306", SCOTT’S LAST EXPEDITION 
to sea by blizzards or some such transporting agent. The pack 
extends in normal years in December from about 66° to 71° S. 
Lat., a distance of 300 miles from north to south, and at times 
evidently fills the whole width of the Ross Sea. 
Pack may be heavy or light, closed or open—the latter condi- 
tions being entirely dependent on local winds and currents. Thus 
heavy pack if open may offer no insuperable bar to navigation, 
whereas in closed pack, whether heavy or light, little progress 
can be made by ships. Heavy pack is usually associated, with 
hummocks or pressure ridges rising to a height of four or five 
feet above the general level of the floe. These hummocks and 
pressure ridges are called upon to furnish ice for cooking and 
other purposes in the pack, being comparatively free from salt, 
owing, as mentioned previously, to the fact that the salt in the 
ice goes into solution and drains away, whenever the temperature 
rises above zero. 
Towards the end of February the Ross Sea becomes com- 
paratively free of pack and offers no bar to navigation. 
SNOW 
Precipitation from the atmosphere occurred always in the 
form of snow in these regions bordering on the continent; some- 
times, when the temperature was high, in the form of delicate SiX- 
rayed stars, or at lower temperatures in the form of hexagonal 
plates, little granular balls, or at still lower temperatures fine 
needle-shaped forms. 
Not long, however, do they keep this form after falling. 
Immediately ‘ the mighty molecule’ starts its work, some crystals 
grow at the expense of others, the whole grows more compact, 
becomes hard, and while still containing much air is white and 
called névé. Later it completes its change by expelling the air 
and becomes the well-known blue ice. 
During the summer one can see the whole transformation 
taking place before one’s eyes in the course of a few days. 
CrysTAL Forms 
Not only in the form of snow, however, do these crystal forms 
occur. In crevasses, on the roof of the stables, on windows, and 
so on, countless varied forms are to be seen, each single form 
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