THE STORAGE OF COLD. 521 



place. The heat conquers, but at a great loss of its valuable sup- 

 plies, and a consequent refrigeration of the adjacent waters, air, 

 and land. 



In the southern seas this effect of the snow-fall is much more 

 considerable. A belt of glacier-forming lands surrounds the south 

 pole, and the annual iceberg fleet is much larger than that of the 

 north. The air indraught to the north polar region is estimated 

 to extend over a disk of fifty-five hundred miles diameter ; that to 

 the south polar region over a disk of seven thousand miles diame- 

 ter. The former is largely composed of land surface ; the latter is 

 nearly all water, and its air is therefore much more charged with 

 moisture. In consequence, the moist air which reaches the south 

 frigid zone is greatly in excess of that which reaches the northern 

 zone of cold, and the snow-fall there must be very much more 

 considerable. It is estimated that the south polar ice-cap can not 

 be less than three miles and may be twelve miles in height. The 

 thrust of this vast ice mountain upon the viscid material beneath 

 it is necessarily enormous, and a lofty ice-cliff is pushed off the 

 land at a rate of not less than a quarter of a mile annually, and 

 this around a circle of great extent. Fortunately, the immense 

 fleet of huge icebergs, thus annually launched, has no continental 

 land to act upon, its refrigerating influence being mainly exer- 

 cised upon stretches of ocean out of the ordinary channels of 

 navigation, and far removed from the important seats of human 

 habitation. 



There was a time, far in the past, but within the era of man's 

 occupancy of the earth, when the influence of the snow was enor- 

 mously greater than at present, and when the atmospheric chill, 

 stored in the falling flakes, rendered a vast region of the northern 

 continents unfit for human habitation, and extended the border 

 of the frozen zone far toward the present limits of tropical heat. 

 Doubtless if at present all the snow which forms in the upper 

 air should reach the earth's surface, a glacial epoch would now 

 exist in the north temperate zone. The experience of balloonists 

 and of mountain-climbers teaches us that snow forms and falls in 

 all seasons of the year. This is melted by the warmed lower 

 strata of air, and the earth thus saved from its chilling influence. 

 The solar heat, which has already done good work for man upon 

 the surface, performs new and useful labor for him in the atmos- 

 phere, by melting this falling snow, so that its water reaches the 

 earth only in the form of rain. 



At the period mentioned the snow limit in the atmosphere 

 was much lower than at present, and the great bulk of the snow- 

 fall reached the surface unmelted. As a result, the region of an 

 annual snow surplus extended much farther south than at present, 

 covering much and perhaps all of British America, and a broad 



