Page:Physical Geography of the Sea and its Meteorology.djvu/309

Rh compensation. If the sun fail in his supply of heat to this region more of its vapours are condensed, and heat is discharged from its latent store-houses in quantities just sufficient to keep the machine in the most perfect compensation. If, on the other hand, too much heat be found to accompany the rays of the sun as they impinge upon the upper circumference of this belt, then again on that side the means of self-compensation are ready at hand: so much of the cloud-service as may be requisite is then resolved into invisible vapour—for of invisible vapour are made the vessels wherein the surplus heat of the sun is stored away and held in the latent state until it is called for, when it is instantly set free, and becomes a palpable and an active agent in the grand design.

523. The latent heat liberated in the processes of condensation from and under the cloud-ring, true cause of the trade-winds—Evaporation under this cloud-ring is suspended almost entirely. We know that the trade-winds encircle the earth; that they blow perpetually; that they come from the north and the south, and meet each other near the equator; therefore we infer that this line of meeting extends around the world. By the rainy seasons of the torrid zone, except where it may be broken by the continents, we can trace the declination of this cloud-ring, stretched like a girdle about our planet, up and down the earth ; it travels after the sun up and down the ocean, as from north to south and back. It is broader than the belt of calms out of which it rises. As the air, with its vapours, rises up in this calm belt and ascends, these vapours are condensed into clouds, and this condensation is followed by a turgid intumescence, which causes the clouds to overflow the calm belt, as it were, both to the north and the south. The air flowing off in the same direction assumes the character of winds that form the upper currents that are counter (Plate I.) to the trade-winds. These currents carry the clouds still farther to the north and south, and thus make the cloud-ring broader. At least we infer such to be the case, for the rains are found to extend out into the trade-winds, and often to a considerable distance both to the north and the south of the calm belt.

524. Imagined appearance of the cloud-ring to a distant observer.—Were this cloud-ring luminous, and could it be seen by an observer from one of the planets, it would present to him an appearance not unlike the rings of Saturn do to us. Such an observer