CLOUDS AND RIVERS, ICE AND GLACIERS. 85 



it, reach a suitable platform, plant our instrument, and 

 set out a second line, No. 2 (G G' upon sketch). We 

 must hasten our work here, for along this couloir stones 

 are discharged from a small glacier which rests upon 

 the slope of Mont Tacul. 



214. Still lower down by another quarter of a mile, 

 which brings us near the Tacul, we set out a third line, 

 No. 3 (H H' upon sketch), across the glacier. 



215. The daily motion of the centres of these three 

 lines is as follows : — 





Inches 



Distances asunder 



No. 1 . 



No. 2 . 



. 20-551 

 . 15-43 J 



. 545 yards. 



No. 3 . 



. 12-75/ * 



. <±87 „ 



216. The first line here moves five inches a day more 

 than the second ; and the second nearly three inches a 

 day more than the third. The reasoning is therefore 

 confirmed. The ice-plug, which is in round numbers 

 one thousand yards long, is shortened by the pressure 

 exerted on its front at the rate of about eight inches a 

 day. 



217. A river descending the Valley du Geant would 

 behave in substantially the same fashion. It would have 

 its motion on approaching Trelaporte diminished, and 

 it would pour through the defile with a velocity greater 

 than that of the water behind. 



