Page:Physical Geography of the Sea and its Meteorology.djvu/383

Rh and, of course, the sailor in command most of all; indeed, a sea voyage more than fulfils my expectations."

665. Winds blow from a high to a low barometer.—It appears, therefore, that the low barometer about the poles and the low barometer of the equator cause an inrush of wind, and in each case the rushing wind comes from the high and blows towards the low barometer; that in one hemisphere the calm belt of Capricorn, and in the other the calm belt of Cancer, occupies the medial line between the equatorial and polar places of low barometer.

660. Polar rarefaction.—It appears, moreover, that the polar refraction is greater than the equatorial, for the mean height of the austral barometer is very much below that of the equatorial, and, consequently, its influence in creating an indraught is felt at a greater distance (Plate XV.)—even at the distance of 50° of latitude from the south pole, while the influence of the equatorial depression is felt only at the distance of 30° in the southern, and of 25° in the northern hemisphere. The difference as to degree of rarefaction is even greater than this statement implies, for the influx into the equatorial calm belt is assisted also by temperature in this, that the trade-winds blow from cooler to warmer latitudes. The reverse is the case with the counter-trades; therefore, while difference of thermal dilatation assists the equatorial, it opposes the polar influx.

667. The tropical calm belts caused by the polar and equatorial calms.—Thus we perceive that the tropical calm belts are simply an adjustment between the polar and equatorial calms; that the tropical calm belts assume their position and change their latitude in obedience to the energy with which the influence of the heated and the expanding columns of air, as they ascend in the polar and equatorial calms, is impressed upon them. 668. The meteorological power of latent heat.—This explanation of the calm places and of the movements of the low austral barometer shows, comparatively speaking, how much the latent heat of vapour, and how little the direct heat of the sun has to do in causing the air to rise up and flow off from these calm places, and consequently, how little the direct action of the solar ray has to do either with the trades or the counter trades. It regulates and controls them; it can scarcely be said to create them.

669. The low barometer off Cape Horn.—The fact of a low