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 the
spectroscope would tell us), contains often large quantities of the
vapor of water, would be as absurd as to believe in the green cheese
theory of the moon, or in another equally preposterous, advanced