THE GEYSERS—CONVECTION, EXPANSION, AND EVAPORATION.

Globe, Volume IX, Issue 1256, 28 March 1878, Page 3

THE GEYSERS—CONVECTION, EXPANSION, AND EVAPORATION.

Professor Tyndall, in a recent lecture on Heat, described the Phenomena and illustrated the principles of the Great Geyser of Iceland, in accordance with Bunsen’s theory. This geyser consists of a tube 74 feet deep and 50 feet and 60 feet in diameter. In the lower portions of the column the water may be heated far beyond its boiling point (212 degrees Fahrenheit) without boiling, through the pressure of the cooler water above it; but when this pressure is removed through the heating of the upper water by the lateral volcanic rocks, the lower water boils, and a violent eruption of water and steam ensues. Dr. Tyndall produced a successful imitation by means of a miniature geyser formed of a tin tube surmounted by a basin, heated at the bottom of the tube and a little distance above it by gas jets, whereby a succession of eruptions was maintained for some time during the lecture. By putting a cork in this tube, and other arrangements, the principle of the Strokkur and other intermittent eruptive springs was clearly illustrated, the discharges being brilliantly illuminated by the electric light. The Professor next exhibited the way in which heat is distributed in air and in water, termed “convection,” the heated currents ascending and the cold ones descending. These various currents, having different refractive powers, produced shadows, which were shown on the screen by the electric 1 light. By this convection the hot air of the tropics is transmitted towards the polar regions, rendering them habitable. The aqueous vapour convoyed is condensed into rain and snow by the mountains, and in their valleys (as in the Alps) gives rise to the icerivers termed glaciers, from which, in Greenland, icebergs arc broken off. The mildness of the continent of Europe is attributed greatly to the diffusion of heat by winds and vapours, and especially by the Gulf Stream. Examples were next given of the expanison of solid bodies; for instance, that of brass was shown to be greater than that of iron; and a bar of steel was broken by the contraction of heated iron who" cold water was poured upon it. The spheroidal state of water also was exhibited. Water dropped into a hot metal basin was not converted into steam, but rolled about the basin, being prevented from touching it by a layer of its own vapour. When the basin was somewhat cooled contact took place, and hissing, with steam, was produced. That there was no contact previous was proved by imitating Poggendorff’e yery interesting

experiment with the electric current. A bell, silent through the interruption of the current by the space between the water and iho b -.sin, was violently rung when the current was reestablished by their contact. Alter referring to the liquefaction of gases by Faraday, by means of intense cold and great pressure, beginning with chlorine in 1823 (the original specimen of which was shown), Dr. Tyndall produced an iron bottle filled with liquid carbonic gas. When ho opened the tap the liquid vaporised, and rushed out with great violence, converting itself and the watery vapour in tiro room into snow, through the intense cold caused by the sudden evaporation. With some of the carbonic acid snow mercury was frozen into a sol d mass ; and when the snow was mixed with ether, mercury was frozen even in a red-hot crucible. In concluding, the professor alluded to M. Raoul Pictet’s recent liquefaction of oxygen gas by the intense cold generated by the combination of liquid sulphurous acid with solid carbonic acid, aided by a pressure of 320 atmospheres.