234 PHYSICAL GEOGRAPny OF THE SEA, AND ITS METEOROLOGY. 



aLundant supply of vapour lo create there by precipitation and 

 tlie liberation of latent heat a degree of rarefaction sufficient to 

 cause a general movement of the air polarward for the distance 

 of 40*^ of latitude all round. That there is an immense volume 

 of comparatively Avarm water going into the Arctic Ocean is 

 abundantly shown by observation, and the rising up there of this 

 water to the surface would afford heat and vapour enough for a 

 vast degree of rarefaction. 



459. The middle ice. — The records of arctic explorations, 

 together with the whalemen's accounts of *' middle ice " in 

 Baffin's Bay and Davis' Straits, go to confirm this view, which 

 is fnrther elaborated in the next chapter (§ 475). The facts 

 there stated, and this "middle ice," go to show that every winter 

 a drift takes place which brings out of the Frozen Ocean a 

 tongue of ice a thousand miles or more in length : it is the com- 

 pact and cold " middle ice." In our fresh- water streams it is the 

 middle ice that first breaks up ; that which is out of the way of 

 the curent remains longest. Not so in this bay and strait ; there 

 the littoral ice first gives way, leaving an open channel on either 

 side in spring and early summer, while the "middle ice" 

 remains firm and impassable. The explanation is simple enough : 

 the middle ice was formed in the severe cold of more northern 

 latitudes, from which it has drifted down, while that on the sides 

 was formed in the less severe climates of the bay and straits. 

 This winter tongue of ice, which we know by actual observation 

 is in motion from December till May, must, during that time, be 

 detached from the main mass of ice in the Arctic Ocean, conse- 

 quently there must be water between the ice that is in motion 

 and the ice that is at rest. Not only so. In early summer the 

 whalemen will run up to the north in the open water at the side 

 of the " middle ice " in Davis' Strait and Baffin's Bay, even as 

 far sometimes as Cape Alexander in 78°, to look for a crossing- 

 place. Here, though so far north, they will find the "middle 

 ice " gone, or so broken up that they can cross over to the west 

 side. They trace it up thus far, becau.se at the south, and in 

 spite of a higher thermometer, they find the " middle ice " com- 

 pact and firm, so much so as to be impassable. In tins fact we 

 recognize another circumstance favouring the theory of an open 

 sea at the north, and giving plausibility to the conjecture that 

 this "middle ice " drifts out from the southern edge of the open 

 sea as fast as it is formed during the winter. According to this 



