CUREENTS OF THE SEA. 195 



liaiil that vrhicli is below to the top, and send that which is on the 

 top do^^^l into the recesses and cavities below. Suppose the en- 

 tire atmosphere to be, from the bottom to the top, nearly of the 

 same temperatm-e, and in a perfect state of the quiescent equilibrium, 

 and that from some cause a certain volume of air above has its 

 specific gra^dty so changed that it commences to descend. As it 

 descends the pressm-e 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 ca- 

 loric 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 hght from the top, and of tm-ning, in course 

 of time, the whole atmosphere upside dov^ii. 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 chculation 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 Vv^ater is com- 

 pressible — 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 compressibihty 

 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 povrer which is capable of 

 sending up to the top water fr'om the uttermost depths of the sea ? 

 Suppose that this cubic measure of water, by supplying vapom* 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 out heat, raising the tempera- 

 ture, and changing the specific gra-v^ty of hke quantities in the va- 

 rious thermal strata through which it has to pass. Thus heat is 

 conveyed from the ton to the bottom of the sea, there to be libe- 



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