1 64 POPULAR LECTURES AND ADDRESSES. 



the whole earth, as we have assumed in the dia- 

 grams (Figs. 48 to 5 1 ), but the surface of the water 

 may be imagined as taking the same figure, so 

 far as there is water, that it would take if there 

 were water over the whole surface of the earth. 

 But here a difficult question comes in namely, 

 the attraction of the water for parts of itself. 

 If we consider the water flowing over the whole 

 earth this attraction must be taken into account. 

 If we imagine the water of exceedingly small 

 density so that its attraction on itself is insensible 

 compared with that of the earth, we have thus 

 to think of the equilibrium theory. But, on the 

 other hand, if the water had the same density 

 as the earth, the result would be that the solid 

 nucleus would be almost ready to float ; and 

 now imagine that the water is denser than the 

 earth, and we put the tides out of consideration 

 altogether. Think of the earth covered over with 

 mercury instead of water a layer of mercury a 

 foot deep. The solid earth would tend to float, 

 and would float, and the result would be that 

 the denser liquid would run to, and cover one 



