over matter. It is possible that the infusoria under the microscope do
the same. No one gave a thought to the older worlds of space as sources
of human danger, or thought of them only to dismiss the idea of life
upon them as impossible or improbable. It is curious to recall some of
the mental habits of those departed days. At most terrestrial men
fancied there might be other men upon Mars, perhaps inferior to
themselves and ready to welcome a missionary enterprise. Yet across the
gulf of space, minds that are to our minds as ours are to those of the
beasts that perish, intellects vast and cool and unsympathetic,
regarded this earth with envious eyes, and slowly and surely drew their
plans against us. And early in the twentieth century came the great
disillusionment.
The planet Mars, I scarcely need remind the reader, revolves about the
sun at a mean distance of 140,000,000 miles, and the light and heat it
receives from the sun is barely half of that received by this world. It
must be, if the nebular hypothesis has any truth, older than our world;
and long before this earth ceased to be molten, life upon its surface
must have begun its course. The fact that it is scarcely one seventh of
the volume of the earth must have accelerated its cooling to the
temperature at which life could begin. It has air and water and all
that is necessary for the support of animated existence.
Yet so vain is man, and so blinded by his vanity, that no writer, up to
the very end of the nineteenth century, expressed any idea that
intelligent life might have developed there far, or indeed at all,
beyond its earthly level. Nor was it generally understood that since
Mars is older than our earth, with scarcely a quarter of the
superficial area and remoter from the sun, it necessarily follows that
it is not only more distant from time s beginning but nearer its end.
The secular cooling that must someday overtake our planet has already
gone far indeed with our neighbour. Its physical condition is still
largely a mystery, but we know now that even in its equatorial region
the midday temperature barely approaches that of our coldest winter.
Its air is much more attenuated than ours, its oceans have shrunk until
they cover but a third of its surface, and as its slow seasons change
huge snowcaps gather and melt about either pole and periodically
inundate its temperate zones. That last stage of exhaustion, which to
us is still incredibly remote, has become a present-day problem for the
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