outside the atmosphere. As the earth condensed
from the original nebula, and cooled and solidified, a certain quantity
of matter remained at its surface in the form of free gases and unstable
compounds, and, within the narrow precincts where these things were,
lying like a thin shell between the huge inert globe of permanently
combined elements below, and the equally unchanging realm of the ether
above, life, a phenomenon depending upon ceaseless changes, combinations
and recombinations of chemical elements in unstable and temporary union,
made its appearance, and there only we find it at the present time.

It is because air and water furnish the means for the continual
transformations by which the bodies of animals and plants are built up
and afterward disintegrated and dispersed, that we are compelled to
regard their presence as prerequisites to the existence, on any planet,
of life in any of the forms in which we are acquainted with it. But if
we perceive that another world has an atmosphere, and that there is
water vapor in its atmosphere--both of which conditions are fulfilled by
Venus--and if we find that that world is bathed in the same sunshine
that stimulates the living forces of our planet, even though its
quantity or intensity may be different, then it would seem that we are
justified in averring that the burden of proof rests upon those who
would deny the capability of such a world to support inhabitants.

The generally accepted hypothesis of the origin of the solar system
leads us to believe that Venus has experienced the same process of
evolution as that which brought the earth into its present condition,
and we may fairly argue that upon the rocky shell of Venus exists a
region where chemical combinations and recombinations like those on the
surface of the earth are taking place. It is surely not essential that
the life-forming elements should exist in exactly the same states and
proportions as upon the earth; it is enough if some of them are
manifestly present. Even on the earth these things have undergone much
variation in the course of geological history, coincidently with the
development of various species of life. Just at present the earth
appears to have reached a stage where everything contributes to the
maintenance of a very high organization in both the animal and vegetable
kingdoms.

So each planet that has attained the habitable stage may have a typical
adjustment of temperature and atmosphe