CURRENTS OF THE SEA. 203 



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 equi- 

 librium, 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 atmo- 

 spherical ocean vs^liich, 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 clown. 

 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 atmo- 

 sphere 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 experi- 

 ment 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. Conse- 

 quently, 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 w^inds 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 



