the upper regions, from the equatorial side, where the cross section between any two given meridians, is the larger; and this upper current, while on its way from the equator, is continually parting with the heat which it received at and near the surface, and which caused it to rise under the equatorial cloud-ring. In this process it is gradually contracted, thus causing the upper surface of the air to be a sort of double inclined plane, descending from the equator and from the poles to the place of the tropical calm belts.

663. Winds in the southern stronger than winds in the northern hemisphere. Observations show that the mean weight of the barometer in high southern is much less (Plate I.) than it is in corresponding high northern latitudes; consequently, we should expect that the polar-bound winds would be much more marked on the polar side of 40° S., than they are on the polar side of 40° N. Accordingly, observations (Plate XV.) show such to be the case; and they moreover show that the polar-bound winds of the southern are much fresher than those of the northern hemisphere.

664. The waves and gales off the Cape of Good Hope.-To appreciate the force and volume of these polar-bound winds in the southern hemisphere, it is necessary that one should “run them down" in that waste of waters beyond the parallel of 40° S., where the winds howl and the seas roar." The billows there lift themselves up in long ridges with deep hollows between them. They run high and fast, tossing their white caps aloft in the air, looking like the green hills of a rolling prairie capped with snow, and chasing each other in sport. Still, their march is stately and their roll majestic. The scenery among them is grand, and the Australian-bound trader, after doubling the Cape of Good Hope, finds herself followed for weeks at a time by these magnificent rolling swells, driven and lashed by the "brave west winds" most furiously. A sailor's bride, performing this voyage with her gallant husband, thus alludes in her "abstract log" to these rolling seas: We had some magnificent gales off the Cape, when the colouring of the waves, the transition from gray to clear brilliant green, with the milkywhite foam, struck me as most exquisite. And then in rough weather the moral picture is so fine, the calmness and activity required is such an exhibition of the power of mind over the elements, that I admired the sailors fully as much as the sea,

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.

666. 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 tempera ture 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 lati tude 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

barometer off Cape Horn was pointed out* as long as 1834. It was considered an anomaly peculiar to the regions of Cape Horn. It is now ascertained by the comparison of 6455 observations on the polar side of 40° south, and about 90,000 in all other latitudes, that the depression is not peculiar to the Cape Horn regions, but that it is general and alike in all parts of the austral seas, as the following table, compiled from the log-books of the Observatory by Lieutenants Warley and Young, shows:

671. Barometer at the poles.-These are the observed heights; for the want of data, no corrections have been applied to them; and for the want of numbers sufficient to give correct means, they lack that uniformity which larger numbers would doubtless give. They show, however, most satisfactorily, that a low barometer is not peculiar to Cape Horn regions alone; they show that it is common to all high southern latitudes; and other observations (§ 362) show that it is peculiar to these and not to northern latitudes. Projecting on a diagram A, with parallels of latitude and the barometric scale as ordinates and abscissæ, a curve S, which will best represent the observations (§ 670), and continuing it to the south pole-also projecting another curve N, which will best represent the observations (§ 362) on the polar side of 40° N., and continuing it to the north pole-we discover that if the Darometric pressure in polar latitudes continue to decrease for

* American Journal of Science, vol. xxvi. p. 54 (1834).

the unknown as it does for the known regions, the mean height of the barometer would be at the north pole about 29.6, at the south about 28 inches. These lines, N and S, represent what may be called the barometric descent of the counter-trades.

672. The "brave west winds "-their barometric descent.—The rarefaction of the air in the polar calms is, as we have seev

(§ 667), sufficient to create an indraught all around to the distance of fifty degrees of latitude from the south pole; also (§ 662) the rarefaction in the belt of equatorial calms is sufficient

to extend with its influence no farther than thirty degrees of latitude. The fact also favours the idea suggested by the diagram (§ 671), that the mean height of the barometer in the polar calms is very much less than it is in the equatorial. Moreover, the counter trades of the southern hemisphere are very much stronger (§ 626) than the counter trades of the other. They are also stronger than the trade-winds of either; these facts likewise favour the idea of a greater exhaustion of air in the antarctic than in the arctic calm place; and it is manifest that actual observations also, as far as they go, indicate such to be the case. In other words, "the brave west winds" of the southern hemisphere have the greatest "barometric descent," and should therefore be, as they are, the strongest of the four winds.

673. Study of the monsoons affords farther information touching the calm belts.-Farther information may be gained upon the subject of high and low barometers, of the "barometric declivity of winds." and of the meteorological influence of diminished atmospheric pressure by studying the calm belts in connection with the

monsoons.

674. The south-west winds of the Atlantic.-Before, however, we proceed to these, let us take a hasty glance at the winds in certain other parts of the ocean. The winds which most prevail on the polar side of the calm belt of Cancer, and as far as 50° N. in the Atlantic, are the west winds. "Wind and weather in this part of the ocean," says Jansen, "are very unreliable and changeable; nevertheless, in the summer months, we find permanent north winds along the coast of Portugal. These north winds are worthy of attention, the more so from the fact that they occur simultaneously with the African monsoon, and because we then find northerly winds also in the Mediterranean, and in the Red Sea, and farther eastward to the north of the Indian monsoon. When, between the months of May and November, during which the African monsoon prevails, the Dutch ships, which have lingered in the calm belt of Cancer run with the north-east trade, and direct their course for the Cape Verd Islands, then it seems as if they were in another world. The sombre skies and changeable-alternately chilly and sultry-weather of our latitudes are replaced by a regular temperature and good settled weather. Each one rejoices in the glorious heavens, in which none save the little trade clouds are to be seen-which clouds in the trade