400 Professor Agabsiz' Obsenations 



7000 or 8000 feet ; and I have frequently examined it shortly after its 

 fall, at heights of 9000 feet and more. But I have never seen it fall in the 

 form of ne've ; the snow was alwaj-s in flakes when the temperature was not 

 under 0° (32° F.) at the surface of the glacier, and jjowdery when the cold 

 was greater. 



" Another phenomenon which has struck me in these lofty regions, is the 

 brightness of the nights when the sky is cloudy, and even when it snows 

 or rains. During such weather, we can always distinctly see the hour on 

 our watches at any time of the night ; whereas, the obscurit}' is much 

 greater when the sky is serene. This apparent anomaly recalls the obser- 

 vations of M. Arago on the light of clouds." 



M. Agassiz then notices his observations relative to the glacier itself; 

 and first of all as to its progressive movement. It would appear that the 

 movement is much greater at the centre than at the eclges ; at least, since 

 last year, the centre has advanced 269 feet, the south edge 160, and the 

 north edge 125 feet only."* The ablation of the surface, resulting from the 

 melting and the evaporation, has also been more considerable at the centre 

 than at the edges, contrary to M^hat theory would lead us to suppose. 

 From the beginning of September last year to the 20th July this year, the 

 ablation in the centre has been 6 feet 5 inches, and that at the edge 

 4 feet 4 inches, without, however, the absolute level of the surface being 

 changed in an appreciable manner. M. Agassiz has likewise noticed, 

 that crevasses are more frequent and wider at the edges, especially at 

 places where little promontories present an obstacle to the progressive 

 movement of the glacier, — than towards the centre and along uniform 

 walls. 



M. Agassiz quotes many facts, which seem to him to prove that the 

 crevasses generally do not traverse the glacier, as is supposed ; and that 

 the water which accumulates there runs off, by being infiltrated into the 

 ice. In order to place this infiltration beyond a doubt, M. Agassiz lately 

 performed an experiment on a large scale. In a mass of ice included 

 between two great crevasses with very smooth sides, of a deep blue 

 colour and extremely compact, he caused to be excavated a horizontaj 

 gallery, 4 feet high by 3 feet wide and 8 feet long. At the surface of the 

 glacier, above the gallery, he bored a vertical hole 5 feet deep, into which 

 he emptied five litres of concentrated tincture of logwood. In half an 

 hour the liquid had all escaped, and, two hours afterwards, it exuded 

 through the capillary fissures along the roof of the gallcrj', having pene- 

 trated a mass of ice of 20 feet. The colour, moreover, extended to the 

 walls of the crevasses, and penetrated below the roof to unknown depths. 

 M. Agassiz has repeated the same experiment a great many times, on a 

 small scale, at different parts of the glacier, and has every where found 

 that the infiltration is much more rapid in the blue than in the white ice; 

 which latter becomes coloured very slowly. An important observation 



. ,ii:oi -}i\z &; #.See this Number of Journal, p. 273^ '^^-^^ --»^ liiolo'i 1^ 



