re thought to be occasioned by floods ensuing upon
this rapid antarctic thaw. It is true that scarcity of moisture would
account for the scantiness and transitoriness of snowy deposits easily
liquefied because thinly spread. But we might expect to see the whole
wintry hemisphere, at any rate, frost-bound, since the sun radiates
less than half as much heat on Mars as on the earth. Water seems,
nevertheless, to remain, as a rule, uncongealed everywhere outside
the polar regions. We are at a loss to imagine by what beneficent
arrangement the rigorous conditions naturally to be looked for can be
modified into a climate which might be found tolerable by creatures
constituted like ourselves.

Martian topography may be said to form nowadays a separate
sub-department of descriptive astronomy. The amount of detail become
legible by close scrutiny on a little disc which, once in fifteen years,
attains a maximum of about 1/5000 the area of the full moon, must excite
surprise and might provoke incredulity. Spurious discoveries, however,
have little chance of holding their own where there are so many
competitors quite as ready to dispute as to confirm.

The first really good map of Mars was constructed in 1869 by Proctor
from drawings by Dawes. Kaiser of Leyden followed in 1872 with a
representation founded upon data of his own providing in 1862-64; and
Terby, in his valuable _Areographie_, presented to the Brussels Academy
in 1873[992] a careful discussion of all important observations from the
time of Fontana downwards, thus virtually adding to knowledge by
summarising and digesting it. The memorable opposition of September 5,
1877, marked a fresh epoch in the study of Mars. While executing a
trigonometrical survey (the first attempted) of the disc, then of the
unusual size of 25" across, G. V. Schiaparelli, director of the Milan
Observatory, detected a novel and curious feature. What had been taken
for Martian continents were found to be, in point of fact,
agglomerations of islands, separated from each other by a network of
so-called "canals" (more properly _channels_).[993] These are obviously
extensions of the "seas," originating and terminating in them, and
sharing their gray-green hue, but running sometimes to a length of three
or four thousand miles in a straight line, and preserving throughout a
nearly uniform breadth of about sixty miles. Further inquiries have
fully substantiated the discovery made at the Brera Observato