Biscay. The cyclones then either come in from the Atlantic and pass south-east between the Scandinavian and Atlantic anticyclones, or else, their progress being impeded, they are arrested or deflected by the anticyclone in the north-east of Europe. Sometimes they are formed to the south of the Scandinavian anticyclone, and advance slowly towards the east, or sometimes even towards the west.

These types are so named because the prevailing wind in each is from south, west, north, and east respectively. The connection of these European groups with those of the United States will be considered under the details of

each type.

Notice will now be directed to the details of these types-first to their main character and seasonal modifications, together with the indications of intensity, and then to any signs of persistence or change of type when possible.

But however much we study details, the above general view of the distribution of pressure in the earth's surface must never be forgotten, as without that we lose the only clue to the ceaseless and complicated changes with which we have to deal.

SOUTHERLY TYPE.

In this type the Atlantic anticyclone extends very little to the northward; another of the tropical belt of anticyclones covers Mexico or the southern states of the American Union; while a third area of high pressure covers Northern and Eastern Europe.

The North Atlantic is occupied by a persistent area of low pressure in which cyclones are constantly being formed; these beat up against the high European pressure, and either die out or are repelled.

Sometimes, especially in summer, small cyclones arising in the easterly side of the area of depression pass rapidly near the British coasts in a north or north-east direction. In either case it is somewhat rare for the centre of a cyclone to reach the coast-line of Europe, so that generally Great Britain is under the influence of the rim or edge of either a cyclone or anticyclone.

At other times the Atlantic low pressure extends over Great Britain, driving the high pressure eastwards, without forming any definite cyclone. In this case, the indications are for tolerably fine weather and little wind, with a very low barometer-a condition which often excites remark.

This type of weather occurs at all seasons of the year, but it is most common and persistent in winter; in fact, the warmth or otherwise of the winter principally depends on the number of days of this type.

No definite sequence of weather to the United States is connected with the occurrence of this type in Europe. While the Mexican anticyclone is tolerably persistent, cyclones which form in the Hudson's Bay Territory usually pass into the Atlantic and are lost there; but at the same time another totally different class of cyclone forms in the col which lies between the Atlantic and Mexican anticyclones, and moves along the northern edge of the former till they reach Europe. The centres, of course, never touch the American continent, but the

gales associated with the western side of these cyclones often do much damage to the United States coast.

The above will be more easily understood by reference to an actual example. In Figs. 64-67, we give charts over a large area, for the four days November 10-13, 1877, at 7.35 a.m. Washington. None of these show the zone of

FIG. 64.-Southerly type of weather.

equatorial low pressure, but in all the tropical belt of anticyclones and the temperate and Arctic zone of low pressure are very obvious. In all we find three persistent anticyclones, one over the lower Mississippi valley, another in mid-Atlantic, and a third over Moscow. The North Atlantic and Hudson's Bay Territory are covered by low

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pressure, and this area is the theatre of the formation of an incessant series of new cyclones, whose history we are now going to trace.

But first let us consider the southern edges of the tropical anticyclones. The east winds under the American high pressure are the trade-winds of Cuba and the Central

the

American republics as shown by the small arrows; Atlantic anticyclone gives the regular trades of that ocean, and the anticyclone, whose edge we see in the chart over Moscow, really extends over the whole of Siberia, and gives the north-east monsoon to the Indian Ocean. This all shows in a very striking manner the

dependence of weather in different parts of the world on each other, and also the true nature of the problems which the meteorologist has to solve. The cyclone which covered Great Britain on November 10, 1877, had its origin in the Atlantic anticyclone which dominates the tradewinds. Its eastward path was deflected by the Asiatic

FIG. 66.-Southerly type of weather.

anticyclone which caused the north-east monsoon in Calcutta, and its intensity was increased by a depression which passed into the Atlantic from the Hudson's Bay. At the same time the actual force of the wind was determined at every station by the exposure; every hill drew a little more or less rain, every tidal river brought