"What is that?" eagerly inquired the commander.

"You can drown them out."

"How? With the canals?"

"Yes, I will explain to you. I have already told you, and, in fact, you
must have seen for yourselves, that there are almost no mountains on
Mars. A very learned man of my race used to say that the reason was
because Mars is so very old a world that the mountains it once had have
been almost completely leveled, and the entire surface of the planet had
become a great plain. There are depressions, however, most of which are
occupied by the seas. The greater part of the land lies below the level
of the ocean. In order at the same time to irrigate the soil and make it
fruitful, and to protect themselves from overflows by the ocean breaking
in upon them, the Martians have constructed the immense and innumerable
canals which you see running in all directions over the continents.

"There is one period in the year, and that period has now arrived when
there is special danger of a great deluge. Most of the oceans of Mars
lie in the southern hemisphere. When it is Summer in that hemisphere,
the great masses of ice and snow collected around the south pole melt
rapidly away."

"Yes, that is so," broke in one of the astronomers, who was listening
attentively. "Many a time I have seen the vast snow fields around the
southern pole of Mars completely disappear as the Summer sun rose high
upon them."

"With the melting of these snows," continued Aina, "a rapid rise in the
level of the water in the southern oceans occurs. On the side facing
these oceans the continents of Mars are sufficiently elevated to prevent
an overflow, but nearer the equator the level of the land sinks lower.

"With your telescopes you have no doubt noticed that there is a great
bending sea connecting the oceans of the south with those of the north
and running through the midst of the continents."

"Quite so," said the astronomer who had spoken before, "we call it the
Syrtis Major."

"That long narrow sea," Aina went on, "forms a great channel through
which the flood of waters caused by the melting of the southern polar
snows flows swiftly toward the equator and then on toward the north
until it reaches the sea basins which exist there. At that point it is
rapidly turned into ice and snow, because, of course, while it is Summer
in the southern hemisphere it is Winter in the northern.

"The Syrtis Major (I am giving our name to the channel of communicati