Some volcanoes are in a continual state of eruption. Isalco, born, as we have seen, in 1770, has remained ever since so active as to deserve the name of the Faro (lighthouse) of San Salvador. Its explosions occur regularly, at intervals of from ten to twenty minutes, and throw up a dense smoke and clouds of ashes and stones. These, as they fall, add to the height and bulk of the cone, which is now about 2,500 feet high. For more than two thousand years, the fires of Stromboli have never been extinct, nor has it ever failed to be a beacon to the mariner while sailing after nightfall through the Tyrrhenian Sea. Mr. Poulett Scrope, who visited Stromboli in 1820, and looked down from the edge of the crater into the mouth of the volcano, some 300 feet beneath him, found the phenomena precisely such as Spallanzani described them in 1788. ‘Two rude openings show themselves among the black chaotic rocks of scoriform lava which form the floor of the crater. One, is to appearance, empty, but from it there proceeds, at intervals of a few minutes, a rush of vapour, with a roaring sound, like that of a smelting furnace when the door is opened, but infinitely louder. It lasts about a minute. Within the other aperture, which is perhaps twenty feet in diameter, and but a few yards distant, may be distinctly perceived a body of molten matter, having a vivid glow even by day, approaching to that of white heat, which rises and falls at intervals of from ten to fifteen minutes. Each time that it reaches in its rise the lip of the orifice, it opens at the centre, like a great bubble bursting, and discharges upwards an explosive volume of dense vapour, with a shower of fragments of incandescent lava and ragged scoriæ, which rise to a height of several hundred feet above the lip of the crater.’