white polar caps--Peculiar surface markings--Schiaparelli's
discovery of the canals--His description of their appearance
and of their duplication--Influence of the seasons on the
aspect of the canals--What are the canals?--Mr. Lowell's
observations--The theory of irrigation--How the inhabitants
of Mars are supposed to have taken advantage of the annual
accession of water supplied by the melting of the polar
caps--Wonderful details shown in charts of Mars--Curious
effects that may follow from the small force of gravity
on Mars--Imaginary giants--Reasons for thinking that
Mars may be, in an evolutionary sense, older than the
earth--Speculations about interplanetary signals from
Mars, and their origin--Mars's atmosphere--The question of
water--The problem of temperature--Eccentricities of Mars's
moons


CHAPTER V

_THE ASTEROIDS, A FAMILY OF DWARF WORLDS_ 129

Only four asteroids large enough to be measured--Remarkable
differences in their brightness irrespective of size--Their
widely scattered and intermixed orbits--Eccentric orbit of
Eros--the nearest celestial body to the earth except the
moon--Its existence recorded by photography before it was
discovered--Its great and rapid fluctuations in light, and
the curious hypotheses based upon them--Is it a fragment of
an exploded planet?--The startling theory of Olbers as to
the origin of the asteroids revived--Curious results of the