

x.] ALPINE TRAVELS, 1844 313 



Having thus measured the rate of motion of one of 

 the smallest glaciers in Switzerland, he next proceeded 

 to measure that of the largest, and descending to Brieg, 

 where he left Mrs. Forbes, he established himself at the 

 chalets of Marjelen, on the brink of the great Aletsch 

 Gletscher. His work was greatly interrupted by bad 

 weather, but he was able to recognize in this glacier a re- 

 markable instance of the manner in which the centre of 

 an ice-stream can descend towards the valley with double 

 or triple the velocity of its lateral parts. * I found,' 

 he writes, 'that while the velocity of the ice at 1,300 

 or about a quarter of a mile from the side, was four- 

 teen inches in twenty-four hours, at 300 feet distant from 

 the side it was but three inches in the same time, and 

 close to the side it had nearly vanished. Facts like these 

 u to show, with evidence, what intelligent men, such 

 liishop Kendu, had only supposed previously to the 

 first exact measures in 1842 that the ice of glaciers, 

 rigid as it appears, has in fact a certain " ductility " or 

 <cosity " which permits it to model itself to the 

 ground over which it is forced by gravity : still retaining 

 its compact and apparently solid texture, unless, indeed, 

 the inequalities of the ground be so abrupt as to force 

 a separation of the mass into dislocated fragments. 

 veil known, occurs to every glacier when the 

 in upon its parts reaches a certain amount, as for 

 mee when it h^s to turn a sharp angle or to 

 descend a rapid or convex slope/ 1 



A few <luy.s afterwards, on arriving at Geneva, Forbes 



learnt from Mr. Hopkins's published papers, which he then 



first time, that that gentleman accounted for 



,11,-ii motion above mentioned, by supposing a 



glacier to consist of strips or plates of ice, parallel to its 



course. And that these, according to the pressure scve- 



xercised upon them, slipped past one another : 



nil on- . on through th.- .linn; 



strip* towards the sides of the glacier, the comparatively 



small motion ,f which was n-mleivd mechanically 



1 Eighth Letter on Glaciers. 



