Regular Currents in the Sea -which equalize the Heat of the Glote. 575 



But the heat evolved in the formation of each fuperficial foot of ice, would be fuf- 

 ficient to raife the temperature of a ftratum of incumben": air 2220 times as thick as th« 

 ice (confequently in the cafe in queftion 265 X 2220 feet or 869 miles thick) 28 degrees, 

 or from the temperature of freezing viiater to that of 50P of Fahrenheit's thermometer, or 

 to the mean annual temperature of the northern parts of Germany. 



The heat given off to the air by each fuperficial foot of water in cooling one degree, is 

 fufEcient to heat an incumbent ftratum of air 44 times as thick as the depth of the water 

 JO degrees. Hence we fee how -very powerfully the water of the ocean, which is never 

 frozen over except in very high latitudes, muft contribute to warm the cold air which flows 

 in from the polar regions. 



But the ocean is not more ufeful in moderating the extreme cold of the polar regions 

 than it is in tempering the exceflive heats of the torrid zone ; and what is very remarkable,, 

 the fitnefs of the fea water to ferve this laft important purpofe, is owing to the very fame 

 caufe which renders it fo peculiarly well adapted for communicating heat to the cold at- 

 mofphere in high latitudes, namely, to the fait luhich it holds in Jolution. 



As the condenfation of fait water with cold continues to go on, even long after it has 

 been cooled to the temperature at which frefli water freezes, thofe particles at the furface 

 which are cooled by an immediate contafl: with the cold winds muft defcend, and take 

 their places at the bottom of the fea, where they muft remain, til! by acquiring an ad- 

 ditional quantity of heat their fpecific gravity is again diminifhed. But this heat they never 

 can regain in the polar regions ; for innumerable experiments have proved beyond all pofTibility 

 of doubt, that there is no principle of heat in the interior parts of the globe, which by ex- 

 haling through the bottom of the ocean could communicate heat to the water which refts 

 upon it. 



It has been found that the temperature of the earth, at great depths under the furface, 

 is different in different latitudes, and there is no doubt but this is alfo the cafe with refpefl 

 to the temperature at the bottom of the fea, in as f^r as it is not influenced by the currents 

 which flow over it -, and this proves to a demonftration, that the heat which we find to exift 

 without any fenfible change during fummer and winter at great depths, is owing to the 

 atlion of the fun, and not to central fires as fome have too haftily concluded. 



But if the water of the ocean, which, on being deprived of a great part of its heat by cold 

 •winds, defcends to the bottom of the fea, cannot be warmed ivhere it defccnds, as its fpecific 

 gravity is greater than that of water at the fame depth in warmer latitudes, it will imme- 

 idiately begin to fptead on the bottom of the fea, and to flow towards the equator ; and this 

 muft neceflarily produce a current at the furface in an oppofitc diredion. There are the 

 jnoft indubitable proofs of the exiftence of both thefe currents. 



The proof of the exiftence of one of them would, indeed, have been quite fufficient to 

 have proved the exiftence of both ; for one of tliem could not poflibly exift without the 

 other : but they are feveral dircft proofs of the exiftence of each of them. 



What has been called the gulph ftrcam in the Atlantic Ccean, is no more than one of 

 thefe curre-nf!, namely that at the furface, which moves from the equator towards the north 

 ^ole, modified by the trade winds, and by the form of the continent of North America ; and 

 the progrefs of the lower current may be confidered as proved direflly by the cold which 

 has been found to exift in tlic fea at great depths in warm latitudes; a degree of tempcratuic 

 4 much 



