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 them. Another form in which the suggestion of interplanetary communication has been urged is plainly an outgrowth of the invention and surprising developments of wireless telegraphy. The human mind is so constituted that whenever it obtains any new glimpse into the arcana of nature it immediately imagines an indefinite and all but unlimited extension of its view in that direction. So to many it has not appeared unreasonable to assume that, since it is possible to transmit electric impulses for considerable distances over the earth's surface by the simple propagation of a series of waves, or undulations, without connecting wires, it may also be possible to send such impulses through the ether from planet to planet. The fact that the electric undulations employed in wireless telegraphy pass between stations connected by the crust of the earth itself, and immersed in a common atmospheric envelope, is not deemed by the supporters of the theory in question as a very serious objection, for, they contend, electric waves are a phenomenon of the ether, which extends throughout space, and, given sufficient energy, such waves could cross the gap between world and world.