400 THE CHEMISTRY OF CREATION. 



it then gradually descends to S. lat. 70, where 

 it is 4,500 feet below the surface. 



Proceeding northwards the same law still ob- 

 tains. Sir J. Ross therefore proposes to divide 

 the regions of oceanic temperature into three 

 two polar and one equatorial. If we imagine 

 the bed of water of invariable temperature to 

 be represented by a curved line, we should find 

 this line beginning at the depth of 4,500 feet 

 in the southern polar region, rising nearer 

 and nearer the surface until it reaches S. lat. 

 56 26', then sinking again to the depth of 

 7,200 feet at the equator; again rising in the 

 corresponding N. lat., and finally descending 

 again to the depth of 4,500 feet in the northern 

 polar region. This curve is determined by the 

 state of temperature at the surface. Near and 

 at the equator, the surface temperature is con- 

 stantly at 80 ; hence the depth of the line of 

 water at 39 is greatest here. At S. lat. 56 26' . 

 the temperature of the surface is 39. Such, 

 also, is the temperature of the surface in the 

 corresponding N. lat. Toward the poles the 

 surface is at the freezing point even in summer, 

 and the line of constant temperature is conse- 

 quently at a depth of 4,500 feet. Hence the 

 'water is warmer as we descend at all latitudes 

 below S. lat. 56 26', and above the correspond- 

 ing N. lat. ; at these points it is of uniform 



