TEMPERATURE OF THE SEA. 13 
uf 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 
