s are visible from pole to
pole.

"These observations also led Professor Pickering to the important
conclusion that all the dark areas were covered with vegetation, and
that the bright or red areas were deserts, the colour of the latter
being exactly that of our deserts when viewed from a great distance.
Herschel's idea had been that the red areas were land covered with
vegetation of a red colour, and that the dark areas were seas.

"It was, however, now quite clear that permanent lines in such numbers
and length could not exist in seas; and other observations have
demonstrated that, instead of appearing smooth and uniform as water
would, these areas are full of detail and variations, and that they pass
through all the changes of colour, according to seasons, that land
covered with vegetation does upon our earth. In the winter time, when
the land is fallow, it appears brown or chocolate colour; in the spring,
the time of early vegetation, it becomes a pale blue-green tint; as the
season advances the blue-green becomes darker; whilst in the autumn it
tends to a light brown, and at length changes into chocolate colour in
the winter. This has been carefully noted time after time when the
planet has been in a position to be observed; and the same sequence of
change--which can only be associated with vegetation--has always
occurred.

"It may, therefore, now be accepted as a proved fact that the dark areas
are land upon which vegetation grows, ripens, and dies away according to
the seasons of the Martian year.

"Professor Pickering also made another discovery, viz. a large number of
isolated, round, darkish spots, most of which occurred where canal lines
joined or crossed each other. Some of these had been seen much earlier
by other observers, but Professor Pickering was the first to see them in
large numbers and call attention to them. He termed them 'lakes,' but
later discoveries from continued observation showed that they were not
water, and they were then given the name of 'oases.' Some are seventy or
eighty miles in diameter, and nearly two hundred are now marked on the
maps. They mostly occur in certain definite positions--in the point
where single canals join or cross each other, or, in the case of double
canals, between the two lines. It has been noted that they undergo the
same seasonal changes as the dark areas do, but only as regards the
outer portion of the circle, which gradually fades away in the latter
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