206 PHYSICAL GEOGRAPHY OP THE SEA, AND ITS METEOROLOGY. 



wliich is deep enougli to have the temperature of its v^ater some- 

 "what influenced by pressure (§ 404), tlie la\v is uniform; as you 

 descend in fresh-water lakes, the temperature decreases to that of 

 maximum density. Saussm^e extended his experiments to the 

 Gulfs of Nice and Genoa — salt-water bays in the neighbourhood of 

 his fresh-water lakes. Here, with the surface temperatm-e of 69°, 

 he found even at the depth of 1720 feet, the water no cooler than 

 55^.8. This salt w^ater might have been cooled 30° lower before 

 it would have reached the maximum density (25°. 6) of average 

 sea water. We see that the severest winters are not sufficient to 

 bridge our deep fresh-water lakes over with ice, though their 

 waters being cooled below 39°. 5, grow light, and remain on the 

 surface to be frozen. On the contrary, sea water contracts, grows 

 heavy, and sinks, until the whole basin, irom the bottom to the 

 top, be reduced to 27°. 2. Yet many confess no surprise at the 

 open water in fresh-water lakes that are comparatively shallow, 

 while they can conceive of no such thing in the Arctic Ocean, 

 though it be very much deeper than the deepest fresh-water lakes ! 

 431. At the very time that the doctor was gazing with longing 

 «o^'d matter annu- eyes upou thoso straugo groeu waters (§ 429), there 

 the polar basin. is kiiown to havo becu a powerful drift setting out 

 from another part of this Polar Sea, and carrying with it from her 

 moorings the English exploring ship '' Eesoiute," which her officers 

 and men had abandoned fast bound in the ice several winters 

 before. This drift carried a field of ice that covered an area not 

 less than 300,000 square miles, through a distance of a thousand 

 miles to the south. The drift of this ship was a repetition of De 

 Haven's celebrated drift (§ 474) ; for in each case the ice in which 

 the vessel was fastened floated out and carried the vessel along 

 with it ; by which I mean to be understood as wishing to convey 

 the idea that the vessel was not drifted through a line or an open- 

 ing in the ice, but, remaining fast in the ice, she was carried along 

 with the whole icy field or waste. This a.t least was the case 

 with De Haven. A field of ice covering to the depth of seven 

 feet an area of 300,000 square miles, would weigh not less than 

 18,000,000,000 tons. This, then, is the quantity of solid matter 

 that is drifted out of the polar seas through one opening — Davis' 

 Straits — alone, and during a part of the year only. The quantity 

 of water which was required to float and drive this solid matter out 

 was j^robably many times greater than this. A quantity of water 

 equal in weight to these tvro masses had to go in. The basin to 



