S4 THE OCEAN. 



In the enclosed basins of inland seas thermometrical observations 

 are much more easily made than in the middle of the great ocean ; 

 because the waters there are generally less deep, and the natural 

 gradations of temperature are less disturbed by currents. Thus the 

 water is not very cold in the depths of the Mediterranean, and 

 presents only slight variations of temperature. At about 100 to 275 

 fathoms below the surface, the fluid mass has already attained per- 

 manently the mean temperature, which it preserves during all the 

 year, and which seems to correspond to the mean annual tem- 

 perature of the neighbouring lands, which are subject to all the 

 abrupt changes of heat and cold.* While in summer the superficial 

 sheet of water has about 73'4 degrees Fahr., the water comprised 

 between 273 fathoms depth and the very bottom of the Mediter- 

 ranean is found at 59 degrees Fahr., which is pretty nearly the 

 mean annual warmth of the bordering countries. In the Greek 

 Archipelago, the deep waters of which are probably colder in conse- 

 quence of the current flowing from the Black Sea, the waters of the 

 surface have in summer from 77 to 78*8 degrees Fahr., and at hardly 

 98 fathoms depth the thermometer reveals a .constant temperature 

 of from 53-6 to 55-4 degrees Fahr. The Mediterranean is divided 

 into distinct basins, separated from one another by intermediate 

 ridges, -which are situated from 98 to 273 fathoms below the surface, 

 the result being that the variations of temperature produced by 

 the movements of currents and counter-currents are arrested on 

 the tops of the ridges. The water of each basin, being relatively 

 tranquil, thus maintains almost constantly the same thermometrical 

 degree, t 



* See below, the section entitled, Climates. 

 t Spratt, Nautical Magazine, Jan. 1860. 



