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492. Hot winds from Africa are felt in neighbouring regions, where they are known under different names. They are subject to important modifications by the nature of the earth's surface over which they pass. The Sirocco blows occasionally over Sicily, South Italy, and adjoining districts. It is a hot moist wind, receiving its heat from the Sahara, and acquiring its moisture in its passage northward over the Mediterranean. It is the plague of the Two Sicilies; and while it lasts, a haze obscures the atmosphere, and so great is the fatigue which it occasions, that the streets of Palermo become quite deserted. The wind sometimes extends to the shores of the Black and Caspian Seas, and to the steppes beyond the Volga, the seat of the dreaded rinderpest, where, by its blighting touch, vegetation withers and dries up, and thousands of cattle are cut off. It is called the Samiel in Turkey, from its reputed poisonous qualities.

493. The Solano of Spain is a south-east wind, extremely hot, and loaded with fine dust. It prevails at certain seasons in the plains of Mancha and Andalusia, particularly at Seville and Cadiz. It produces dizziness, and heats the blood to an unusual degree, causing great uneasiness and irritation; hence the Spanish proverb, “ Ask no favour during the Solano.”

494. The Harmattan of Guinea and Senegambia belongs to the same class of winds. It is a periodical wind blowing from the dry desert of Africa to the Atlantic, from N. lat. 15° to S. lat. 1°, during December, January, and February. It blows with moderate force, is often highly charged with fine particles of dust, and since under its influence no dew falls, vegetation grows languid and withers.

495. The Pampero is a wind which blows chiefly in the summer season from the Andes across the pampas of Buenos Ayres to the sea-coast. It is thus a north-west wind, or part of the anti-trade of the southern hemisphere, and in this respect it is analogous to the stormy winds which sweep over Europe from the south-west. But since it blows from the Andes over the South American continent, it is a dry wind, frequently darkening the sky with clouds of dust, and drying

up the vegetation of the pampas. The cause of its prevalence in the summer season will be evident on examining the isobarometric lines on Plate II.

496. The Nortes, or “Northers,” are dry cold winds which frequently prevail from September to March in the regions bordering on the Gulf of Mexico. They result from the high pressure of the interior of North America during winter, taken in connection with the low pressure to the south (Plate II.) In his .Climate of America,' R. Russell gives an instance of the temperature falling in Southern Texas, with a “norther,” from 81° to 18° in 41 hours, and adds that “such great and sudden changes are rendered still more disagreeable by the

northers' frequently blowing with extreme violence.” The influence of these cold winds on the vegetation of the Southern States is very deleterious. A temperature of 18° with a violent wind is almost unknown in Great Britain.

497. In the south of Europe north winds are notorious for their violence. The great differences of the temperature of the Alps, the Mediterranean, and Africa explain them; and when the polar current, with a high atmospheric pressure accompanying it, is descending at the same time over Europe, the effect is greatly heightened. Of these the most notorious is the Bora, which, descending from the Julian Alps, sweeps over the Adriatic—the bitterly cold tempestuous wind of that much-vexed sea. It is probably the Euroclydon mentioned in the Acts of the Apostles. The Mistral is a steady violent north-west wind which blows from France down on the Gulf of Lyons. It is immediately caused by a low atmospheric pressure in the Gulf of Lyons, as compared with the pressure to the north, and is most severe when at the same time very high pressures occur from France northwards towards the Arctic regions. The great cold which prevailed in the north of Italy and south of France in the beginning of last January (1868) arose in this way. While it lasted, atmospheric pressure was very low in the north of the Mediterranean, 29.450 inches, whence it rapidly rose in advancing northwards to the almost unprecedented height of 30.905

inches in the north of Russia, thus drawing over the northern shores of the Mediterranean the polar current in its full strength, which became still colder and drier in crossing the Alps in its southward course. Atmospheric pressure was at the same time high in Scotland, but as this country lay to the west of, and beyond, the cold polar current which set in from Russia towards the Mediterranean, the temperature was only slightly under the average of the season; in other words, no unusual cold occurred in Scotland. There are other winds of a stormy character peculiar to different parts of the Mediterranean, such as the Levanter in the east. The heating of the Sahara in summer causes a general and continued flow of the cooler air of the Mediterranean to the south to take the place of the heated air which rises from the sandy desert. These are the Etesian winds of Southern Europe.

CHAPTER XII.

STORMS.

498. STORMS are violent commotions of the atmosphere, occurring in all climates, and differing from other atmospheric disturbances in their destructive power and the extent over which they spread. There is, perhaps, no question in physical science in which there has been so large an admixture of speculation with fact as in attempts made to reduce the phenomena attendant on storms to general laws; the reason being, that meteorological observations were, for long, too few in number, and too far apart, to enable any one to give the atmospheric pressure, the general course of the winds, the temperature, and the rainfall, without drawing largely on conjecture. Now, however, owing to the growing popularity of meteorology, and the countenance happily given to it by most civilised nations, sufficient data may be obtained for a fuller and more satisfactory statement of the question. I shall first state the chief facts of observation regarding storms as obtained from synchronous charts of the weather over a considerable portion of the globe. Since such charts present the principal elements of the weather at a given instant, they may be regarded as successive photographs of storms in their passage across the earth's surface. The Scottish Meteorological Society has been for some time in a very favourable position for examining the storms of Europe. The sources of information are the following :-Observations (1) from the Society's stations on the mainland and in the outlying islands; (2) from Farö and Iceland ; (3) from several places in Norway, from Christiania round the coast to Vardo, east of the North Cape, sent monthly by Professor Mohn ; (4) from sixteen places in Austria sent monthly by Dr Carl Jelinek; to which may be added (5) the daily Weather-Telegrams published in The Times ;' and (6) the Observations and Chart published daily in the 'Bulletin International.' Through the courtesy of Dr Buys Ballot, any of the observations published in the · Jaarboek' are available when required in particular discussions. There are thus ample materials for investigating European storms. The most valuable of these observations are those from Iceland, Farö, Scotland, and Norway ; indeed, without these, most European storms could not be satisfactorily investigated, since the position, extent, and nature of the area of least pressure, and hence the drawing force of the storm, could not be certainly known.

499. In discussing storms, the most important by far of all the observations are those made by the barometer. Three different methods have been adopted to represent the relations of atmospheric pressure to storms :First Method. By iso barometric lines drawn through places of equal pressure, for every tenth or two tenths of an inch of pressure. Lines for every two tenths are very suitable, since the disturbing force is sufficiently represented by them, and the eye is not distracted by the overcrowding of lines, which would be the result were smaller differences represented on the charts. This method of charting the barometric observations really leaves nothing to be desired, and no doubt it will soon be the only method used in investigating storms.

500. Second Method.-In place of lines of equal barometric pressure, some Continental meteorologists draw lines of equal barometric disturbance—that is, the difference between the barometer on the particular day, and the mean height of the barometer for the place and season. As this method can only suit a limited space of the earth's surface, it ought to be discarded. Thus, suppose on the 15th January the barometer in Western Europe was the average of the month—-viz.,

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