Phenomena._--The monotony and darkness of the
polar night are decreased a good deal by the long twilight. Light from
moon and stars, and from the aurora, also relieves the darkness. Optical
phenomena of great variety, beauty and complexity are common. Solar and
lunar haloes, and coronae, and mock suns and moons are often seen.
Auroras seem to be less common and less brilliant in the Antarctic than
in the Arctic. Sunset and sunrise colours within the polar zones are
described as being extraordinarily brilliant and impressive.

_Physiological Effects._--The north polar summer, as has been pointed
out, in spite of its drawbacks, is in some respects a pleasant and
healthful season. But the polar night is monotonous, depressing,
repelling. Sir W. E. Parry said that it would be difficult to conceive
of two things which are more alike than two polar winters. An
everlasting uniform snow covering; rigidity; lifelessness;
silence--except for the howl of the gale or the cracking of the ice.
Small wonder that the polar night has sometimes unbalanced men's minds.
The first effects are often a strong desire for sleep, and indifference.
Later effects have been sleeplessness and nervousness, tending in
extreme cases to insanity; anaemia, digestive troubles. Extraordinarily
low winter temperatures are easily borne if the air be dry and still.
Zero weather seems pleasantly refreshing if clear and calm. But high
relative humidity and wind--even a light breeze--give the same degree of
cold a penetrating feeling of chill which may be unbearable. Large
temperature ranges are endured without danger in the polar winter when
the air is dry. When exposed to direct insolation the skin burns and
blisters; the lips swell and crack. Thirst has been much complained of
by polar explorers, and is due to the active evaporation from the warm
body into the dry, relatively cold air. There is no doubt that polar air
is singularly free from micro-organisms--a fact which is due chiefly to
lack of communication with other parts of the world. Hence many diseases
which are common in temperate zones, "colds" among them, are rare.

_Changes of Climate._

_Popular Belief in Climatic Change._--Belief in a change in the climate
of one's place of residence, within a few generations, and even within
the memory of living men, is widespread. Evidence is constantly being
brought forward of apparent climatic variations of greater or less
amount which are now taking pla