TEMPERATURE OF THE SEA. 13 



of the high seas. Thus the Mediterranean, when evaporation is 

 favoured by heat, contains about one half per cent, more salt 

 than the ocean ; while the Baltic, which, on account of its 

 northern position, is not liable to so great a loss, and receives 

 vast volumes of fresh water from a number of considerable 

 rivers, is scarcely half so salt as the neighbouring North Sea. 



In the open ocean, the perpetual circulation of the waters 

 produces an admirable equality of composition ; yet Dr. Lenz, 

 who accompanied Kotzebue in his second voyage round the 

 world, and devoted great attention to the subject, found that 

 the Atlantic, particularly in its western part, contains a some- 

 what larger proportion of salts than the Pacific ; and that the 

 Indian Ocean, which connects those vast volumes of water, is 

 more salt towards the former than towards the latter. 



As water is a bad conductor of caloric, the temperature of the 

 seas is in general more constant than that of the air. 



The equinoctial ocean seldom attains the maximum warmth of 

 83°, and has never been known to rise above 87°; while the sur- 

 face of the land between the tropics is frequently heated to 

 129°. In the neighbourhood of the line, the temperature of the 

 surface-water oscillates all the year round only between 82° and 

 85°, and scarce any difference is perceptible at different times of 

 the day. 



The wonderful sameness and equability of the temperature of 

 the tropical ocean over spaces covering thousands of square 

 miles, particularly between 10° N. and 10° S. lat., far from the 

 coasts, and where it is not intersected by pelagic streams, 

 affords, according to Arago, the best means of solving a very 

 important, and as yet unanswered question, concerning the 

 physics of the globe. "Without troubling itself," says that 

 great natural philosopher, "about mere local influences, each 

 century might leave to succeeding generations, by a few easy 

 thermometrical measurements, the means of ascertaining whether 

 the sun, at present almost the only source of warmth upon the 

 surface of the earth, changes his physical constitution, and varies 

 in his splendour like most stars, or whether he has attained a 

 permanent condition. Great and lasting revolutions in his 

 shining orb would reflect themselves more accurately in the 



