SNOW AND ICE. 
IO9 
Hamel’s guides, who perished in a crevasse on the 
Grand Plateau (Mont Blanc) on 20th August 1820, 
were found in 1861 near the lower end of the 
Glacier des Boissons, having moved some 4 miles in 
forty-one years, or nearly at the rate of about 500 feet 
a year. 
It has been calculated that a particle of ice 
would take at least 250 years to descend from the 
Strahleck to the lower end of the Under-Aar Glacier; 
from the summit of the Jungfrau to the end of the 
Aletsch Glacier about 500 years. 
During the Middle Ages the Swiss glaciers appear 
on the whole to have been increasing in size, and to 
have reached a maximum about the year 1820. 
After that they retreated till about 1840, when they 
again advanced until about i860, since which time 
they have greatly diminished, though some are now 
again commencing to advance. Those of northern 
Europe appear to be also increasing.* It is, of 
course, impossible to make any decided forecast as 
to the future. 
Cause of Movement. 
But why do glaciers descend? 
Scheuchzer in 1705 suggested that the water in 
* Heim, Gletscherkunde. 
