1(3 M. Andiv de Luc on the Glaciers of the Alps. 



and if the ice at the bottom move, it arises from other causes, 

 since it can experience none of the alternations of freezing 

 and melting. 



I believe that the movement of a glacier is owing to two 

 principal causes. The first is the pressure of the snows ac- 

 cumidated on its upper parts : these snows are converted into 

 ice, and as at the commencement of a glacier the sides are 

 very steep, this ice or snow exerts a considerable pressure on 

 the glacier, and urges it forwards. This inference may at 

 least be derived from the fact that glaciers advance most re- 

 gularly in years when a greater quantity of snow has fallen 

 than usual, and when the heat of the summer has been too in- 

 considerable to melt them. 



The second cause of the progressive movement of glaciers, 

 is the continual melting of the ice in that part which rests on 

 the earth, in consequence of the effect of the internal heat of 

 the earth. This melting causes the glacier to sink down, ren- 

 ders it cavernous beneath, and, as it is always inclined, the 

 glacier must necessarily slip forwards. " We often see," says 

 Saussure, " large crevices form in a short time, because the 

 ice being eroded by the waters which flow beneath it, or rest- 

 ing unequally on the irregularly inclined bed which serves as 

 its base, descends and leaver the other masses of ice behind." 



M. Agassiz supposes that winter is the season when gla- 

 ciers are at rest. This, indeed, should result from his theory, 

 but has he assured himself of the fact, — has he inquu*ed of 

 those dwelling in their vicinity •'' It is possible, on the con- 

 trary, that they maj' move as much in winter as in summer. 

 This conjectiu-e is confirmed by M. Saussure and M. Alb. 

 Haller of Berne The former states that, in 1764, he had a 

 proof of the motion of glaciers, at a season which may be re- 

 garded as winter among the Alps. The latter wi'ote to me 

 on the 10th of November 1822, that the upper glacier of the 

 Grindelwald had begim to move in 1817, and that the motion 

 had never been discontmued, even in winter, up to the autumn 

 of 1822 ; and yet in winter the alternations of freezing and 

 tha^\*ing are interrupted. 



I shall next proceed to extract a few fragments from my 

 notes on the history of glaciers. It is known that from the 



