There are a set of experiments by the Baron Cagniard de la Tour, which appear to have a very important bearing on some conditions that may be supposed to prevail in nature, particularly if we adopt the view of a constantly increasing temperature towards the centre of our earth. If water, alcohol, or ether, is put into a strong glass tube of small bore, the ends hermetically sealed, and the whole exposed to a strong heat, the fluid disappears, being converted into a transparent gas; but, upon cooling, it is again condensed, without loss, into its original fluid state.[77] In this experiment, fluid bodies have been converted into elastic transparent gases with but small change of volume, under the pressure of their own atmospheres. We can readily conceive a similar result occurring upon a far more extensive scale. In volcanic districts, at great depths, and consequently under the pressure of the superincumbent mass, the siliceous rocks, or even metals, may, from the action of intense heat, be brought into a fluid, or even a gaseous condition, without any change of volume, since the elastic force of heat is opposed by the rigid resistance of the pressure of the surrounding rocks. Some beautiful experiments by Mr. Hopkins, of Cambridge, have proved that the temperature necessary to melt a body must be considerably elevated as the mechanical pressure to which it is subjected is increased. Directly connected with the results of Cagniard de la Tour are a yet more remarkable set of phenomena, which have been investigated by M. Boutigny,[78] and generally known as the “spheroidal condition” of bodies. If water is projected upon very hot metal it instantly assumes a spheroidal form--an internal motion of its particles may be observed--it revolves with rapidity, and evaporates very slowly. If a silver or platinum capsule, when brought to a bright red heat, is filled with cold water, the whole mass assumes the spheroidal state, the temperature of the fluid remaining considerably below the boiling point, so long as the red heat is maintained. If we allow the vessel to cool below redness in the dark, the water then bursts into active ebullition, and is dissipated into vapour with almost explosive violence. An equal quantity of water being projected into two similar vessels, over the fire, one cold and the other red hot, it will be found that the water in the cold vessel will boil and evaporate long before that in the one which is red hot. Another form of this experiment is exceedingly instructive. If a mass of white hot metal is suddenly plunged into a vessel of cold water, the incandescence is not quenched, the metal shines with a bright white light, and the water is seen to circulate around, but at some distance from the glowing mass, being actually repelled by calorific agency. At length, when the metal cools, the water comes in contact with it, and boils with energy.