Page:The fairy tales of science.djvu/206

172 from the beds of lava of which the wonderful volcanic island is chiefly composed. A jet of boiling water, accompanied with a great evolution of vapour, first appears, and is ejected to a considerable height; a dense volume of steam succeeds, and is thrown up with prodigious force, and a terrific noise like that produced by the escape of vapour from the boiler of a steam-engine. Nature's cauldron boils over! This operation sometimes lasts for more than an hour, and after an interval of repose of uncertain duration, the same phenomena are repeated. The Great Geyser is the most celebrated of these boiling fountains. Sir George Mackenzie, who was the first to describe it, states that its eruptions were preceded by a sound resembling the distant discharge of heavy ordnance, and the ground shook sensibly; the sound was rapidly repeated, when the water in the basin, after heaving several times, suddenly rose in a large column, accompanied by clouds of steam, to the height of ten or twelve feet. The column then seemed to burst, and sinking down produced a wave, which caused the water to overflow the basin. A succession of eighteen or twenty jets now took place, some of which rose from a height of from fifty to ninety feet. The last eruption was the most violent; this being over, the water suddenly disappeared from the basin, and sunk down a pipe in the centre to a depth of ten feet; but in the course of a few hours the phenomena were repeated with increased energy. The basin of the