and South America another, not
quite so large; then come Australia, Greenland, Madagascar, and so
forth; all the lands being islands, larger or smaller. On the other
hand, except the Caspian Sea and the Sea of Aral, there are no large
seas entirely land-bound. In the case of Mars a very different state
of things prevails, as you will see from the three accompanying
pictures (hitherto unpublished), drawn by the famous English observer,
Dawes (called the Eagle-eyed). The third and best was drawn with
a telescope constructed by your famous optician, Alvan Clark, of
Cambridge, Massachusetts. The dark parts are the seas, the light parts
being land, or in some cases cloud or snow. But in these pictures most
of the lighter portions represent land; for they have been seen often
so shaped, whereas clouds, of course, would change in shape.

The planet Mars, like our earth, turns on its axis, so that it has day
and night as we have. The length of its day is not very different from
that of our own day. Our earth turns once on its axis in ---- but
before reading on, try to complete this sentence for yourself. Every
one knows that the earth's turning on its axis produces day and night,
and nine persons out of ten, if asked how long the earth takes in
turning round her axis, will answer, 24 hours; and if asked how many
times she turns on her axis in a year, will say 365 times, or if
disposed to be very exact, "about 365-1/4 times." But neither answer
is correct. The earth turns on her axis about 366-1/4 times in each
year, and each turning occupies 23 hours 56 minutes and 4 seconds and
1 tenth of a second. We, taking the ordinary day as the time of a
turning or rotation, lose count of one rotation each year. It is
necessary to mention this, in order that when I tell you how long the
day of Mars is, you may be able correctly to compare it with our own
day. Mars, then, turns on his axis in 24 hours 37 minutes 22 seconds
and 7 tenth-parts of a second. So that Mars requires 41 minutes 18
seconds and 6-tenths of a second longer to turn his small body once
round than our earth requires to turn round her much larger body. The
common day of Mars is, however, only about 39 minutes longer than our
common day.

Mars has a long year, taking no less than 687 of our days to complete
his circuit round the sun, so that his year lasts only about one month
and a half less than two of ours.

[Illustration: APPEARANCE OF MARS, 1852, MARCH 23, 5 H. 45