THE AGE OF ICE. 835 



apsides ; C and D are, respectively, the vernal and autumnal equi- 

 noxes ; E F is the section of a plane passing through the poles of the 

 earth at right angles with the plane of its orbit. It is evident that 

 this plane will coincide with the line of the apsides once every 10,500 

 years ; E is the winter solstice ; F the summer solstice ; C is the ver- 

 nal equinox. While the earth is passing through B to D the north 

 pole is inclined toward the sun. This period is the summer of the 

 northern hemisphere. 



D is the autumnal equinox. While the earth is passing from D 

 through A to C, the north pole is inclined from the sun. This period 

 is the winter of the northern hemisphere. In the southern hemisphere 

 these seasons are reversed. 



By consulting the diagram it will appear that the arc C B D is 

 greater than the arc DAC. Therefore, the summer of the northern 

 hemisphere is now longer than its winter. On the contrary, the winter 

 of the southern hemisphere is now longer than its summer. At pres- 

 ent, this difference is about eight days. It has been greater, but is 

 gradually diminishing. 



The southern hemisphere has at present a winter of 187 days, and 

 a summer of 179 days. We may justly infer that during this winter 

 more snow and ice accumulated at the south pole than the heat of the 

 shorter summer is able to melt. The amount of this increase is very 

 slight in a single year, but it accumulates a large aggregate in the 

 course of ages. 



This accumulation of ice at the south pole is continually increased 

 and thickened by the deposition of moisture from the atmosphere. 

 Every wind from warmer regions that passes over it adds to its mass. 



The " Antarctic Continent " is an ice-cap, nearly circular in form, 

 and about 3,000 miles in diameter, unexplored and uninhabitable. 

 We can not easily ascertain its thickness. The arctic ice-cap is 

 much smaller, and is honeycombed by the Kuro Siwa, or Japan Cur- 

 rent, and the Gulf Stream. Nevertheless, the Greenland Archipelago 

 seems covered with glaciers often several thousand feet in depth. 

 If we could assign to the Antarctic ice-cap a thickness of 15,000 

 feet, we should have a mass of ice large enough to displace the earth's 

 center of gravity nearly a mile to the southward of its center. A 

 gradual displacement of this sort, caused by the slow accumulation 

 of ice, would produce an imperceptible drainage of the oceans from 

 the north to the south, and the gradual emergence of northern and 

 submergence of southern continents. 



If we examine the globe, we seem to discover an actual result of 

 this sort. The greatest mass of the ocean is gathered about the south 

 pole. The northern hemisphere includes about five sixths of the land- 

 surface of the globe. 



Moreover, geologists affirm, that this inequality is increasing ; they 

 assert that the northern continents are slowly rising, and that the isl- 



