The Theory of Glacier motion, 75 



to be ascribed to natural causes. The water flowing from 

 the sides of the mountain on to the glacier enters its fissures 

 and interstices, freezes again, and as it needs more space 

 when thus frozen, as experiments have shown, it causes the 

 glacier to thrust forward, and to carry with it sand and stones, 

 some of them of great size," etc. He goes on to say that his 

 opinion in the matter had been confirmed by observations 

 made by two of his friends. 



The theory thus hinted at was revived by Toussaint de 

 Charpentier and Canon Biselx in 1819, and was published 

 in " The Transactions of the Swiss Natural History Society" 

 for 1 82 1, p. jj^ where it is stated that rainwater as well as 

 water from the melted snow finds its ways into the cracks 

 and cavities of the ice-mass. The water which thus 

 percolates freezes again, swells out, and causes the ice to 

 split and to move. The theory was worked out in 

 detail by T. de Charpentier's more famous brother, J. de 

 Charpentier, and by Agassiz, and is known as the Dilatation 

 theory. 



Agassiz, its best known advocate, states his case thus : 

 " Ce mouvement parait plutot etre du a la dilatation de la 

 glace resultant de la congelation de I'eau qui s'infiltre con- 

 tinuellement dans les fissures capillaires que presente la 

 glace, dans toute son epaisseur, et surtout a la partie la plus 

 voisine de la surface ou elle est moins compacte. Cette eau, 

 dont la temperature est constamment voisine du point de 

 congelation, se transforme en glace au moindre abaissement 

 de temperature, et tend a dilater le glacier dans tous les 

 sens. Cependant, comme il est contenu des deux cotes pas 

 les flancs de la vallee, et en amont par le poids des masses 

 superieures, toute Taction de la dilatation, aidee d'ailleurs 

 de celle de la gravitation, se porte dans le sens de la pente, 

 vers le seul cote qui offre une libre issue" (" Notice sur les 

 glaciers," published with Desor's Journal (Tune course attx 

 glaciers^ etc.y iS/j-d). 



