208 FOURTEENTH LETTER ON GLACIERS. [1847. 



I know to have been made with excellent instruments, and, it 

 may be hoped, with due care. Until such a publication takes 

 place, we must be permitted to withhold our final assent from 

 a conclusion which is in contradiction to observations on at least 

 three other glaciers, and to former observations on the same one. 

 Should it prove correct in the particular case of the Glacier of 

 the Aar, I suspect that it can only arise from a curious balance 

 of two opposing influences occasioned by the peculiar circum- 

 stances of restraint under which that glacier moves, and pro- 

 bably may apply to only a very limited portion of its surface. 



But I repeat, we must wait for the observations. The 

 public cannot but receive with distrust, reports of conclusions 

 drawn from unpublished observations so repeatedly contradict- 

 ing one another, as those which have been furnished by ob- 

 servers on this same Glacier of the Aar. Not to go farther 

 back, within four years we have had four positive statements of 

 fact said to have been deduced from observation, three of which 

 are irreconcileable. First, we were told that the glacier was 

 absolutely quiescent in winter, and moved onwards during the 

 summer months only.* It was next admitted, that in winter 

 there is also motion, only the summer motion is greatly in ex- 

 cess.f Next year (1844) we were told that the variation of 

 velocity is not confined to summer and winter, but is extended 

 to every variety of meteorological condition, in fact, is left on 

 the basis on which I had already placed it (as regarded the 

 Mer de Glace of Chamouni) two years previously. In the mid- 

 dle of summer, but during cold and snowy weather, which lasted 

 nine days, the velocity of the Glacier of the Aar fell below the 

 mean velocity of the same point for the entire year ; whilst 

 during the succeeding sixteen days of fine weather, the daily 

 average increased in amount by exactly one-half, and rose con- 



* Agassiz, 1842. " Ce que je puis annoncer positivement des a present, c'est 

 quele glacier est immobile en hiver." Letter to M. Arago, dated from the Glacier 

 of the Aar, Comptes Sendus, 8th August J842. Compare Ech'n. Phil. Jour., 1842, 

 vol. xxxiii., p. 253, 254. 



f Agassiz, 1 843. " Le mouvement est beaucoup plus accelere en ete qu'en 

 hiver." Bulletin de la Societe des Sciences Naturelle de Neufchatel, 8th Nov. 1843. 



