348 THE REVOLUTIONS OF THE CRUST OF THE EARTH. 



placement of the center of gravity of the earth, is a thick stratum of ice- 

 and snow with which the southern hemisphere is covered. When the 

 winters of the boreal hemisphere coincide with the aphelion, the snow 

 will collect upon that hemisphere ; the austral glacier will melt, the 

 waters will return to our continents, and will cover them to the depth of 

 five or six hundred meters in the latitude of Paris. This elevation of 

 the level of the sea will be double in the latitude of Greenland, and null 

 upon the equator. 



M. Adhe'mar made the eccentricity of the fluid mass too great, and, 

 therefore, in his efforts to establish the time of the formation of the gla- 

 cier, obtained exaggerated results. A cupola of ice from 20 to 40 leagues 

 (from 69 to 138 miles) in thickness, occupying a space 400 miriameters 

 in diameter, is difficult to imagine. We can, on the contrary, conceive 

 great density of the ice, on account of the strong pressure. The mass 

 of ice is, in fact, less, as well as the supposed eccentricity of the fluid 

 envelope. 



Still, the evident traces of water in localities at considerable heights 

 imply a great displacement of the fluid mass, and consequently great 

 accumulations of snow upon the pole. Thus the Alps must have been 

 submerged after they had acquired their present form. The traces of 

 water are seen in the lines of erosion upon the sides of the mountains, 

 the marine shells found at high levels, and the alluvial terraces. The 

 highest line of erosion is found, according to M. Sharpe,* at an elevation 

 of from 9,000 to 9,100 feet. A deeply-marked line passes entirely 

 around the mountains. The sea must have remained for a long time at 

 this level. The elevation of the second line is about 7,500 feet. It is 

 found in many parts of Switzerland, and was observed by M. Forbes. 

 The third line is at a height of 4,800 feet. Analogous lines are found iu 

 Scotland, Sweden, and upon some of the African islands. 



The circumstance, according to Mr. Adhe'mar, which most contributes 

 to the cooling of a hemisphere is the greater duration of the nights as 

 compared with the days. At present the year of the boreal pole is 

 composed of 4,464 hours of day and 4,296 hours of night, while the re- 

 verse is the case at the austral pole. If we consider the year as a single- 

 day, the sum of duration of the nights surpassing the sum of duration, 

 of the days of the austral hemisphere, there will be loss of heat by radia- 

 tion which is not compensated for by the solar heat. The reverse is 

 the case in the boreal hemisphere; the sum of the days there is greater 

 than that of the nights, therefore there will be conservation of heat. 

 The difference of temperature between the two hemispheres will be 

 equal to the heat lost by radiation in a hundred and sixty-eight hours, 

 plus the heat received from the sun in the same length of time; that is 

 to say, this difference is equal to three hundred and thirty-six times th( 

 quantity of heat the earth received from the sun or loses by radiation 

 in an hour. When the eccentricity was at its extreme, this difference 

 * Quart. Journ. Geolog. Soc, 1855, t. xii, 46, p. 102-123. 



