Professor Tyndall's explanation is in substance this: Suppose that by the entrance of steam from the ducts near the bottom of the tube the geyser column is elevated six feet, a height quite within the limits of actual observation; the water at A is thereby transferred to B. Its boiling point at A is 255°, and its actual temperature is 251°; but at B its boiling point is only 249°, hence when transferred from A to B, the heat which it possesses is in excess of that necessary to make it boil. This excess of heat is instantly applied to the generation of steam; the column is thus lifted higher, and the water below is relieved of pressure, and its boiling point lowered. More steam is generated; this lifts the column still higher, and compels the generation of more and more steam, until the whole upper portion of the column bursts into ebullition, and the water, mixed with steam-clouds, is projected into the atmosphere, and we have the geyser eruption in all its grandeur. One confirmation of this theory of Bunsen's is that small stones suspended in the lower part of the geyser-tube are not thrown out during an eruption; and a stronger confirmation lies in the fact that all the peculiarities of geyser action can be imitated. Professor Tyndall uses for this purpose an apparatus consisting of a tube of iron six feet long, surmounted by a basin, and heated by fires underneath. To imitate, as far as possible, the conditions of the geyser, he encircles the tube with a second fire, two feet from the bottom. As the water in the tube becomes heated, the phenomena of geyser eruption are repeated in miniature with beautiful regularity. By stopping the mouth of the tube with a cork, the enforced explosions of the Strokr are reproduced; and by similar simple devices the action of all other eruptive springs may be accurately imitated. All through the Firehole Basin and around Yellowstone Lake are many extinct geysers; sometimes, as in the case of Old Faithful, an active geyser is surrounded by a number of deserted cones, the remains of ancient "roarers." What occasions their decline? Earthquakes may, and no doubt frequently do, derange their mechanism, as observed in the old Strokr. But most of them probably die a natural death, from old age and decrepitude.