According to the researches and observations of Franklin, Cooper, Redfield, Reid, &c. &c., these storms are great rotatory winds, that move along a curved line in increasing circles. In the northern hemisphere, the rotatory movement follows a direction contrary to that of the hands of a clock; while the opposite takes place in the southern hemisphere. The knowledge of the laws which regulate the movements of storms is of great importance to the mariner, since it points out to him the direction he has to give his ship to gain the external limits of the tornado, and thus to remove it from danger. _Water-spouts_ are formed by two winds blowing in opposite directions, and raising or sucking up the water in their vortex. They generally form a double cone; the superior part with its apex downwards, consisting of a dense cloud, while the inferior cone, the apex of which is turned upwards, consists of water, which is thus sometimes raised to a height of several hundred feet. [Illustration] [Illustration] Water-spouts seldom last longer than half-an-hour. Their course and movements are irregular; straight forwards; in zig-zag lines; alternately rising and falling; stationary; slow; or progressing with the rapidity of thirty miles an hour. The rotatory movement is also variable; its power is often very great, but sometimes water-spouts pass over small vessels without injuring them. They are more frequent near the coast than on the high seas; and are more commonly seen in warm climates. They seem to occur particularly in regions where calms frequently alternate with storms, which is not to be wondered at, since they owe their origin to miniature storms or whirlwinds. [Illustration] How do the aqueous vapours with which evaporation impregnates the atmosphere, again descend upon the surface of the earth? Everybody knows that when in summer a bottle filled with cold water is brought into the room, it soon gets covered with thick dew-drops, which presently trickle down its sides, although it was perfectly dry on entering. Whence does this moisture come from? Not from the inside of the bottle as ignorant people might imagine, but from the surrounding atmosphere; in consequence of the capacity of the air to absorb and retain moisture, increasing or diminishing, as its temperature grows warmer or colder. Thus when the cold bottle is introduced into the room, the warm sheet of air, which is in immediate contact with its surface, immediately cools, and being no longer able to retain all the moisture with which it was impregnated, is obliged to deposit it on the sides of the vessel. This familiar example suffices to explain the formation of dew, rain, hail, snow, hoar-frost, and all other atmospherical precipitations. They all result from the influence of some refrigerating cause upon the air; such as the passage of a warm current into a cooler region; the influx of a cold wind; a cold-radiating chain of high mountains; a forest, and so forth.