The vacuum is greater than any ordinary air-pump is capable of
producing. We can hardly suppose that so small a quantity of air
could be of any benefit whatever in sustaining life; an animal
that could get along on so little could get along on none at all.

But the proof of the absence of life is yet stronger when we
consider the results of actual telescopic observation. An object
such as an ordinary city block could be detected on the moon. If
anything like vegetation were present on its surface, we should
see the changes which it would undergo in the course of a month,
during one portion of which it would be exposed to the rays of the
unclouded sun, and during another to the intense cold of space. If
men built cities, or even separate buildings the size of the
larger ones on our earth, we might see some signs of them.

In recent times we not only observe the moon with the telescope,
but get still more definite information by photography. The whole
visible surface has been repeatedly photographed under the best
conditions. But no change has been established beyond question,
nor does the photograph show the slightest difference of structure
or shade which could be attributed to cities or other works of
man. To all appearances the whole surface of our satellite is as
completely devoid of life as the lava newly thrown from Vesuvius.
We next pass to the planets. Mercury, the nearest to the sun, is
in a position very unfavorable for observation from the earth,
because when nearest to us it is between us and the sun, so that
its dark hemisphere is presented to us. Nothing satisfactory has
yet been made out as to its condition. We cannot say with
certainty whether it has an atmosphere or not. What seems very
probable is that the temperature on its surface is higher than any