the heavens. Its brightness is exceedingly variable; sometimes
it scintillates, and sometimes it shines with a steady light. Its
marked peculiarities demand a close study. We find it to be Mars,
the fiery god of war. Its orbit is far from circular. At perihelion
it is 128,000,000 miles from the sun, and at aphelion 154,000,000;
hence its mean distance is about 141,000,000. So great a change
in its distance from the sun easily accounts for the change in
its brilliancy. Now, if Mars and the earth revolved in circular
orbits, the one 141,000,000 miles from the sun, and the other
92,000,000, they would approach at conjunction within 49,000,000
miles of each other, and at opposition be 233,000,000 miles apart.
But Mars at perihelion may be only 128,000,000 miles from the sun,
and earth at [Page 160] aphelion may be 94,000,000 miles from the
sun. They are, then, but 34,000,000 miles apart. This favorable
opportunity occurs about once in seventy-nine years. At its last
occurrence, in 1877, Mars introduced to us his two satellites, that
had never before been seen by man. In consequence of this greatly
varying distance, the apparent size of Mars differs very much (Fig.
62). Take a favorable time when the planet is near, also as near
overhead as it ever comes, so as to have as little atmosphere as
possible to penetrate, and study the planet. The first thing that
strikes the observer is a dazzling spot of white near the pole which
happens to be toward him, or at both poles when the planet is so
situated that they can be seen. When the north pole is turned toward
the sun the size of the spot sensibly diminishes, and the spot at
the south pole enlarges, and _vice versa_. Clearly they are
ice-fields. Hence Mars has water, and air to carry it, and heat to
melt ice. It is winter at the south pole when Mars is farthest from
the sun; therefore the ice-fields are larger than at the north pole.
It is summer at the south pole when Mars is nearest the sun. Hence
its ice-fields grow smaller [Page 161] than those of the north pole
in its summer. This carrying of water from pole to pole, and melting
of ice over such large areas, might give rise to uncomfortable
currents in ocean and air; but very likely an inhabitant of earth
might be transported to the surface of Mars, and be no more
surprised at what he observed there than if he went to some point of
the earth to him unknown. Day and night would be nearly of the same
length; winter would lin