ICE AND GLACIERS 235 



ceive that such displacements must ultimately be observed, 

 notwithstanding the slow rate at which they take place, and 

 in spite of the chaotic confusion of crevasses and rocks 

 which the glacier exhibits. 



Besides rocks and stones, other objects which have acci- 

 dentally alighted upon the glacier are dragged along. In 

 1788 the celebrated Genevese Saussure, together with his 

 son and a company of guides and porters, spent sixteen 

 days on the Col du Geant. On descending the rocks at the 

 side of the cascade of the Glacier du Geant, they left behind 

 them a wooden ladder. This was at the foot of the Aiguille 

 Noire, where the fourth band of the Mer de Glace begins; 

 this line thus marks at the same time the direction in which 

 ice travels from this point. In the year 1832, that is, forty- 

 four years after, fragments of this ladder were found by 

 Forbes and other travellers not far below the junction of 

 the three glaciers of the Mer de Glace, in the same line (at 

 s, FIG. no), from which it results that these parts of the 

 glacier must on the average have each year descended 375 

 feet. 



In the year 1827 Hugi had built a hut on the central 

 moraine of the Unteraar Glacier for the purpose of making 

 observations; the exact position of this hut was determined 

 by himself and afterwards by Agassiz, and they found that 

 each year it had moved downwards. Fourteen years later, 

 in the year 1841, it was 4,884 feet lower, so that every year 

 it had on the average moved through 349 feet. Agassiz 

 afterwards found that his own hut, which he had erected on 

 the same glacier, had moved to a somewhat smaller extent. 

 For these observations a long time was necessary. But if 

 the motion of the glacier be observed by means of accurate 

 measuring instruments, such as theodolites, it is not neces- 

 sary to wait for years to observe that ice moves a single 

 day is sufficient. 



Such observations have in recent times been made by 

 several observers, especially by Forbes and by Tyndall. They 

 show that in summer the middle of the Mer de Glace moves 

 through twenty inches a day, while towards the lower ter- 

 minal cascade the motion amounts to as much as thirty-five 

 inches in a day. In winter the velocity is only about half as 



