']6 Mr. H. H. Howorth on 



The position is thus stated with his usual clearness and 

 fairness by Principal Forbes : "The snow is penetrated by- 

 water, and gradually consolidated. It remains, however, 

 even in the state of ice, always permeable to water by 

 means of innumerable fissures which traverse the mass ; 

 these are filled with fluid water during the heat of the day, 

 which the cold of the night freezes in these fissures, 

 producing, by the expansion which freezing water undergoes 

 in that process an immense force, by which the glacier tends 

 to move itself in the direction of least resistance — in other 

 words, down the valley. This action is repeated every night 

 during summer, in winter the glacier being assumed to be 

 perfectly stationary " {Forbes' s Travels^ 34). 



When J. de Charpentier read a paper in 1838 before the 

 Helvetic Society of Natural Science on the dilatation theory, 

 M. Merian replied that if the theory were true, glaciers ought 

 to augment in height alone, since the direction of least resist- 

 ance would be vertically. In this he was supported by M. 

 Studer, who quoted what takes place when anhydrite is con- 

 verted into gypsum, or lime into dolomite, when the mass 

 swells upwards. This view was also pressed by Hopkins. But 

 the notion that a glacier swells upwards is quite contrary to 

 the careful observations of Forbes. Studer also pointed out 

 that the nocturnal cold only freezes a very superficial layer of 

 the glacier, and that in order that the water should freeze in 

 the crevasses or cracks the temperature must be below zero of 

 Reaumur, which is lower than we know the temperature to 

 be at the base of glaciers {Memoires^ op. cit.^ pages 113 — 1 14). 



Hopkins argued that while it is true that water freely 

 percolates through certain kinds of glacier ice, it cannot be 

 proved that it freezes in the interstices. "The tempera- 

 ture of the upper portion of a glacier," he says, "where 

 the percolation has been observed, is very little below that 

 of freezing, and does not appear to be sufficiently low to 

 convert water into ice while moving with the freedom with 



