M.,
Greenwich Mean Time. Power of Telescope, 358; 6-1/3 inch object-glass]

[Illustration: APPEARANCE OF MARS, 1852, FEBRUARY 3, 6 H. 50 M.,
Greenwich Mean Time. Power of Telescope, 242 and 358 on 6-1/3 inch
object-glass.]

[Illustration: APPEARANCE OF MARS, 1860, JULY 6, 11 H. 33 M.,
Greenwich Mean Time. Power of Telescope, 201; 8-1/4 inch object-glass.
Planet very low, yet pretty distinct.]

Like the earth, Mars has seasons, for his polar axis, like that of
the earth, is aslant, and at one part of his year brings his northern
regions more fully into sunlight, at which time summer prevails there
and winter in his southern regions; while at the opposite part of his
year his southern regions are turned more fully sunward and have their
summer, while winter prevails over his northern regions.

Around his poles, as around the earth's, there are great masses of
ice, insomuch that it is very doubtful whether any inhabitants of Mars
have been able to penetrate to his poles, any more than Kane or Hayes
or Nares or Parry, despite their courage and endurance, have been
able to reach our northern pole, or Cook or Wilkes or James Ross our
antarctic pole.

In the summer of either hemisphere of Mars, the north polar snows
become greatly reduced in extent, as is natural, while in winter
they reach to low latitudes, showing that in parts of the planet
corresponding to the United States, or mid-Europe, as to latitude,
bitter cold must prevail for several weeks in succession.

The land regions of Mars can be distinguished from the seas by their
ruddy color, the seas being greenish. But here, perhaps, you will be
disposed to ask how astronomers can be sure that the greenish regions
are seas, the ruddy regions land, the white spots either snow or
cloud. Might not materials altogether unlike any we are acquainted
with exist upon that remote planet?

The spectroscope answers this question in the clearest way. You
may remember what I told you in October, 1876, about Venus, how
astronomers have learned that the vapor of water exists in
her atmosphere. The same method has been applied, even more
satisfactorily, to the planet of war, and it has been found that he
also has his atmosphere at times laden with moisture. This being so,
it is clear we have not to do with a planet made of materials utterly
unlike those forming our earth. To suppose so, when we find that the
air of Mars, formed like our own (for if it contained other gases th