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 planet may have some mountains, and on a globe the
greater part of whose shell is smooth any projections would be
conspicuous, particularly where the sunlight fell at a low angle across