POLAR ICE-CAPS AND SEA LEVELS. 325 



thoroughly correct, and shows the remarkable 

 power he possessed of grasping the subject, and 

 dealing with it by a simple geometric construction 

 which led to the same result as Laplace's mathe- 

 matical analysis. For the stability of the ocean it 

 is necessary that the specific gravity of water be less 

 than the specific gravity of the solid, and it is less 

 as we know. The mean density of the earth is 

 about 5 or more exactly 5 '6 times the specific 

 gravity of water. This statement favours La- 

 place's theory as to the requisite for stability, but it 

 is curious that Laplace did not notice the simple 

 view that if the solid part of the earth had a 

 specific gravity less than that of water it would 

 tend to float and leave the water on either side 

 of it. For example, take a globe of liquid of 

 any size (Fig. i) and let us suppose a small 

 spherical portion at A to become solid. The 

 configuration of solid and liquid , would remain 

 stable provided the solidified portion remained 

 of the same density as the liquid. If the solidified 

 portion acquired a density greater or less than that 

 of the liquid the configuration as shown in the 



