MEAN DISTANCE FROM THE SUN, 141,000,000 MILES. DIAMETER, 4211 MILES. REVOLUTION, AXIAL, 24H. 37M. 22.7S.; ORBITAL, 686.98 DAYS. VELOCITY PER MINUTE, 899 MILES. SATELLITES, TWO. [Illustration: Fig. 62.--Apparent Size of Mars at Mean and Extreme Distances.] At intervals, on an average of two years one month and nineteen days, we find rising, as the sun goes down, the reddest star in 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 linger longer in the lap of spring; summer would be one hundred and eighty-one days long; but as the seas are