surface instead of three quarters, as on the earth, and there is
consequently a smaller evaporation and rain and snow-fall."
They were too much interested to think of sleeping that night,
and so, after dining comfortably returned to their observatory.
When within four million miles of Mars the Callisto began to
swerve perceptibly, its curve, as when near the moon beginning
with a spiral. They swung on unconcernedly, however, knowing
they could check their approach at any time. Soon Mars appeared