330 Professor Forbes** s Fourteenth Letter on Glaciers. 



motion is greatly in excess.* 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 middle 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 considerably above the 

 annual average.! Now (1846), we are desired to consider 

 these opinions and deductions to be erroneous, as well as the 

 measured distances ascertained by M. Wild, who has hitherto 

 been believed to be a competent surveyor, and who had 

 found the advance of the points of his triangulation on the 

 glacier to be more than one-half more rapid during summer 

 than in the remainder of the year. J The opinion of MM. 

 DoUfuss, Martins, and Collomb, is, that seasons and weather 

 make no difference whatever on the motions of the glacier of 

 the Aar ! 



t Agassiz, 1843. — " Le mouvement est beaucoup plus acc^l^r^ en et€ qu'en 

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

 1843. 



t Comptes RenduSy 9tli Dec. 1844, p. 1301. — " L'avancement [journalier] 

 ^tait loin d'etre uniforme, il variait consid^rablement suivant les conditions 

 atmospheriques." Compare Ninth Letter, in this Journal. 



X Bull, de la Soc. de Neufchdtel, No. 1. From the results there mentioned, I 

 give the comparative motion of seven points of the glacier during fifty-seven 

 days of summer, and for the same length of time taken from the average of 

 the remainder of the year. 



