mpbell. Of the fifty foreign
associates chosen by this society for their eminence in astronomical
research, no less than eighteen--more than one-third--are Americans.

VII

LIFE IN THE UNIVERSE

So far as we can judge from what we see on our globe, the production of
life is one of the greatest and most incessant purposes of nature. Life
is absent only in regions of perpetual frost, where it never has an
opportunity to begin; in places where the temperature is near the
boiling-point, which is found to be destructive to it; and beneath the
earth's surface, where none of the changes essential to it can come
about. Within the limits imposed by these prohibitory conditions--that
is to say, within the range of temperature at which water retains its
liquid state, and in regions where the sun's rays can penetrate and
where wind can blow and water exist in a liquid form--life is the
universal rule. How prodigal nature seems to be in its production is
too trite a fact to be dwelt upon. We have all read of the millions of
germs which are destroyed for every one that comes to maturity. Even
the higher forms of life are found almost everywhere. Only small
islands have ever been discovered which were uninhabited, and animals
of a higher grade are as widely diffused as man.

If it would be going too far to claim that all conditions may have
forms of life appropriate to them, it would be going as much too far in
the other direction to claim that life can exist only with the precise
surroundings which nurture it on this planet. It is very remarkable in
this connection that while in one direction we see life coming to an
end, in the other direction we see it flourishing more and more up to
the limit. These two directions are those of heat and cold. We cannot
suppose that life would develop in any important degree in a region of
perpetual frost, such as the polar regions of our globe. But we do not
find any end to it as the climate becomes warmer. On the contrary,
every one knows that the tropics are the most fertile regions of the
globe in its production. The luxuriance of the vegetation and the
number of the animals continually increase the more tropical the
climate becomes. Where the limit may be set no one can say. But it
would doubtless be far above the present temperature of the equatorial
regions.

It has often been said that this does not apply to the human race, that
men lack vigor in the tropics. But human vigor de