Mount Vesuvius rises rather abruptly from the plain on which it stands. The circuit of the base is about twelve miles, and the height of the summit above the level of the sea about three thousand feet. This latter measurement, however, alters from time to time, owing to the variable height of the cone. Its moderate elevation, and the ease with which it may be approached, have induced many travellers to ascend the mountain; and not a few have recorded their experiences. So frequent are the eruptions of the volcano, however, and so much do they change the aspect of the crater, that any description remains correct for only a limited time. Within the last hundred years the crater has been five times wholly altered, in consequence of its interior having been completely blown out, and its walls having crumbled down. When Sir William Hamilton ascended the mountain in 1756, it had no less than three craters and cones, one within another. The outermost was a very wide-mouthed cone. Within it rose centrically another, smaller in size and narrower in the mouth; and within that again was the third and highest, having a smaller base and still narrower opening at the top, whence the greatest volume of vapour ascended. In 1767 this innermost cone merged in the second, which was greatly enlarged; and by a subsequent eruption the interval between the first and second was obliterated, so that only a single cone remained. In 1822 the whole interior of the cone was blown out, and its walls crumbled down, so as to lower the height of the mountain several hundred feet. But within the vast gulf, nearly a mile in diameter, which was thus left yawning open, there soon began to be formed a new cone, which showed itself erelong above the jagged edge of the crater. Eventually this cone increased, by the accumulation of ejected matters, to such an extent as to obliterate the division between it and the rim of the former crater--thus once more establishing a continuous cone. Since that time, the cone and crater have twice undergone similar changes.