ETC. 225 



do after passing over land and mountain heights of America, 

 Europe, and Asia, must be robbed of much of their moisture ere 

 they reach that ocean ; it will require an abundant supply of vapour 

 to create there by precipitation and the 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 warm 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 records of arctic explorations, together with thewhale- 

 Tue middle ice. men's accounts of " middle ice " in Baffin's Bay and 

 Davis' Straits, go to confirm this view, which is further 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 compact and cold " middle ice." 

 In our fresh- water streams it is the ^nicldle ice that first breaks up ; 

 that which is out of the way of the current remains longest. Not 

 so in this bay and strait ; there the littoral ice first gives way, leav- 

 ing 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, consequently 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, because at the south, and in 

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

 and firm, so much so as to be impassable. In this fact we recognize 

 another circumstance favoiuring 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 



Q 



