1846.] DEDUCTIONS FROM OBSERVATIONS OF VELOCITY. 135 



The arch at the source of the Arveiron fell in, and did not form 

 again during the season. 



September. Also a changeable month. Rain twelve days. 



October. A very fine month. No rain mentioned after 

 the 7th. 



A careful examination of this interesting register will ex- 

 plain several of the apparently irregular inflections of the curves 

 of glacier motion. Thus (to continue our general remarks, p. 

 130) we find, 



V. At the upper station on the Glacier des Bois the least 

 velocity occurred in December, whilst at the lower station (and 

 at both of those on the Bossons) a minimum, coinciding also 

 with that of the temperature of the air, took place in January. 

 This coincides with the important fact noted in the preceding 

 register, that the upper part of the Mer de Glace was covered 

 with snow from the 16th of October, which only lay in the valley 

 of Chamouni from the 20th of January ; the snow screening 

 the ice from the extremity of the cold. 



VI. The comparative march of the two glaciers bears a 

 remarkable relation to their positions and form. In the Bossons 

 we detect at once the sudden transitions and seemingly capri- 

 cious changes of a torrent ; in the Mer de Glace we have the 

 stately and regulated flow of a river, in which the slighter 

 variations are absorbed by the predominant inertia of a com- 

 paratively stable mass. Now the glacier of Bossons is, as every 

 one who has seen it knows, a mere icy torrent, " a frozen cata- 

 ract," which descends in a continuous mass from the level of 

 the Grand Plateau of Mont Blanc to that of the Valley of 

 Chamouni with very little impediment, with no confining bul- 

 warks of rock, ho contracting straits ; and throughout this 

 great vertical height of at least 9000 feet, the angle of descent 

 is very steep indeed for so vast a mass. On the other hand, 

 though the part of the Mer de Glace, called the Glacier des 

 Bois under the Chapeau, is very steep, its " regime " is regulated 

 by the supply derived from the reservoir glacier above, and, 



