3 2o POPULAR LECTURES AND ADDRESSES. 



loyally calling attention, in his opening words, to 

 the fact of his having been anticipated by M. 

 Adhemar, (in a work Revolutions de la Mer^) in the 

 suggestion of heaped-up ice being a probable cause 

 of the submergence and emergence of land, Mr. 

 Croll proceeds to investigate the probable effect 

 of an ice-cap of a given description. In this con- 

 nection Mr. Croll refers to an article on the 

 subject published by him in the Reader for 

 January 13, 1866, and the extract which I will 

 now read to you from this volume, Climate and 

 Tune (pp. 372-374), consists of a note written 

 by myself, at Mr. Croll's request, in regard to the 

 objection brought forward in that article : 



" Mr. Croll's estimate of the influence of a cap of 

 " ice on the sea level is very remarkable in its rela- 

 " tion to Laplace's celebrated analysis, as being 

 "founded on that law of thickness which leads to 

 "expressions involving only the first term of the 

 " scries of 'Laplace's functions,' or ' spherical har- 

 " monies.' The equation of the level surface, as 

 " altered by any given transference of solid matter, 

 " is expressed by equating the altered potential 



