322 POPULAR LECTURES AND ADDRESSES. 



" of gravity of the altered solid and altered liquid 

 " that the altering liquid surface adjusts itself 

 " expresses the essence of Laplace's celebrated 

 " demonstration of the stability of the ocean, and 

 "suggests the proper elementary solution of the 

 " problem to find the true alteration of sea-level 

 " produced by a given alteration of the solid. As 

 "an assumption leading to a simple calculation, 

 " let us suppose the solid earth to rise out of the 

 " water in a vast number of small flat-topped 

 " islands, each bounded by a perpendicular cliff, 

 " and let the proportion of water area to the whole 

 " be equal in all quarters. Let all of these islands 

 " in one hemisphere be covered with ice, of thick- 

 " ness according to the law assumed by Mr. Croll 

 " that is varying in simple proportion to the sine 

 " of the latitude. Let this ice be removed from the 

 " first hemisphere and similarly distributed over the 

 " islands of the second. By wo eking out according 

 " to Mr. Croll's directions, it is easily found that 

 " the change of sea-level which this will produce 

 "will consist in a sinking in the first hemisphere 

 " and rising in the second, through heights varying 



