252 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



licavier waters below from the cold, for l)e Ilaven invariably 

 found the temperature of the water under the ice 28°, which is 

 the temperature that average sea water invariably assumes 

 during the process of congelation (§ 442). Moreover, the specific 

 gravity of the surface water which l^odgers measured in the 

 Arctic Ocean was (§ 427) less than that of average sea water — a 

 fact in confirmation of this conjecture as to the office of rain and 

 river water in the polar sea's. The freezing-point of strong brine 

 is 4° ; consequently the freezing-point of water in the sea raay 

 vary according to the proportion of salts in it, from 4° all the 

 way up to just below 32°. Thus the salts of the sea impart to its 

 waters an elasticity, as it were, giving a law, — a sort of sliding- 

 scale — both for the thermal dilatation and of congelation, which 

 varies between that of fresh water and the saltest sea water 

 according to the degree of its saltness. 



480. Layers of water of different temperature in the Arctic Ocean. — 

 Eodgers tried with his hydrometer and thermometer the waters 

 of the Arctic Ocean at the surface, below, and at the bottom, and 

 as often as he tried he found this arrangement : warm and light 

 water on the top, cool in the middle, " hot and heavy " at the 

 bottom. His experiments were made near Behring's Straits in 

 August, 1855, between the parallels of 71°-2'', and are as per 

 example following : 



Date. 



Au- 13 



Aier. 15 



Lut. 72° 2' Long. 174° 37' W. 



1=21' „ 175° 22' 



1 Near bottom. 



Assuming the surface water which Kodgers used for these experi- 

 ments to be a fair average of arctic surface waters generally, this 



winter drift ^Yould have brought them down safely into milder cKraates, and 

 into the glad waters of the Atlantic Ocean, as it did those four other vessels. 



"The frequent, if not the regular anmial occurrence of this drift down 

 tlirough Baffin's Bay is a fact which will be considered by all future arctic 

 explorers as one of great importance, for it atfords the means of escaping from 

 the Arctic Ocean in the severest winter." — Transactions of the American Geo. 

 Society, 1860. 



