Page:Popular Science Monthly Volume 59.djvu/424

414 magnets, and messages can thus be transmitted practically simultaneously to any number of stations. It is said also that the magnets may, in this way, be used as a telephonic relay, which would be a result of the utmost practical importance.

THE PLANET EROS.

The little planet Eros bids fair to hold the attention of astronomers for several years to come. Before the observations necessary for the determination of the sun's distance had been completed, came the announcement, by Dr. Oppolzer, of the planet's variability, A variable planet, with a range of variation, such as Eros has shown, is in itself something new and striking, but this is only the beginning of the problem. Several hundred stars are known to vary their light periodically, and some advance has been made in the theory of their variability. Variable stars, however, do not become invariable, neither do invariable stars, after a time, become variable. From a variable planet, having an extremely short period and large range of variation, Eros recently became invariable.