Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.2): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

50 INDICATIONS OF SQUALLS. Jan. weatlier, although no change should be foretold by the glasses. A mistake may be made by the observer, or a variation in the height of the column may have passed unlieeded ; while it is seldom that a practised eye can be deceived by the visible signs of an approaching squall or gale of wind. Undoubtedly the worst wind, next to a hurricane, which a vessel can encounter, is a violent ' white squall,' so called because it is accompanied by no cloud or peculiar appearance in the sky, and because of its tearing up the surface of the sea, and sweeping it along so as to make a wide sheet of foam. By squalls of this description, frequent in the West-Indies, and occasionally felt in other parts of the world, no notice will be given much above the horizon ; but by consulting a good barometer or sympiesometer, and frequently watching the surface of the sea itself, even a white squall may be guarded against in sufficient time. Squalls accompanied by clouds are so common, and at sea every one is so much accustomed to look out for them, that I may cause a smile by these notices ; yet as there is often much doubt in a young officer's mind, whether an approaching cloud will be accompanied by wind or rain, or by both, and many persons are unable to distinguish, by the mere appearance of a cloud, what is likely to come with or from it, I will venture to mention that when they look hard, or hard- edged (like Indian ink rubbed upon an oily plate), they indicate wind, and perhaps rain; but before the rain falls, those clouds will assume a softer appearance. When they are undefined, and look soft, rain will follow, but probably not much wind. Dark clouds, hard mixed with soft, and inky fragments in rapid motion beneath them, accompanied perhaps by light- ning and distant thunder, are the fore-runners of a heavy squall. Soft, shapeless clouds, in which it is impossible to point out a definite edge, usually bring rain, but not wind : and, generally speaking, the more distinctly defined the edges of clouds are, the more wind they foretell. A little attention