Page:Physical Geography of the Sea and its Meteorology.djvu/229

Rh power which, after the heaviest air has settled at the bottom of its subtile sea—after the lightest has come to rest at the top, and the whole arranged itself according to specific gravity—can haul that which is below to the top, and send that which is on the top down into the recesses and cavities below. Suppose the entire atmosphere to be, from the bottom to the top, nearly of the same temperature, and in a perfect state of the quiescent equilibrium, and that from some cause a certain volume of air above has its specific gravity so changed that it commences to descend. As it descends the pressure upon it increases—and air, being compressed, contracts and gives out heat. A like volume ascends to take its place, and in ascending it expands and grows cool. Thus the total mass, and the total pressure, and the total amount of caloric remain the same; but there is a transfer of heat from the top to the bottom, by which the equilibrium of the mass is destroyed, and a force established at the bottom of the atmospherical ocean which, with the assistance of an agent at the top to alter specific gravity, is capable of sending up the heavy air from the bottom, of drawing down the light from the top, and of turning, in course of time, the whole atmosphere upside down. All philosophers acknowledge the power of this omnipresent agent in the air, and that, by alternately assuming the latent and the sensible form, it, to say the least, assists to give to the atmosphere the dynamical force required for its system of vertical circulation as well as its horizontal. So with water and the salt sea where we do have an agent that is continually altering specific gravity at the surface. Notwithstanding the Florentine experiment upon water in the gold ball, it has since been abundantly proved that water is compressible—so much so, that at the depth of ninety-three miles its density would be doubled. Consequently, a given quantity of water—such, for instance, as a cubic foot measured at the surface—would not, if sunk to the depth of four miles, measure a cubic foot by seventy-two cubic inches. As a rule, the compressibility of water in the depths of the sea is one per cent, for every 1000 fathoms. Here, then, in the latent heat which is liberated in the processes of descent, have we not a power which is capable of sending up to the top water from the uttermost depths of the sea? Suppose that this cubic measure of water, by supplying vapour to the winds at the surface, to have its saltness so increased as to alter its specific gravity to sinking: Like the air, it is compressed, and contracts in its descent, giving