-cap at the
north pole will begin to melt in like manner, and the water be
distributed in a similar way. The melting begins about the 1st April and
lasts till July, and sometimes considerably later in the year.

Thus, during the Martian year there are two distributions of water--one
from the north pole and one from the south pole; and the growth of
vegetation follows the passage of the water as it flows downwards from
the poles to the equator.

On our earth vegetation progresses in an exactly opposite direction.
Beginning near the tropics, where it is always summer, as the sun passes
northward of the equator so vegetation gradually appears and develops
onwards towards the north pole. It is exactly the same in the southern
hemisphere; after the sun crosses the equator into the south the
vegetation grows and spreads towards the south pole.

The reason of this is that on the earth the supply of water by rainfall
and snows is abundant, and it only requires the warmth of the sun to
cause vegetation to spring up again at the proper season when the winter
has passed.

On Mars the sun has the same action, but until the water comes down from
the poles and furnishes the necessary moisture, the sun can produce no
effect and there can be no fresh vegetation. Thus, on Mars, the flow of
water is the determining factor, and vegetation follows its course from
the poles towards the equator.

Observation shows that this is the case, and it has formed one of the
strongest arguments in support of the idea of water conveyance by means
of artificial canals. The opponents of the canal theory seem carefully
to avoid any mention of this argument.

While we were watching the melting of the snow at the south pole, I
mentioned to Merna and Tellurio, who accompanied me, that one of our
scientific men, relying for support on a speculation by a lady writer,
had arrived at the conclusion that the snow-caps could not possibly
supply anything like the amount of water required. The writer in
question had stated that the maximum area of the southern snow-cap was
2,400,000 square miles; and, assuming it was composed of snow of an
average depth of twenty feet, this would only give an average depth of
about one foot of water over its whole area.

The whole of the dark areas on the planet covered at least 17,000,000
square miles, and as this was seven times the area of the snow-cap, it
followed that the dark areas could not be covered with more than t