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 had by far the larger
and more powerful telescope; Schiaparelli had much the more steady and
favorable atmosphere for astronomical observation. Yet these differences
in equipment and circumstances do not clearly explain why each observer
should have seen what the other did not.

There may be a partial explanation in the fact that an observer having
made a remarkable discovery is naturally inclined to confine his