CHAPTER IX.

ON STORMS IN HIGH LATITUDES.

XI.

HAVING traced hurricanes to the fortieth degree of CHAP. north latitude, with their courses pointing in the direction of the islands of the Azores and the continent of Europe, we are naturally led to consider whether the gales of our own country partake also of a rotatory character; and whether those of the corresponding latitudes in the other hemisphere revolve in the contrary direction. Whilst we pursue this subject, however, following it up as facts may lead us onward, we must not suppose the rotatory storm (though probably the greatest) is the only disturbing cause of the regular atmospheric currents; and we should bear in mind not to carry its application too far.

The further we go from the equator, the more complicated this subject becomes; and gales succeed each other so fast during our stormy season, that it is not easy to identify the particular storm we may wish to study. It has been shown, that the hurricanes which originate within the tropics increase in diameter, and diminish in force, as they proceed towards the poles; and as the meridians approach each other the gales may become huddled together. They may, therefore, frequently neutralize each other, and become irregular. Their force, too, may often fall off, until the strength of the wind on that side of the circle where it blows

IX.

CHAP. from east is unable to reverse the regular westerly atmospheric current, and to convert it into a temporary easterly gale; and this may be a reason why easterly storms are less frequent in both hemispheres in the latitudes within which Great Britain is situated.

What is here meant will be better understood by turning to the two figures at page 410. These two figures, which are intended to represent the manner in which great storms revolve in both hemispheres, will also serve to show that on the sides of the circles next the poles the wind always blows from the east; and on the sides next the equator from the west.

The wind's force on the polar sides of the figures may be expressed by the rotatory velocity diminished by that of the regular westerly atmospheric current; and if they should be equal a calm would be the consequence; on the contrary, the same atmospheric current would add its force to the westerly and opposite sides of the storms in both hemispheres. Within the tropics, however, the violence of the hurricanes is so great, that the difference here alluded to is not perceptible.

Circles have been used in illustration of the movements of progressive whirlwinds; but the curves described are most likely not circles. It is more probable that they resemble the figures annexed, the degree of curvature altering with the rate of progress of the storms; and this may be another cause why, in high latitudes, westerly winds, in storms, blow harder than easterly. These two figures will serve to explain what is here meant, and the manner in which squalls may, perhaps, revolve in both hemi

spheres, if, for the sake of illustration, we may suppose СНАР.

them to be continuous.

. IX.

NORTHERN HEMISPHERE.

SOUTHERN HEMISPHERE.

The Cause of the Barometer falling with a Southerly
Wind in the Northern Hemisphere, and with a
Northerly Wind in the Southern Hemisphere, ex-
plained.

On the south coast of England, violent gales usually
set in with the wind about south, or south-south-east,
and veer by the west towards north-west. The baro-
meter, falling at the commencement, rises as the wind
becomes northerly. In the corresponding latitude in
the southern hemisphere, this order, as regards both
the wind and barometer, is reversed.

Captain King, in his sailing directions for Terra Weather. del Fuego, says

СНАР.

IX.

Winds.

Easterly winds.

North and north-west

"Gales of wind succeed each other at short intervals, and last several days. At times the weather is fine and settled for a fortnight; but those times are few.

"Westerly winds prevail during the greater part of the year. The east wind blows chiefly in the winter months, and at times very hard; but it seldom blows in summer.

"Winds from the eastern quarter invariably rise light, with fine weather; they increase gradually, the weather changes, and at times end in a determined heavy gale. More frequently they rise to the strength of a treble-reefed topsail breeze, then die away gradually, or shift to another quarter.

"From the north the wind always begins to blow winds, moderately, but with thicker weather and more clouds than from the eastward; and it is generally accompanied by small rain. Increasing in strength, it draws to the westward gradually, and blows hardest between north and north-west, with heavy clouds, thick weather, and much rain.

denly to

"When the fury of the north-wester is expended, which varies from twelve to fifty hours, or even while shift sud- it is blowing hard, the wind sometimes shifts suddenly into the south-west quarter, blowing harder than before. This wind soon drives away the clouds, and in a few hours you have clear weather, but with heavy squalls passing occasionally.

southwest.

"In the south-west quarter the wind hangs several days (generally speaking), blowing strong; but moderating towards its end, and granting two or three days of fine weather.

66

Northerly winds then begin again, generally

IX.

of the summer.

during the summer months; but all manner of shifts CHAP. and changes are experienced from north to south by the west during that season, which would hardly Nature deserve the name of summer, were not the days so much longer, and the weather a little warmer. Rain and wind prevail much more during the long than the short days.

"It should be remembered, that bad weather never comes on suddenly from the eastward; neither does a south-west or southerly gale shift suddenly to the northward. South-west and southerly winds rise suddenly and violently; and must be well considered in choosing anchorages, and preparing for shifts of wind at sea.

weather.

"The most usual weather in these latitudes is a Common fresh wind between north-west and south-west, with a cloudy overcast sky.

and sym

"Much difference of opinion has prevailed as to the Barometer utility of a barometer in these latitudes. I can only picsometer. say, that during twelve months' constant trial of a barometer and sympiesometer (Adie's) I found their indications of the utmost value. Their variations do not, of course, correspond to those of middle latitudes; but they correspond to those of high northern latitudes in a remarkable manner, changing south for north (east and west remaining the same).”

Captain King makes also the following remarks on the same subject:

"The mercury stands lowest with north-west winds, and highest with south-east. With the wind at northwest, or northerly, the mercury is low: if it falls to 29 inches, or to 28.80, a south-west gale may be expected; but it does not commence until the column has