7^ Mr. H. H. Howorth 07t 



surrounding it cannot take it ; for being already at 32°, it 

 would melt it. It can, therefore, only be slowly conveyed 

 away through the ice to the surface, on the supposition that 

 the cold is sufficiently intense and prolonged to reduce the 

 upper part of the ice considerably below 32°. The progress 

 of cold and congelation in a glacier will therefore be, in 

 general, similar to that in the earth, which, it is well known, 

 can be frozen to the depth of but a few inches in one night, 

 however intense the, cold. Such a degree and quantity of 

 freezing as can be attributed to the cold of a summer's night 

 must therefore be absolutely inefficient on the mass of the 

 glacier" {Forbes' s Travels, 36 — 37.) 



This reasonmg seems unanswerable. Forbes elsewhere 

 refers to an experimental proof He says, " The most 

 direct observation shews that the nocturnal congelation 

 which is so visible at the surface, drying up the streamlets 

 of water, and glazing the ice with a slippery crust, extends,, 

 but to the most trifling depth, into the mass of the glacier. 

 This is so evident upon consideration that, when fairly 

 placed before him, M. de Charpentier has been obliged to 

 abandon the idea that the diurnal variation of temperature 

 produces any effect. In truth there is positive evidence 

 that no internal congelation takes place during the summer 

 season, when the motion is most rapid, and when, therefore,, 

 the cause of motion must be most energetic" {id. 358). 

 He then goes on to describe how on one occasion he traversed 

 the Mer de Glace up to the higher part of the Glacier de 

 Lechaud, while it was covered with snow to a depth of 

 six inches at Montanvert, and three times as much in the 

 higher part. It was snowing at the time, and for a week the 

 glacier had been in the same state nearly, the thermometer 

 havingfallen, meanwhile, to 20° Fahr. . . . All the superficial 

 rills were frozen over, there were no cascades in the 

 " Moulins," all was as still as it could be in mid-winter ; yet 

 even on the Glacier de Lechaud my wooden poles sunk to 



