362 On the Physical Geography of the Alps. 
chapter (pp. 104-124) he enters upon the subject of the Motion 
of Glaciers, describing his method of observation, 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; an- 
nual movement; motion of secondary glaciers and of “ firn’- 
masses; and with remarks on the causes of the motion of gla- 
ciers, on the “sliding” theory ;* the theory of “infiltration” or 
“dilatation” ;+ the plasticity of glaciers; and the interstitial 
movability [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 Jess than in the higher parts; 
but irregularities of the valley-bottom, depressions, 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 absolute maximum hitherto obtained (by Prof. Forbes in 
the Glacier des Bois) amounts to 132 centim. a day :—64. 
direction of the progressive movement usually agrees very nearly 
with the direction of the length of the glacier, yet also, from 
local conditions, lateral deviations either towards the side or the 
centre may take place :—6. the smaller (and all secondary ) gla- 
- 
° 
the underlying surface and by the vertical height of the ice, t 
both of which conditions the retarding influence of the friction 1s 
more or less due :—8, heat or considerable atmospheric pree!pita- 
tions 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. ihe rate of progressive movement is subject t0 
considerable retardation from the friction of the ice on the stp- 
porting surface ; the base, however, of the glacier is not usually 
1ce-bound. 
Chapter vi,t (pp. 125-146) treats of the “Oscillation” of Gla- 
ciers, that is, the alterations and fluctuations in the absolute bulk 
-— * Saussure, . Charpentier. ” ecccee ated 
_ $ This and the following chapter are also by M. Hermann Schlagintweit. 
as 
