and fro over this globe about their little affairs, serene in their
assurance of their empire 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