effects of the condensation of vapour borne by those surcharged winds, and to the immense precipitation in the austral regions, shall we ascribe this diminution of the atmospherical pressure in high south latitudes? It is not so in high north latitudes, except about the Aleutian Islands of the Pacific, where the sea to windward is also wide, and where precipitation is frequent, but not so heavy. The steady flow of "brave" winds towards the south would seem to call for a combination of physical conditions about their stopping-place in the antarctic regions, exceedingly favourable to rapid, and heavy, and constant precipitation there. The rain-fall at Cherraponjie and on the slopes of the Patagonian Andes reminds us what those conditions are. There mountain masses seem to perform in the chambers of the upper air the office which the jet of cold water does for the exhausted steam in the condenser of the engine. The presence of land, not water, about this south polar stopping-place is therefore suggested; for the sea is not so favourable as the mountains are for aqueous condensation.
835. The topographical features of the antarctic hands.—By the terms in which our proposition has been stated, and by the manner in which the demonstration has been conducted, the presence in the antarctic regions of land in large masses is called for; and if we imagine this land to be relieved by high mountains and lofty peaks, we shall have in the antarctic continent a most active and powerful condenser. If, again, we tax imagination a little farther, we may, without transcending the limits of legitimate speculation, invest that unexplored land with numerous and active volcanoes. If we suppose this also to be the case, then we certainly shall be at no loss for sources of dynamical force sufficient to give that freshness and vigour to the atmospherical circulations which observations have abundantly shown to be peculiar to the southern hemisphere. Neither under such physical aspects need it be any longer considered paradoxical to ascribe the polar tendency of the "brave west winds" to rarefaction by heat in the antarctic circle. This heat is relative, and though it be imparted to air far below the freezing-point, raising its temperature only a few degrees, its expansive power for that change is as great when those few degrees are low down as it is when they are high up on the scale. If such condensation of vapour do take place, then liberation of heat and expansion of air must follow, and con-
