well, p. 207 _et seq._]

Granted the existence of such a race as is thus described, and to them
it might not seem a too appalling enterprise, when their planet had
become decrepit, with its atmosphere thinned out and its supply of water
depleted, to grapple with the destroying hand of nature and to prolong
the career of their world by feats of chemistry and engineering as yet
beyond the compass of human knowledge.

It is confidence, bred from considerations like these, in the superhuman
powers of the supposed inhabitants of Mars that has led to the popular
idea that they are trying to communicate by signals with the earth.
Certain enigmatical spots of light, seen at the edge of the illuminated
disk of Mars, and projecting into the unilluminated part--for Mars,
although an outer planet, shows at particular times a gibbous phase
resembling that of the moon just before or just after the period of full
moon--have been interpreted by some, but without any scientific
evidence, as of artificial origin.

Upon the assumption that these bright points, and others occasionally
seen elsewhere on the planet's disk, are intended by the Martians for
signals to the earth, entertaining calculations have been made as to the
quantity of light that would be required in the form of a "flash signal"
to be visible across the distance separating the two planets. The
results of the calculations have hardly been encouraging to possible
investors in interplanetary telegraphy, since it appears that
heliographic mirrors with reflecting surfaces measured by square miles,
instead of square inches, would be required to send a visible beam from
the earth to Mars or _vice versa_.

The projections of light on Mars can be explained much more simply and
reasonably. Various suggestions have been made about them; among others,
that they are masses of cloud reflecting the sunshine; that they are
areas of snow; and that they are the summits of mountains crowned with
ice and encircled with clouds. In fact, a huge mountain mass lying on
the terminator, or the line between day and night, would produce the
effect of a tongue of light projecting into the darkness without
assuming that it was snow-covered or capped with clouds, as any one may
convince himself by studying the moon with a telescope when the
terminator lies across some of its most mountainous regions. To be sure,
there is reason to think that the surface of Mars is remarkably flat;
yet even so the p