§431. THE SPECIFIC GRAVITY OF THE SEA, ETC. 211 



Lucerne and Thun. In these it was 41°, or 1° colder than the 

 bottom of Geneva, their surface water being about 60°. In Lago 

 Sabatino, near Rome, with the surface water at 77°, Barlocci re- 

 ports 44° at the depth of 490 feet. The winter in Rome is not se- 

 vere enough to cool such a mass of water below 44°. But with the 

 exception of the Lake of Geneva, which is deep enough to have 

 the temperature of its water somewhat influenced by pressure 

 (§ 404), the law is uniform ; as you descend in fresh-water lakes, 

 the temperature decreases to that of maximum density. Saussure 

 extended his experiments to the Gulfs of Nice and Genoa — salt- 

 water bays in the neighborhood of his fresh-water lakes. Here, 

 with the surface temperature of 69°, he found even at the depth of 

 1720 feet, the water no cooler than 65°.8. This salt water 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 89°. 5, 

 grow light, and remain on the surface to be frozen. On the con- 

 trary, sea water contracts, grows heavy, and sinks, until the whole 

 basin, from 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 

 Solid matter annual- evcs UDOU thcsc strauffc grccn watcrs (S 429), there 



ly drifted out of the . -^ ^ i r> ^ i -n • 



polar basin. IS known to havc been a powerful drift setting out 



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

 mooring the English exploring ship Resolute, 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 thou- 

 sand miles to the south. The drift of this ship was a repeti- 

 tion 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 opening in the ice, but, remaining fast in the ice, 

 she was carried along with the whole icy field or waste. This 



