224 
THE FORMATION OF GLACIERS. 
count of the different degrees of moisture in the 
atmosphere. At great heights, there is never 
dampness enough to allow the fine snow-crystals 
to coalesce and form what are called “ snow- 
flakes.” I have even stood on the summit of 
the Jungfrau when a frozen cloud filled the air 
with ice-needles, while I could see the same cloud 
pouring down sheets of rain upon Lauterbrunnen 
below. I remember tliis spectacle as one of the 
most impressive I have witnessed in my long 
experience of Alpine scenery. The air immedi- 
ately about me seemed filled with rainbow-dust, 
for the ice-needles glittered with a thousand hues 
under the decomposition of light upon them, 
while the dark storm in the valley below offered 
a strange contrast to the brilliancy of the upper 
region in which I stood. One wonders where 
even so much vapor as may be transformed into 
the finest snow should come from at such heights. 
But the warm winds, creeping up the sides of 
the valleys, the walls of which become heated 
during the middle of the day, come laden with 
moisture which is changed to a dry snow like 
dust as soon as it comes into contact with the 
intense cold above. 
Currents of warm air affect the extent of the 
glaciers, and influence also the line of perpetual 
snow, which is by no means at the same level, 
even in neighboring localities. The size of gla- 
