﻿MM. SCHLAGINTWEIT ON THE ALPS. 



17 



tion, and giving tabular views of the rate of motion of the Pasterze, 

 Hintereis, and Vernagt glaciers, with notices of the alterations of 

 velocity ; influence of temperature and effect of the weather ; relative 

 velocities in a diagonal and straight line ; lateral movement ; annual 

 movement ; motion of secondary glaciers and of " firn" -masses ; and 

 with remarks on the causes of the motion of glaciers, on the " sliding" 

 theory*; the theory of "infiltration" or ' ' dilatation" f ; the plas- 

 ticity of glaciers ; and the interstitial moveability [verschiebbarkeit] 

 of large masses of ice. It results from these observations, that : — 

 1. in all glaciers the centre moves faster than the edges : — 2. in the 

 most regularly formed glaciers the rate of motion near the end is less 

 than in the higher parts ; but irregularities of the valley-bottom, de- 

 pressions, or greater width of troughs, have considerable influence on 

 the alterations of the velocity : — 3. the maximum rate of motion occurs 

 in the first summer months ; the velocity in autumn in all glaciers is 

 next to that of the mid-year : — 4. a motion of 20-40 centimetres in 

 twenty-four hours takes place locally in all extensive glaciers ; the ab- 

 solute maximum hitherto obtained (by Prof. Forbes in the Glacier des 

 Bois) amounts to 132 centim. a day : — 5. the direction of the progres- 

 sive movement usually agrees very nearly with the direction of the 

 length of the glacier, yet also, from local conditions, lateral devia- 

 tions either towards the side or the centre may take place : — 6. the 

 smaller (and all secondary) glaciers move more slowly than the larger 

 ones, since the influence of the friction becomes more sensible, if the 

 thickness of the ice be diminished : — 7. the phsenomena of glacier- 

 motion appear to be connected with the moveability of the integral 

 parts [verschiebbarkeit] of the ice, and this arises from the fine splin- 

 tering of the mass in consequence of its dryness, the enormous pres- 

 sure, and the friction of the underlying rock-surface. The rate of 

 progress becomes essentially altered by the degree of the inclination 

 of the underlying surface and by the vertical height of the ice, to 

 both of which conditions the retarding influence of the friction is more 

 or less due : — 8. heat or considerable atmospheric precipitations hasten 

 the motion, since, by the infiltration of the thaw- or rain-water into 

 the ice-cavities, the absolute weight of the glacier is increased : — 

 9. the rate of progressive movement is subject to considerable re- 

 tardation from the friction of the ice on the supporting surface ; 

 the base, however, of the glacier is not usually ice-bound. 



Chapter vi.J (pp. 125-146) treats of the "Oscillation" of Glaciers, 

 that is, the alterations and fluctuations in the absolute bulk of the gla- 

 ciers, — 1. dependent on fluctuations of temperature, — 2. arising from 

 accumulations of snow and the formation of moraines, — 3. owing to 

 the irregularity of the valley-bottoms, causing irregular rates of pro- 

 gress in individual glaciers. The TV asting of Glaciers is noticed in the 

 seventh chapter (pp. 147-159), and the conclusions arrived at from 

 researches on the distribution and quantity of the water, the terminal 

 cavities of glaciers, the influence of superficial thawing, the measure 

 of the waste, and the repair of the waste, are : — 1. the mass of ice 



* Saussure. f Charpentier. 



% This and the following chapter are also by M. Hermann Schlagintweit. 

 VOL. VII,—- PART II. C 



