1845.] FURTHER CONFIRMATIONS OF THE AUTHOR'S RESULTS. 73 



motion for three months with the state of the thermometer, 

 and exhibited the result in numbers and diagrams.* Here, 

 again, the observers on the Aar glacier have confirmed this fact, 

 so important in a theoretical point of view. " The advancement 

 of the glacier," they say, " was far from uniform ; it varied 

 considerably, according to the condition of the atmosphere." 

 During nine days of cold snowy weather in August 1844, the 

 mean daily advance was 155 millimetres, but during the sixteen 

 fine days which followed, it moved through 230 millimetres 

 per day.f 



It is worthy of remark, that the entire annual motion of 

 the part in question of the glacier of the Aar was ascertained 

 to be 60 metres, or 164 millimetres per day.;); Now the mean 

 motion during 35 days of August and September was 203 

 millimetres, or but one-fourth above the annual mean (and 

 during part of the time, we have seen, it fell to 155 millimetres, 

 or below the annual mean) ; proving sufficiently that the annual 

 motion is not entirely effected during the warm season, and that 

 even in winter it must bear a very sensible proportion to its 

 summer motion, as it has been directly proved in the case of 

 the Mer de Glace of Chamouni. 



IV. The extreme inequality of motion of the central and 

 lateral parts of glaciers is the best direct proof of the very 

 considerable plasticity of their mass ; and in the paper before 

 us this is shewn, in a still more striking manner, than in the 

 experiments which I have published. A glacier, like the Mer 

 de Glace of Chamouni, has so considerable a velocity (on an 

 average at least three times that of the glacier of the Aar), that 

 the ice is impetuously borne along, and torn from the sides at 

 the expense of innumerable lacerations and crevasses. So that 

 in the whole extent of the middle and lower regions of that 

 glacier, in no place do the ice and ground meet without the 



* Travels in the Alps, p. 148. f Comptes Rendus, p. 1301, at the bottom. 



| Ibid, p. 1301, line 29. 



$ Travels in the Alps, p. 151, 420 ; and Fifth Letter on Glaciers, [p. 38 of this 

 volume]. 



