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PHYSICAL GEOGRAPHY. 



The temperature of the surface is of the most importance, in relation to physical climate, 

 an the superior stratum of the ocean is the only one that has an immediate influence upon 

 the thermal condition of the atmosphere. It diminishes gradually from within the tropics 

 as the latitude increases, till towards the poles the sea is ice-bound. But in high latitudes 

 the waters of the northern hemisphere are warmer than those of the southern ; and, as 

 compared with the other oceans, the temperature of the Atlantic is higher in high latitudes, 

 and lower in equatorial regions. This appears from the following table : 



A considerable number of observations have yielded the following results, upon which 

 general dependence may be placed : 



1. At noon, the open sea is colder than the atmosphere noticed in the shade, and at 

 midnight warmer ; an assertion first made by M. Peron, and confirmed by a large 

 number of observations. 2. Morning and evening, the temperature of the sea and of 

 the atmosphere usually correspond. 3. Observations taken at six in the morning, at 

 midday, at six in the evening, and at midnight, of the temperature of the ocean at 

 the surface, and of the atmosphere, show the mean to be higher with reference to the 

 sea in every latitude. The ocean is thus in general wanner than the atmosphere with 

 which it is immediately in contact. 4. Banks diminish the temperature of the sea, 

 so that it is always colder over them than where it is deeper ; and the difference is 

 greater, the greater the shallows. 5. The oceanic warmth equator, or the line of 

 greatest warmth at the surface, does not coincide with the geographical equator, but 

 runs for the most part on the north of it. At one point, in the Gulf of Mexico, 

 the greatest heat is situated 28, or about 1500 miles to the north. 



GREATEST OCEANIC HEAT. 



Atlantic Ocean. The line of the greatest heat of the surface-water is entirely north of 

 the equator, the temperature varjang in different places from 77 to 88 5'. The minimum 

 is found near the coast of Guinea : the maximum in the Gulf of Mexico. 



Indian Ocean. The line of the greatest heat is here also in the northern hemisphere, 

 except in the eastern region, between Sumatra and New Guinea. The minimum tempera 

 ture, 85 5', is found in the Molucca Sea ; the maximum in the Arabian Gulf. 



Pacific Ocean. In the eastern portion, the warmth equator lies in the northern hemi 

 sphere ; in the western portion, in the southern. The minimum temperature, 81 7', is 

 found between the Galapagos and Sandwich Islands ; the maximum, 88 5', in the haven 

 of Dororei, New Guinea. 



There is no sensible difference between the general temperature of the tropical waters, 

 north or south. Beyond the southern tropic, also, as far as 35 or 40, the temperature 

 corresponds with that of similar extra-tropical northern latitudes ; yet it is generally 

 supposed that towards the poles the cold of the seas is greater in the southern than in 

 the northern hemisphere, though the difference between the temperature of these high 



