MARINE BIOLOGICAL STATION AT PORT ERIN. 53 



The chief hydrographic results which have benefited 

 navigation are, according to Tizard : — 



(1). The proof that the variation of the compass can 

 be determined as accurately in a ship as on shore, if the ship 

 is magnetically suitable. 



(2). The determination for the first time of the depths 

 and main contour lines of the great ocean basins. It was 

 shown that some of the great depths formerly reported had 

 been much exaggerated, and the deepest sounding obtained 

 was 4,475 fathoms, in the neighbourhood of the Marianna 

 Islands in the N. Pacific, The investigations of many other 

 expeditions (such as the " Tuscarora," the " Gazelle," the 

 " Vettor Pisani," and the " Valdivia ") since the " Challenger " 

 have not altered in any material degree the contour lines of 

 the great oceans drawn by our expedition in 1876, and have 

 not resulted in the discovery of any depth exceeding 5,269 

 fathoms, about six statute miles. The "Challenger" explora- 

 tions give no support to the fanciful theory of a lost " Atlantis." 

 Microscopic investigations have revealed no traces of mythical 

 continents now beneath the sea. 



(3). The determination of oceanic temperatures and 

 their independence of seasonal variation below the depth 

 of 100 fathoms. 



(4). The proof of constant bottom temperatures over 

 large areas in the ocean. Thus, in the N. Atlantic the tem- 

 perature at depths exceeding 2,000 fathoms was found to be 

 constant at about 36*5° F., while in the N. Pacific the bottom 

 temperature was constant at 35° ; in parts of the S. Atlantic 

 the temperature at the bottom fell to 32*7°, while in the Sulu 

 Sea it is 50*5°, and in the Arafura Sea 38-6°, while it is known 

 that the bottom temperature of the Mediterranean is constant 

 at 55*5°, and that of the Ked Sea at 69°, these differences 

 being due to certain oceanic areas being separated from each 

 other by submarine ridges, which prevent a more general 



