this moment Sir Edgar, with the two ladies and the children, came on deck and looked round with startled eyes upon the portentous scene; but, upon my earnest recommendation, the youngsters were at once sent below again, the ladies holding themselves in readiness to follow at a moment's notice. Sir Edgar, however, announced his determination to remain on deck, upon the chance of his becoming useful; upon which, Lady Emily, without saying a word, went below and brought up on deck not only her husband's, but also my own mackintosh coat--a little piece of thoughtful consideration for which I was deeply grateful, since the aspect of the weather was now such that I dared not leave the deck for a single instant.