22 THE POLAR GLACIERS. 



1,150 feet above the sea. In like manner, South America would 

 have a height of 1,130 feet ; North America of 750 feet ; and 

 Europe of 670 feet. The averasjp of the whole he estimates at 

 920 feet. Of the mainlands not included in the above namely, 

 Africa, Australia, the polar lands, and islands about as much is 

 north as south of the equator. So that w r e may safely estimate 

 that there is in the northern hemisphere an excess of 28,000,000 

 square miles of land, of the average height above-mentioned, to 

 be counterpoised by something yet to be found in the southern 

 hemisphere. 



If there is an excess in the quantity or bulk of water south of 

 the equator over that north of it, then the difference of weight 

 between this excess and so much land, which is about in the 

 proportion of one to two and a half, must be added to the un- 

 known quantity which we are soon to look for above the southern 

 seas. As there is, of course, the same excess of water-surface 

 south of the equator that there is of land-surface north of it, and 

 as we may very safely assume that the oceans have a mean depth of 

 at least 3,220 feet (3^- X 920) and that the southern waters average 

 as deep as the northern, it follows that our unknown quantity is at 

 the very least doubled by the above considerations. We have, 

 therefore, to seek in the southern hemisphere what will balance 

 28,000,000 square miles of land at least 1,840 feet high. 



We look over the map of the world, and down near the bottom 

 we find some uncertain landmarks with many breaks, but on the 

 whole tracing out very nearly the antarctic circle, and indicating 

 that there is, covering nearly all that zone, an unexplored and 

 scarcely discovered country. This impenetrable region is esti- 

 mated to be as large as the continent of North America, about 

 8,000,000 square miles. A very little arithmetic will now prove 

 the bold claim which I here make, that, even supposing the w r hole 

 of this region to be land of the average continental height, there 

 is still required over it all an average thickness of two and a half 

 miles of solid ice to make the southern hemisphere equal the 

 northern in weight. 



This result of calculation is well confirmed by the information 

 which all southern navigators have brought back from those most 



