Variation of Motion at different Seasons. 339 



vert, but some patches remain on the way to the Jardin. The Mer 

 de Glace is much higher in level (about forty feet) than in former 

 years, and the marks made in the rock at the Angle (in 1842) are 

 all covered. The crevasses much the same as usual. The glacier 

 of Bossons has also increased greatly, and appears to be approaching 

 its old moraines. The register for the greater part of July has not 

 come to hand. 



August. — A very changeable rainy month. 8th or 9th, 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 explain se- 

 veral of the apparently irregular inflections of the curves of glacier 

 motion. Thus (to continue our general remarks, p. 186), 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 remark- 

 able relation to their positions and form. In the Bossons we detect 

 at once the sudden transitions and seemingly capricious 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 comparatively stable mass. Now, the gla- 

 cier of Bossons is, as every one who has seen it knows, a mere icy 

 torrent, " a frozen cataract," 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 

 bulwarks of rock, no 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 de- 

 rived from the reservoir glacier above, and, precisely as in rivers of 

 great magnitude and length of course, and of moderate declivity, it 

 yields sluggishly to impulsive or retarding forces which are checked 

 and opposed by the multitude of sinuosities, the embaying of the 

 ice in rock-bound expansions of the channel, the struggle of its pas- 

 sage through defiles, and the enormous friction of its lower surface. 



