no 
SCENERY OF SWITZERLAND. 
the fissures of the glaciers, freezing there and ex- 
panding as it froze, was the power which urged 
them forwards. Altman and GrUner in 1760 en- 
deavoured to explain it by supposing that the glaciers 
slid over their beds; and no doubt they do so to 
some extent, but this is quite a subordinate form of 
movement. Bordier regarded the ice of glaciers 
“not as a mass entirely rigid and immobile, but as a 
heap of coagulated matter or as softened wax, flexible 
and ductile to a certain point.” This, the “Viscous” 
theory, was afterwards most ably advocated by Forbes. 
No doubt the glacier moves as a viscous body would; 
but the ice, far from being viscous, is extremely 
brittle. Crevasses begin as narrow cracks which 
may be traced for hundreds of yards: a slight dif- 
ference of inclination of the bed will split the ice 
from top to bottom. It is, in fact, deficient in that 
power of extension, which is of the essence of a 
viscous substance. 
The explanation now generally adopted is that 
which we owe mainly to Tyndall. Faraday in 1850 
observed, that when two pieces of thawing ice are 
placed together they freeze at the point of contact. 
Most men would have passed over this little observa- 
tion almost without a thought, or with a mere feeling 
of temporary surprise. Eminent authorities have 
