After the great explosion of 79, Vesuvius sank again into repose. It was not until 1056 that vigorous eruptions again began. From time to time slight explosions occurred, none of which yielded lava flows; it was not until the date last mentioned that this accompaniment of the eruption began to appear. In 1636, after a repose of nearly a century and a half, there came a very great outbreak, which desolated a wide extent of country on the northwestern side of the cone. At this stage in the history of the crater the volcanic flow began to attain the sea. Washing over the edge of the old original crater of Monte Somma, and thus lowering its elevation, these streams devastated, during the eruption just mentioned and in various other outbreaks, a wide field of cultivated land, overwhelming many villages. The last considerable eruption which yielded large quantities of lava was that of 1872, which sent its tide for a distance of about six miles. Since 1636 the eruptions of Vesuvius have steadily increased in frequency, and, on the whole, diminished in violence. In the early years of its history the great outbreaks were usually separated by intervals of a century or more, and were of such energy that the lava was mostly blown to dust, forming clouds so vast that on two occasions at least they caused a midnight darkness at Constantinople, nearly twelve hundred miles away. This is as if a volcano at Chicago should completely hide the sun in the city of Boston. In the present state of Vesuvius, the cone may be said to be in slight, almost continuous eruption. The old central valley which existed before the eruption of 79, and continued to be distinct for long after that time, has been filled up by a smaller cone, bearing a relatively tiny crater of vent, the original wall being visible only on the eastern and northern parts of its circuit, and here only with much diminished height. On the western face the slope from the base of the mountain to the summit of the new cone is almost continuous, though the trained eye can trace the outline of Monte Somma--its position in a kind of bench, which is traceable on that side of the long slope leading from the summit of the new cone to the sea. The fact that the lavas of Vesuvius have broken out on the southwestern side, while the old wall of the cone has remained unbroken on the eastern versant, has a curious explanation. The prevailing wind of Naples is from the southwest, being the strong counter trades which belong in that latitude. In the old days when the Monte Somma cone was constructed these winds caused the larger part of the ashes to fall on the leeward side of the cone, thus forming a thicker and higher wall around that part of the crater.