that by the increasing amount of sun-heat it is
converted, partly into liquid and partly into vapour. Coincident with
this disappearance and as a presumed result of the water (or other
liquid) producing inundations, the bluish-green tinge which appears on
the previously dark portion of the surface is supposed to be due to a
rapid growth of vegetation.

But the evidence on this point does not seem to be clear or harmonious,
for in the four coloured plates showing the planet's surface at
successive Martian dates from December 30th to February 21st, not only
is a considerable extent of the south temperate zone shown to change
rapidly from bluish-green to chocolate-brown and then again to
bluish-green, but the portions furthest from the supposed fertilising
overflow are permanently green, as are also considerable portions in the
opposite or northern hemisphere, which one would think would then be
completely dried up.

_No Hills upon Mars._

The special point to which I here wish to call attention is this. Mr.
Lowell's main contention is, that the surface of Mars is wonderfully
smooth and level. Not only are there no mountains, but there are no
hills or valleys or plateaux. This assumption is absolutely essential to
support the other great assumption, that the wonderful network of
perfectly straight lines over nearly the whole surface of the planet are
irrigation canals. It is not alleged that irregularities or undulations
of a few hundreds or even one or two thousands of feet could possibly be
detected, while certainly all we know of planetary formation or
structure point strongly towards _some_ inequalities of surface. Mr.
Lowell admits that the dark portions of the surface, when examined on
the terminator (the margin of the illuminated portion), do _look_ like
hollows and _may be_ the beds of dried-up seas; yet the supposed canals
run across these old sea-beds in perfect straight lines just as they do
across the many thousand miles of what are admitted to be deserts--which
he describes in these forcible terms: "Pitiless as our deserts are, they
are but faint forecasts of the state of things existent on Mars at the
present time."

It appears, then, that Mr. Lowell has to face this dilemma--_Only if the
whole surface of Mars is an almost perfect level could the enormous
network of straight canals, each from hundreds to thousands of miles
long, have been possibly constructed by intelligent beings for purposes
of irriga