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

1835. SQUALLS OVER LOW ISLANDS. 507 and so far as I have heard or observed, it is usually the case that on land, a wide tract of flat country, Avithout hills, or at sea, a considerable space of partly-covered ground, nowhere rising much above high-water, is subject to more frequent and violent blasts of wind than mountainous or even hilly regions, whether continental or island. Clouds are certainly attracted, even if their formation be not hastened, by land ; especially when it is covered by trees : and as low islands (such as those of the Dangerous Archipelago, between 14° and 20° south) have no hill or height of any kind, about which clouds attracted by the archipelago (taken toge- ther) can gather and discharge a portion of their contents, electrical as well as fluid, it may, I think, be inferred, that the want of such a conductor as Avould be furnished by a mountain five or six thousand feet high, is the reason why clouds in various electrical conditions unite or oppose one ano- ther, as the case may be ; and, in consequence, cause rapid changes in the atmosphere around them ; of which the effects are seen in squalls (sometimes with heavy rain, sometimes without), and even in whirlwinds. Where high land acts as a conductor between the earth and certain portions of our atmo- sphere, there may be a continual, though unperceived, electrical action. In connection with this subject I would, if I were able, consider the effects of rapidly varying temperature over land, and comparatively uniform temperature over ocean during twenty-four hours; which latter fact I might suspect to be one reason why the great Humboldt could not discover any particular electrical action, as indicated by his electrometers, while sailing from Europe to Brazil : although those same instruments were far from inactive after he landed. But I feel myself out of my depth, and will leave such speculations to those who are qualified to indulge in them.* On the 13th, after having passed some anxious nights in very squally weather,-f- we were gratified by seeing an islet whose existence we had not suspected. Tairo is the name by * See note («) at tlie end of this chapter, t All the squalls were from the westward.