the earth gets. Mars' year (period of revolution round the sun) is 687
days. Its mean density is 71 per cent of the earth's, and the force of
gravity on its surface is 38 per cent of that on the surface of the
earth; i.e., a body weighing one hundred pounds on the earth would, if
transported to Mars, weigh but thirty-eight pounds. The inclination of
its equator to the plane of its orbit differs very little from that of
the earth's equator, and its axial rotation occupies 24 hours 37
minutes. so that the length of day and night, and the extent of the
seasonal changes on Mars, are almost precisely the same as on the
earth. But owing to the greater length of its year, the seasons of
Mars, while occurring in the same order, are almost twice as long as
ours. The surface of the planet is manifestly solid, like that of our
globe, and the telescope reveals many permanent markings on it,
recalling the appearance of a globe on which geographical features
have been represented in reddish and dusky tints. Around the poles are
plainly to be seen rounded white areas, which vary in extent with the
Martian seasons, nearly vanishing in summer and extending widely in
winter. The most recent spectroscopic determinations indicate that
Mars has an atmosphere perhaps as dense as that to be found on our
loftiest mountain peaks, and there is a perceptible amount of watery
vapor in this atmosphere. The surface of the planet appears to be
remarkably level, and it has no mountain ranges. No evidences of
volcanic action have been discovered on Mars. The dusky and reddish
areas were regarded by the early observers as respectively seas and
lands, but at present it is not believed that there are any bodies of
water on the planet. There has never been much doubt expressed that
the white areas about the poles represent snow.

It will be seen from this brief description that many remarkable
resemblances exist between Mars and the earth, and there is nothing