339 



Linear expansion of ice for an interval of 100 of the Centigrade 

 thermometer. 



0-00524, Schumacher. 

 00513, Johrt. 

 0-00518, Moritz. 



Ice, therefore, has nearly twice the expansibility of lead, so that a 

 sheet of ice would, under similar circumstances, have descended a 

 plane similarly inclined, twice the distance that the sheet of lead 

 referred to in the preceding article descended. Glaciers are, on an 

 increased scale, sheets of ice placed upon the slopes of mountains, 

 and subjected to atmospheric variations of temperature throughout 

 their masses by variations in the quantity and the temperature of 

 the water, which flowing from the surface everywhere percolates 

 them. That they must from this cause descend into the valleys is 

 therefore certain. That portion of the Mer de Glace of Chamouni 

 which extends from Montanvert to very near the origin of the Glacier 

 de L6chaud, has been accurately observed by Professor James Forbes*. 

 Its length is 22,600 feet, and its inclination varies from 4 19' 22" 

 to 5 5' 53". The Glacier du Geant, from the Tacul to the Col du 

 Geant, Professor Forbes estimates (but not from his own observa- 

 tions, or with the same certainty) to be 24,700 feet in length, and 

 to have a mean inclination of 8 46' 40". 



According to the observations of De Saussure, the mean daily 

 range of Reaumur's thermometer in the month of July, at the Col 

 du Geant, is 4 c -257f, and at Chamouni 10'092. The resistance 

 opposed by the rugged channel of a glucier to its descent cannot but 

 be different at different points and in respect to different glaciers. 

 The following passage from Professor Forbes's work contains the 

 most authentic information I am able to find on this subject. 

 Speaking of the Glacier of la Brenva, he says, " The ice removed, 

 a layer of fine mud covered the rock, not composed however alone 

 of the clayey limestone mud, but of sharp sand derived from the 

 granitic moraines of the glacier, and brought down with it from 

 the opposite side of the valley. Upon examining the face of the 

 ice removed from contact with the rock, we found it set all over 



* Travels through the Alps of Savoy. Edinburgh, 1843, 

 t Quoted by Professor Forbes, p. 231. 



