76 THE FORMS OF WATER IN 



E E' ? we have the following series of velocities of three 

 pairs of equivalent points : — 



Eastern points ; motion in inches • 



. 15 



18 



19 



Western points „ „ 



. 13 



15 



17 



183. Here the three points on the eastern side move 

 more rapidly than the equivalent points on the western 

 side. 



184. It is thus proved : — 



1. That opposite the Montanvert the eastern half of the 

 Mer de Glace moves more rapidly than the western half 



2. That opposite les Ponts the western half of th<> 

 glacier moves more rapidly than the eastern half 



3. That opposite Trelaporte the eastern half of the 

 glacier again moves more rapidly than the western half 



4. That these changes in the place of greatest motion 

 are determined by the flexures of the valley through which 

 the Mer de Glace moves. 



§ 25. New Law of Glacier Motion. 



185. Let us express these facts in another way. Sup- 

 posing the points of swiftest motion for a very grea t 

 number of lines crossing the Mer de Glace to be deter- 

 mined ; the line joining all those points together is 

 what mathematicians would call the locus of the point 

 of swiftest motion. 



186. At Trelaporte this line would lie east of the 

 centre ; at the Ponts it would lie west of the centre ; 

 hence in passing from Trelaporte to the Ponts it would 



