al surface of the corresponding
hemisphere of the planet deepens in color, and displays a constantly
increasing wealth of details as summer advances across it, is an
experience of the most memorable kind, whose effect upon the mind of the
observer is indescribable.

Early in the history of the telescope it became known that, in addition
to the polar caps, Mars presented a number of distinct surface features,
and gradually, as instruments increased in power and observers in
skill, charts of the planet were produced showing a surface diversified
somewhat in the manner that characterizes the face of the earth,
although the permanent forms do not closely resemble those of our
planet.

Two principal colors exist on the disk of Mars--dark, bluish gray or
greenish gray, characterizing areas which have generally been regarded
as seas, and light yellowish red, overspreading broad regions looked
upon as continents. It was early observed that if the dark regions
really are seas, the proportion of water to land upon Mars is much
smaller than upon the earth.

For two especial reasons Mars has generally been regarded as an older or
more advanced planet than the earth. The first reason is that, accepting
Laplace's theory of the origin of the planetary system from a series of
rings left off at the periphery of the contracting solar nebula, Mars
must have come into existence earlier than the earth, because, being
more distant from the center of the system, the ring from which it was
formed would have been separated sooner than the terrestrial ring. The
second reason is that Mars being smaller and less massive than the earth
has run through its developments a cooling globe more rapidly. The
bearing of these things upon the problems of life on Mars will be
considered hereafter.

And now, once more, Schiaparelli appears as the discoverer of surprising
facts about one of the most interesting worlds of the solar system.
During the exceptionally favorable opposition of Mars in 1877, when an
American astronomer, Asaph Hall, discovered the planet's two minute
satellites, and again during the opposition of 1879, the Italian
observer caught sight of an astonishing network of narrow dark lines
intersecting the so-called continental regions of the planet and
crossing one another in every direction. Schiaparelli did not see the
little moons that Hall discovered, and Hall did not perceive the
enigmatical lines that Schiaparelli detected. Hall ha