704 THE POPULAR SCIENCE MONTHLY. 



rier of the south pole. Discoverers suppose what they have looked 

 upon to be land, but rarely have they ever seen any thing but rolling 

 ranges of ice and snow rising higher and higher as far as the eye could 

 reach. In the most open of the south -polar seas, Sir James Ross, in 

 1841, sailed 450 miles along an unbroken cliff of ice from 150 to 250 

 feet high, and of unknown depth beneath the water. It was one of 

 the vast antarctic glaciers pushing down into the sea, from which some 

 of those southern icebergs were broken off, that navigators have fre- 

 quently laid down for islands, while the next sailor that voyaged that 

 way found open water where they were charted. 



Not a sign of vegetation, not an indication of thawing, has ever 

 been discovered within or near the antarctic circle, whereas there 

 are aboriginal races and numerous settlements of civilized communi- 

 ties on every side within the arctic circle. The whaleboat or the dog- 

 sledge has traversed the arctics and found the sea-level in almost every 

 degree of high latitude. In the south no adventurer has yet pene- 

 trated within probably 1,500 miles of the centre of greatest cold. 

 Whence comes this great difference in the climate and ice accumula- 

 tions of the two poles of the earth ? It is the object of this article to 

 inquire if in the astronomical relations of our planet there are found 

 any sufficient causes for such differences. 



The path of the earth about the sun once every year is an ellipse, 

 with the sun in one of the foci or centres. An ellipse is a circular 

 figure having two centres instead of one; that is, the circumference is 

 everywhere equally distant from the two centres taken together the 

 sum of the two distances is always the same. Therefore, the sun being 

 in one of these centres, the earth is nearer to it in one half of the year 

 than in the other. At the present time the nearest approach, or the 

 perigee, occurs about the 1st day of January; and the earth is at 

 that time 3,200,000 miles nearer to the sun than it is on the 1st day 

 of July. 



It is a peculiar property of bodies revolving in elliptical orbits, 

 that they travel faster when near the centre of attraction than when 

 farther away. It follows, from the second of the three great laws of 

 planetary motion discovered by Kepler, that the line connecting the 

 two bodies must pass over equal areas in equal times. The earth 

 passes through our winter portion of its orbit, that is, from autumnal 

 to vernal equinox, in eight days less time than through the summer 

 part of it. In the southern hemisphere, of course, the condition of 

 things is reversed, and the winter there is eight days longer than the 

 summer. Moreover, the sun is at its greatest distance from the earth 

 during the long southern winter, and at its least in the short northern 

 winter. 



Of the two causes, I regard the first as of main importance. Dis- 

 tance from the sun, whatever theory may be, does not seem to have 

 much effect upon climate. The southern summers, when the sun is 



