110 THE FORMS OF WATER IS 



is one of tension. Across this latter the glacier breaks, 

 and longitudinal crevasses are formed. 



277. Examples of this kind of crevasse are furnished 

 by the lower part of the Glacier of the Rhone, when 

 looked down upon from the Grimsel Pass, or from any 

 commanding point on the flanking mountains. 



§ 42. Crevasses in relation to Curvature of Glacier. 



278. One point in addition remains to be discussed, 

 and your present knowledge will enable you to master 

 it in a moment. You remember at an early period of 

 our researches that we crossed the Mer de Glace from 

 the Chapeau side to the Montanvert side. I then 

 desired you to notice that the Chapeau side of the 

 glacier was more fissured than either the centre or the 

 Montanvert side (75). Why should this be so ? Know- 

 ing as we now do that the Chapeau side of the glacier 

 moves more quickly than the other ; that the point of 

 maximum motion does not lie on the centre but far east 

 of it, we are prepared to answer this question in a per- 

 fectly satisfactory manner. 



279. Let A B and c D, in the diagram opposite, re- 

 present the two curved sides of the Mer de Glace at the 

 Montanvert, and let mwbea straight line across the 

 glacier. Let o be the point of maximum motion. The 

 mechanical state of the two sides of the glacier may 

 be thus made plain. Supposing the line m n to be a 

 straight elastic string with its ends fixed ; let it be 



