s therefore much affected by the conditions of adjacent
continental masses. Nevertheless, the general characteristics are
apparently much the same over both, so far as is now known, the
antarctic differing from the arctic chiefly in having colder summers and
in the regularity of its pressure and winds. Both zones have the lowest
mean annual temperatures in their respective hemispheres, and hence may
properly be called the _cold zones_.

_Temperature._--At the solstices the two poles receive the largest
amounts of insolation which any part of the earth's surface ever
receives. It would seem, therefore, that the temperatures at the poles
should then be the highest in the world, but as a matter of fact they
are nearly or quite the lowest. Temperatures do not follow insolation in
this case because much of the latter never reaches the earth's surface;
because most of the energy which does reach the surface is expended in
melting the snow and ice of the polar areas; and because the water areas
are large, and the duration of insolation is short.

A set of monthly isothermal charts of the north polar area, based on all
available observations, has been prepared by H. Mohn and published in
the volume on Meteorology of the Nansen expedition. In the winter months
there are three cold poles, in Siberia, in Greenland and at the pole
itself. In January the mean temperatures at these three cold poles are
-49 deg., -40 deg. and -40 deg. respectively. The Siberian cold pole
becomes a maximum of temperature during the summer, but the Greenland
and polar minima remain throughout the year. In July the temperature
distribution shows considerable uniformity; the gradients are relatively
weak. A large area in the interior of Greenland, and one of about equal
extent around the pole, are within the isotherm of 32 deg.. For the year
a large area around the pole is enclosed by the isotherm of -4 deg.,
with an isotherm of the same value in the interior of Greenland, but a
local area of -7.6 deg. is noted in Greenland, and one of -11.2 deg. is
centred at lat. 80 deg. N. and long. 170 deg. E.

The north polar chart of annual range of temperature shows a maximum
range of about 120 deg. in Siberia; of 80 deg. in North America; of 75.6
deg. at the North Pole, and of 72 deg. in Greenland. The North Pole
obviously has a continental climate. The minimum ranges are on the
Atlantic and Pacific Oceans. The mean annual isanomalies show that the
interior of G