the remaining
50,000,000 square miles land.

Mars has a surface area of about 56,000,000 square miles, about
35,000,000 square miles being desert, and the remaining 21,000,000
square miles land which may be habitable, as most of it is covered with
vegetation. There are no large areas of water anywhere upon Mars. This
calculation, however, makes no allowance for the lines of vegetation
which cross the desert, and contain canals, and, with the oases, may
have a very large population.

From the 50,000,000 square miles of land upon the earth must be deducted
the very large areas which are frozen during the greater part of the
year, and also the large areas which are deserts or bare rocks. This
would probably bring down the really habitable area to about 30,000,000
square miles.

Making a similar deduction in the case of Mars, but remembering that
more of the regions near the poles would be habitable during part of the
year than is the case on the earth (as there is practically no permanent
glaciation and the temperate zones extend nearly to the poles) the
habitable area would be reduced to, say, 15,000,000 square miles.

It will thus be seen that although the total surface area of Mars is
only rather more than one-quarter of that of the earth, the area of its
habitable land, even under its present unfavourable circumstances,
amounts to about half of the habitable area of the earth.

Looking at Mars from this point of view, it does not contrast so
unfavourably with the earth as is usually thought, especially when it is
remembered how small a proportion of the earth's area is really
populated.

Were it not for the great eccentricity of the planet's orbit, the
seasons upon Mars would be very much the same in the different zones as
they are on our world, as the inclination of the planet's equator is
only very slightly less than that of the earth. According to the latest
determination, the inclination in the case of Mars is 23 deg. and 13'.

As the Martian year is nearly twice as long as ours (being 668 Martian
days, which are equal to 687 of our days) the seasons are of course
proportionately longer in duration. The eccentricity of the orbit,
however, causes a much greater difference between the lengths of summer
and winter in the two hemispheres.

* * * * *

In the northern hemisphere of Mars, spring lasts 191 Martian days;
summer, 181 days; autumn, 149 days; and winter, 147 days.