Page:Physical Geography of the Sea and its Meteorology.djvu/469

Rh out of the sea, or separated from it only by lowlands—that seems to be necessary to bring down the rain in such floods. Colonel Sykes quotes the rain-fall of Cherraponjie at 605.25 inches for the 214 days from April to October, the season of the south-west monsoons. Computing the Cape Horn rains according to the ratio given by King and Fitzroy for their 41 days of observations, we should have a rain-fall in Patagonia of 825 inches in 214 days, or a yearly amount of 1368.7 inches. Neither the Cape Horn rains, nor the rains anywhere at sea on the polar side of 45° S., are periodical. They are continuous; more copious, perhaps, at some seasons of the year than at others, but abundant at all.

828. Influence of highlands upon precipitation.—Now, considering the extent of water surface on the polar side of the south-east trade-wind belt, we see no reason why, on these parallels, the engirdling air of that great watery zone of the south should not, entirely around the earth, be as heavily charged with vapour as was that which dropped this flood upon the Patagonian hills. If those mountains had not been there, the condensation and the consequent precipitation would probably not have been as great, because the conditions at sea are less apt to produce rain; but the quantity of vapour in the air would have been none the less, which vapour was being borne in the channels of circulation towards the antarctic regions for condensation and the liberation of its latent heat; and we make, as we shall proceed to show, no violent supposition, if, in attempting to explain this activity of circulation south of the equator, we suppose a cloud region, with a combination of conditions in the antarctic circle peculiarly favourable to heavy and almost incessant precipitation. But, before describing these conditions, let us turn aside to inquire how far precipitation in the supposed cloud region of the south may assist in giving force and regularity to the winds of the southern hemisphere.

829. The latent heat of vapour.—If we take a measure, as a cubic foot, of ice at zero, and apply heat to it by means of a steady flame that will give off heat at a uniform rate, and in such quantities that just enough heat may be imparted to the ice to raise its temperature 1° a minute, we shall find that at the end of 32 minutes the ice will be at 32°. The ice will now begin to