USES OF SALT SEAS. 23 



with the waves of the Polar Sea, form a bed of mean density light 

 enough to maintain itself and flow off towards the Atlantic Ocean. 

 These surface movements determine in the lower regions certain 

 contrary movements, whence originate the powerful counter currents 

 which ascend the Straits from Baffin's Bay and reappear in the 

 mysterious 'Polynia' of Kane, diffusing there its treasure of heat 

 brought from intertropical seas." Dr. Kane, in his interesting 

 narrative, reports an open sea north of the parallel of 82^, which he 

 and his party crossed a barrier of ice eighty miles broad to reach, 

 and before he reached it the thermometer marked 60°. Beyond this 

 ice-bound region he found himself on the shores of an iceless sea, 

 extending in an unbroken sheet of water as far as the eye could 

 reach towards the Pole. Its waves were dashing on the beach with 

 the swell of a great ocean ; the tides ebbed and flowed. Now the 

 question arises, Where did those tides have their origin ? The tidal 

 wave of the Atlantic could not have passed under the icy barrier 

 which De Haven, found so finn ; therefore they must have been 

 cradled in the cold sea round the Pole ; in which case it follows that 

 most, if not all, the unexplored regions about the Pole must be 

 covered with deep water, the only source of strong and regular tides. 

 Seals were sporting, and water-fowl feeding, in this open sea, as Dr. 

 Kane tells us ; and the temperature of the water which rolled in and 

 dashed at his feet with measured beat was 36°, while the bottom of 

 the icy barrier of eighty miles was probably hundreds of feet below 

 the surface level. 



" The existence of these tides," says Maury, " with the immense 

 flow and drift which annually take place from the Polar Seas and the 

 Atlantic, suggests many conjectures as to the condition of these 

 unexplored regions. Whalers have always been puzzled as to the 

 breeding-place of the great whale. It is a cold-water animal, and, 

 following up the train of thought, the question arises, Is not the 

 nursery for the great whale in this Polar Sea, which is so set about 

 and hemmed in by a hedge of ice, that man may not attempt to 

 trespass there?" 



One or two points worthy of notice may be recorded here. 

 Shallow water, and water near the coast, or covering raised sand- 

 banks, is colder than water in the open sea. Alexander von 

 Humboldt explains this phenomenon by supposing that deep waters 

 of higher temperature re-ascend from the lowest depths and mingle 

 with the upper beds. Fogs are frequently formed over sand-banks, 

 because the cold water which covers them produces a local precipita- 

 tion of atmospheric vapour. The contour of these fogs are perfectly 



